Application Of Cement Soil Concrete Core Stiffening Wall In Soft Soil Foundation Pit

Composite cement soil wall has a variety of forms.The common types of support include steel SMW method piles,cement soil inserted micro-shaped steel pipe pile,and cement soil inserted pine wood pile.This paper mainly focuses on the research of the mechanism and application of the similar rigid large diameter rotary jet mixing stiffening wall.Similar rigid large-diameter rotary jet(stirring)piles are cement-soil piles with comprehensive characteristics of high strength,large diameter,and strong soil cutting ability.The similar rigid strength index is as follow: in the flow-plastic sludge layer with water content is about 80%,the cement soil which is more than or equal to 28 d in age should satisfy ≥ 1.5-2.0MPa;the pile diameter can reach 2m,the maximum pile length can reach 32 m,and the pile end can be embedded in(fully)strong weathered formation.The stiffened piles which consist of similar rigid large-diameter jet mixing piles and concrete cores have large lateral stiffness,and they have great advantages in the support selection of large-scale foundation pit which requests "external anchor cables and no support inside."But so far there has been very little research on this type of support,and its mechanism and design method are still not mature enough.This paper will systematically study the deformation,stress mechanism and actual engineering application effects of this composite retaining wall,combining previous research results on composite stiffening piles.the specific work results mainly include the following points:(1)Establishing a plane strain model of a rigid large-diameter jet(stirring)wall by using the Midas NX finite element software,the effects of factors such as wall width,pit depth,and wall elasticity on wall deformation and stress distribution were studied,and the destruction mode of cement and concrete wall material was explored.(2)On the basis of the plane strain model mentioned above,a three-dimensional finite element model of similar rigid large-diameter rotary jet mixing stiffening wall was established.The specific influence of the concrete core on the displacement field,internal force field and the distribution ratio of the bending moment of the foundation pit and support are studied,and several factors affecting the effect of the concrete core were analyzed,including the factors such as the embedded-ratio,the center distance of the inner core,the diameter of the inner core,the elastic modulus of the mixing pile,and the diameter of the mixing pile.(3)In combination with a real project in Guangzhou,the project was simulated using Midas NX finite element software.By comparing the results of the analysis with the actual monitoring data,some of the stress deformation characteristics and application of the composite retaining wall in the actual excavation process were summarized.After research,it has been found that the supporting effect of the similar rigid large-diameter rotary spray mixing stiffening wall is worthy of recognition.This combined structure can effectively control the deformation of the foundation pit and has good stress performance.