Influences of vertical drainage wells on stability of expansive soil canals in North Xinjiang
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摘要: 北疆输水渠道是周期性供水渠道,渠水渗漏会使得渠基土经历“干湿”循环作用,将显著降低膨胀性渠基土的强度,进而影响渠道的稳定性。为了降低渠水渗漏对渠坡稳定性的威胁,建管部门对渠道进行了渗水速排系统改造。其中,竖向排水井的主要作用是将渗水集中抽排；此外,还可能发挥类似抗滑桩的作用。因此,针对该问题开展了数值分析,结果表明：若竖向排水井抽排作业将渗漏断面的膜后水位降低至0 m,可以确保渠道断面在最危险工况下稳定性系数Fs大于1.35,渠坡处于稳定状态；若不进行渗水抽排,膜后水位大于1 m的断面在运行10年以上时,Fs将小于1.05,渠坡处于欠稳定或不稳定状态。仅分析竖向排水井作为抗滑桩的作用,排水井在当前位置（桩心距离渠沿6 m）起到的抗滑作用基本可以忽略,滑弧将会出现在排水井前方；将排水井向靠近渠坡的方向移动至渠沿时,单根排水井对渠坡抗滑保护范围最大,为44 m。Abstract: The water conveyance canal in North Xinjiang is a periodic water supply canal, and the "wetting-drying" circulation caused by canal water leakage may significantly reduce the strength of expansive soils and further affect the stability of the expansive soil canals. In order to reduce the threat of canal leakage to the stability of canal slopes, the Construction and Management Department has carried out the transformation of the seepage quick drainage system. Based on this, the stability characteristics of the canals before and after the reform are analyzed through numerical calculation. The results show that if the water level behind the membrane of the leakage section is reduced to 0 m by the vertical drainage well pumping operation, the stability factor of the section under the most dangerous condition is greater than 1.35, which means the canal slope is stable. If the seepage pumping is not carried out, when the section with water level greater than 1 m after membrane is operated for more than 10 years, the stability factor will be less than 1.05, and the canal slope is understable or unstable. Only the function of the vertical drainage wells as the anti-slide piles is analyzed, then the function can be ignored, and the sliding arc will appear in front of the drainage wells. If the location of a drainage well is moves forward, the maximum protection range of a single pile is 44 meters when the drainage well moves to the edge of the canal.
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Keywords:
- expansive soil /
- canal /
- wetting-drying cycle /
- slope stability /
- drainage well
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图 3 渠坡稳定性系数Fs与运行时间的关系
Figure 3. Relationship between stability factor Fs and operation years
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图 6 方案6单桩保护范围示意图
Figure 6. Schematic diagram of protection scope of single pile in Scheme 6
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图 7 方案5单桩保护范围示意图
Figure 7. Schematic diagram of protection scope of single pile in Scheme 5
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图 8 方案1单桩保护范围示意图
Figure 8. Schematic diagram of protection scope of single pile in Scheme 1
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图 11 单桩保护范围最大时桩所在位置示意图
Figure 11. Schematic diagram of pile position under maximum protection range of a single pile
表 1 边坡稳定性状态划分
Table 1 Division of slope stability state
稳定性系数Fs Fs<1.0 1≤Fs<1.05 1.05≤Fs< Fst Fs> Fst 稳定性状态 不稳定 欠稳定 基本稳定 稳定 注： Fst为边坡稳定安全系数,一级、二级和三级安全等级的永久边坡,一般工况对应的Fst分别为1.35,1.30和1.25。本计算边坡取Fst=1.35。
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表 2 数值计算方案
Table 2 Numerical schemes
方案编号 方案1 方案2 方案3 方案4 方案5 方案6 排水井状态 初始位置 前移1.5 m 前移3.0 m 前移4.5 m 前移6.0 m 前移7.5 m 排水井圆心坐标 -6.0 m -4.5 m -3.0 m -1.5 m 0 m 1. 5 m
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