Applied Research Of Improved Backfill Soil

After construction of general buildings or highways and bridges,backfill should be carried out.However,in the actual construction process,the quality of backfill often fails to meet the requirements due to objective factors,which will lead to a series of problems.Relevant codes have different requirements for the quality of backfill used in subgrade,foundation and groove.This paper studies the following two kinds of problems.For roadbed backfill,the relevant specifications require that the compactness of backfill can be reduced properly under the premise of ensuring the strength.Therefore,this paper studies the low-pressure compactness roadbed backfill,through adding soil solidifying agent and concrete,after mixing and maintenance,the improved backfill can ensure the strength requirements.To this problem,the unconfined compressive strength is adopted.Degree is the control index.Firstly,the selection requirement of raw material soil,solidifying agent,cement and water of improved soil is determined.Secondly,the sample preparation method and mixture ratio of unconfined compressive strength test are determined.Finally,according to the comparison of unconfined compressive strength of improved soil with different dosage of solidifying agent with the standard value,the "optimum" of low-pressure compactness backfill is obtained.Dosage of curing agent.The improved backfill is applied to the actual subgrade engineering,and good engineering results have been achieved.On this basis,the construction quality control method of improved backfill is put forward.For groove and foundation backfill,relevant codes do not consider the problem of reducing the compactness of backfill under a certain strength.Therefore,this paper studies other strength indexes of backfill in groove and foundation,which provides a reference for compiling relevant codes applicable to the standard of consolidating agent modified backfill.The research and conclusions on this kind of problem are as follows:The backfill used in trenches and pipelines often encounters the problem that when groundwater pipelines leak due to various factors,sewage will change the physical and mechanical properties of the backfill around the pipeline,water will increase the water content of the backfill around the pipeline,reduce its shear strength and compressive strength,resulting in uneven settlement and collapse of the surface.In order to solve this problem,firstly,direct shear test is carried out to obtain the variation law of cohesion and internal friction angle between weak expansive soil and improved soil under different water content.Then,the pipeline groove model is established by using finite element software ABAQUS to study the variation of pipeline stress and the development law of backfill plastic zone under different water content.The backfill soil has better water stability than the unmodified soil,which can effectively reduce the pipe stress,slow down the development of the soil plastic zone and prevent the ground collapse caused by the soil failure.It is suggested that the shear and compressive strength of the backfill soil should be set as the strength index of the relevant specifications of the stabilizer-modified backfill soil,that is,to ensure the shear and resistance of the backfill soil.Under the condition of compressive strength,the degree of compaction can be reduced appropriately.For the backfill used in the foundation,in the seismic design of the building,the calculation of the seismic resistance of the foundation generally separates the superstructure from the foundation,ignoring the restraint of the superstructure on the foundation and the seismic effect of the backfill on the foundation.In this paper,the finite element software ABAQUS is used to establish the superstructure-independent foundation-backfill-foundation soil model,and to study the change of the peak displacement time-history curve of the foundation under earthquake when the foundation is buried in weak expansive soil and improved backfill soil.