Study On Cement-jute Fiber Modified Expansive Soil And Its Application In Sponging Modification

China is one of the world’ s most underdeveloped landlocked countries.In areas with expansive soil today,all kinds of projects often suffer long-term potential,repeated,multiple and huge damages and cause serious economic losses due to the extremely poor engineering geological properties of expansive soil such as water expansion softening,water loss shrinkage cracking,and so on.By using modified materials to improve the expansion and shrinkage properties of expansive soil,relevant scholars have obtained abundant results.But a single modification method inevitably has limitations,and finding a sustainable green expansive soil modification material for environmental protection has a very important significance.In this paper,Nanyang expansive soil was used as the test soil,the modified material was cement and jute fiber,and the changing factors were the content and curing age of the modified material.The basic physical and mechanical properties of the composite modified expansive soil were studied,and based on MIDAS,the numerical simulation of total water head,pore water pressure and saturation in the expansive soil area of sponge modification was carried out.The main research contents and conclusions are as follows:(1)To explore the change rule and modification effect of basic physical properties of composite modified expansive soil,tests such as free expansion rate,particle analysis,liquid-plastic limit,and compaction were carried out.It is found that the expansibility of expansive soil is reduced by the addition of cement and jute fiber.The expanding property of the modified soil initially decreases and then increases with the increase in the content of the modified composite material,and the modified effect is the best when the content of cement is6% and jute fiber is 0.5%,and the free expansion rate decreased from 52% to 32%.(2)Unconfined compressive strength and direct shear tests were carried out to explore the change rule and modification effect of mechanical properties of composite modified expansive soil.The results show that the addition of cement and jute fiber can enhance the mechanical properties of expansive soil to different degrees.With the addition of modified materials,brittle axial compression failure occurred.As the jute fibre content increased,the compressive strength,shear strength,adhesion and internal friction angle of the surface samples increased,decreased and then decreased,and reached the maximum value when the jute fiber content was 0.5%,which were 2.56 MPa,451.58 k Pa,298.29 k Pa and 20.51 °,respectively.An appropriate amount of jute fiber could improve the mechanical properties of expansive soil,excessive jute fiber could restrain the mechanical properties of expansive soil.With the increased in cement content and curing age,the related parameters of mechanical properties of expansive soil increased.(3)To eexplore the feasibility of the sponge transformation in the expansive soil area based on the permeable filter element,and the change law of pore water pressure,total water head and saturation in the permeable filter site and free site with different spacing in the expansive soil area,MIDAS GTS NX was used to establish the numerical model of the original field test.Under the condition of heavy rainfall,the seepage in the permeable filter element field and the free field with different spacing in the expansive soil area was numerically calculated and analyzed.The results show that the total water head,pore water pressure,and saturation at each site increased with increasing spacing of the filter elements and rainfall.The replacement of modified expansive soil and the arrangement of the permeable filter element can effectively accelerate the seepage rate of surface rainwater and alleviate the phenomenon of surface water.