Characteristics Of Interface Between Excavated Soils And Drainage Reinforcement And Optimal Design Of Reinforced Slope In Soft Soil Area

With the acceleration of urbanization and the large-scale development and construction of underground space in China,huge amounts of excavated soils has been produced.In China's soft soil areas,excavated soils has the characteristics of high saturation,slow drainage consolidation and low shear strength,which is easy to induce landslides,collapses and other disasters in the landfill process.In view of the above problems,this thesis put forward a solution that the drainage reinforcement method is used to shorten the drainage path and speed up the consolidation process,so as to improve the shear strength of soil and the interface strength of reinforcement and soil.In this thesis,laboratory tests,theoretical analysis and numerical simulation methods were used to studied the basic characteristics of excavated soils,interface characteristics and influencing factors of excavated soils-drainage reinforcement,strengthened interface characteristics and influencing factors of excavated soils-drainage reinforcement and influencing factors of slope stability reinforced by excavated soils.And the design optimization of a high fill slope in Lishui City was carried out.The main conclusions are as follows:(1)Excavated soils samples were collected from a foundation pit excavation project in Hangzhou,and the basic physical properties,permeability characteristics,compression characteristics and shear strength characteristics were tested by laboratory tests.The results show that the excavated soils belongs to poor graded clay in plastic state,which has the characteristics of high water content,large pore ratio,high compressibility,low shear strength and weak permeability.(2)The direct shear test of the interface between excavated soils and drainage reinforcement was carried out,and the effects of vertical stress,consolidation degree and reinforcement arrangement on the characteristics of reinforcement-soil interface were studied.The results show that the shear curve of the interface between reinforcement and soil presents strain hardening characteristics,and the greater the vertical stress,the more obvious the strain hardening phenomenon is.With the increase of consolidation degree of excavated soils,the interfacial shear strength gradually increases,the interfacial cohesion remains basically unchanged,and the interfacial internal friction angle increases linearly.Under the same vertical stress condition,with the increase of consolidation degree of excavated soils,the interface friction coefficient gradually increases and the interface friction coefficient ratio gradually decreases.The shear curve of reinforcementsoil interface can be simulated by hyperbolic model.There is a linear positive correlation between the ultimate shear stress of the interface and the vertical stress,and the change of initial tangent modulus with vertical stress is significantly affected by consolidation degree.(3)A direct shear test of strengthened interface between Sandwich-type excavated soils-drainage reinforcement was carried out,and the influence of sand layer thickness and density on the interface characteristics of reinforcement and soil was studied.The results show that with the increase of sand thickness,the interfacial cohesion decreases gradually,while the interfacial internal friction angle,the friction coefficient between reinforcement and soil and the ratio of interfacial friction coefficient increase first and then remain basically unchanged.With the increase of sand compaction,the interface internal friction angle and interface friction coefficient increase gradually,the interface cohesion decreases slightly,and the interface friction coefficient ratio decreases gradually.The shear curve of reinforcement-soil interface can be simulated by hyperbolic model.The ultimate shear stress increases with the increase of sand thickness and compactness,and the initial tangent modulus of interface increases with the increase of vertical stress.Compared with excavated soils-drainage reinforcement interface,the strength of sandwich-type excavated soils-drainage reinforcement strengthened interface is obviously improved,and better reinforcement effect can be obtained when the thickness of sand filling layer reaches about 10 mm.(4)The numerical simulation software Geo-Studio was used to analyze the influence of different landfill processes,slope forms and reinforcement arrangements on the stability of excavated soils slope of drainage reinforced engineering.The results show that the faster the filling rate lead to smaller the safety factor of the slope and the limit filling height.If the layout of reinforcement is changed from longitudinal to transverse,or coarse aggregate is used to replace the excavated soils on both sides of reinforcement,the slope stability can be further improved.Under the condition of the same slope height,with the decrease of slope gradient,the increase of slope grade and the increase of platform width,the safety factor of slope gradually increases.With the increase of reinforcement length and strength and the decrease of reinforcement spacing,the safety factor of slope gradually increases,until the reinforcement length reaches 32 m.The original design scheme of a high fill slope in Lishui city was optimized.The safety factor of slope was improved,and the cost of reinforcement was saved by about 18.13%.