The Water Retention Properties Of Silt Under Consolidation Stress And Temperature Effects

The soil water characteristic curve is the variation regularity of water holding capacityof soil pore with the change of suction, and it is an important way to obtain the waterholding capacity of the unsaturated soil. According to saturated soil parameters, thepermeability coefficient, the moisture diffusion coefficient and shear strength of theunsaturated soil can be predicted. It has a very important significance in the unsaturatedsoil mechanics. In geotechnical engineering, such as the disposal of underground nuclearwaste and carbon sequestration and so on, are need to consider the soil moisture propertiesunder the impact of overlying load and temperature. But scholars haven’t come to anagreement on how to obtain the soil moisture properties under the impact of overlying loadand temperature and the influencing mechanism.Based on the previous studies, a set of multifunctional soil-water characteristic curvetest instrument is developed, the silt water retention curve tests under the effect of differentconsolidation stress and temperature are carried out, the microscopic tests under the actionof different consolidation stress are carried out to revealing its influence mechanism, and anew method is built to forecast water holding capacity based on the soil pore sizedistribution curve. Main contents and results of this research are as following:1） A set of multifunctional soil-water characteristic curve test instrument isdeveloped. The machine uses simple sample forming methods to reduce the workload andimprove the quality. By designing a set of temperature control system and using themethod of poise loading to exert axial load, the experimental research under the jointaction of temperature and stress has been achieved. The accuracy of the test results can beensured because the deformation of the sample is measured through the data acquisitionsystem in the process to revise the test results and the drainage is weighed directly by highprecision balance. The instrument’s operation procedures are worked out, and mattersneeding attention are also introduced. It provides technical support for subsequent testing.2） The silt water retention curve tests under the five kinds of consolidation stress arecarried out. The tests were carried out under25℃. The volume change rule and evolutionlaw of silt soil water-holding performance are obtained. The microscopic tests under theaction of different consolidation stress are carried out for revealing its influencemechanism. The volume shrinkage deformation also was measured at the same time toamendment miscount caused by volume change. It is found that the shrinkage is obvious during the drying process, and the small consolidation stress is, the more shrinkage is. Butthe soil volume is remaining unchanged in the wetting process. The consolidation stresshas a great influence on the air-entry value and wetting (drying) rates. The air-entry valueand wetting (drying) rates are greater when the consolidation stress increased.3） The microscopic tests under the five kinds of different consolidation stress arecarried out for revealing its influence mechanism. The test results show that the large porebetween the soil aggregate were compressed mainly by consolidation stress, but the porebetween soil particles were less effect by it. The soil-water properties are related to thepore size and its distribution mold closely. The large pores were influence on the air-entryvalue and the distribution mold was influence on the wetting (drying) rates.4） The silt water retention curve tests under the three kinds of different temperatureare carried out. The volume shrinkage deformation also was measured at the same time toamendment miscount caused by volume change. It is found that the shrinkage is obvious inthe drying process, and the shrinkage is basically the same under the different temperature.The water holding capacity are significant different under the action of differenttemperature. The air-entry value is smaller when the temperature increased, but thedifference is decreasing with the suction increased. The water physical properties, waterand gas’s occurrence are changed under the different temperature and it lead to the changedof the water holding capacity.5） A new method of forecasting soil water holding capacity is built based on thebasic theory of soil mechanics for unsaturated soil, this method can taking hysteretic effectinto accounts. Finally, estimated values are compared with tests and found that there is acertain deviation between the predicted and experimental values. Analysis shows that thedeviation is mainly due to the simplified pore distribution pattern in the process modeltransformation and uncontrollable factors in the process of test, etc.The innovation points of this paper:①A set of multifunctional soil-watercharacteristic curve test instrument which can consider consolidation pressure andtemperature at the same time is developed.②The mechanism between consolidationstress and water-holding mechanism are carrying out by fine microscopic test.③Water-holding mechanism under the temperature action is discussed from the point of viewof water, gas occurrence state.