地基承载力深度和宽度修正系数分析

Analysis of depth and width correction factors for bearing capacity of foundation soil

在大面积人工填土的地基承载力计算中,中国现行《建筑地基基础设计规范》(以下简称《规范》)不考虑对基础宽度的修正,得到的地基承载力偏小,对工程安全有利,但在一些情况下却不够经济。该文对这一问题进行探讨,分析了地基承载力的定义、度量方法、相关理论原理和容许承载力的取值方法,探讨并推测了此前在人工填土、软弱下卧层等地基承载力修正系数选择上的可能依据。考虑到当前施工和监测技术相较于早期规范制定时已有很大进步,认为在满足一定条件下可考虑修正地基承载力宽度,并且可适当提高现有的深度和宽度修正系数取值。

[Objective]The determination of bearing capacity of foundation soil is one of the classical research fields of soil mechanics.For large area artificial fill projects,the current specifications of China do not consider the correction factor of foundation width in the calculation of bearing capacity.This paper discusses this problem,and investigates the definition and measurement methods of the foundation bearing capacity,related theoretical principles,and the method of determining allowable bearing capacity.We also discuss and speculate the possible basis for the selection of correction factors of the bearing capacity of foundation soil made of artificial fill and soft underlying stratum.It may provides theoretical guidance for width and depth correction of bearing capacity of foundation soil in large area artificial fill under current technical conditions.[Methods]In this paper,two main approaches for calculating bearing capacity of foundation soil are studied.One is to determine the bearing capacity of the foundation soil according to the extension range of the plastic zone;the other is to use the ultimate load as the ultimate bearing capacity,and then divide it by the safety factor to obtain the bearing capacity.The width and depth correction of bearing capacity is also based on these theories.We reviews the sources of the calculation method of bearing capacity together with the width and depth correction factors in the current specifications of China.On the basis of deriving the calculation formula and analyzing the principle of bearing capacity of foundation soil,two cases are investigated in this paper:one is a homogeneous foundation soil,and the other is that the shear strength of the soil outside the foundation boundaries is lower than the foundation soil.The possible essence for the correction factors of the bearing capacity is then discussed in order to guide the determination of the width and depth correction factors for large area artificial fill.[Results]For large area artificial fill projects,the correction factor of width is not considered in current specifications of China.The main reasons may be as follows:1)The compaction quality of the foundation soil is not be able to guarantee easily.2)The quality control standard of the soil under the foundation is stricter than that outside the foundation boundaries.3)Post-construction settlement may occur for artificial fill.Since that the existing construction technology and quality control level has made great progress compared to the past,it is theoretically feasible to increase the correction factors of width and depth for large area artificial fill such as in island and reef.However,the following items are needed:1)The degree of compaction should meet the requirement in the fill site.2)The engineering quality of the fill outside the foundation boundaries should also be guaranteed not to be lower than the foundation soil.3)Settlement calculation of the buildings are necessary.[Conclusions]Based on the theories of determining the bearing capacity of the foundation soil,this paper investigates the method of selecting the values of correction factors of width and depth.It is thought that the correction factors of width and depth can be appropriately increased under certain conditions for large area artificial fill.This will have good economic benefits,especially for offshore islands and reefs.