地下工程开挖问题计算方法的再认识

Rethinking of the calculation method of excavation issues in underground engineering

开挖方法的选择既取决于施工技术,也受制于地层特性.如何计算开挖过程中的变形和稳定性一直以来都是国内外学界与工程界研究的热点.随着城市地下工程建设逐步向高精度、微变形的方向发展,针对开挖问题的一些计算方法也需要重新认识.本文对传统开挖问题计算方法的基本假定进行了阐述和讨论,提出了考虑开挖应力释放效应来对开挖计算方法进行修正,探讨了开挖过程中与工法相关的应力释放问题,为今后对开挖问题的理论研究与地下工程的设计施工计算提供一种思路.

The key to the construction of the underground engineering is to solve the deformation and stability problems caused by the excavation.Evolutions and attempts of various construction methods in history have been carried out for excavation.The evolution of various construction methods is not only related to construction technologies,but also closely related to the characteristics of the soil stratums.How to calculate the deformation during excavation,or how to evaluate the stability caused by excavation in a precise way,is still controversial in academia.In engineering practice,the excavation calculation is still limited to traditional continuum mechanics,even if the surrounding soil is cohesionless.As a result,the calculation precision cannot be guaranteed.Furthermore,limited to the strict deformation control of existing adjacent buildings,the excavation of the urban underground engineering should meet the requirement of high precision and micro-deformation,which brings more challenges for traditional continuum theoretical methodologies.From a microscopic point of view,soil is a type of typical granular material.After the excavation,the local stress release in the soil particle structure will be constrained by the other parts of the soil.As a result,the deformation and stress release are hindered,and the residual stress is observed.Studies have shown that the macroscopic performance of the stress residual characteristics of the particle system caused by the excavation is result from the stress release effect.The stress release effect of the excavation problem is significantly different from the traditional excavation load or excavation stress release coefficient.The former is the mechanical expression of the interaction between particles in the engineering influence range,while the latter is an approximate treatment of the excavation boundary.Based on the latest research results of the loading and unloading characteristics of the bulk material and the excavation stress release,the basic assumptions of the traditional excavation calculation method are expounded and discussed in this paper.A calculation method for correcting the traditional excavation problem by considering the excavation stress release effect is proposed.This paper also discussed the stress release problems related to the construction method during the excavation process,which can provide a way of rethinking for the theoretical research on the excavation issues and the design and construction calculation of the underground engineering.