Study On The Vertical Bearing Mechanism Of Cement Soil Rigid Composite Piles With Fly Ash

Cement soil rigid composite pile is a pile type formed by concentrically implanting rigid core pile before the initial setting of cement soil mixing pile.This pile type combines the advantages of high lateral friction resistance of cement soil pile and high bearing capacity of core pile,and has been used in domestic coastal areas.China is a large coal-producing country,and in recent years,China has produced more than 500 million tons of fly ash every year,and more than 100 million tons of fly ash are piled up every year because it cannot be utilized in time.The disposal of fly ash by open piles not only pollutes the atmosphere but also poses a serious threat to the health of the surrounding residents,so the comprehensive utilization of fly ash is an important issue facing the national economy and social development in China at present.Based on the above background,this paper firstly investigates the effects of cement dosing,fly ash replacement rate,calcium hydroxide dosing and curing age on the strength of fly ash cement soil through unconfined compressive strength test and scanning electron microscope test,and determines its better fly ash replacement rate through cement soil economic analysis,then the vertical bearing mechanism of fly ash doped cement rigid composite pile is studied through model test and numerical simulation analysis.The main results of the study are as follows:(1)When the total amount of cementitious materials remains unchanged,the unconfined compressive strength of fly ash cement soil decreases with the increase of fly ash substitution rate;when the substitution rate of fly ash remains unchanged,the unconfined compressive strength of fly ash cement soil increases with the increase of total amount of cementitious materials.(2)When the amount of cementitious materials and fly ash is certain,the unconfined compressive strength of fly ash cement soil increases and then decreases with the increase of calcium hydroxide,and reaches the maximum when the amount of calcium hydroxide is 5%;when the total amount of cementitious materials and calcium hydroxide is constant,the unconfined compressive strength of fly ash cement soil increases and then decreases with the increase of fly ash substitution rate,and reaches the maximum when the substitution rate of fly ash is 10%.(3)When the total admixture of cementitious materials and calcium hydroxide are 15%and 5%,and the fly ash replacement rate of cement is 10%,20% and 30%,the cost of fly ash cement soil is reduced by 2.5%,10.8% and 18.3%,respectively,while the unconfined compressive strength of pure cement soil remains comparable;When the total amount of cementitious material and calcium hydroxide are 20% and 5%,and the fly ash replacement rate of cement is 10% and 20%,the cost is reduced by 2.5% and 10.1%,respectively;when the total amount of cementitious material and calcium hydroxide are 25% and 5%,and the fly ash replacement rate of cement is 10% and 20%,respectively,the cost is reduced by 3% and 10.7%.(4)The core pile axial force of fly ash cement rigid composite pile is greater than that of pure cement rigid composite pile when the maintenance age is the same.For example,the core pile axial force of fly ash cement rigid composite pile is increased by 2.70% compared with the core pile axial force of pure cement rigid composite pile when the maintenance age is 28 days and the pile top load and pile depth are 5.88 k N and 450 mm;the pile end resistance of fly ash cement rigid composite pile is greater than that of pure cement rigid composite pile when the maintenance age is the same.For example,when the maintenance age is 28 days and the pile top load is 5.88 k N,the pile end resistance of fly ash cement rigid composite pile is increased by 4.55% compared with that of pure cement rigid composite pile.(5)Numerical simulation analysis of the vertical bearing characteristics of the rigid composite pile with fly ash cement soil using finite element software ABAQUS shows that the axial force of the rigid composite pile with fly ash cement soil is greater than the axial force of the rigid composite pile with pure cement soil when the maintenance age is the same;the lateral friction resistance of the inner and outer core pile interface of the rigid composite pile with fly ash cement soil is greater than the lateral friction resistance of the inner and outer core pile interface of the rigid composite pile with pure cement soil;the load sharing ratio of the inner and outer core pile of the rigid composite pile with fly ash cement soil is greater than the load sharing ratio of the inner and outer core pile of the rigid composite pile with pure cement soil.