Anuchit Uchaipichat

A Temperature Controlled Triaxial Apparatus for Testing Unsaturated Soils

This paper describes a modified Bishop–Wesley triaxial apparatus for testing unsaturated soils at elevated temperatures. The suction is applied using the axis translation technique. The cell liquid temperature is controlled through a heating element, and a thermal sensor installed inside the triaxial cell. Experiments are carried out at temperatures up to 60°C. Potential difficulties in the use of the equipment are identified and solutions are discussed for their mitigation. The image-processing and the cell liquid measurement techniques are used to measure the overall volume change of the sample. The performance of these two techniques is reported.

Bearing Capacity Characteristic of Unsaturated Granular Soils

An experimental program of laboratory bearing tests was performed to characterize the bearing capacity of foundation on unsaturated granular soils. All tests were performed by pushing a circular rod on the surface of compacted sand specimens with different values of matric suction until failure. The test results show an increase in ultimate bearing capacity with increasing matric suction at low suction value but a decrease in that at high level of suction. The comparisons between the test results and simulations using the expressions proposed in this paper are presented and discussed. Good agreements are achieved for all testing values of suction.

Compaction Characteristics of Non-Gravel and Gravelly Soils Using a Small Compaction Apparatus

The standard Proctor test has been widely used and accepted for characterizing soil com- patibility for field compaction control. This paper presents a time- and cost-effective method to predict standard Proctor compaction characteristics of non-gravel and gravelly soils using a proposed small appa- ratus. This small apparatus is similar to the standard Proctor apparatus and easily introduced into soil mechanics laboratory. A comparison of the compaction characteristics of non-gravel soils measured from the proposed small apparatus and from the standard Proctor apparatus shows that this small apparatus can be used as an alternative to the standard Proctor apparatus and regarded as a practical tool for non-gravel soils. For gravelly soils, gravel content mainly controls compaction energy transmitted to the fine fraction and hence its compaction characteristics. A relationship between the generalized optimum water content of the fine fraction in the gravelly soil and the gravel content is established. This relationship leads to an effective method of predicting standard Proctor compaction characteristics of gravelly soils com- pacted in standard molds using compaction results from the proposed small apparatus. Comparisons between the predicted and the measured compaction characteristics are in very good agreement.

Simulations of Bearing Capacity of Foundation on Unsaturated Granular Soils

Typically a shallow foundation is chosen to support several types of common structure. Several equations for the ultimate bearing capacity of shallow foundation have been proposed with assumption of fully saturated or completely dry conditions. In fact, almost 40 percent of natural soils on the earth surface are in an unsaturated state. Therefore, the ultimate bearing capacity of shallow strip foundation on unsaturated granular soils is developed in this paper using limit equilibrium concept. The simulations from the developed equation for a laboratory-compacted-sand are performed. The results are carefully presented and discussed.

Influence of Curing Pressure on Unconfined Compressive Strength of Cemented Clay

The soil-cement columns are generally installed and cured in the soft clay layers under confining pressure. The strength of the soil-cement columns may be influenced by confining pressure during curing period. In this study, the main objective was to study the influence of curing pressure on unconfined compressive strength of cemented clay. A series of unconfined compression tests was performed on a cement admixed clay sample cured under pressure values of 0 kPa (atmospheric pressure), 25kPa, 50kPa and 100 kPa using a typical unconfined compression equipment. The test samples with values of cement content of 0.5, 1.0 and 2.0 percent were cured for 28 days.The stress-strain curves obtained from all tests show a peak value of stress. The unconfined compressive strength or peak stress obviously increased with increasing cement content for all curing pressure conditions. It can be observed that the strength of samples gradually increased with curing pressure for cement content of 0.5 percent. For cement contents of 1.0 and 2.0 percent, the strengths of samples cured under pressures of 25 kPa dramatically increased from the strength of samples cured without pressure (0 kPa), however, the strengths of samples for curing pressures of 25, 50 and 100 kPa were not clearly different.

Effect of Curing Pressure on Compression and Consolidation Behaviors of Cement Admixed Clay

The cemented soils are typically produced and cured under confining pressure of soil. The cemented soil properties are, however, obtained from laboratory tests on the cement admixed clay samples cured under atmospheric pressure. Thus, the parameters of cemented soil obtained from laboratory tests are not representative of the actual values in the field. In this research, a series of consolidation tests using oedometer apparatus on cement admixed clay samples with different curing pressure conditions was carried out. The samples was cured under pressure values of 0 kPa (atmospheric pressure) and 50 kPa. The test samples with values of cement content of 0, 1 and 2 percent were cured for 28 days before testing. The compression curves of cement admixed kaolin showed the elasto-plastic deformation in all cases of the tests. It was found that the range of void ratio of the samples with curing pressure of 0 kPa (atmospheric pressure) was higher than that of the samples with curing pressure of 50 kPa. With increasing curing pressure and cement content, the value of recompression index decreased while the value of compression index was approximately constant. It was also observed that the preconsolidation pressure increased with increasing cement content for both cases of curing pressure. It should be noted that the values of preconsolidation pressure increased with increasing curing pressure. Moreover, the values of coefficient of consolidation decreased with increasing effective vertical stress in all cases. It was also found that the values of coefficient of consolidation increased with increasing curing pressure and cement content.

Influences of Temperature and Suction on Pile Capacity in Homogeneous Silt Layer

This paper presents the simulation results of variation in pile capacity with temperature and suction. The end bearing, shaft friction and ultimate bearing capacities at various values temperature and matric suction were simulated. The simulation results show that the end bearing capacity decreased with increasing temperature but increased with increasing matric suction. The results also show that, with increasing temperature, the shaft friction and ultimate bearing capacities decreased at low to moderate level of suction but increased at low temperature and high level of suction. With increasing matric suction, the shaft friction and ultimate bearing capacities increased at moderate to high level of temperature but decreased at low temperature and high level of suction.

Temperature and Suction Effects on Slope Stability under Undrained Condition

In this paper, the variation of safety factor of unsaturated soil slope with temperature and matric suction was simulated. The simulation was performed using modified ordinary method of slices for unsaturated soil slope including temperature and suction effects. The expression for factor of safety of unsaturated soil slope at elevated temperature under undrained condition was derived. The ranges of temperature and suction in simulation were 25 to 60 degree Celsius and 0 to 100 kPa, respectively. The simulation was performed using soil parameters presented in literature. The simulation results shows the variation in factor of safety of soils slope with matric suction and temperature. The factor of safety of soil slope with circular failure surface increased with increasing matric suction for all values of temperature but decreased with increasing temperature for all values of matric suction.

Effective Stress Parameter for Unsaturated Soils under Drying and Wetting Processes

This paper presents a variation of effective stress parameter with matric suction for unsaturated soils using a comprehensive data set of suctioned-controlled shear tests under drying and wetting processes. The effective stress parameter is determined by assuming that the slope of the critical state line in the plane of deviator stress against mean effective stress is independent of matric suction. This study shows a different in relationship between the effective stress parameter and matric suction for drying and wetting processes. The values of effective stress parameter obtained from the experiments were compared with those obtained from the expressions proposed in literature.

Pile Capacity in Homogeneous Unsaturated Sand Layer

Generally, pile foundation is typically chosen to support heavy structures. However, the developments of expressions to determine the pile capacity is usually based on fully saturated and completely dry conditions. In fact, almost 40 percent of natural soils on the earth surface are in an unsaturated state. Thus, in this paper, an expression for pile capacity in homogeneous unsaturated sand layer is developed. The simulations using developed expression are performed and discussed. Typical results show that the pile capacity and the factor of safety are affected by matric suction. However, the influence of matric suction may be ignored for a long pile.