| Peat soils(collectively referred to as peat and peat soil)is a special soil composed of organic residues,minerals and humus.Peat soils is a special soft soil with poor engineering properties,which have the characteristics of a large void ratio,high moisture content,strong compressibility,low shear strength and remarkable secondary consolidation deformation.Depending on statistics,peat soils is widely distributed in 59 countries and regions around the world,with a total area of more than 4.153 million km~2,accounting for about 5%or 8%of the earth’s land area.Construction of expressway on peat foundation is often faced with the problems of large settlement and significant settlement after construction.At present,there are few engineering cases for peat foundation treatment of expressway at home and abroad,and there are not many experiences that can be used for reference,and the application effect of common soft foundation treatment technology in peat foundation is not clear.At present,there are few engineering practices on peat foundation treatment of expressway at home and abroad,and there is not much experience that can be used for reference,and there is a lack of theoretical guidance in choosing the scheme of peat foundation treatment of expressway.Therefore,to explore the soft foundation treatment method suitable for highway peat foundation has important theoretical value and practical significance.This paper is based on the CKE(Colombo-Katunayake Expressway)highway project in Sri Lanka,based on on-site monitoring data analysis,laboratory test,combined with theoretical analysis to explore the treatment of highway deep peat foundation.The specific research contents and conclusions are as follows:(1)The existing geological data are collected and sorted out,the physical and mechanical properties of peat soil along the CKE project in Sri Lanka are analyzed,the design and construction of overload preloading method,sand(gravel)pile-overload preloading method and plastic drainage belt-overload preloading method in deep peat foundation are introduced in detail.(2)Based on the on-site monitoring data of CKE project,the surface settlement,surface horizontal displacement rate and 6-year post-construction settlement during preloading period of peat foundation are analyzed,and the consolidation coefficient of typical cross-section peat foundation is inversed by Asaoka method and improved Asaoka method on the basis of measured settlement data.The economy,construction difficulty and construction time difference of four soft foundation treatment methods in peat soil foundation are analyzed.Finally,based on the above research results,the applicability and feasibility of four soft foundation treatment methods in deep peat soil foundation are evaluated.(3)The indoor model test of peat foundation treatment with sand pile and overload preloading method was carried out by using self-made model box.The relationship between the area replacement ratio of the sand pile and the surface settlement of peat soil,the change law of pore water pressure and the change law of undrained shear strength is quantified.(4)Using indoor one-dimensional consolidation test to simulate the construction process of overload preloading method,the influence of different overload ratio on the deformation characteristics of peat soil was studied.Based on the calculation theory of soft soil secondary consolidation,this paper studies the reasonable value of overload ratio when using overload preloading method to treat peat soil foundation.The results show that overload preloading can reduce the post-construction settlement of peat foundation.The larger the overload ratio is,the more obvious the attenuation of the primary consolidation coefficient of peat soil is and the smaller the post-construction settlement is after unloading the overload.After overloading,the deformation of peat soil goes through three stages:the main springback stage,the stabilization stage and the secondary consolidation stage.When the peat foundation is treated by overload preloading method,the overload ratio of 0.25 can meet the engineering requirements,and too large overload ratio is not necessary. |
