Deformation And Stability Analysis Of Unsymmetrical Soft Soil Subgrade Of An Expressway In Lake Area

With the rapid development of China’s economy,the demand for high-grade roads is increasing.By August 2021,China has built 161000 kilometers of expressways,ranking first in the world.In order to meet the good smoothness and comfort of highgrade highway,it is necessary to ensure the high required horizontal and vertical alignment index.Sometimes,in order to reduce the bridge tunnel ratio and reduce the construction cost,the method of high excavation and high filling is often used to pass through some sections with complex landform and special soil areas,which naturally can not avoid the soft soil subgrade in the lake area.Soft soil has the characteristics of poor permeability,low shear strength,low foundation bearing capacity,large void ratio,high water content,high sensitivity and high compressibility.It is prone to soil extrusion failure under load,with large settlement deformation and long settlement stability.Generally speaking,it is not suitable for natural subgrade.Therefore,it is necessary to study the deformation and stability of soft soil subgrade.This paper mainly completes or draws the following work or conclusions:(1)The typical diseases,general design principles and treatment measures of soft soil subgrade are expounded,and the geological composition,hydrological condition data and section monitoring scheme of the accident site are collected.(2)The calculation principles of simplified bishop method and strength reduction method are introduced,and the landslide in the accident section is simulated by reduction.The stability coefficient obtained is in line with the actual situation,and it is found that the supplementary pile foundation in some sections is not in the slip zone,so the reinforcement effect is limited;In addition,the consolidation settlement simulation is briefly carried out after the implementation of the remedial measures on site,and the future development trend is reasonably predicted.(3)Comparing the laws and trends of deformation and stability of foundation under the condition of uneven single factor parameters or asymmetric cross-section shape of soil on both sides,and the significance level under orthogonal analysis.In a certain parameter range,it is found that under the action of uneven cohesion and bulk density of the foundation,the settlement trend changes little,but the uneven elastic modulus,internal friction angle and Poisson’s ratio of the foundation have certain characteristics.In the weakened area of soil,the decrease of elastic modulus will increase the settlement extreme value and the difference between left and right sections;The decrease of internal friction angle will lead to the increase of settlement on the same side,while the displacement on the other side will slightly rise.The stronger the Poisson’s ratio is,the smaller the displacement is,and the curves do not coincide from the settlement of the left slope foot.(4)The influence of coincidence degree between subgrade and pond is studied.As the intersection point moves inward,the displacement gradually increases and the safety factor decreases.It has basically reached the most dangerous point when the right boundary of the pond meets the middle of the fill.Further increasing the filling area of the pond,the range of the place with large displacement will be enlarged,and the safety factor will not be obviously reduced.This is due to the weak growth of the overall extreme value after the soil distribution is relatively uniform.