摘   要

      由于软土具有含水量高、孔隙比大、压缩性高、抗剪强度低、灵敏度高、具流变性等工程特点，故软土地区建筑物发生倾斜破坏等质量事故的概率比较高。对发生质量事故的建筑物如何进行分析、处理是本文的研究内容。

      本文以软土的特性当作为研究的出发点，对既有建筑物的质量事故表现、质量事故原因、原建筑物的鉴定评估、地基基础承载力的充分利用及适用于软土地区的加固方法进行了分析、探讨，其目的在于建立一套从“事故表现----原因分析----原建筑物性能评估----地基基础承载力的充分利用”，到“选择加固方法”的机制，使得在既有建筑物加固时更具针对性。

      要想更有效、更经济地对既有建筑物进行加固，应充分利用既有建筑物地基基础承载力潜力。本文根据软土的工程特性，从土力学的角度出发，对软土在建筑物荷载作用下强度的增长进行了分析研究，推导了其承载力随时间增长的公式。对于既有建筑物失效桩基承载力的计算，本文提出，应根据具体的失效原因进行计算。对由于软土固结所产生的负摩擦力对桩基承载力的影响，具体进行了分析。当无法确定桩基失效的原因时，本文建议按实际的沉降量估算其承载力潜力，并提出了经验公式。

       对既有建筑物加固，本文总结了其原则和程序。对适于软土地区的既有建筑物的加固尤其地基基础加固，文中根据已有的文献结合本人经验对此进行了总结。

       在具体的工程实践中，本文以南海市某建筑物的加固为例，对前述的分析、评估与加固方法进行了应用，并取得了良好的效果。

Abstract

    The rate which constructions are inclined and destroyed in the district of soft soil is high because soft soil has the engineering characters of high water content, big coid ratio, high compressibility, low shear strength, high sensitivity and rheology. It is the thesis’s study content how to analyse and deal with the existing building’s problems in quality.

    As study’s starting with soft soil’s characters,the questions about the representations and causes of quality accident, judgement and appraisement on existing building, full use of bearing capacity of ground foundation and reinforcing ways applying to the districts of soft soil are analyzed and discussed herein. The aim is to build a suit of mechanism from ‘accident representations -- causes analysis-- existing building appraisement of capacity--ground foundation bearing capacity full use’ to ‘reinforcing ways choice’,so that the pertinence is better when the existing building is reinforced.

    The potential of bearing capacity of ground foundation should be taken full advantage of if the existing building need be reinforced more effectively and more economically. Soft soil strength’s increasing in the effect of buildings load is analysed and studied from angle of soil mechanics in term of soft soil engineering characters while the formulas of bearing capacity increasing with time are put forward herein. To ineffective piles in existing building , its bearing capacity should be calculate in term of material cause.The effect on pile of negative friction because of soft soil consolidation is analysed too in detail. When the cause why the piles are ineffective cannot be confirmed, it is suggested to count its potential of bearing capacity according to actual settlement value and its experimental formulas are put forward herein.

    The reinforcing principle and process on existing building are summarized herein. The summarization is done too about reinforcement ways special to foundation reinforcement of existing buildings applying to soft soil according to existing literatures and author’s experiments.

     In real engineering practice, forementioned ways of analysing, appraising and reinforcing have been applied and gained a favorable effect by the instance of a building reinforcement in Naihai.

Key words: soft soil; analysis of accident; bearing capacity; ground foundation; reinforcement and rectifying deviation