砖-土结构劣化及入侵建筑物拆除对榆林卫城稳定性影响

The effects of the degradation of brick-clay structure and demolition of embedded buildings on the stability of Yulin City Wall

研究古城墙在环境和人为破坏因素下的稳定性对于古城墙保护和修复工程具有重要科学意义。以陕西榆林卫城为研究背景,对其保存现状进行大量调研,对砖墙砌体及夯土材料力学特性进行原位测试和室内试验,再基于数值方法来综合评判砖-土结构劣化及入侵建筑物在拆除过程中古城墙的整体稳定性和受力性态。结果表明:(1)城墙夯土受水分入渗后平均含水率w≥11.5%或顶部剥蚀长度L≥2.5m时,安全系数低于设计值[Fs]=1.3,而外墙砌体劣化对城墙整体稳定性影响不大,表明夯土的强度对城墙整体稳定性起着决定性作用;(2)拆除2层以上、入侵深度超过3.0m的民居或拆除1层的入侵深度超过2.5m的邻近建筑物时,城墙顶部夯土塑性区几乎贯通至城墙顶部;(3)拆除高2.0m宽超过4.0m的贯通城墙的门洞或层高4.0m宽超过2.5m的贯通城墙的民居时,建筑物顶部以上夯土塑性区贯通至城墙顶部,可能会出现坍塌危险,而拆除断面尺寸低于2.0m×2.0m的贯通城墙的建筑物时,对其城墙稳定性影响不大。

It is significant to study the stability of ancient city wall for its conservation and restoration under the environmental and human destruction conditions.In this study,the current preservation situation of Yulin City Wall (YCW) were investigated,and the mechanical properties of masonry structures and rammed soil in city wall were tested by in-situ tests and laboratory experiments.The overall stability and stress-strain state of the city wall were analysed with numerical method when the brick-clay structures turned degraded,and the embedded buildings were demolished.The research results show that:1) The safety factor Fs is smaller than the design value of 1.3 when the average water content of the rammed soil is larger than 11.5% during the rainfall infiltration stage or the denudation length of rammed soil at the top of the city wall larger than 2.5 m.However,the degradation of masonry structures has little effect on the stability of the city wall,which indicates that the strength of the rammed soil plays a determining role on the overall stability of the city wall.2) The plastic zone almost extends to the top of the city wall,when 2 or 3-storey high buildings embedded 3.0 m depth or 1-story high buildings embedded 2.5 m depth in the bottom of the city wall are demolished.3) The plastic zone may extend to the top of the city wall and will collapse,when the penetrative door with the width larger than 4.0 and 1-storey high building with the width larger than 2.5 m are demolished,respectively.It has no influence on the stability of the city wall,when the penetrative buildings with the section size smaller than 2.0 m×2.0 m are demolished.