Monday, April 4, 2016

How to Check Slab Foundations in Central Mississippi

A minimum foundation check should involve a complete floor elevation survey that should at least accurately describe the locations of the highest and lowest floor elevations. These descriptions should have enough detail so that anybody can locate those two points. It should include a calculation of apparent maximum differential movement which is the difference between the highest elevation and the lowest elevation corrected for any differences in floor thickness between those two points. I should note that these things have not always been done in the past. The average annual movement is computed with the age of the structure. This is a more important number than the apparent total differential movement.

Experience has shown that the average annual movement rate tends to continue unless repairs are made that specifically address the cause of the movement. A cookie cutter foundation repair that just involves releveling will not reduce the movement rate if the movement is heaving (upward) from expansive soils. Many of the foundation releveling procedures will help to retard settlements.  But many foundations have a mixture of settlement and heave. Some in central Mississippi are all heave. My view is that when the movement rate is over 1/4 inch per year you have a potentially serious foundation problem that probably includes significant heave. The worst case scenario is when the movement rate is 3/4 inch per year of maybe a bit higher. The 1/4 inch per year limit is strictly an arbitrary number. I assume that no one wants to have foundation repairs done any more often than once every 12 to 15 years. So over this time frame you can accumulate 3 to nearly 4 inches of differential movement with the 1/4 inch per year arbitrary limit. Total movements in this range is a limit that is often used in the real estate industry.

Experience has also shown that if you have an average movement rate of about 1/4 inch per year that a residence will begin to show damage when it is about 3 to 5 years old and that damage may first look like minor cosmetic issues. By the 5th or 6th year the damage begins to look more like it is related to foundation movements. So if you buy a house that is less than six years old it could have a fairly significant foundation issue that might only show up through a floor elevation survey. So for a rule of thumb in central Mississippi I recommend that if you are buying a house that is newer than say 6 or 7 years and does not show any evidence of foundation damage, the floor elevations should be checked and the average annual movement rate computed. A residence that may not need a foundation check would be at least 8 years old and show no damage that might be attributed to foundation movement.

I recommend a detailed foundation evaluation for any residence with 1/4 inch or more annual movement rate. The detailed check should include the minimum check requirements but also show floor elevations and contours plotted on a scaled floor plan. If the owner does not provide a scaled floor plan then the house has to be measured and a floor plan produced with those measurements. With a detailed check I like to show the lowest elevation equal to zero. Elevations are adjusted for different floor thicknesses. I show on the plan the base elevation survey measurement and the adjusted elevations, I then draw floor elevation contours typically at ½ inch intervals. In addition to recommending the kind of foundation repair, I may recommend checking the plumbing lines for leaks or soil borings. Generally I like to see these things done before I make recommendations for repair.

The benefit of the detailed foundation study is that it maps out the details of the movement. It shows what parts of the house have more slope than others and sometimes directs you to a serious problem like a broken plumbing line or an area with poor drainage. It is also important to look at how nearby larger trees are related with the movements.

Following this procedure it is possible that a newer house with minimum damage could be flagged because the movement rate is excessive. This does not mean that it has a foundation problem, but that it is at higher risk for future foundation problems. With a detailed study of the structure maybe a related drainage problem can be found and corrected. Also there are exceptions - not every structure with a high movement rate will continue to move at that rate and there is another issue in that not all structures with differential movement will result in wall cracks. It is rare but a structure can move so that it has an even slope across the whole structure (pure tilt). In this case the only damage is floor slope. Whereas there are no cracks, it does make the structure less usable if the slope becomes excessive.

Sunday, January 17, 2016

A Link to:What Happened Before the Big Bang

In my conclusions I state that: Scientists believe that a previous universe may have contracted to a point and then bounced to create a big bang and our universe. But I think that bounce cosmology is just a special case of all possible bang events that could occur when we consider quantum gravity in a multiverse environment. I think that if we want to consider all possible bang events in a multiverse where quantum gravity functions, we must also consider bang events from black holes that are equivalent to a contracted universe. So when we move bounce cosmology into a multiverse, another path to a bang becomes possible because the bounce occurs at some maximum density and that same density could eventually occur in a black hole if it obtains enough mass.

If you find this thought process interesting I invite you to read my complete blog at this address: http://www.the-cosmic-corner.com/2016/01/what-happened-before-big-bang.html

Saturday, February 14, 2015

Biblical Accounts of Volcanic Eruptions with Tsunamis-Part II

“a huge mountain, all ablaze, was thrown into the sea” Revelations 8:8

In part I of this blog I reviewed the geologic and geographical setting of the Mediterranean and looked at a detailed account of a volcano in 2 Samuel 22. In the second part I look at some passages that just hint at a volcano with a tsunami.

2.-- Nahum 1:3-8 This account provides much less detail but it still includes language that sounds like a tsunami. Pinker (2004) provides theological perspective of this passage.

3 The LORD is slow to get angry. He is very powerful. The LORD will not let guilty people go without punishing them. When he marches out, he stirs up winds and storms. Clouds are the dust kicked up by his feet. 4 He controls the seas. He dries them up. He makes all of the rivers run dry. Bashan and Mount Carmel dry up. The flowers in Lebanon fade. 5 He causes the mountains to shake. The hills melt away. The earth trembles because he is there. So do the world and all those who live in it. 6 Who can stand firm when his anger burns? Who can live when he is angry? His anger blazes out like fire. He smashes the rocks to pieces. 7 The LORD is good. When people are in trouble, they can go to him for safety. He takes good care of those who trust in him. 8 But he will destroy Nineveh with a powerful flood. He will chase his enemies into the darkness of punishment.

ANALYSIS  In this passage references to a tsunami are (4) “He controls the seas. He dries them up” and in verse 8 Nahum prophecies “ a powerful flood.”  Nahum’s possible reference to pyroclastic flow is interesting, in verse 3 he says “Clouds are the dust kicked up by his feet .” This is similar to David’s account in 2 Samuel 22: 10, but in this case Nahum might be talking about a dust storm, because in verse 4 he seems to talk about a drought in the region from Carmel to Lebanon. But he maybe connecting this drought as a possible environmental consequence the Thera eruption. Figure 2 is a map of the eastern Mediterranean Sea showing the location of Nahum’s drought, Thera and other relevant locations. Other than the cross reference with possible pyroclastic flow, this account seems to be independent of David’s account of Thera. The possible mixing of the description of the volcano with other natural disasters is also done by Amos (see below).

OTHER POSSIBLE BIBLICAL PASSAGES
Again we are looking for any reference to something that sounds like a volcano and a tsunami in a Biblical passage. Amos uses a writing style where two chapters are joined into a single thought by repeating this phase almost verbatim in both chapters:  “The whole land rises like the Nile River. Then it settles back down again like that river in Egypt.” If we use that bridge between chapters, we get a story of a possible volcano and a tsunami mixed with something that sounds like an earthquake and maybe an eclipse.

1.--Amos 8:8-9
8 “The land will tremble because of what will happen. Everyone who lives in it will mourn. So the whole land will rise like the Nile River. It will be stirred up. Then it will settle back down again like that river in Egypt.”
9 The Lord and King announces, “At that time I will make the sun go down at noon.
   The earth will become dark in the middle of the day.

     Amos 9:5-6
5 The Lord rules over all. The Lord touches the earth, and it melts. Everyone who lives in it mourns. The whole land rises like the Nile River. Then it settles back down again like that river in Egypt.
6 The Lord builds his palace high in the heavens. He lays its foundation on the earth. He sends for the waters in the clouds. Then he pours them out on the surface of the land. His name is the Lord.

ANALYSIS: In this text Amos seems to reference tectonic activity that now understood as tectonic plate movements in this region. Amos 9:6 might be a reference to a tsunami with “He sends for the waters in the clouds. Then he pours them out on the surface of the land.” and the description of a volcano in” The Lord touches the earth, and it melts” lacks the expected reference to a mountain. Here Amos 8:8 sounds like an earthquake. But in the next verse he says “I will make the sun go down at noon and darken the earth in broad daylight.” This could be a the clouds of the Thera volcano or a solar eclipse. But the mixing of an eclipse and a earthquake is a less likely meaning, so I think it is more likely that Amos is talking about the Thera eruption.

2.--Revelations 8:8-9. (New International Version)
8 The second angel sounded his trumpet, and something like a huge mountain, all ablaze, was thrown into the sea. A third of the sea turned into blood,
9 a third of the living creatures in the sea died, and a third of the ships were destroyed.

In Revelations seven trumpets are sounded. This is the second. Here a tsunami is implied by a huge mountain being thrown into the sea and ships being destroyed. Although the writer of Revelations was on the Island of Patmos (only 88 miles or 140 km from Santorini), it was written about 1700 years later (see figure 1 and 2). But I think this passage by John of Patmos as a very remarkable summary of the Thera caldera collapsing into the sea and causing a mega-tsunami. However, we can not exclude this passage as being a reference to a more recent event at Mount Etna or the much older event at Etna when the Valle del Bove was formed 8300 years ago. So this could be an event that has happened more than once in the Mediterranean, and the geologic setting suggests that it will certainly happen again sometime in the future.

SUMMARY AND CONCLUSIONS

If we accept the traditional timelines given for the Bible and the dates scientifically determined for the Thera eruption, then this event occurred roughly 640 years before 2 Samuel 22 and Psalms 18 was written. An observer analysis made of this account indicates that it is a volcanic eruption with a tsunami from the perspective of several independent points of view in time and distance. There are three or maybe four components of the Thera eruption known by scientific study that are included in the King David account: a tsunami, pyroclastic flow, lava bombs, and lava. Scientific studies also show that it was a Plinian eruption with a column of smoke that rose high in the atmosphere. We know that these eruptions darken the sky for days this also matches the 2 Samuel account and that by Amos. I think that David inadvertently helps to prove not only his existence but his kingdom by referencing the historic Thera eruption in detail, because only he could have been in a position to hear these stories of this event (see his kingdom in figure 2 Part I of this blog).

Related with the geologic environment of the Mediterranean volcanoes is plate tectonics. The concept (continental drift) for this was proposed by Alfred Wegener in 1915. An important part of this is to recognize that the surface of the Earth moves, so maybe this aspect should be attributed to Amos in the Bible. Both Amos and Naham seem to refer to historic events and make projections about the future with that information. Amazingly this basic idea is what is done today. We study past earthquakes and volcanic activity to determine the risk for the future.

All of these accounts of the Thera eruption provide detail that was not previously known to science. There appears to be a continuous loss of detail about the event as it becomes more distant in the past. This indicates that the knowledge of the event in each case is being passed down orally. By the time we get to Amos and Nahum the story of Thea seems to be more diluted and also mixed in with other natural phenomena like an eclipse and earthquakes.


References

Barber, E.W. and Barber P.T. (2004) When They Severed Earth from the Sky - How the Human Mind Shapes Myth. Princeton Univ. Press.

Cita, M. B. and Rimoldi, B. (2005). Prehistoric mega-tsunami in the eastern Mediterranean and its sedimentary response. Rend. Fis. Acc. Lincei. Vol: 16:137-157.

Foster K. P. and Ritner R.K. (1996) “Texts, Storms, and the Thera Eruption.”  Journal of Near Eastern Studies 55 (1): 1–14.

Galili E., Horwitz L. K., Hershkovitz I., Eshed V., Salamon A., Zviely D., Weinstein-Evron M., and Greenfield H. (2008) “Comment on: Holocene tsunamis from Mount Etna and the fate of Israeli Neolithic communities" Geophysical Research Letters. Volume 35, Issue 8.

Goodman-Tchernov B. N., Dey H. W., Reinhardt E. G., McCoy F., Mart Y. (2009) “Tsunami waves generated by the Santorini eruption reached Eastern Mediterranean shores.” Journal Geology , vol. 37, no. 10, pp. 943-946.

Mastrolorenzo G., Petrone P., Pappalardo L., and Sheridan M.F. (2009) “The Avellino 3780-yr-B.P. catastrophe as a worst-case scenario for a future eruption at Vesuvius” Geological Society, London, Special Publications. 322 (1) 105-119.

McCoy F.W. and G. Heiken (2000) Tsunami Generated by the Late Bronze Age Eruption of Thera (Santorini), Greece,  Volcanic Hazards and Disasters in Human Antiquity, Geological Society of America, Special Paper No. 345: 43-70.

Milia A., Raspini, A. & Torrente, M.M. (2002) Evidence of slope instabilities and tsunami associated with the 3.5 ka Avellino eruption of Somma–Vesuvius volcano, Italy. Geological Society, London, Special Publications 01/2009; 322(1):105-119.

Pinker, Aron (2004) “Nahum’s Theological Perspectives” Jewish Bible Quarterly. Vol. 32, No. 3

Soloviev, S. L., Solovieva O.N., Go, C.G., and Kim, K.S. (2000) Tsunamis in the Mediterranean Sea 2000 B.C.-2000 A.D. Advances in Natural and Technological Hazards Research, Vol. 13. 237.

Stothers R. B. and Rampino M. R. (1983) Volcanic Eruptions in the Mediterranean Before A.D. 630 From Written and Archaelogical Sources,  Journal Geophysical Research, 88, 6357–6371.

Taddeuci and Wohletz, (2001) Temporal evolution of the Minoan eruption (Santorini, Greece), as recorded by its Plinian fall deposit and interlayered ash flow beds. Journal of Volcanology and Geothermal Research, Volume 109, p.299-317

Vespa, M., Keller, J., and Gertisser, R. (2006) Interplinian explosive activity of Santorini volcano (Greece) during the past 150,000 years. Journal of Volcanology and Geothermal Research, Volume 153, Issue 3-4, p. 262-286.

Yokoyama, I. (1978), The tsunami caused by the prehistoric eruption of Thera. In Thera and the Aegean World II, Dumas, C., ed. London, Thera and the Aegean World, 277-283.

APPENDIX

A list of references to volcanic eruptions in the Bible. The number of times that a volcanic event is mentioned is shown in parentheses. Passages that also have a possible tsunami (looked at in this blog) are marked with an asterisk:

(2) Exodus 13:21, 19:18
(5) Deuteronomy 4:11, 5:4-5, 5:22-23, 9:15, 10:4
(1) Judges 5:5
(1) 2 Samuel 22:5-16*
(1) 1 Kings 19:11-12
(1) Nehemiah 9:19
(5) Psalm 18;4-15*, 83:14, 97:2-5, 104:32, 144:5
(2) Isaiah 4:5, 64:1-3
(1) Jeremiah 51:25
(1) Ezekiel 1:4
(1) Joel 2:10
(1) Amos 8:8-9*, 9:5-6
(1) Micah 1:4
(1) Nahum 1:5-6*
(1) Acts 2:19-20
(1) Hebrews 12:18
(1) Revelations 8:8*

Sunday, January 25, 2015

Biblical Accounts of Volcanic Eruptions with Tsunamis-Part I of II

The waves of death were all around me. A destroying flood swept over me.” 2Samuel 22:5

INTRODUCTION

There are at least 26 references in the Bible to smoking or melting mountains but there are only a few references that also include language that sounds like a tsunami. In an appendix at the end of this blog I list all the Bible passages that seem to reference volcanoes. Only two known volcanic events, that happened before the Bible was written, may have produced tsunamis in the Mediterranean Sea. Connecting these events with the Bible was not possible until the last 40 or 50 years because the details of these eruptions were unknown until scientists investigated and dated them. This means that these Biblical accounts are references to recently discovered actual historical events and I think they provide the most detail of the Thera eruption (3600 years ago) from any source. This eruption , also known as the Minoan Eruption, was the most violent and the most catastrophic event known to science in the Mediterranean Sea. It also produced a mega-tsunami.

The Bible is rarely referenced in volcanic research. Stothers and Rampino (1983) wrote “like others, we find that Biblical and Egyptian literature is generally too sparse and too ambiguous concerning natural phenomena to be really useful and is applicable mostly to the period before ca. 700 B.C.” They discuss the Thera eruption but provide no literary accounts. Foster and Ritner (1996) looked more closely at possible Egyptian references of the Thera eruption. They used a datable text (Tempest Stela) that might be a reference to the effects of this cataclysmic eruption. However, this in text expressions like “rain, darkness, louder than the cries of the masses” is much more ambiguous than the Biblical text that I will consider. Surely the story of Thera was not excluded from the Bible, but if it is included where is it? Many have tried to make this connection before mainly by trying connect the story of Exodus with this eruption. But if we accept traditional timelines for this period, we find that the Thera eruption occurred at least 150 years before the Exodus and before any dates proposed for the birth of Moses. In writing this I only considered widely accepted Biblical dates and timelines.

TIMELINE OF MEDITERRANEAN VOLCANIC EVENTS AND BIBLICAL ACCOUNTS

Figure 1 shows a timeline of Biblical dates and period volcanic activity in the Mediterranean starting with the Thera and Avellino eruptions. The first passage I consider was written or edited
www.thecosmiccorner.blogspot.comprobably late in life by King David (1040-970 BCE). The second account I review was written by Nahum and it is thought that this book was written before 612 BCE when Nineveh was destroyed and after 663 BCE when Thebes in Egypt was destroyed. So David is writing roughly about 990 BCE and Nahum is writing sometime before 612 BCE. So we are looking for violent volcanic eruptions prior to these times that produced a tsunami. The Thera eruption apparently occurred between 1570 BCE and 1628 BCE. Radiocarbon dating places the eruption closer to the 1628 BC date. So the text of David was written roughly 640 years after the Thera eruption and the Nahum text was written roughly 350 years after the text of David and nearly 1000 years after the Thera eruption. The last account considered was written about 1700 years after Thera but only 190 years after an eruption at Mount Etna.

GEOLOGICAL SETTING

The Mediterranean and adjacent areas rank among the seismically most active regions of the world and are the second largest source for tsunami around the globe. The reason for this seismicity is the collision between the African and the Eurasian tectonic plates. Besides seismicity there exist other sources for tsunami, such as, volcanic eruptions and landslides. Tsunamis are created when a large amount of water is suddenly displaced by a geologic event.  A tsunami in the Indian Ocean 2004 killed 290,000 and another in 2011 killed 15,885 in Japan. These tsunami’s were caused by earthquakes. The Thera and the Avellino eruptions are considered to be Plinian, because they were similar to the eruption of Mount Vesuvius in AD 79. These powerful eruptions produce plumes of ash that rise up to 45 kilometers (28 miles) into the atmosphere. They are called Plinian because of well known written account of the AD 79 event by Pliny the Younger.

When I first started working on this, I thought that these Biblical accounts could have only been descriptions of the Thera eruption at Santorini Greece, I still think that is correct but there are other possibilities that should be considered. This includes the more distant and smaller Avellino eruption of the Somma-Vesuvio Volcano, Italy and a third event at Mt Etna several thousand years before. However, in the last case the tsunami might not have been produced by volcanic activity. So this event does not correlate well with the Biblical accounts that I consider. Continued study of ancient Mediterranean eruptions will certainly add to our understanding of these Biblical connections.

THE VOLCANIC CANDIDATES

1. The Thera eruption at Santorini occurred about 1000 kilometers (620 miles) from the eastern coast of the Mediterranean. According to radiocarbon dating the Thera eruption occurred sometime over a 28 year span between 1596 and 1624 BCE. This eruption is believed to be the second or maybe the third largest in human history. To evaluate the size of an eruption, scientist compute the (DRE) dense rock equivalent of ejected magma, pumice and ash. This eruption had a DRE of 60 cubic kilometers (14 cubic miles) of ejected material. The eruption created tsunami’s mainly because it occurred on a small island out in the Aegean Sea that joins the Mediterranean Sea. Geologists have studied deposits made by the eruption and have pieced together what caused the related tsunamis. McCoy and Heiken (2000) describe 4 phases of the Thera eruption and explain how each could have produced tsunamis. This included large pyroclastic flows that encountered the sea and later when the caldera collapsed into the evacuated magma chamber below to create an island ring caldera and a mega-tsunami. In 1981 Kastens and Cita reported that “the collapse of the caldera of the volcano of Santorini caused a huge tsunami which is recorded archaeologically and geologically around the eastern Mediterranean.” The most comprehensive evidence that a tsunami from this eruption reached the Eastern Mediterranean coast came from a study by Goodman-Tchernov, B. N. et al. 2009. They found Thera age tsunami deposits at Caesarea Israel (see Figure 2) in off shore core samples. McCoy and Heiken (2000) estimated that the wave heights along coastal areas were about 7- 12 m based on other tsunami deposits. According to a University of Rhode Island press release:
An eruption of this size likely had far-reaching impacts on the environment and civilizations in the region. The much-smaller Krakatau eruption of 1883 in Indonesia created a 100-foot-high tsunami that killed 36,000 people, as well as pyroclastic flows that traveled 40 kilometers across the surface of the seas killing 1,000 people on nearby islands. The Thera eruption would likely have generated an even larger tsunami and pyroclastic flows that traveled much farther over the surface of the sea.
2. The Avellino eruption. The much wider time frame of this eruption overlaps that of the Thera eruption. Studies of this eruption show it occurred sometime between 1500 and 2000 B.C.E. and it was about 10 times smaller than the Thera eruption. It was also twice as far from the Eastern Mediterranean coast. The evidence for a related tsunami has been disputed. If there was a tsunami created by the eruption, the effects probably were limited to the area near the volcano. A group of researchers found evidence for a tsunami that effected the Bay of Naples. For the people living nearby there were evacuations recorded as footprints in the volcanic ash. Mastrolorenzo, Pappalardo, and colleagues (2009), analyzed ash deposits and reconstructed the Avellino event in detail. This “ plinian eruption produced an early violent pumice fallout and a late pyroclastic surge sequence that covered the volcano surroundings as far as 25 km away, burying land and villages. “

3. Mount Etna. This event seems to be a tsunami that may have been connected with volcanic activity of unknown magnitude. In 1996 Calvari and Groppelli attributed part of the Chiancone deposit (a volcaniclastic fan on the eastern flank of Mt. Etna) to a huge mud flow that may have been associated with an important eruptive event. In 2007 Pareschi et al. wrote “About 8.3 ka (8300 years) ago a devastating tsunami flooded the coasts of the Eastern Mediterranean Sea. That tsunami was triggered by a landslide from the collapse of the eastern flanks of Mt. Etna volcano... inducing a scar on the slopes, named Valle del Bove... The tsunami had a large impact, effecting... Lebanon and Israel. In Israel the tsunami ravaged the Neolithic village of Atlit-Yam caused the death of villagers and animals...” The impact of this event on the coast of Israel was disputed by Galili et al. (2008).

Other events occurred near Mt. Etna after the Prophetic Books of the Hebrew Bible were written, but before the New Testament and the book of Revelations was written. These events occurred between 425 and 122 BCE (see Figure 1).The nearby Vucanello volcano was active during this period and built a new island, but there are no known tsunamis associated with this activity.

THE BIBLICAL ACCOUNTS OF VOLCANOES WITH TSUNAMIS

Figure 2 shows a map of the Eastern Mediterranean Sea showing the locations of places mentioned in these Biblical accounts. It also shows how the tsunami could
www.thecosmiccorner.blogspot.com
Figure 2. Map of the Eastern Mediterranean Sea showing locations
of Biblical references made by Nahum, David's Kingdom, the island
of Patmos and the Thera volcano. Contours show tsunami distance-
arrival times by Yokoyama, 1978.
have propagated eastward and the location of Caesarea where offshore tsunami deposits were found. The following passages are from the New International Reader’s Version of the Bible. It is interesting to read different versions of this passage. This version seems to describe the tsunami better than others. The most detailed account is also the oldest account and closer in time to the Thera eruption.

1.-- 2 Samuel 22; 5-16 NIRV (also Psalm 18: 4-15).
5 The waves of death were all around me. A destroying flood swept over me. 6 The ropes of the grave were tight around me. Death set its trap in front of me. 7 When I was in trouble I called out to the Lord. I called out to my God. From his temple he heard my voice. My cry for help reached his ears. 8 The earth trembled and shook. The pillars of the heavens rocked back and forth. They trembled because the LORD was angry. 9 Smoke came out of his nose. Flames of fire came out of his mouth. Burning coals blazed out of it. 10 He opened the heavens and came down. Dark clouds were under his feet. 11 He got on the cherubim and flew. The wings of the wind lifted him up. 12 He covered himself with darkness. The dark rain clouds of the sky were like a tent around him. 13 From the brightness that was all around him flashes of lightning blazed out. 14 The LORD thundered from heaven. The voice of the Most High God was heard. 15 He shot his arrows and scattered our enemies. He sent flashes of lightning and chased the enemies away. 16 The bottom of the sea could be seen. The foundations of the earth were uncovered. It happened when the LORD's anger blazed out. It came like a blast of breath from his nose. 17 “He reached down from heaven. He took hold of me. He lifted me out of deep waters. 18 He saved me from my powerful enemies. He set me free from those who were too strong for me.

ANALYSIS:  This passage as written in Psalms is one of the theophany events of the Bible. According to the Dictionary of Bible Themes a theophany is a visible manifestation of God that may also be a natural phenomena.  I will attempt to show that this passage is actually a recently discovered but a well known and established historical event. The possible references to a tsunami are: (5) “ The waves of death were all around me. A destroying flood swept over me. ”; (12-other translations) “gathering of waters”, and (16) “The bottom of the sea could be seen.” Seeing the bottom of the sea must be a tsunami. References with a volcano are self evident but there are added elements like “lightning” that occurs in the smoke of larger Plinian volcanic eruptions and possible pyroclastic flows in (10) “ Dark clouds were under his feet.” Taddeuci and Wohletz, (2001) reported that the pyroclastic deposits of the Thera eruption are well documented in the volcano-logical literature. In this text there are references to lava or volcanic bombs in verses 9 “Burning coals blazed out of it” and 13. In verse 13 (other translations) lava bombs are expressed as “coals of fire flamed forth.”  Barber and Barber (2004) show a photo of a Minoan structure at Akrotiri (Santorini) destroyed by a large lava bomb from the Thera eruption.

This is an eruption that we know from scientific studies produced pyroclastic flows, lava bombs and a tsunami that all match this Biblical passage. Is there any other passage in the Bible that provides this kind of detail of an event established through scientific studies? 


To best understand this passage we must perform an observer analyses that considers the location of the observer and the chronology of the observation. This shows whether the whole story is one of a single observer or a collection of observations made by more than one person. We must also understand that these are ancient descriptions made of an eruption. The people that experienced this event did not have a modern language with words we use today to explain this kind of event. There was no word for tsunami, volcano or lava or any pyroclastic material. The result is description of a volcano and a tsunami made without any of the words of a modern language to describe these events.

Lets begin with verse 16: “The foundations of the earth were uncovered.” I think that if you walked across a desolate land recently covered with lava or ash you might conclude that the ground is not ordinary and that it might be ground underneath the normal surface of the earth and that you might describe this in this way. This part of the story is produced by the understanding that the normal rock, sand or soil normally seen on the surface of the Earth is missing.  If this is correct then this is most likely a description of the land made long after the event when people began to go back into the area. Also to survive the “mega-tsunami” produced by this eruption you would most likely be hundreds of miles away from the volcano, maybe to far away to see the lightning and the pyroclastic flows and certainly to far away to see lava bombs. So these verses seem to be mixed descriptions of a volcanic eruption from the point of view of someone far away caught in the tsunami, someone else close enough to see lightning,  pyroclastic flow and lava bombs and thirdly someone that saw the land long after the event occurred.

From reading these passages we might conclude that King David was a part of this terrible event, that is certainly a possibility, but there is no known volcanic event during his life (see timeline in Figure 1). I list 5 possible passages about volcanoes (see appendix) in Psalms, but if David had actually been a part of this event, I think he would have had even more to say about it. It seems most likely that David heard the stories of this eruption that were passed down from survivors and he then parallels with this event with and his own life struggles and his relationship with the Lord. This passage includes at least 3 different points of view indicating that it is a collection of stories. If we assume that this is the Thera eruption, we can see David comparing the story of Thera with his own story in verses 17 and 18. Verse 18 has no reference to the event in question but I included it because it shows this context for the other verses. David compared with other Biblical writers had a unique advantage to hear stories of past events as a ruler of a large part of the Eastern Mediterranean. His kingdom as described in earlier passages in 2 Samuel is shown in Figure 2.

David references this eruption again in Psalm 97: 2-5, Psalm 104:32, and Psalm 144: 5-7. In Psalm 97 he repeats the reference to lightning in verse 4 and adds a reference to lava in verse 5 with “The mountains melt like wax.” There had to be lava to produce lava bombs as we saw in 2 Samuel 22. But in this case there is no reference with a tsunami but in Psalm 144: 7 he cross references this event with the phrase “rescue me from the mighty waters.” This phase is repeated from 2 Samuel 22:17 and Psalm 18:16.

Lastly I must ask the question: Why is there two slightly different versions of this event in the Bible?  Did David or his writer make two versions of the same story and just change a few words or is the result of latter editing? In some commentaries it is suggested that 2 Samuel was the original version. If this is a collective account of the Thera eruption then the 2 Samuel version provides more detail of that event. Note that in the 2 Samuel account “chords of death” is replaced by “waves of death”.  If you Google “waves of death” you find a documentary of the disastrous 2004 tsunami and this 2 Samuel account. There is a great deal more information about this event in this account than anywhere else in the Bible or any other text that I know about.

In part II of this blog I will look at other possible accounts in Nahum, Amos, and Revelations and then provide a summary and conclusion. I will talk more about 2 Samuel 22 in that conclusion.

Friday, November 15, 2013

The Origin of Hogwallows and Gilgai Landforms - PART II

You can scroll down to see my most recent blogs including Part I of this blog or you can click on this link:
The Origin of Hogwallows and Gilgai - PART I10/31/2013. This is a closer look at a theory I published in 1994 to explain these landforms. Included in this blog is a great photo of gilgai at ground level taken from Google street view in Waxahachie Texas.


PREBUCKLING STRESS AND DIFFERENTIAL REBOUND IN OVERCONSOLIDATED EXPANSIVE CLAYS

It maybe that there has been some confusion about what buckling is and how it is applied in this case. Generally buckling is deformations produced by an axial load. There is a critical load at which buckling produces a sudden failure. However, prior to the critical buckling load there are internal stress reactive changes that resist the applied load as the load builds. It is important to understand the difference between a pre-buckling load (axial) that is not critical and a critical buckling load. The internal stresses associated with critical buckling do not just suddenly appear when the load becomes critical. So prior to a critical buckling load the normal internal stresses are altered. Expansive soils react to this because they react to changes in confining pressure. That is they swell more with less confining pressure and swell less as the confining pressure increases.

A deeply buried expansive soil will not expand if the confinement pressure (from the weight of the soils above) equals or is greater than the expansion pressure. As this confining pressure is decreased, the clay can expand more and more. The key idea is that prior to a critical buckling load there are internal changes in stress that alters the normal confining pressure (in the horizontal direction) that then triggers differential rebound. Where mounds will appear the normal confining pressure is decreased and where depressions will occur the normal confining pressure is increased. These internal changes in stress, less than the critical buckling load can trigger differential heave and create the appearance of buckling. The evidence that gilgai are not caused by a critical buckling load are:

1. Gilgai do not appear suddenly. Critical buckling happens suddenly. Farmers that have plowed gilgai flat report that gilgai will reappear in a few years. I.e. if the movement rate is more like normal shrink-swell movements, then this is not a critical (sudden) buckling issue.
2. Gilgai only happen in expansive soils. If critical buckling was involved it would happen in other clays like Kaolinite, Illite and Chlorite.

So this means that the normal shrink-swell behavior of expansive clays must be the energy that is creating the gilgai. If you were to place some heavy lead plates on the ground in a pattern resembling gilgai depressions, in a few years there would be a differential rebound that would mimic gilgai with the plates in the depressions. In this case Ko >1 had nothing to do with the movement. However, Ko >1 but less than the critical buckling load can take the place of the lead plates. This is because an elastic member can carry a significant axial load up the critical buckling load but not without reacting to the load internally. This is what I call prebuckling. When this happens expansive soil senses a change in vertical load just like there were lead plates on the surface of the ground. So in one sentence Ko >1 and shrink-swell behavior work together to produce differential rebound. I think we can say that once the buckling load represented by Ko approaches 25 to 50% of the critical buckling failure load then differential heave kicks in to create gilgai. But that is just a guess as to those percentages. The true analytics of the problem are quite complex because there are a lot of related properties that change with depth such as Ko, expansion potential and soil strength and others.

I will now show you in more detail how this works using a simplified model constructed from a long strip of elastic material that has self weight and can buckle like a continuous sine wave. Think of this as a heavy very long column (an axial loaded member) that is lying down. It is fully braced in the z direction (in and out of the page) due to self confinement. Oddly in this case the material self weight helps to brace the column, so for true buckling to occur it has to overcome the buckling strength of the material and it also has to lift the material as well. But there is a lifting influence prior to the critical buckling load.

Simplified Elastic Model showing prebuckling
I zoom in to look at a random segment of this longer strip in Figure 2. I have made several simplifications to show what happens internally and more importantly how the weight of the material is supported at the base of the material. A technically correct drawing would have roller supports along the sides and below. I have removed these for clarity. This drawing shows three levels of Ko in the material. This is the ratio of horizontal stress with the vertical stress. In the first drawing the model has Ko =1 the horizontal loading on the side matches the weight of the material. In the second drawing Ko =Kcr (the critical buckling load) and the strip of material has buckled due to the higher horizontal loading. We don't know the actual value of Ko in this case, but we assume it is higher than the Rankin failure I show in Figure 1. So in this 2nd case, the material is a stronger material than a clay deposit for this behavior to occur. In the third drawing there is less horizontal load but it is still higher than the vertical (self weight due to gravity). Although the load is not high enough to produce buckling, changes in the internal stress are still there. You could say that the material it trying to buckle and producing a differential load (see support reactions) on the subsurface layers. This should trigger a differential rebound that would only occur in an expansive soil. The effect is the same as if you placed some heavy lead plates in locations of future depressions.

HOW MOUNDS TRANSFORM INTO MICRORIDGES (POLYGONS)

Figure 3 shows how mounds and depressions (a) change into more commonly seen polygon (c) shapes. My photo in PART I shows gilgai that are in transition (b) in-between. In mature gilgai mounds are replaced by interconnected micro-ridges to create polygons. If you look at the aerial image at location (32.419913,-96.77876) dated 2-27-2001 you can see better developed polygonal gilgai in the yard behind the house. You can also see where contours have been plowed through the gilgai to help retain water and where the gilgai have been plowed flat in adjacent fields.

The Three Stages of Gilgai Development
In 1994 I defined the term "shear joint" to describe the special subsurface fracturing that forms around gilgai mounds and micro-ridges. In the literature you find these joints also called slickensides. However, the term slickensides has been used to describe lots of different shiny surfaces with different origins.  This is a special kind of fracture related only with gilgai and I think a special name should be used for these fractures. In Jackson Mississippi I have seen shear joints that indicate that gilgai existed thousands of years ago and were eroded away leaving only the shear joints as remnants of gilgai. Joeckel (1999) calls this kind of fracture synformal slickensides. Williams etal (1998) excavated two sections through gilgai and described the subsurface fractures. These are the best descriptions I have seen for subsurface gilgai fractures.

The key concept of this final part of this theory shown in Figure 3 is that once mounds and depressions develop there is a slight loss of horizontal self confinement. This then promotes additional lateral movement toward the mound. This squeezes the mounds into narrow ridges that eventually connect to create a continuous micro-ridge system or polygons. The development of shear joints around the perimeter of the mounds enables additional horizontal movement. The formation of linear gilgai on slopes occurs for the same reason that polygons form; the slope allows downhill creep to occur, this releases self confinement in the downhill direction. This means that Ko >1 becomes directional occurring only perpendicular with the slope. This also means that Ko >1 is providing some of the energy into downhill creep that is well known in expansive clays. Linear gilgai prove that there are strong horizontal forces that are behind the formation of gilgai.

Mound squeezing explains several phenomenons associated with gilgai mounds. Some of these are:

1. Tightly wrinkled shear joints inclined at steep angles under the mound perimeter. A photo of this can be seen in Figure 3-32 in Chapter 3 of the Soil Survey Manual. They do not relate these fractures with gilgai but these look the shear joints I have seen in the local Yazoo clay. Another image of this can be seen in Joeckel(1999). Search for image "0728_f10.jpg" in Google images.
2. Features called first called chimneys where the subsurface strata appears to be pushed up under the mounds. These features have been compared with diapirs(Gustavson 1975).

Nature "turns off" or switches off gilgai when the Ko >1 soils become too deep or when expansive soils are replaced with non expansive soils. This means that when you find a large field with polygons (c) around the perimeter you will occasionally see less mature forms (a) or (b) where nature is preventing the mature forms from developing. The transition is most often represented by the micro-ridges being wider. My guess is that this is most often happens when Ko >1 soils are buried by soils where Ko is equal to or less than one. Because the rate of erosion is slow, there is no reason for gilgai to be actively forming, at least in the southeastern United States unless surface soils have removed by human activities and elevated Ko >1 expansive soils nearer to the surface. This means that the gilgai we see have been there for at least hundreds and maybe thousands of years. So if we see the less mature forms of gilgai that simply means that there is not enough expansive energy to push the gilgai into the mature stage.

The development of salt polygons in desert environments appears to occur by an almost identical process as I describe here, except in the case of salt polygons the horizontal force is produced by the growth of salt crystals (see the textbook Geomorphology of Desert Environments (2009). This parallel process maybe the best supporting evidence for Ko >1 theory of gilgai. 

Surface cracks vs Ko>1 theory

1. Surface cracks or shrinkage theories can't explain polygons or linear gilgai; the two most common forms. The big problem is that the surface crack theories only seem reasonable in 2 dimensional section drawings. If you try to create a plan view, you can not do it and make something you would expect to find in nature. So these theories do not work in 3 dimensions.
2.  If gilgai resulted from surface cracks, it could be established by mapping the surface cracks as related to the topography or maybe by filling cracks with soil or by running water in the cracks in the field or by correlating moisture content with cracks. These kinds of studies have not shown correlations that support these theories. Two examples are Spotts (1974) and Kishne, Morgan and Miller (2009).
3. Surface cracks theories were first proposed from 1840-1930 before modern soil mechanics discovered that horizontal stress naturally occurs in overconsolidated expansive clays. I think this negates these awkward attempts to generate horizontal thrust with a shrinkage crack.
4.  Shrinkage crack theories would not function under pavements, and pavement undulations have been associated with gilgai.
5.  Not all gilgai have surface cracks. There are two sites in Mississippi on public land that don't have shrinkage cracks even during drought conditions. What causes these gilgai?
6.  The Ko>1 origin of gilgai can create gilgai of all forms with or without surface cracks. This is the only gilgai theory discussed in a peer reviewed engineering journal.There are no valid published criticisms that have not been answered since this theory was introduced in 1994. l would be happy to respond any questions or criticisms.
7. The Ko>1 condition is well established in overconsolidated clays, if in the case of expansive clays, that gilgai are not produced, then what does happen? How could an expansive clay ignore the presence of Ko>1 instability without reacting in some way that is out of the ordinary?

A FEW FINAL THOUGHTS

If you want to see gilgai in the field based on Google Earth images, you must realize that gilgai you see in aerial photos may not always be visible on the ground. The relief is typically less than 1 foot so if the grass or brush is higher than 1 foot, you may not be able to see the gilgai on the ground. So you need a fresh mowed field, yard or an actively used pasture to see gilgai on the ground. Your best bet is a pasture or land that is mowed regularly. Also occasionally owners plow the gilgai flat. In this case the gilgai may come back but you may have to wait a few years. If you find this subject interesting and wish to read more please check out Riddell's two publications. His hogwallow descriptions are most interesting. I don't think his work has ever been referenced in recent gilgai research, so his work is herein being brought back in the history of gilgai research. Also the paper by Mayne and Kulhawy is considered to be a classic in geotechnical engineering.

REFERENCES:

Gustavson, T. C. (1975). "Microrelief (gilgai) structures on expansive clays of the Texas coastal plain--Their recognition and significance in engineering construction." Bur. Econ. Geology--Geological Circular No. 75-7, University of Texas, Austin, Tex.

Hilgard, E. W. (1906). "Soils" New York, The Macmillan Company. 593 p.

Howard, A. (1932). "Crab-Hole, Gilgai and Self-Mulching Soils of the Murrumbidgee Irrigation Area" Pedology (Pochvovedeni), p.14-18.

Joeckel, R.M. (1999). " Paleosol in Galesburg Formation (Kansas City Group, Upper Pennsylvanian), Northern Midcontinent, U.S.A.: Evidence for Climate Change and Mechanisms of Marine Transgression." J Sedimentary Research. Vol. 69, No.3, p720-737.

Kishne, A. S., Morgan, C. L. S. and Miller W.L. (2009) "Vertisol Crack Extent Associated with Gilgai and Soil Moisture in the Texas Gulf Coast Prairie" SSSAJ: Vol. 73: No. 4. p. 1221-1230.

Maxwell, B. (1994). "Influence of Horizontal Stresses on Gilgai Landforms." J Geotech Eng., ASCE 120:1437–1444.

Mayne, P.W. and Kulhawy, F.H. (1982). "Ko-OCR Relationships in Soil." J Geotech Eng. ASCE 108 No. GT6:851-872.

Michalowski, R. L. (2005) "Coefficient of Earth Pressure at Rest." J Geotech Geoenv Eng., ASCE 131:11, 1429-1433.

Riddell, J.L. (1839) "Art. II.- Observations on the Geology of the Trinity Country, Texas. The American Journal of Science and Arts, Vol. 37, Nov., p. 211-217.

Riddell, J.L. (1840) "37. Hog Wallow Prairies.*--Extract of a letter to the Editors…May23, 1840." The American Journal of Science and Arts, Vol. 39, Oct., p. 211-212.

Spotts, J.W. (1974) "The role of water in gilgai formation." P.H.D. Dis. Texas A&M University, College Station, TX.

Williams, D. Wilding L., Lynn, W. Kovda, I. and Chervenka, G. (1998) "Slickenside arrangement in Burleson clay - a udic haplustert" 16th World Soils Congress. Vol.1, p. 89


Thursday, October 31, 2013

The Origin of Hogwallows and Gilgai Landforms - PART I

INTRODUCTION

Gilgai and hogwallows are the same thing. They are naturally occurring landforms that are called microrelief. The higher areas have been called microknolls, mounds, and microridges and the lower areas are called depressions, microlows or microdepressions. According to Gustavson (1975) the maximum relief produced by these landforms is about 18 inches.The three basic forms are mounds and depressions, polygons (with microridges) and linear that are elongated in the direction of slope. The expression "hogwallows" appeared first (in print) in the United States but the Australian expression "gilgai" has become the more commonly used word. These landforms are caused by montmorillonitic expansive soils. The study of these landforms is compelling because the resulting micro-topography is anomalous with regard to surface moisture and the expected shrink-swell behavior. Low spots collect water, this should make these areas heave and disappear. So we would expect expansive soils to dampen out low areas, but the exact opposite occurs with these landforms. This means that there must be some special mechanism or process that starts and maintains these landforms. At stake is an unknown process that produces extraordinary differential movements in expansive clays.

There is a similar class of microrelief that are sometimes confused with gilgai that are not related with expansive soils. These landforms have a flat or tableland area between the microknolls without clearly defined microlows. These landforms can have higher relief than gilgai and are more appropriately called pimple mounds, mima mounds, hillocks, prairie mounds, nebkhas, and hummocks. In Texas there are pimple mounds in the same general area as gilgai.

In 1994 I published a new theory that shows a connection between these landforms and overconsolidated (OC) expansive clays, since then I have found several hundred sites in Mississippi and Alabama and several thousand sites in Texas using Google Earth, Bing Maps and sometimes Yahoo Maps. But Hilgard without the benefit Google Earth first made this connection. In 1860 he wrote"..the Hog-Wallow prairie region, in which only the clay marls of the Jackson Group are to be looked for." Most of the expansive clay deposits from Texas to Alabama related with gilgai are either Eocene or Cretaceous age. This results in an approximate age in the range of 34 to 145 Million years. These deposits have had hundreds of feet of sediments eroded from above. This creates the condition of overconsolidation that gets gilgai started. Even the more recent Pleistocene era Beaumont Formation of Texas has been shown to have properties of unloading that produces overconsolidation and a naturally occurring horizontal stress. The result is instability that promotes weathering, shearing, and the formation of gilgai landforms. This blog (Part I) is a close look at the meaning of overconsolidation and how high horizontal stress is connected.

In the solution I proposed, structural and geotechnical engineering concepts are used to solve a geomorphology problem that has been scientifically recognized since 1840. That year John Leonard Riddell published the first surface crack theory about hogwallows in Texas. Riddell speculated that rains would wash earth into shrinkage cracks and convert "them into little valleys, and leaving intermediate hillocks."Amazingly the hogwallows that Riddell first saw in April and May of 1839 are still there 173 years later! Unfortunately there are not clear online images. If you carefully study other sites in Texas and this area you can tell that there are gilgai at this site. I direct you to Google Earth at Lat. 31.338337 and Long. -95.729792.  To see these landforms look at the 1-22-1995 and the 3-8-2011 images at an elevation of about 2350 feet. These images have poor resolution (compare with other locations below) but those are Riddell's hogwallows. You can find several clusters of hogwallows totaling over 200 acres in this neighborhood that he might have seen. This site is associated geologically with the Claiborne Group that includes the Cook Mountain Formation. I located these hogwallows by using Riddell's description that was eighteen miles above Robbins Ferry on the Trinity River. This ferry has a historical marker at 31.074917, -95.701623. Note you can copy and paste these locations into the GE search box.
In Texas gilgai are so common, they sometimes appear in Google Street View as on Broadhead Road in Waxahachie Texas. This amazing photo was taken at 32.419913,-96.77876. Another good street view image of gilgai can been seen at 32.642325, -96.522785. To find these landforms you usually have to look at historical images taken between December and March because during this period gilgai may be holding water and this makes them more visible. This is fairly typical of aerial photos in the southeastern United States. Higher resolution images are also a requirement. There is also a chance it will be dry even it the images are made during the optimum period. Presently the extreme rural areas of Mississippi and Texas does not have adequate coverage to map and define the distribution. This is unfortunate because these landforms could help map unknown areas where damaging expansive clays exist.

An example of gilgai near Macon Mississippi can be seen at 33.118497,-88.507111 and near Marion Alabama at 32.613375, -87424533. I could not find these gilgai in Alabama until new aerial photos were taken during the wet season this past January. Both of these sites are associated with the same geological units, the lower Demopolis and the Mooreville which are chalky Cretaceous deposits. Maybe the most interesting gilgai are near Denton Texas like at 33.179328, -97.220062 (see image 2-27-2001). At a hill top there are polygonal gilgai but it appears that 2 or 3 depressions (darker spots) are usually grouped together. Here linear gilgai run downhill around the hill but still have the occasional depression in the valleys. The elongated or linear gilgai were mentioned by Riddell (1840) and also by Gustavson (1975) but there are no theories to explain this form of gilgai I have seen until now (see PART II of this blog).

E. W. Hilgard (1906) the former state geologist of Mississippi added the element of expansion with "the heavier and more continuous rains wet the land fully, also causing the consolidated mass in the crevices to expand....the result being that the intermediate portions of the soil are compelled to bulge upward, sometimes for six or more inches." In 1932 or maybe 1939 A. Howard wrote "…further penetration of rain will only take place in isolated points where root channels, burrows, ect. have broken down the natural impermeability. When the B1 and B2 horizons become saturated in these isolated spots, the swelling due to the high clay content causes a mound to form."  My 1994 paper was titled Influence of Horizontal Stresses on Gilgai Landforms. In this paper I proposed a whole new concept to explain the origin of these landforms. This paper was referenced in a textbook titled Geomorphology of Desert Environments (2009). J.C. Dixon wrote the chapter that includes gilgai. This is the best review of gilgai theory that I have read. But there was a paper with the title: Structure development in surficial clay soils: A synthesis of mechanisms by Kodikara, Barbour and Fredlund (2002). These writers stated" Maxwell (1994) suggested that continuum buckling due to lateral swelling pressures might be responsible for gilgai undulations." I was surprised when I read this because in my paper I state "It is proposed that at a lower level of stress (than buckling stress), there are changes in vertical stress in a prebuckling mode… This effect could then induce a differential rebound with a buckled appearance." I also state that "measured horizontal stresses in OC (overconsolidated) expansive clays are far below a critical buckling load."  To me differential rebound is clearly not buckling, but if this has been misunderstood, I feel I must clarify this concept. So this blog is inspired by this and I will attempt to fill in the gaps and expand this theory as I published in 1994 in the Journal of Geotechnical Engineering. Because this is a long blog I have left out some of the general information about gilgai and focused on aspects related with this theory and split the blog into two parts. I will explain the three parts of this theory in detail, but here is a quick summary:

1.  THE ORIGIN OF Ko >1: Kis called the (at rest) lateral earth stress coefficient or the ratio of horizontal (effective) stress with the vertical (effective) stress. OC expansive clays have naturally occurring horizontal stress (Ko >1) that creates the instability needed to form gilgai. I will explain the origin of this stress state as a result of it's geologic history where it is loaded and unloaded. Because of horizontal self confinement and shear strength, Ko increases during unloading created by normal erosion, this creates a pre-buckling stress (item 2) that alters the natural confinement pressure in the soil profile.

2.  DIFFERENTIAL REBOUND IN A PREBUCKLING MODE: In part II of this blog, I will contrast the difference between a prebuckling internal stress and a buckling internal stress and show how a prebuckling stress creates differential rebound and the initial mounds and depressions.

3.  HOW POLYGONS AND LINEAR GILGAI FORM: I will then show how mounds and depressions change into the more commonly seen polygons. This happens because the initial mounds and depressions cause a release of self confinement and allows more lateral movement. I will also show how linear gilgai form on slopes. I have developed this since 1994 so this is new information.

THE ORIGIN OF Ko>1; I.E. THE HORIZONTAL STRESSES THAT CREATES GILGAI

An OC clay is a clay that has had more stress (or load) applied to it in the past than presently exists. This creates telltale changes in pore pressure and stress state of the clay deposit that can be measured. In my paper I explained the origin of Ko >1 as follows: "horizontal stresses larger than the vertical in OC clays are primarily residual consolidation stress" and that "when these clays rebound from unloading, internal friction causes a lag in the release of horizontal stress induced during consolidation."  To show this in more detail, I have altered the classic stress history chart that shows the origin of Ko >1.The following interpretation of the chart is my own understanding of what is happening. This chart shows how unloading produces the actual values of Ko. There are ways to measure the horizontal stress of a clay during compression or consolidation and then under a later cycle of erosion or unloading as the clay becomes overconsolidated. Mayne and Kulhawy (1982) state that "any reduction of the effective overburden stress results in overconsolidation of the soil." The vertical stress or the effective overburden stress is simply the effect of the weight of the material above corrected for the effect of pore pressure. Thus the changes in horizontal and vertical stress created by changes in load can be plotted as a stress history. The combined cycles of virgin (first) loading and subsequent unloading are referred to as the stress history of a clay.
Simplified Stress History of an Expansive Clay by Britt Maxwell
A simplified stress path or stress history of an expansive clay is shown in Figure 1. An expansive soil deposit like in the Eocene or the Cretaceous has a much more complex loading and unloading history than is shown by this chart. Whenever there is an unconformity in the deposits above an expansive clay we know that there was a period of unloading, reloading and then a final unloading. This creates loops in the path, but the end effect when the clay is finally unloaded should be essentially the same as the unloading path shown in this chart.

Any straight line through the origin (0) is a line of constant Ko with Ko increasing counterclockwise. In the middle of the chart is the Ko =1 line. This would be the path of a hypothetical frictionless material (like a compressible fluid) during any loading or unloading. Above this line Ko >1, below this line Ko <1. The stress path varies from Ko =1 only because of internal friction. So this chart shows how internal friction causes values of Ko to vary. The internal friction does not change during the loading cycle so Ko is a constant value (a straight line). This value is called the virgin loading and is expressed as Ko here but Konc  has also been used in the literature where the nc stands for "normally consolidated." At the end of the virgin loading cycle (point B) there is an increase in internal friction or shear strength caused by a dropping pore water pressure. This then causes Ko to increase throughout the unloading cycle. So this plot contrasts the difference between the virgin loading cycle and the unloading cycle under the influence of internal friction that begins to change when unloading starts at point B. These two cycles of the stress history are described in more detail as follows:

THE CONSOLIDATION OR LOAD PATH (A TO B): Initially a deposit of clay is a soft mixture of clay and water particles. As more deposits accumulate above, the clay is subject to more compression. The clay becomes denser because water is squeezed out with positive pore pressures. This effect causes the transfer of the vertical compressive force into the horizontal direction at a constant rate. Ko is less than one and constant during the whole loading cycle. The actual number usually varies between .4 and .8 and the value depends on the clay.

THE UNLOADING PATH (B TO C): The overconsolidated coefficient of earth pressure at rest has been represented by different symbols in the literature. Some of these are Kou , Ko(oc), and Kooc. An Equation was proposed for this coefficient by Mayne and Kulhawy (1982). More recently Michalowski (2005) reviewed the proposed Ko functions for loading and unloading. Note that this paper is available online. As the clay is unloaded it becomes unsaturated and overconsolidated and as the vertical load decreases a negative pore pressure increases. This causes the clay to gain strength and develop more resistance against the particles from sliding past each other. If you could freeze the material and lock the particles together at point B the unloading path would be horizontal and the horizontal stress would not change. So any drop in horizontal stress during unloading is allowed by interparticle shifting. This is what I call “unloading shear.”

Because of the increase of internal friction at the beginning of unloading, the stress path shifts horizontally when unloading begins and the horizontal stress drops slower than then the vertical stress. This causes Ko to steadily increase as unloading progresses. Ko >1 and a negative pore pressure now identifies the clay as being overconsolidated. As Ko increases the clay becomes more unstable. The dryer inter-particle shifting must create fractures or distort the clay to relieve horizontal stress. The process of losing horizontal stress during rebound is herein named “unloading shear” and it is this process that produces gilgai and the associated shear joints in expansive clays.

In my paper I use Rankine theory to compute a maximum value of Ko. This is shown as point C (the end of the unloading path) in Figure 1. For an average friction angle Ko is limited to a value of about 3. I don't know the smallest values of Ko that could produce gilgai, but it might be as low 1.5 in ideal conditions. It depends on the state of the surface soils. I think often the surface soils would be highly weathered and have Ko close to unity. When this happens these soils can't participate in forming gilgai and surface cracks can appear. Two gilgai sites in Mississippi on public land do not have any significant surface cracks even in drought. In the photo above there are no surface cracks visible, but the ground is dry. I interpret this as meaning that Ko must be greater than one very near the surface. These are sites where a surface crack origin would not work and provide evidence that surface crack theories are not correct. It is important to realize that Ko and instability steadily increases during the unloading cycle and the formation of gilgai with the related shear joints is an important (horizontal) stress release mechanism. This process contributes to the weathering of expansive clays. Shear joints initially form in the subsurface around the perimeter of gilgai mounds and are explained in more detail in part II of this blog. I will also perform a more detailed comparison with this theory and the older surface crack theories.

Here is a link to part II of this blog:

The Origin of Hogwallows and Gilgai - PART II  The conclusion of this blog.


Saturday, August 3, 2013

Extreme Building Damage Caused by Yazoo Clay


Everytime I look at this picture I can't help but compare it with earthquake damage. The end result can be very similar. Geologic deposits like the Yazoo clay are often called "highly active" and the movement is not sudden like an earthquake. You get a little bit every day and some days you get a retraction where cracks close, door that would not close last month suddenly work fine. But when you get heaving (or uplift) in high rise construction, the second floor tries resist the movement and the first floor behaves like it's being squeezed in a giant vice.

Extreme damage to structures can result from expansive soil movements. This photo is a reproduction of a Polaroid that I took before I went to the University of Texas. It shows the first floor of a high rise building in Jackson Mississippi. This might be the most dramatic photograph of interior building damage from expansive soils ever taken. Each floor of the building was a flat plate structural slab (self supporting). The first floor slab was constructed with an undrained 6 inch open void underneath. However, by the time the building was 8 years old, the void had closed and first floor had heaved as much as 8 inches. The problem was that the expansion potential (uplift) of the Yazoo clay was seriously underestimated. 

Expansive soil damage to the first floor of a high rise
building in Jackson Mississippi.

The floor of this room was a structural slab that was supported by the same concrete columns that supported every floor. On the first floor heaving of the slab caused the structural slab to disconnect from the columns in an odd reversed punching shear failure. A punching shear failure is when a structural slab shears away from a supporting column. Normally the slab falls down; but in this case the slab moved up (in reverse) from expansion of the clay. The columns were supported by deep drilled piers and were not damaged. Fortunately, this part of the building structure was stable.

Damage seen in this photo is the result of crushing metal stud partitions (in compression) that were constructed from the first floor to the bottom of the second floor slab. The damage was so severe that most interior doors had been removed on the first floor. In the left side of the photo is a door that has been replaced by tapping sheets of brown wrapping paper over the opening (a common solution). The door near the center of the photo and the one on the right has been removed. In the room in the foreground partitions have failed by rupturing the wallboard. In the background the wallboard buckled and disconnected from the studs.

In Central Mississippi this kind of construction represented the first efforts by engineers to isolate the bottom floor (using structural self supporting slabs) from the expansive soils in the 70's and early 80's. Numerous buildings were built just like this. I doubt that any of them still exist like they were originally built. We now know that a typical rate of heave for a normal soil profile with Yazoo clay is about ¾ inch per year. So a 6 inch void like this building had, couldn't last more than 8 years in a typical setting. In this particular case the expansive clay was exposed at the surface, there was poor drainage, and it potentially heaved at a rate of more than double the amount from a typical condition. That is the highest heave rate that that I know of in Central Mississippi.  One end of the building was built several feet below the surrounding natural grade. So construction required the removal of natural inactive soils above the clay. This created an unloading condition that promoted rebound of the expansive clay. This construction also created a condition of poor drainage around the structure.  Surface drainage that was constructed rapidly deteriorated from heaving that occurred in the ground around the building.

To repair the building, the entire first floor and the slab was completely removed and replaced when this building was about 9 years old. As a result this building is still in service today. The repair involved increasing the void space size to 30 inches. However, clearances under plumbing in the crawl space had to be recently dug out again in part of the crawl space. At the other end of the building the new crawl space was still intact and some shrinkage had actually increased the crawl space by a few inches.

Unfortunately buildings on drilled piers like this one today are still having issues with Yazoo clay in Central Mississippi. My studies of these newer buildings indicate these primary issues:

1. Inadequate clearances specified for utilities or specific elements of the foundation.

2. Inadequate retainage to prevent soil flow into the crawl space or voids under grade beams.

3.  Inadequate drainage of the void spaces or crawl spaces.

4.  Inadequate construction review of void or crawl spaces.


All rights reserved by Britt Maxwell P.E.