Research On Mechanics Behavior And Extrusion Effect Of Cemented-soil Mixed With Expansion Agent

Cement soil is widely used in various engineering projects,such as the treatment of soft soil foundations,the foundation of highway engineering,the construction of reservoirs and dams,and river embankment protection.It has the advantages of easy construction,low compressibility and high strength.But there are problems such as large shrinkage deformation and poor crack resistance.In engineering,expansion agents are often added to cement-based materials to solve the problem of compensated solid phase volume shrinkage.However,the influence of expansive agents on the compaction effect and mechanism of cement-soil remains to be studied.In this thesis,cement-soil mixed with expansive agent is the research object.The action mechanism of cement-soil mixed with expansive agent is analyzed.The influence of incorporation ratio of expansive agent,content of cementitious materials,soil moisture content,mixing method and other factors on the swelling-shrinkage rate,compressive strength,and stress-strain curve of cement-soil are discussed.Using the least-square method and the theory of cylindrical cavity expansion,the constitutive equation of cement-soil mixed with expansion agent and the theoretical solution of expansion and compaction effect are obtained.1)Experimental study on the swelling-shrinkage of cement-soil mixed with expansion agent.Carry out expansion test and dry shrinkage test.Analyze the expansion and contraction rate of cement soil and the development law of expansion and contraction.Studies have shown that there are hydration,ion exchange,agglomeration,carbonation,hardening,and skeleton effects in cement soil mixed with expansion agents.Under these effects,the expansion process of cement-soil can be divided into three stages: framework support,pore filling,and expansion and stability.The different expansion rate leads to different dry shrinkage and auto-shrinkage of cement soil.Its shrinking process can be divided into two stages: pore compaction and framework support.The early swelling rate and overall swelling rate of cement-soil increase with the addition of expansion agent and cementitious material.If the amount of expansion agent exceeds a certain range,the cement soil will expand and crack,and the shrinkage rate will be larger.Different mixing methods affect uniformity.Wet-mixed cement-soil is easy to agglomerate to cause local expansion,and dry-mixed cement-soil produces uniform and effective expansion support force to inhibit shrinkage,but the overall expansion and contraction development law is similar.2)Experimental study on unconfined compressive strength of cement-soil mixed with expansion agent.Carry out unconfined compressive strength test.And analyze the characteristics of the full stress-strain curve.This curve is divided into ascending and compacting section,ascending elastic section and descending section.The nonlinear constitutive relationship model of cement-soil mixed with expansion agent under uniaxial compression is established.The least square method is used to fit the relationship between various factors and the compressive strength and the test curve.Calculate the test model parameters.The compressive strength decreases with the increase of the expansion agent blending ratio.With the increase of the cementitious material,it shows a parabola that first increases and then decreases.It decreases linearly with the increase of water content.A small amount of swelling agent only plays a pore filling role in the hydration product framework.This can effectively improve the compressive strength of cement-soil.At the same time this can produce slight expansion.Obtaining a large amount of expansive agent will cause the cement-soil particles to produce expansion force from the inside to the outside.This will cause cracks to degrade the compressive performance of cement-soil.It shows that the fitting effect of the three-stage constitutive relationship is better.3)Experimental study on expansion and compaction of soil mixed with expansive cement.Research on the compacting effect of cement-soil mixed with expansive agent on the surrounding soil during the expansion process.The squeeze test after expansion is designed.Analyze the deformation and density change law of the central standard sand column.Expansion compaction test is designed.Analyze the change law of the surrounding soil earth pressure under different spacing.Study the pressure distribution and pressure change law of the surrounding foundation soil.Based on the column cavity expansion theory,the relationship between expansion rate and expansion force.Calculate the expansion pressure field and displacement field in the surrounding soil.The result shows.In the surrounding foundation soil,it is the combined effect of the pressure in the soil and the swelling pressure.When the unloaded expansion rate of cement soil is less than 2%,the expansion energy generated will first act on the inside of the cement soil under the closed constraint condition,the spacing between the cement soil particles is shortened,and the cement soil becomes more dense.When the unloaded expansion rate is greater than 2%,when the expansion force continues to increase,the cement soil will produce lateral expansion force,which will expand and compact the external standard sand.Finally,as the expansion force decreases until it balances with the earth pressure,the expansion and compaction effect tends to be stable.