Deformation Characteristics Of Sloped Soft Soil Subgrade And Control Technology Research

There are many problems in the construction of transportation facilities in southwest China,and the slope soft soil foundation is one of them.Due to the special generation and occurrence environment,there is still insufficient understanding of its nature and harmfulness,resulting in engineering problems in the operation and construction stages of the roadbed.Based on the construction of Yiyi Expressway project,this thesis takes a slope soft soil subgrade section as the research object.Through indoor test,numerical simulation,field monitoring,theoretical analysis and other means,the physical and mechanical properties of slope soft soil,the deformation characteristics of slope soft soil subgrade,the analysis of deformation mechanism and its control technology are studied.The specific conclusions are as follows:（1）The indoor test results show that the natural water content,natural density,liquid limit and plastic limit of the slope soft soil are 45%～60%,1.67g/cm³,54%and30.3%respectively,which are high liquid limit clay.The shear strength gradually decreases with the increase of water content,showing a trend of first fast and then slow.The value range of cohesion c is 5.6～22.1k Pa,and the value range of internal friction angle is 1.4～15.3°.The permeability coefficient of slope soft soil increases with the increase of void ratio,and the relationship between them is k=10^-8·exp（3.3095e⁰）.The consolidation coefficient is 1.32～1.6210^-3·cm²·s^-1.（2）Through XRD and SEM microscopic tests,the analysis shows that the slope soft soil is mainly composed of four minerals,among which illite and quartz are the main components,accounting for about 85%of the whole,kaolinite accounts for about13.6%,chlorite accounts for about 2.3%.The secondary mineral composition has strong activity,strong structure and sensitivity;compared with the soft soil before consolidation,the’domains’in the cohesive body of the clay are arranged more closely after consolidation.With the increase of the proportion of point-surface and surface-surface contact,the pores in the cohesive body are obviously smaller.（3）Aiming at the five working conditions of subgrade base transverse slope rate of 0,1:10,1:8,1:6 and 1:4,the numerical simulation analysis shows that with the increase of subgrade base transverse slope rate,the horizontal stress at the foot of subgrade slope increases as a whole,and the horizontal stress along the depth of foundation decreases first,then increases and then decreases.The horizontal stress at the foot of subgrade slope is the largest,which is-15.6k N/m²,-23.7k N/m²,-30.8k N/m²,-39.5k N/m² and-53.4k N/m² respectively.The horizontal and vertical deformation and deformation rate of subgrade are increasing,which is easy to cause uneven settlement.The transverse slope of the foundation is an adverse factor,which has a more obvious influence on the horizontal deformation,which is consistent with the horizontal stress distribution.（4）Considering four working conditions of natural foundation,plastic drainage plate method,cement soil mixing pile composite foundation and CFG pile composite foundation,numerical analysis shows that considering four working conditions of natural foundation,plastic drainage plate method,cement soil mixing pile composite foundation and CFG pile composite foundation,numerical analysis shows that compared with natural foundation,the vertical settlement of roller treated by plastic drainage plate method is reduced to a certain extent,but the settlement is still relatively large,and the roller is in danger of falling into soft foundation.These two working conditions do not meet the filling conditions;comparing the cement mixing pile and CFG pile composite foundation,it is found that the foundation treated by CFG pile has a decreasing trend in deformation and deformation rate,but the two conditions have not reached the filling height,and the deformation and deformation rate have occurred.The measured value and the numerical simulation value are similar in the trend of change,and the difference is not large.The simulation data can basically reflect the actual situation in the process of embankment filling,so as to verify the rationality of the model.Comparing the deformation control effects of the four control measures can provide a basis for the selection of subsequent control technologies.（5）Through literature review,field investigation and this study,this thesis summarizes the selection principle of slope soft foundation engineering control technology,the main control measures in three aspects:strengthening foundation,strengthening embankment and doing well in waterproof and drainage,and clarifies its application scope and conditions;combined with the practical engineering application of Yiyi Expressway,the effectiveness of pile-plate composite foundation treatment for slope soft foundation is proved by numerical simulation,which can provide reference for similar projects.