北疆供水一期工程膨胀性渠坡滑动破坏机制与稳定分析

SLIDING FAILURE MECHANISM AND STABILITY ANALYSIS OF EXPANSIVE CANAL SLOPE IN NORTH XINJIANG WATER SUPPLY PHASE I PROJECT

北疆供水一期工程属于季节性供水工程,渠道运行多年,渗漏现象严重,渠坡滑动破坏现象频发。为深入探究渠坡的滑动破坏机制,首先对渠基土开展力学特性研究,然后利用其强度特性变化规律对渠坡的不同工况进行数值模拟分析。结果表明:在湿干-冻融循环条件下,膨胀土抗剪强度c、φ值与弹性模量E衰减严重,白砂岩c值随含水率的增加劣化明显而φ值基本不变,戈壁料c和φ值受含水率和循环条件影响不显著;通水期间,多次湿干-冻融循环后渠坡均未发生滑动破坏,原因在于渠坡结构面上静水压力的法向分量增加了渠基土沿滑动面的抗滑力,切向分量减少了渠基土沿滑动面的下滑力,提高了渠坡的安全稳定性;停水期间,湿干-冻融循环和膜后水位耦合作用导致渠坡发生滑动破坏,膨胀土性能衰减、白砂岩遇水软化及膜后水位引起孔隙水压力变化是其主要诱因,浅层土体置换、受力结构优化和降低膜后水位能够起到缓解作用;现有排水井对渠坡无抗滑作用,将排水井移至渠坡中部,局部稳定性提升最显著,且单桩保护范围最大,分别为44.3%和45 m^(2)。

The first phase of water supply project in northern Xinjiang belongs to seasonal water supply project,and the leakage of channel operation is serious for many years;what’s worse,the sliding failure of channel slope is frequent.In order to further explore the sliding failure mechanism of canal slope,the mechanical properties of canal foundation soil are studied,and the numerical simulation analysis under different working conditions of canal slope is carried out by using the variation law of its strength characteristics.The results show that:Under the condition of wet-dry-freeze-thaw cycles,the shear strength c,φvalues and elastic modulus E of expansive soil decrease seriously.The c value of white sandstone decreases obviously with the increase of water content,while theφvalue is basically unchanged.The c andφvalues of gobi material are not significantly affected by water content and cyclic conditions;During the water supply period,the sliding failure did not occur on the canal slope after multiple wet-dry-freeze cycles,which can be explained by that the normal component of hydrostatic pressure increases the anti-sliding force of channel foundation soil along the sliding plane,while the tangential component reduces the sliding force of channel foundation soil along the sliding plane,thus improving the safety and stability of channel slope;During the period of water shut-down,the coupling effect of wet-dry freeze-thaw cycle and water level behind the membrane leads to the sliding failure of the canal slope.The main causes are the attenuation of expansive soil performance,the softening of white sandstone under water and the change of pore water pressure caused by water level behind the membrane.The replacement of shallow soil,the optimization of stress structure and the reduction of water level behind the membrane can play a mitigation role;The existing drainage wells have no anti-slide effect on the canal slope,the local stability of the canal slope in the middle of the drainage well is the most obvious,and the single pile protection range is the largest,which is 44.3%and 45 m^(2),respectively.