Alvarado Final Paper

8/12/2019 Alvarado Final Paper

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BIO-MEDIATED SOIL IMPROVEMENT: CEMENTATION OF

UNSATURATED SAND SAMPLES

Submitted to: NEES Inc.Submitted by: Daniel AlvaradoHome Institution: Arizona State UniversityHost Institution: University of California, DavisPhD Advisor: Jason DeJong


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Table of Contents1 Introduction ............................................................................................................. 32 Methodology............................................................................................................ 53 Results.................................................................................................................... 114 Discussion .............................................................................................................. 16

5 Acknowledgements................................................................................................ 17

FiguresFigure 1: Loose Sand to Sandstone............................................................................. 3Figure 2: Bio-Mediated Calcite Precipitation (DeJong et al) ..................................... 5Figure 3: Shear Wave Signal ...................................................................................... 6Figure 4: Scanning Electron Microscope.................................................................... 7Figure 5: Distribution of Calcite on Sand Grain Particles .......................................... 7Figure 6: Initial Load Frame Setup (not to scale)....................................................... 9Figure 7: Percolation Test 2 Setup............................................................................ 10Figure 8: Test Cell with Bender Element ................................................................. 10

Figure 9: Test Cells with Bender Elements and Split Spoon Aquarium Rock ......... 10Figure 10: pH vs Time .............................................................................................. 11Figure 11: Shear Wave Velocity............................................................................... 12Figure 12: Cameco Unconfined Compression 1....................................................... 13Figure 13: Cameco Unconfined Compression 1....................................................... 13Figure 14: SEM Ottawa 50-70 before Bio-Soil Treatment....................................... 14Figure 15: SEM Ottawa 50-70 after Bio-Soil Treatment.......................................... 14Figure 16: SEM Ottawa 50-70 after Bio-Soil Treatment X 10.00k zoom on calcitestructures at particle to particle contact .................................................................... 15Figure 17: SEM Ottawa 50-70 after Bio-Soil Treatment X 2.00k zoom on calcitestructures at particle to particle contact .................................................................... 15

EquationsEQ. 1: Net Urea Hydrolysis ReactionEQ. 2: Net pH increase: [OH-] generated from NH4+ production >> [Ca2+]EQ. 3: Shear Wave Velocity V (m/s)

Abstract

Bio Mediated Soil Improvement (Bio-Soil) is new and innovative research withingeotechnical engineering which can be used in the fields of earthquake engineering andliquefaction prevention. During events of cyclic loading from earthquakes and otherevents, liquefaction in loose sands can occur, causing foundation deformation and/orfailure. The Bio-Soil method is an interdisciplinary field consisting of collaboration withthe studies of microbiology, geochemistry, and civil engineering to find naturaltreatments for ground improvement. In this process, technically termed as MicrobiallyInduced Calcite Precipitation, calcium carbonate is precipitated within the sand particlesto form bonds; therefore the process transforms loose sand susceptible to liquefaction intosandstone. Laboratory findings, observations, and test results are presented along withfuture plans of optimization, up scaling, and transferring Bio-Soils into practicalapplication.


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1 Introduction

1.1 Current Soil Improvement Practice

With over 40,000 yearly projects and approximately $6 billion/ year worldwide in the

industry, new environmentally friendly techniques for soil improvement have becomenecessary (DeJong et al). Current grouting and ground improvement techniques inpractice include grouting via cement, chemical, compaction, fracture and jet, micro piles,jacked piers, driven piers, ground anchors, shoring, soil nailing vibro compaction,concrete columns and piers (Hayward Baker). Focusing on just grouting with theexception of sodium silicate, almost all of these manmade synthetic chemical groutingtechniques are hazardous and/or toxic (DeJong et al).

1.2 Background and Motivation for Research

The purpose of the Bio-Mediated Soil Improvement research is to find a way to use

bacteria produced calcium carbonate to strengthen cohesive soils in the attempt toeliminate the risk of liquefaction and generally increase the stability of soil during eventssuch as earthquakes, landslides, etc. Liquefaction is a geotechnical phenomenon whichoccurs mostly in unconsolidated saturated cohesive soils such as loose sands and silts. Inthe event of liquefaction, a soils consistency may go from a solid state to having theproperties of a heavy liquid. This occurs from the rise of pore water pressures duringcyclic undrained loading or softening (e.g. an earthquake) (Ishihara 353). The soilseffective stress decreases as each grain of sand or silt is suspended and surrounded by athin layer of water. Water has no shear strength which in effect causes structures to sinkuntil the displaced soil matches its weight (Youd).

With current practice of synthetic man made grouting techniques being harmful to theenvironment and people, the Bio-Soil method is being studied as a natural solution tosynthetic grouting. Bacteria is harnessed to help prevent liquefaction and possibly usedfor other applications by forming calcite structures within the sand particles to increasethe stiffness of the soil.

Figure 1: Loose Sand to Sandstone

Loose Sand Sandstone


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1.3 Overview of Use of Calcite Precipitation to Increase Soil Strength

Bio soils are an integrated observation and experimentation between geotechnicalengineering, microbiology, and chemistry. Bio mediated soil improvement is the processin which a bacteria precipitates calcium carbonate within a soil sample in attempt to

increase its shear strength and overall resistance to liquefaction. Sporosarcina Pasteurii, used to precipitate the calcite, is an aerobic bacterium which is found to naturally occurin soil deposits (Fritzges). Since the bacteria are innate to the earth, it may not poseenvironmental risk in ideas of future in field use (Fritzges).

When the bacteria are microbially induced, meaning it is controlled biologically; it canprecipitate calcite through the chemical process and alter the engineering properties ofloose sand. Outlined by EQ 1-2 and displayed in Fig. 1 is the chemical process involvedin the precipitation of calcite throughout a typical sand sample during the biologicaltreatment process. The main catalyst for the precipitation of calcite and food for thebacteria is the Urea Broth Solution (ubroth) consisting of variable concentrations of

NaHCO3, NH4Cl, CaCl2, Urea, and Bacto (trademarked various blend of nutrients).Microbially Induced Calcite Precipitation (MICP) is a chemical process in which thebacteria consumes and breaks down urea to form ammonia, bicarbonate and carbonateions. The calcium ions within the ubroth solution fed to the bacteria are then free to bondwith the carbonate to form a level of cementation on each sand grain. This makes amore cohesive bond within the soil sample particle matrix as it is one of the most reactiveand common minerals found in the earths surface (Morse). During this process theammonia plays an important role as it helps increase the pH making an ideal environmentfor the bacteria to feed on the urea and precipitate calcite (Fritzges).

Net Urea Hydrolysis Reaction: NH2CONH2+3H2O2NH4++ HCO3

-+ OH- EQ. 1

Net pH increase: [OH-] generated from NH4+ production >> [Ca2+] EQ. 2


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Figure 2: Bio-Mediated Calcite Precipitation (DeJong et al)

2 Methodologies

2.1 Process Monitoring and Collecting Data

Characteristics of liquefaction in soils have been determined by a combination oflaboratory tests of undisturbed samples and in situ tests. The in situ tests used include the

standard penetration test (SPT), the cone penetration tests, and the dilatometer test.Considering these all are in situ penetration tests that are somewhat unreliable at differentdepths and unfeasible for lab testing, shear wave velocity measurement has also beenused (Tokimasu 33).

Shear Wave Velocity

The shear wave velocity is a property of soil that can help identify density and moredirectly stiffness (Lee). It is used directly in liquefaction analysis and to identify thegeneral characteristics of a soil in both the lab and in situ testing (Tokimasu 33). Astandard loose sand may have a shear velocity between 100-200 m/s. A liquefiable soil is

any soil falling under a shear velocity of 500 m/s. The goal of the MICP is to raise thatshear wave velocity above 500 m/s and to stay in the range of 500-1000 m/s with theproperties more associated with that of sandstone. This shear wave velocity is the timemeasured using bender elements in a sample to propagate a wave and measure the returnof that wave through the sample using an oscilloscope (Fritzges). Fig. 3 shows a typicalshear wave signal achieved during a Bio-Soil treatment. The bottom of the first arrivaltime is recorded as seen in Fig. 3 as T and inserted into a conversion equation EQ 1. ABio-Soil process that is precipitating calcite will have a gradual increase in shear wave


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velocity in relation to the short time (2-4 hours, 1 treatment) after the pH reaches anaverage of ideal pH 9.

V (m/s) = [Tip to Tip Distance of Bender Elements (mm)]/[(T (sec)-5)/1000] EQ. 3

Figure 3: Shear Wave Signal

pH

PH is monitored as a technique to check if biological activity within the sand sample isoccuring. The effluent of each sample is measured using a pH strip after it has beensitting in the sample for the alloted time (approx 1.5 -2.5 hours) as a reasurrance ofcalcite precipitating in the sand sample. The ideal range of pH falls between 8.5 and 9.3,specifically at 9 for bacteria to precipitate calcite.

SEM

In addition to the pH and bender element readings Scanning Electron Microscope (SEM)observations have been conducted on extruded samples to compare with data from thepumped samples. The SEM (see Fig. 4) is a tool used in most material sciences when themagnification is needed to have more contrast. How the SEM works is that it images thesample surface by scanning it with a high energy beam of electrons in a certain patterncalled the raster scan pattern much like in a television. The scan gives us clear images ofthe topography of the item observed or as in this case the sand particles and calcitestructures. The ideal distribution of calcite would be having calcite precipitated only atthe particle contact points only as seen in Fig. 2. What actually happens though is mostof the calcite precipitating with a layer of calcite structures forming on the sand particles.Fig. 11-14 in the Results section displays the SEM of what the percolation methods

treatment accomplished as somewhat more preferential distribution. The SEM also givesus a clear image of where the bacteria was precipitating calcite and an idea of how denseand dispersed the bacteria was throughout the sample.


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Figure 4: Scanning Electron Microscope

Figure 5: Distribution of Calcite on Sand Grain Particles

The data collected from both percolation device tests will give a better comparison of anon saturated sample to a saturated sample which is treated with calcite precipitationalong with the effects of increasing the concentration of the ubroth.

Unconfined Compression and Flow Rates


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Future additional data collected for the unconfined compression and flow rates of thepercolation method in comparison to the pumping method will give valuable data oncomparing to the two methods for optimization. Further tests can also be conducted afterextruding the sample and performing triaxial and/or direct shear testing (DeJong et al).

2.2 Set-up for the Percolation Device

Several methods and variations of those methods have been used for the microbialinduced cementation process at the UC Davis Soil Interactions Laboratory. The testing isstill at the small scale laboratory stage with optimization as the primary objective. Thecurrent method of pumping with complete saturation has been used with severalvariations of continuous pumping with effluent, reverse directional pumping, nutrientcirculation, and using pH and bender element readings to observe the shear wave velocityand calcite precipitation as process monitoring techniques. An additional test ofobserving percolation and the bacterias calcite precipitation through a soil sample willdisplay valuable data to compare when a sample is not completely saturated. An

important factor to note within the percolation method is that the ubroth concentrationhas also been increased which may have effected the results of calcite precipitated.

2.3 Test 1: 4 day Percolation Test

The percolation device is set up much like the standard 6 inch cells that have been usedfor previous tests. Four 12 cells with a 2 diameter were assembled and observed forthe first percolation test. To begin, 3 large porous stones were to be used for each cell.One stone was placed on the bottom cap with the cell then connecting to the bottom cap.The soil sample was then pluviated into the cell at 4.25 inches tall. The following layerconsisted of two more porous stones with a drilled top cap resting above (see Figure 6).The test cell was then placed in the load frame with 45 lbs of confining stress. A tube foreffluent was attached and the test began (see Figure 6).


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Figure 6: Initial Load Frame Setup (not to scale)

The percolation device test 1 spanned over a 4 day testing period. For the day 1 test abatch of bacteria with the new ubroth concentration was poured through at approximately.75 pore volumes. A three hour set time was observed just as the ubroth 1 withoutbacteria was allowed to percolate through. At 1.5 hours after the new ubroth 1 wasintroduced, the effluent was then poured through the sample and allowed to percolatethrough for another 1.5 hours. During this time, pH readings were made to make surethat precipitation was occurring along with observation of percolation using differentcolored dyes. After this 3 hour time for the ubroth 1 a new batch of ubroth 2 was madeand allowed to percolate through at the same method. This process continued until 12AM where day 1 was complete. Day 2 began the next day at 6 AM and observed thesame process excluding the initial bacteria ubroth. This process continued for days 3 and4 with the same procedure. At the end of day 4 the sample was then allowed to beextruded, cleaned, and observed for calcite precipitation. The final step was to clean upthe equipment and gather the effluent pH data and observations for analysis.

2.4 Percolation Test 2: Bender Elements

The percolation device test 2 is identical to the original 4 day span test with the additionof bender elements on the cells and test time decrease to 48 hours (see Figures 7-9).Ottawa 20-30, 50-70 and Aquarium Rock are more poorly graded sands or samples usedin Test 2 with bender elements. Cameco being a more well graded sand is also sampledwith bender elements for Test 2. As pH readings are being taken the bender elements areused to collect shear wave velocities throughout the test. In addition to the 4 bender

4.25

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1.5

12

8.25

45lbs


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3 Results

Using the process monitoring techniques of pH levels, shear wave velocity, unconfinedcompression, flow rates, and scanning electron microscopy (SEM), valuable data hasbeen collected to help optimize the biological process of calcite precipitation. The

following results and data observations were made from Percolation Test 2 conductedover 48 hours.

Observing Fig. 6 the pH reached the optimum range pH between 8.5 and 9.3 afterapproximately 20 hours of treatment. This steady measurement averaging out to a pH of9 is the ideal environment for the bacteria to precipitate calcite.

pH

7.0

7.5

8.0

8.5

9.0

9.5

0.00 4.00 8.00 12.00 16.00 20.00 24.00 28.00 32.00 36.00 40.00 44.00 48.00

Time (hr)

pH

Aquarium Rock

Ottawa 20-30

Cameco

Ottawa 50-70

Figure 10: pH vs. Time


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Observing Figure 11 the shear wave velocity of 500 m/s, beyond the limit of a liquefiablesoil, correlates with the ideal pH level of 9 as most of the test samples reach over thatlevel at about 25 hrs into the test. The highest shear wave velocity of 1600 m/s occurs inthe Ottawa 20-30 sample which is a poorly graded sand sample.

Shear Wave Velocities

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

1600.0

1800.0

0.00 4.00 8.00 12.00 16.00 20.00 24.00 28.00 32.00 36.00 40.00 44.00 48.00

Time (hr)

Shea

rWaveVelocity(m/s)

Aquarium Rock

Ottawa 20-30

Cameco

Ottawa 50-70

Figure 11: Shear Wave Velocity

Figures 12 (psi) and 13 (kPa) display the unconfined compression results obtained fromthe Cameco sand sample. The maximum stress of approximately 300 psi and strain of1.39% was achieved before any cracking or deformation occurred.


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Cameco Unconfined Compression

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

0.00% 0.20% 0.40% 0.60% 0.80% 1.00% 1.20% 1.40% 1.60%

Strain (%)

Stress(psi)

Figure 12: Cameco Unconfined Compression 1

Cameco Unconfined Compression

0.00

500.00

1000.00

1500.00

2000.00

2500.00

0.00% 1.00% 2.00% 3.00% 4.00% 5.00% 6.00% 7.00%

Strain (%)

Stress(kPa)

Figure 13: Cameco Unconfined Compression 1


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The SEM images (Figures 14-17) display the before and after affect of Bio-Soil treatmentfor the Ottawa 50-70 sample for the Percolation Test 2. Figure 14 displays the gaps andvoids in which water can fill during an earthquake leading to liquefaction. Figure 15 isan overview of the treated sand sample with calcite precipitated throughout the soilsample. Closely observing the Ottawa 50-70 from the zoom on the calcite structures (see

Figures 16-17) the preferential precipitation of calcite at the particle contacts can be seen.Also, observing Fig. 17 the bacteria indentations can be seen as being dispersedthroughout the entire calcite structure. It can be roughly assumed that with these SEMobservations that calcite was evenly distributed throughout the Ottawa 50-70 sample.

Figure 14: SEM Ottawa 50-70 before Bio-Soil Treatment

Figure 15: SEM Ottawa 50-70 after Bio-Soil Treatment


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Figure 16: SEM Ottawa 50-70 after Bio-Soil Treatment X 10.00k zoom on calcitestructures at particle to particle contact

Figure 17: SEM Ottawa 50-70 after Bio-Soil Treatment X 2.00k zoom on calcitestructures at particle to particle contact


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4 Discussion

4.1 Optimization

The main goal of research to be achieved in the 2008 summer REU program was

optimization of the laboratory Bio-Soil treatment methods. The first month involvedpumping treatments through fully saturated samples. The next 6 weeks involved thepercolation of treatments through unsaturated samples with increased ubrothconcentrations. It has been observed that the percolation method has displayed results ofstiffer extruded sand samples. It is still unknown if these results occur from the actualmethod of percolation or the fact that the ubroth concentration increase may give thebacteria more to feed on and precipitate calcite or possibly a combination of both.Calculations of the number of particle to particle contacts and volume of liquid retainedat those contacts are currently being conducted as a way to better optimize andunderstand the effect of unsaturated media and varying the concentration of ubroth.

4.2 Up scaling

Recent funding for the up scaling to centrifuge modeling has been approved for futureresearch studies of Bio-Soil treatments. The UC Davis centrifuge will be used inconjunction with the findings from laboratory tests from the SIL to move closer topractical field applications.

4.3 Future Research and Goals

Some purpose to the further conduction of these tests may also come from the correlationof shear wave velocity to liquefaction resistance having fairly new findings with limited

field testing (Tokimasu 34). There have been recent advances in the research of biomediated soil improvement to allow for more accurate measurements of bacteria calciteprecipitation and up-scaling to centrifuge experiments (DeJong et al). The accuracy mayincrease from the measurement of the ratio between urea injected and urea found in theeffluent measured by a spectrometer as the centrifuge tests will give more in fieldresults (DeJong et al). The Nesslerization Method of using spectrometer readings fromammonia in ubroth effluent will assist in the optimization of both laboratory tests andcentrifuge modeling for the Bio-Soil process. The end result may be achieved in thepossible future replacement of chemical and synthetic man made grouting techniques oftoday and with the natural, more environmentally friendly Bio-Mediated SoilImprovement techniques.


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5 Acknowledgements

The research conducted at the University of California, Davis is supported by the GeorgeE. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) with fundingprovided by the National Science Foundation (NSF). A special thanks is extended out to

NEES CEO Steve McCabe and all NEES staff for offering opportunities toundergraduates to obtain research experience and including but not limited to the SoilInteractions Laboratory PI Jason DeJong, Centrifuge PIs Bruce Kutter and Dan Wilson,graduate student mentors Brina Mortensen, Brian Martinez, Matt Weil, Robbie Jaegerand Nick Yafrate, and undergraduate student researcher Jack Waller.


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References

DeJong, Jason et al [2008]. Bio-Mediated Soil Improvement, 1stInternationalConference on Bio-Geo-Civil Engineering. Delft, The Netherlands.

Fritzges, Michael B. [2005]. Biologically Induced Improvement of the Response ofSands to Monotonic Loading,M.S. thesis, Department of Civil & EnvironmentalEngineering., University of Massachusetts, Amherst, Massachusetts.Ishihara, K. [1993]. Liquefaction and flow failure during earthquakes,Geotechnique43, No. 3, 351-415

Hayward Baker. Services. 2003. 9 Sept 2008

Lee, J.S., and Santamarina, J.C. [2007]. Seismic monitoring short-duration events:

liquefaction in 1g models, Canada Geotech. J. 44: 659-672

Morse, J.W. [1983]. The Kinetic of Calcium Carbonate Dissolution Precipitation,Carbonates: Geology and Chemistry, 227-264

Tokimatsu, K., and Uchida, A. [1990]. Correlation Between Liquefaction ResistanceAnd Shear Wave Velocity, Soils and Foundations, Vol. 30, No.2, 33-42

Youd, T.L., and Idriss, I.M. [2001]. "Liquefaction Resistance of Soils: Summary reportfrom the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation ofLiquefaction Resistance of Soils",Journal of Geotechnical andGeoenvironmental Engineering, ASCE, 127(4), 297-313

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Alvarado Final Paper