Deformation And Reinforcement Characteristics Study On Sandy Soil Foundation

As a ubiquitous foundation type,natural sand foundation is widely distributed around the world.Because sand has the characteristics of no natural cohesion,it is prone to destabilization,liquefaction and other damage phenomena.How to deal with sand foundation is becoming a difficult problem in geotechnical engineering.In Leipzig,Germany,there is a wide range of natural sand foundation.Especially,the southern part of Leipzig is the largest open-pit lignite mine in East Germany.Due to successive years of mining,a lot of unstable geological conditions such as sand slopes and loose sand foundations have been generated,which need targeted reinforcement treatments.This paper summarizes the previous research results,and conducts deformation and reinforcement characteristics research on the sand foundation in Leipzig.The main work and research conclusions are as follows:In terms of the deformation characteristics of sand slopes,a multi-functional indoor model test box designed by the laboratory and combined with particle image testing technology(PIV)were used to simulate and analyze the deformation process of the soil slope under load.By setting up a comparative model test with different load widths and distances from the top of the slope,combined with numerical simulation,the deformation characteristics of the sand slope under different working conditions were studied.The research results show that with the decrease of the load width and the load distance,the displacement of the top of the sand slope increases continuously,and the load-slope top displacement curve is basically linear.With the decrease of the load width and the distance of the load,the particle displacement vector of sand slope gradually increases,and the particle displacement distribution shows a trend of deepening in the center and expanding on both sides.As the width of the load decreases,the influence of the applied load increases in depth and the horizontal width decreases.The deformed cloud image develops from ellipse to spinning cone.Using the finite element analysis software ABAQUS,a finite element model of the sand slope was established to simulate the step-by-step loading test process.The analysis results show that the thickness of the sand slope model has little effect on the deformation test of the sand slope in this paper,and the distribution error of the top displacement of the slope Less than 2%.In terms of the sand foundation reinforcement characteristics,the self-designed model test device was used to simulate the sand foundation.Based on the PIV measurement system,the dynamic compaction characteristics of the sand foundation from German Leipzig under different initial relative densities were studied through laboratory tests.The results show that the speed-time curves of the experimental groups with different number of hits basically coincide in the rapid decline stage.In the rebound stage,the higher the number of hits,the higher the rebound speed and the shorter the duration,indicating that the energy release time is different under different number of hits.The greater the initial relative density of the test group,the smaller the drop in the energy release time of the dynamic ram between each hit.The higher the initial relative density,the greater the impact force of the ram and the smaller the difference in impact force between each number of hits.As the number of ramming increases,the peak value of the dynamic force of the ram gradually increases,the slope of the upward curve becomes smaller,and the impact stroke gradually shortens.The ID0.4,ID0.5,and ID0.7 test groups are horizontal after the 20 th,18th,and 15 th hits,respectively.The direction of effective reinforcement range growth is greater than the depth direction.