覆盖型岩溶塌陷的塌陷机制分析

Analysis of collapse mechanism for mantled karst collapse

以覆盖型岩溶塌陷为研究对象,首先分析了覆盖型岩溶塌陷的演化机制,然后考虑土体自重、真空负压、降雨和爆破等因素的共同作用,并基于极限平衡理论建立了覆盖型岩溶塌陷土体稳定系数及塌陷范围的计算方法,以重庆市南岸区涂山湖二外桥梁左侧塌陷为例,发现计算出的塌陷范围与现场塌陷范围基本一致,并分析出该处土体在爆破、真空负压、自重和渗透等因素作用下的稳定系数和塌陷范围变化规律为:稳定系数在土层厚度增加时可增大46%,而当水深从0.1m增加到1m和真空负压由0kPa增大到50kPa时,可降低30%~35%。最后考虑爆破的时效性,探讨了土柱稳定系数随着爆破振动的变化规律,在考虑爆破荷载作用后,土柱稳定系数将降低4%,爆破对土柱的作用时间约为6s。

Tushan lake of Nanshan street in Nan＇an district of Chongqing municipality is a low mountain area characterised by karst valley landforms where developing 7 karst zones and ever taking place a mantled karst collapse at the VHSC bridge. In order to provide theoretical basis for the governance, monitoring and early warning of mantled type karst collapse, and to ensure that human life and property are secured in karst col- lapse zones, this paper took mantled karst collapse as the research object. At first, the evolution mechanism of mantled karst collapse is analyzed. Then the calculation expressions of sliding force and anti-sliding force of mantled karst collapse are obtained considering the joint interaction of soil load, vacuum negative pres- sure, rainfall and blasting. At the same time, based on the limit equilibrium theory,the methods for calculazing collapse soil stability coefficient and determining possible collapse extent of the mantled karst collapses were established; and these methods were applied to the collapses on the left of VHSC bridge. The calculated result of collapse extent is basically consistent with the field observation. In addition, soil thickness that affects stability coefficient and combined effect of soil load, vacuum negative pressure, rainfall and blasting on the collapse extent are were. The results shows that the stability coefficient can increase by 46 ~ when the thickness of the soil increases, and when the depth of water increases from 0. 1 m to 1 m and the vacuum pressure increases from 0 kPa to 50 kPa, the stability coefficient can reduce by 30G to 35%. Collapse extent also increases with the increase of soil thickness and explosive amount; and it decreases with the increase of explosive distance and internal friction angle. The reduction of collapse range is larger with the explosive dis- tance increase at start, when the explosive distance increase to 110 m, the collapse diameter decreases by 17 %. The collapse range decreases exponentially with the increase of internal friction angle, when the internal friction angle increase from 10% to 26% , the collapse diameter decreased 1% . At last, considering the timeliness of blasting, the soil slump＇s change law of stability coefficient with blasting vibration is analyzed. After blasting, the stability coefficient decreased 4% . Blasting effect the soil duration is about 6 s.