The Research On Structural Design And Behavior Of The Rubble Pressed Method In Reinforcing Shallow Layer Soft Ground In Sichuan Basin

In the construction process of expressway engineering, we often encounter large area of shallow soft soil, it will cause subgrade settlement even instability and other diseases in the process of filling or operating if treated improper.This paper will use the Liangzhong Expressway project as the research object.First, classifying the soft soil at typical site along the expressway and comparing the existing method of soft subgrade treatment,then analysising the suitability of rubble pressing method used in Liangzhong Expressway project.Second, summarizing the indoor model tests of the rubble pressing method.Third, using the finite element calculation program to study the behavior of composite foundation under different working conditions. Finally,this paper presents a design method for rubble pressing method through analysising the indoor model tests,field experiments and numerical simulation results. The method can provide technical support for the use of rubble pressing method in the construction of Liangzhong Expressway project.The results of the suitability analysis of rubble pressing method show that rubble pressing method is not only suitable to the Liangzhong Expressway which is along with large area of shallow soft soil but also better than the existing methods of soft subgrade treatment.The results of indoor model tests indicate that rubble pressing method can form composite foundation with high elasticity modulus and high soil strength to achieve the purpose of foundation treatment. Numerical simulation results indicate that:(1) Rubble pressing method can reduce the subgrade settlement and horizontal displacement, and improve overall stability of subgrade;(2) The modulus of soft soil、the thickness of soft soil、the modulus of composite subgrade and the height of filling are the main factors which influence composite subgrade settlement;(3) The modulus of soft soil、the thickness of soft soil、the strength parameter of composite subgrade and the height of filling are the main factors which influence composite subgrade horizontal displacement;(4)The strength parameter of composite subgrade and the height of filling are the main factors which influence the stability of composite subgrade; (5)Geogrid can also reduce the composite subgrade settlement and horizontal displacement, and improve overall stability of composite subgrade.Numerical simulation results show that the effect of rubble pressing method is significant. Analysising the indoor model tests,field experiments and numerical simulation results.the treatment method for large area of shallow soft soil along Liangzhong Expressway is as follows:(1) The thickness of shallow soft soil is less than 2 m;(2) It is better to improve the depth of foundation treatment, When the embankment height H<5m,the depth of treatment is 0.3m; When the embankment height 5m<H≤6m, the depth of treatment is 0.5m; When the embankment height 6m<H<7m, the depth of treatment is 1m;When the embankment height H>7m, rubble pressing method and geogrid should be used at the same time;(3) The range of composite subgrade should be 2m width than toe of the embankment slope; (4)Considering the vehicle load,the ultimate filling height of composite subgrade is 7.1m; And the ultimate filling height is 10m after laying geogrid according to the description in this paper.