Three-Dimensional Swell Test

University of Texas at Arlington

Civil Engineering Department

Laboratory Test Report

Three-Dimensional Swell Test on Soil from Burleson, Texas

Written by:

Richard Benda

Joseph Muhirwa

Robert Sargent

July 11, 2012

Table of Contents                                                                                                           Page
Abstract..............................................................................................................................3
Introduction........................................................................................................................4
Equipment and Materials...................................................................................................5
Methods and Procedure......................................................................................................5
Data, Results, and Discussion............................................................................................6
Conclusion.........................................................................................................................8
References.........................................................................................................................8
Appendices

            Appendix A: Dial Readings and Corresponding Vertical Swell…………………10

List of Tables and Figures                                                                                             Page
Figure 1 – Sample Preparation……………………………………………………………..3

Figure 2 – Sample in Gyratory Compactor………………………………………………...4

Figure 3 – Samples in Water Tub……………………………………………………….….5

Table 1 – Natural Soil vs. Lime Treated Soil………………………………………………6

Figure 4 – Vertical Swell Strain vs. Elapsed Time…………………………………...…….7

Figure 5 – Swell of 0% and 6% Lime…………………………………………………..…..8

Table 2 – Burleson, 0% Lime……………………………………………………………...11

Table 3 – Burleson, 6% Lime…………………………………………………………...…12

Abstract

            In this laboratory test, a high-plasticity clay from Burleson, Texas, underwent a three-dimensional free swell test in order to find the heave potential of the soil. Soils with smectite clay minerals such as montmorillonite, bentonite, and illite tend to adsorb a high amount of water which results in large volume changes. These volume changes can cause dramatic damage to road and building foundations which can be very costly to repair. It is for this reason that performing the three dimensional swell test to determine soil heave is important. For this particular test, a soil with no lime was compared to a sample with 6% lime in order to observe the heave potential of both soils as well as the reduction of swell that will result from adding lime to the soil. The soil used in this test was a high plasticity clay from Burleson, Texas, with a high sulfate content (roughly 3000 parts per million). The process of this test started with bringing a soil to its optimum moisture content, which was found earlier from a standard proctor test. Prior to this, the amount of soil required to fit in the cylindrical mold was determined using the optimum moisture content as well as the dry density of the soil. It was at this point that the lime was added to one of the samples. Additional water was added to this sample to compensate for the hydration of the lime. A gyratory compactor was then used to compact the sample into the mold. After, a triaxial machine was used for the purpose of extruding the sample from the mold. The height and diameter of each sample cylinder is taken at this point. Pore stones were placed on the top and bottom of both samples, and a membrane was placed around both samples. These samples were placed into a water bath with a dial indicator on the top to measure vertical swell. Readings are taken periodically for seven days, after which the samples are taken out and the diameter and height is measured. This data is used to determine the heave potential of the soil.

Introduction

            A three-dimensional free swell test is a useful test to perform upon an expansive soil to determine the swelling nature of the expansive clay in the soil. In this particular three-dimensional swell test, a control sample with no lime was compared to a sample with 6% lime in order to observe how much lime will reduce swelling in expansive soil. It is important to perform this experiment and determine these properties because according to the US Department of Housing and Urban Development, the repair of damage on structures caused by expansive soils costs about 9 billion dollars per year. Soils expand because certain clay minerals tend to adsorb a high amount of water, which in turn causes the clay to expand. Likewise, in the drier seasons the water is evaporated from the clays which causes them to shrink. Smectite clay minerals such as montmorillonite, bentonite, and illite are responsible for this behavior. It is expected that the 6% lime sample will swell much less compared to the sample with no lime. However, since the soil contains a fairly high amount of sulfate, it is likely that the lime will react with the sulfate and form Ettringite, which may induce some additional swelling.

Equipment and Materials

• Balance
• Porous stones
• Rubber membrane
• two gauges and stands
• tub
• gyratory compacter
• bowls and mixing utensils
• ziploc bags
• mold
• caliper and a Pi Tape

Methods and Procedure

The following procedure was used to perform a 3-D swell test on the soil from Burleson, Texas

1.      On the first day the 0 percent lime and 6 percent lime samples were prepared. The preparation started out by collecting enough soil so the samples will be compacted to the right dimensions. Next the appropriate amount of lime was collected for the 6 percent lime sample and mixed in with the soil. After that water was added to the two masses of soil. The amount of water was determined by the optimum moisture content for that soil plus some additional water for the 6 percent lime mixture. After the two mixtures were mixed to satisfaction they were put in ziploc bags and transported to the civil engineering lab to be compacted into cylinders. The samples were put into a mold which was put into a gyratory compactor to be compacted. After that the samples were taken out of the mold and the dimensions and mass of each cylinder were taken. To prepare each cylinder for the test a porous stone was put on the top and bottom and then a membrane was placed on each cylinder. After the cylinders were ready they were placed in a tub that was filled with water. A gauge was placed on top of each cylinder to monitor the vertical movement. The cylinders were left in this tub for 7 days and readings were taken twice a day.

2.      After seven days the cylinders were taken out of the tub and their dimensions and mass were once again taken.

3.      Using the initial and final dimensions of the cylinders the change in volume of each cylinder was calculated. Also the gauge readings were used to plot the vertical strain % vs. time.

Results, Data and Discussion

Table 1 - Natural Soil vs. Lime Treated Soil

	Natural Soil	Lime Treated Soil
Initial volume	234.909	256.596
Final volume	302.54	292.021
Volume change	67.631	35.425
Volumetric Strain (%)	28.79	13.806

Vertical Swell Strain vs. Elapsed Time

Figure 4 - Vertical Swell Strain vs. Elapsed Time

From observing Table 1 and Figure 4, it was very apparent that combining lime with expansive soil was effective in reducing overall swell. Vertical swell strain was reduced by around 0.65 percent, and volumetric strain was reduced by 14.98 percent. Some swell may have resulted from the lime in the 6% sample reacting with the sulfate in the soil to form Ettringite, but even with this additional swell the sample with lime was effective in reducing swell.

Conclusion

            After completing the three-dimensional free swell test, it was determined that even though the sulfate in the soil may have resulted in some additional heave, the addition of lime into a soil was quite effective in reducing swell. The sample with lime reduced vertical swell strain by over 0.6%. Volumetric strain was reduced by a considerable amount as well at around 15%. The goal of this laboratory test was to observe just how effective lime is in reducing expansive soil heave, and from observing the graph that goal was accomplished. There was only one likely source of error in this laboratory test. Due to the sample with 6% lime having additional height since it had additional material in the cylinder, at one point the top of it swelled out of the water. Additional water had to be added to ensure that the sample with 6% lime would continue adsorbing water at the same rate as the control sample.

References

Das, Braja M. (2009). Principles of Geotechnical Engineering, 25th ed., Cengage Learning, Stanford, CT.

Miller, D. J., Nelson, J.D. (1992). Expansive Soils: Problems and Practice in Foundation and Pavement Engineering, John Wiley & Sons, Inc., Toronto, Canada.

Punthutaecha, Koonnamas. (2002). Volume Change Behavior of Expansive Soils Modified with Recyclable Materials. ProQuest Dissertations and Theses, Ann Arbor, MI.

Appendix A

Dial Readings and Corresponding Vertical Swell

Table 2 – Burleson, 0% Lime
Time (Hrs)	Dial Reading	ΔH  (inches)	(ΔH/H)%
0	0	0	0
0.5	20	0.02	0.431096
1	40	0.04	0.862193
2	60	0.06	1.293289
4	80	0.08	1.724386
8	120	0.12	2.586579
12	160	0.16	3.448772
24	222	0.222	4.785171
36	226	0.226	4.87139
48	232	0.232	5.000719
60	234	0.234	5.043828
72	237	0.237	5.108493
84	239	0.239	5.151603
96	240	0.24	5.173157
108	246	0.246	5.302486
120	252	0.252	5.431815
132	258	0.258	5.561144
144	265	0.265	5.712028

Table 3 - Burleson, 6% Lime
Time (Hrs)	Dial Reading	ΔH  (inches)	(ΔH/H)%
0	0	0	0
0.5	20	0.02	0.431096
1	40	0.04	0.862193
2	60	0.06	1.293289
4	80	0.08	1.724386
8	120	0.12	2.586579
12	160	0.16	3.448772
24	182	0.182	3.922978
36	196	0.196	4.224745
48	222	0.222	4.785171
60	224	0.224	4.82828
72	228	0.228	4.9145
84	229	0.229	4.936054
96	230	0.23	4.957609
108	231	0.231	4.979164
120	232	0.232	5.000719
132	235	0.235	5.065383
144	235	0.235	5.065383