Study On Settlement Prediction And Preloading Design Method Of Soft Soil Subgrade Based On Measured Data

The settlement prediction and control of soft soil subgrade is a hot issue in the process of expressway construction and operation.Once excessive settlement or uneven settlement occurs,road diseases will occur frequently.Therefore,it is of great significance to propose an accurate and convenient method to predict the settlement of soft soil subgrade,it can provide an effective engineering basis for the subgrade settlement control scheme.By analyzing the existing research results,this paper summarizes the shortcomings of the settlement prediction method based on measured data:Traditional settlement prediction method depends on the measured data of constant load,can not consider the gradation loading process of subgrade,and can not skip a grade to predict settlement.With the filling of subgrade,the mechanical properties of soft soil change,but the existing settlement prediction method based on measured data cannot consider the change of properties of foundation soil in the process of filling,resulting in a certain deviation between predicted results and measured data.At the same time,preloading is an important measure to control the settlement of soft subgrade after construction.Due to the limitation of the settlement prediction method mentioned above,the det0ermination of preloading amount and preloading time is always a difficult problem in the engineering field.In order to solve the above problems,based on the immediate settlement calculation method and the improved Terzaghi method,this paper proposes a prediction method for the settlement of soft soil subgrade considering the change of calculation parameters,and on this basis,a preloading design model is proposed.Taking the soft soil subgrade section of Xihuan expressway in Zhaoyang as the research object,the deformation data of the subgrade is obtained by monitoring the deformation of the soft soil subgrade section on site,which provides the data basis for this study.The main work includes:(1)According to the actual situation,the burying scheme of deformation monitoring equipment was developed.The advantages and disadvantages between traditional deformation monitoring method and automatic deformation monitoring method are compared.Combined with the deformation measurement results,the deformation law of soft soil foundation is discussed.(2)Based on the measured height-time-settlement curve,the prediction effect of hyperbolic method,three-point method and hushino method under the subsequent application of small load is studied.It is found that hyperbolic method,three-point method and hushino method are all very sensitive to the loading of subgrade.(3)A soft soil settlement prediction method considering the change of calculation parameters is proposed.Firstly,the immediate settlement is determined according to the measured data,and then the elastic modulus is calculated based on the immediate settlement.Then,the elastic modulus is substituted into the immediate settlement calculation of the next level,and the elastic modulus is dynamically adjusted based on the measured value.The primary consolidation settlement calculation method considering the change of consolidation parameter β was proposed.Firstly,the relationship of consolidation parameters with staged filling was established,and the new formula was deduced by substituting it into the improved Terzaghi method.Through linear fitting and iterative calculation,relevant calculation parameters were obtained,and the new prediction formula could be used to predict the subsequent settlement.Then,the validity of the new method is verified by the measured data,and the prediction accuracy of the new method is compared with that of the traditional settlement prediction method.(4)In view of the difficulty in determining the amount of preloaded earth and the time of preloading in actual engineering,a preloading design model is further proposed based on the settlement prediction method in Chapter 3 to realize the quantitative determination of the amount of preloaded earth and time.An example is given to illustrate the application method.