| Soil structure has large effect on physical and mechanical properties,which lead to a series of problems in road construction.Large settlement in Jinghu highway Jiangsu section is analyzed.The properties of soil within 20 m under subgrade are detailedly analyzed by geotechnical survey and laboratory tests,including consolidation test and undrained triaxial test.Shanghai model is used to simulate subgrade settlement and the effect of soil structure on settlement which the initial soil structure,over-consolidation can be considered in the model.To compare the effect of different foundation treatment methods,three settlement controlling measurements are analyzed.A new method to get soil paraameters of undisturbed soil by disturbed soil test data is proposed.The settlement results simulated by soil-water couplied FEM software GLEAVES is close to monitoring data,which indicates the validity of new menthod.The finite element analysis results show that soil structure,stress history,permeability,thickness of soft clay,controlling parameter of plastic strain ratio(parameter A)have large influences on subgrade settlement and settling time.The main conclusions are as follows.1.The laboratory tests and parameters simulation show that the soil sample retrieved under subgrade are all soft clay with low liquid limit.The whole five layers are structural soft clay and structure of layer 4,6 are strongest.The consolidation curve of these two layers can be obviously divided into three parts and the shear strength falls off in large strain.The whole mechanical properties indicate that the large compression appears when high pressure is applied.2.The sample retrieved under subgrade is compressed by subgrade load for several years,the soil parameters have already been changed which means the parameters of undisturbed soil can not obtain from test data directly.A new method to get soil parameters of undisturbed soil by disturbed soil test data is proposed to solve this problem.The idea of method is treated soil sample as the undisturbed soil that compressed by subgrade load and then unload to zero.The consolidation test curve is the re-compression curve of undisturbed soil.The stress state of soil before sampling can be calculated by FEM simulation.The parameters of undisturbed soil can be obtained by adding this stress state in simulation to correct the parameters of disturbed soil.The simulated settlement is close to the monitoring data,which prove the effectiveness of new method.3.The effect of stress history,soil structure,permeability,thickness of soft clay,parameter A on development of subgrade settlement are analyzed.The result show that stress history changed initial soil structure and the calculated settlement is much smaller than monitoring data.The simulation results show that structural soft soil has great influence on settlement,the stronger the initial soil structure,the larger pore pressure and roadbed construction settlement in loading stage.With the gradual destruction of soil structure after completion,it was positively correlated with the amount of layer compression and soil structural parameters.The permeability affects settlement and settling time.The smaller the permeability,the larger is total settlement of the roadbed and more proportion of post-construction settlement.Thickness of the soft soil can also affect settlement and settling time.The thicker the soil layer,the larger is the settlement of the roadbed with longer settling time.Parameter A has large effect on simulation,which reduces the final settlement and lateral displacement significantly.What's more,three protective treatments of grouting reinforcement,EPS material and porous concrete filling are simulated.It is shown that three protective treatments can reduce the settlement effectively.Grouting reinforcement improve the permeabilty of soil clay and settling time reduced obviously. |
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