Mechanics Behavior Of Expansive Clay In Different Pore Solutions And Temperatures

At present,expansive soil is widely used in engineering field,which not only involves the daily engineering of foundation and slope,but also special projects such as tunnel excavation,underground disposal of nuclear waste,landfill and so on.The chemical environment is very complex in these engineering.Expansive soil is very sensitive to the pore environment because of its water-sensitive properties.The physical and mechanical properties obtained in different test environments(such as temperature,etc.)and test methods are quite different.It is necessary to conduct detailed study on the mechanical properties of the expansive soil in different pore solution,test environments,and test methods.The expansive soil is as the test material in this paper.The mechanical behavior was investigated in sodium chloride solution with different concentration and in different test temperature.And different swelling pressure testing methods were used to measure the swelling pressure.The specific research content and results are as follows:(1)The experimental study on the middle expansive soil with different initial water content and dry density was carried out by using three different ways to determinating swelling pressure.The results show that the effect of initial water content on the swelling pressure is weaker than that of initial dry density.The swelling pressure is very different from the three test methods under the same condition.The maximum swelling pressure is obtained by the free expansion-compression method,and the swelling pressure of the loading-expansion method is the smallest.Finally,the difference of three methods is analyzed by NMR tests.The specimens can adequately expand,which results the disappearing of the intra-element pore by using the test method of free expansion-compression.The pore is the biggest in these specimens.(2)Tests on the strong expansive soil were conducted to investigate the swelling pressure and swelling deformation in different test temperature by using conventional consolidation modified by thermostatic.The viscosity coefficeient of water decrease as the increasing in temperature,which induce the water in crystal lattice flowing into pore.And thses water has no more contribution to swelling.So the swelling pressure and swelling deformation decrease with increasing the temperature.(3)The swelling characteristics of expansive soils in different sodium chloride concentrations were tested by loading-swelling test.There is Donnan osmotic pressure in specimens because of the negative charge on the surface of the particles.The Donnan osmotic pressure decrease with increasing the sodium chlorid solution concentration,which results in the decreasing of the swelling pressure.Under same vertical pressure,the saturated void ratio decarease with the increasing in sodium chlorid solution concentration.Based on the results obtained from the samples saturated by distilled water,the relative value of the chemical force produced by different concentration solution is obtained,which is mainly affected by void ratio and solution concentration.And the relationship among the chemical force,void ratio and solution concentration is established.(4)A series confined swelling tests with no vertical pressure were carried out on the middle expansive soil.The results show that the sodium chlorid solution affect weakly on the specimens with lower initial water content,oppositely,the effect is strong.The results of NMR tests show that the strong bound water content is the boundary point,and when the initial water content is less than that,the specimens is not affected by the sodium chloride solution.Conversely,the sodium chloride solution strongly inhibited the swelling of the specimen.When the initial water content larger than the strongly bound water content,swelling pressure decreas as the increasing in sodium chloride solution concentration.While,when the soil has only strongly bound water,the sodium chlorid solution has two inverse effects on the swelling pressure.(5)The direct shear test was carried out on the weak expansive soil saturated by sodium chloride solution with different concentrations in drainage consolidation.The specimens hinder from generating the shear surface in the shear procedure.The inhibition is the shear strength.The results of NMR tests show that the pore size of the specimen saturated by distilled water is smaller.The inhibition is the strongest in these specimens,thus the shear strength is higher.