Study On The Influence Of Load And Dry-wet Cyclic Stress Path On Dry-wet Cyclic Expansion And Shrinkage Deformation Of Compacted Expansive Soil

Expansive soil is widely distributed in China.It is a kind of high-plastic clay with both cracking,over-consolidation and strong expansion and contraction.It exhibits remarkable water swelling and water shrinkage characteristics.Due to its special engineering properties and the development of infrastructure construction in China,expansive soil has caused a series of engineering problems to be solved urgently.Therefore,it is extremely necessary to study the expansion and contraction characteristics of expansive soil.In this context,the experimental results of the effects of stress and dry-wet paths on the expansion and contraction characteristics of expansive soil under dry-wet cycle conditions are analyzed,and the relevant deformation laws are obtained.Finally,the particle flow discrete element method is used for indoor test wet and dry.The results of the cycle test were demonstrated.The main contents are as follows:(1)The distribution and distribution characteristics of expansive soil in China and the engineering disasters caused by it are introduced.The special and complex engineering properties of expansive soil are expounded in detail,and the research difficulties and the research significance of this paper are pointed out.(2)Explain in detail the research status of deformation law,constitutive theory and particle flow method of expansion and contraction of expansive soil,and clarify the advantages and disadvantages of previous studies.(3)The system summarizes the test methods for the expansion and contraction characteristics of expansive soil under dry and wet cycling conditions,and explains the advantages and disadvantages of each method.(4)Decomposition mechanism and dry and wet steady state of dry and wet expansion and contraction deformation are described: the expansion and contraction deformation of the expansive soil under dry and wet circulation conditions can be decomposed into irreversible expansion and contraction strain components and reversible strain components.After several cycles of dry and wet cycles,the expansive soil will exhibit a stable state.When it is in a stable state,it will accumulate in the direction of compression or expansion and accumulate as an irreversible expansion and contraction strain component.With the increase and decrease of the current suction force.The increase or decrease exhibits a characteristic that the cyclic reciprocal change is a reversible expansion and contraction strain component.(5)The influence of stress on the expansion and contraction characteristics of expansive soil under dry-wet cycle conditions is introduced.The test results are decomposed and the influence of stress on each component is summarized.The increase of vertical stress will shorten the stability of the sample.The time of the state enhances the tendency of the irreversible strain component to accumulate in the direction of compression,and at the same time reduces the expansion potential and the reversible strain component of the sample;the maximum expansion and contraction deformation,the magnitude of the change with water and the magnitude of the change of saturation are both Occurred in the initial dehumidification step,the expansion and contraction deformation is also larger than the subsequent dry and wet cycle steps;the irreversible strain components are accumulated in the compression direction,and reach a steady state after the 4th dry and wet cycle step;The dry-wet expansion and contraction deformation is characterized by reversibility,while the water content change amplitude and saturation change amplitude are stable.(6)The effects of dry and wet paths on the expansion and contraction characteristics of expansive soil under dry-wet cycle conditions are introduced.The test results are decomposed and the influence of dry and wet paths on the components is summarized: dry and wet in the saturation space.The shortening of the path and the irreversible strain component decrease;the magnitude of the reversible strain component is not only related to the expansion potential of the soil sample and the length of the wet and dry path,but also to the regional space where the saturation and water content of the soil sample change;The steady state of the wet and dry cycle has a certain path dependence.When the subsequent dry and wet circulation path area cannot cover the previous dry and wet circulation path area,the history of the dry and wet cycle in the early stage after changing the dry and wet circulation path may be followed by the wet and dry cycle.The cyclic deformation has a certain influence,which is manifested by the fact that the irreversible strain component of the subsequent dry-wet cycle continues to accumulate until reaching a steady state,and the initial sample preparation state is different from the state in which the dry-wet cycle causes the soil sample to reach.(7)Based on the double structure of expansive soil,the physical mechanism of the deformation law of expansive soil is explained from the change of the mesostructure of the soil and the microscopic deformation of the aggregate.The results of the indoor dry and wet cycle test are demonstrated by the mesoscopic particle deformation test.