传统改性土工程性能试验研究及在城墙修复中的应用

Experimental Study on Engineering Properties of Traditional Modified Soil and Its Application in City Wall Restoration

以某明城墙后期修复段的坍塌事故为背景,分析了该城墙坍塌的原因。基于室内试验和城墙缩尺模型试验,研究了传统改性土及素土的非饱和特性、强度软化特性及不同土类夯筑城墙的抗渗性、抗剥蚀性、抗裂性等工程性能;采用非饱和渗流原理和边坡稳定性分析方法探索了不同改性土夯筑城墙的降雨入渗规律及整体稳定性,最终针对6类传统改性土在城墙修复中的适宜性进行了对比分析。结果表明:相对于素土,三七灰土和糯米灰膏改性土具有较良好的抗渗、抗剥蚀和抗裂等综合工程性能;不同降雨工况下,素土夯筑城墙的入渗深度及增湿影响程度最大,入渗最深达2.9 m,三七灰土整体的入渗深度最小,约为1.0 m,其次为三合土,采用三七灰土或糯米灰膏改性土修复后城墙的整体稳定性相对较高;降雨积水入渗是导致修复段城墙坍塌失稳的外因,新修筑夯土的用料不当及排水系统失效是导致墙体失稳的内因;适当采用改性夯土进行古城墙修复并避免墙体顶部出现积水,将有利于提高修复后城墙的整体稳定性。

Taking he collapse accident of late restoration section of a Ming city wall as the background,the collapse reasons of the city wall were analyzed.Based on laboratory test and scale model experiment of the city wall,the unsaturated properties,strength softening properties of traditional modified soil(MS)and plain soil(PS)and the anti-permeability,anti-denudation and anti-cracking properties of rammed city wall with different types of soil were studied.According to the unsaturated seepage principle and slope stability analysis method,the rainfall infiltration regularity and stability of the rammed city wall with different MS were explored.The results show that compared with PS,the MS of lime soil(LS)and sticky rice and lime powder soil(SPL)have better comprehensive engineering properties such as the properties of anti-permeability,anti-denudation and anti-cracking.Under different rainfall conditions,the rainfall-influenced infiltration depth of the rammed city wall with PS is the largest,and the maximum infiltration depth is 2.9 m.The infiltration depth of rammed city wall with LS is the smallest,which is about 1.0 m and then followed by the tabia soil(TB).The overall stability of the rammed city wall with LS or SPL is relatively high.Rainfall infiltration and water accumulation on the top of the city wall are the external causes of the collapse and instability of the repaired section of the city wall.Improper materials used in the new construction of rammed earth and the failure of drainage system are the internal causes of the instability of the city wall.Appropriate use of MS to repair the ancient city wall and avoiding water accumulation on the top of the city wall will benefit improving the overall stability of the restored city wall.