城市软弱围岩隧道塌方特征及演化规律试验研究

TEST STUDY OF COLLAPSE CHARACTERISTICS OF TUNNELS IN SOFT GROUND IN URBAN AREAS

塌方是城市软弱围岩隧道施工过程中的主要安全风险之一,而明确塌方特征及其演化规律是防控隧道塌方的前提和基础。通过模型试验,针对均质软弱围岩深埋隧道和浅埋隧道2种情况分别研究其塌方特征和演化规律。结果表明,2种埋深条件下均表现出围岩破坏的渐进性和隧道塌方的突发性等典型特征,但也各有特点:(1)深埋隧道围岩破坏不会波及地表,塌方一般发生多次且每次均会形成短时稳定的塌落拱,并最终形成一个稳定的塌落拱,且所有塌落拱形状均表现出典型的二次抛物线特征;(2)浅埋隧道围岩破坏会波及地表并最终造成地表塌陷,围岩破坏过程中也会形成短时稳定的塌落拱,其形状也可以用二次抛物线进行拟合;(3)深埋隧道围岩破裂面自洞室两侧边墙处开始并逐渐向上方发展,而浅埋隧道的地表则先于洞周围岩发生破裂,因此,深埋隧道塌方防控的重点应放在洞内,而浅埋隧道塌方防控的重点则应洞内和地表并举。

Collapse is one of the main risks during the construction of tunnels through soft ground in urban areas. Understanding the characteristics of tunnel collapsing helps the prevention of the problem in tunneling through the soft ground. Model tests were performed to study the collapsing characteristics of a deep tunnel and a shallow tunnel under the same soft ground condition respectively. The results showed that collapses of the tunnels in soft ground under different covering depths had two similar characteristics,the progressive failure of surrounding rock and the sudden occurrence of tunnel collapse. However,the characteristics of collapses in the deep tunnel were different from ones in the shallow tunnel in the following aspects：（1） The failures of surrounding rock around the deep tunnel did not spread to the ground surface. Collapses occurred several times and there was a short-time and stable collapsing arch during each collapse. The collapses did not stop until the formation of a stable collapsing arch. All the boundaries of collapsing arches were in the shapes of typical quadratic parabolas. （2） The failures of surrounding rock around the shallow tunnel spread to the ground surface,and eventually caused the ground surface to collapse. A short-time and stable collapsing arch was also observed to exist during the failures of surrounding rock,and its boundary was also in the shape of a typical quadratic parabola. （3） The failures first occurred on the two sides of the tunnel and then at the tunnel crown in the case of the deep tunnel,while the ruptures of the ground surface occurred earlier than the surrounding rock around the tunnel during the construction of the shallow tunnel. Therefore,the key measures of preventing the collapses should be taken in the tunnel for deep tunnels,and both in the tunnel and on the ground surface for shallow tunnels.