Three-dimensional Stability Study Of Embankment On Soft Foundation Treated By Cement Mixing Pile For Dhaka Railway In Bangladesh

With the development of the “Belt and Road”,domestic construction units are increasingly exposed to international projects.The geological conditions of overseas countries are different,and each country has its own characteristics.The main unfavorable geological condition in the area passed by Bangladesh ’s Dhaka Railway is soft soil,and the local soft soil mica content is high.The railway soft foundation is treated by deep cement mixing pile reinforcement method.Since the undisturbed soil has a great influence on the strength of the cement mixing pile,it is clear that the influence of the mica content and mesh number of Bangladeshi soft soil on the strength of the cement soil is of great significance to the development of the project.At the same time,the strength of the cement soil directly determines the strength of the cement mixing pile,which directly affects the stability and settlement of the embankment.Embankment design,especially high embankment design,must perform stability and settlement calculations.However,the calculation of the stability of the embankment considering piles in the domestic code only refers to the BS8006 method and the composite shear strength method.The calculation results are significantly different from the actual engineering and cannot guide the design and construction.In addition,the failure forms of actual engineering embankments have three-dimensional effects,so it is necessary to carry out research on the three-dimensional stability of soft foundation embankments with cement mixing piles.In this paper,by studying the effect of the content of mica content and particle size of soft soil on the strength of cement soil and the influence of design parameters of cement mixing piles on the stability of embankment,a three-dimensional stability calculation that facilitates engineering calculations and is close to the actual treatment of soft foundations(1)Through the unconfined compressive strength test of cement soil considering the influence of mica,the influence law of mica content and mesh on the strength of cement soil is summarized and the formula is fitted: z = 1.1569-2.6526 x + 0.0025y(x: mica content;y:mica mesh number;z: unconfined compressive strength)provides a basis for the numerical simulation of the selection of cement mixing pile strength parameters.(2)Using PLAXIS 3D finite element software as a platform,the impact of cement mixing pile diameter,length,and pile spacing on the stability of the embankment is comprehensively analyzed.At the same time,the failure mode partition of the cement mixing pile at different positions under the embankment can be divided into compression failure and impact.Three types of bending failure and tensile failure occur respectively under the embankment center,under the embankment slope surface,and near the slope foot.It provides a basis for the three-dimensional stability calculation method of embankment proposed in this paper.(3)Taking the representative cross section of Dhaka railway in Bangladesh as an example,the practicability of this method is illustrated by comparing the results of this method,BS8006 method,composite shear strength method,and numerical calculation.