Research On Settlement Characteristics And Prediction Methods Of Saline Soil Subgrade In Hihgway

Subgrade is the foundation of smooth and stable road surface.The settlement and deformation of subgrade will cause damages to roads,which affects road safety.Meanwhile,large amount of manpower,materials and money are needed to deal with these damages.Expressway settlement observation and prediction is an important step to ensure the quality of expressway construction.Systematic and complete observation and analysis of expressway subgrade settlement can help people not only master the occurrence and development of settlement but also predict the trend of settlement.The observation and analysis serves as reference for controlling the settlement rate of subgrade,guiding the construction of the project and ensuring the quality of project construction.Based on the subgrade project of Lin-Bai Expressway LBGL-7 section,this thesis studies the settlement characteristics and prediction methods of expressway subgrade with saline soil.Based on the observation of the settlement during and after the subgrade filling process,combined with the settlement observation data,comparative analysis is carried out by using logarithmic fitting method,hyperbolic method,three-point method and gray model GM(1,1),etc.This thesis discusses the settlement prediction methods that are applicable to saline soil subgrade,predicts the settlement and the amount of settlement of expressway subgrade,analyzes the occurrence and trend of expressway subgrade settlement,and serves as reference for the construction of similar projects in similar areas.The thesis mainly draws the following conclusions:(1)With the indoor physical and mechanical tests of the saline soil,it is concluded that the dry density varies within the range from 1.83g/cm3 to 1.948/cm3,and the optimum moisture rate changes from 13.21% to 14.93%,and the maximum dry density of saline soil increases with the salt content.Also,cohesive force and internal friction angle decrease first and then increase with the increase of salt content,reaching the minimum value when salt solution reaches saturation.Cohesive force and internal friction angle decrease with the increase of moisture content.(2)By combining the construction examples of subgrade engineering in other drought-stricken areas in the north,this paper proposes the method of constructing with stuffed materials during the subgrade filling process,which reduces the construction time of subgrade filling,shortens the subgrade filling cycle,saves construction cost and improves construction efficiency.The construction process is significantly improved.(3)The settlement trend of the same section of subgrade is generally the same,and the settlement amount is basically the same.The settlement amount at the center of the subgrade is the largest and gradually decreases from the center to the shoulder.The settlement amount at the center of subgrade is slightly larger than that in the shoulder.The settlement amount and settlement trends of different sections are always different although the subgrade filling height is the same.(4)The prediction accuracy and correlation coefficient of the hyperbolic method,the three-point method and the gray model method are all high,and the predicted settlement development trend is close to the actual settlement.So these methods can be applied to the settlement prediction of the expressway subgrade with saline soil to better reflect the changing trend of subgrade settlement.(5)For different settlement observation points,different settlement prediction methods are adopted.For a certain settlement point,it’s better to adopt several prediction methods so that the result is mostly close to the real situation.(6)The subgrade filling height of section A is 5.8m,and its final settlement amount is 109 mm to 119 mm.The subgrade filling height of section Bis 6.6m,and the final settlement amount is 131 mm to135mm.Both the settlement amount of the two sections meet the specification requirements.(7)The settlement of the subgrade accounts for about 70% of the total settlement during the subgrade filling process,about 83% of the total settlement at the 6th month after the completion of the subgrade filling,about 89% at the 12 th months,about 93% at the18 th months,and about 95% at the 24 th months.This indicates that the settlement of the subgrade mainly occurs in the subgrade filling process and within 6 months after the completion of the filling process.24 months after the completion of the filling process,the settlement of subgrade basically stops.