Back silting and slope stability of foundation trench in Shenzhen-Zhongshan immersed tunnel project
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摘要: 跨海沉管隧道因其回淤强度大、晾槽时间长等特点,大量累积的回淤物威胁到沉管隧道的安全性。以深中通道沉管隧道为背景,总结试挖槽试验中回淤时空变化规律,研究回淤对基槽边坡稳定性的影响,深入分析坡面回淤的局部稳定性影响因素,结果表明：①回淤平面分布差异明显,槽底、北坡、南坡的回淤量依次减小；回淤竖向分布不均,从上至下呈递减趋势；回淤全年分布不均,洪季时回淤量大,进入枯季后回淤量减小。②基槽边坡稳定性主要受坡面回淤控制,放坡清淤可明显改善坡面回淤的稳定性；回淤厚度、清淤坡率、基槽坡高、边坡坡率增大及回淤抗剪强度降低均不利于坡面回淤的稳定性,清淤坡率应考虑各影响因素和所处季节综合确定。Abstract: Due to the large intensity of back silting and long-term idleness of foundation trench, back silting will threaten the safety of immersed tunnel. Relying on Shenzhen-Zhongshan immersed tunnel project, the change rules of back silting with time and space in the trial trench tests are summarized. A numerical model is established to study the influences of back silting on the stability of foundation trench slope. The factors affecting the local stability of back silting are deeply analyzed. The results show that: (1) The horizontal distribution of back silting is obviously different, that is, the amount of back silting at the bottom, north slope and south slope decreases in turn. The vertical distribution of back silting is uneven, and the thickness of back silting from top to bottom decreases. The amount of back silting varies greatly through out the year, large in flood season but small in dry season. (2) The stability of foundation trench slope is mainly controlled by the back silting, and the stability of back silting can be significantly improved by desilting with slope. The safety factor of back silting decreases with the increase of thickness of back silting, desilting gradient, slope height, slope gradient or the decrease of shear strength of back silting.
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Keywords:
- immersed tunnel /
- foundation trench /
- back silting /
- stability /
- trial trench
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图 4 回淤物厚度及平均密度–时间曲线
Figure 4. Thicknesses and average density-time curves of back silting
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图 5 放坡清淤前后回淤分布对比
Figure 5. Comparison of back silting before and after desilting with slope
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图 7 不同回淤厚度时基槽边坡的安全系数
Figure 7. Safety factors of slope with different thicknesses of back silting
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图 11 不同坡高的基槽坡面回淤局部安全系数（边坡坡率1∶3）
Figure 11. Local safety factors of back silting with different slope heights (slope rate of 1∶3)
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图 12 不同坡高的基槽坡面回淤局部安全系数（边坡坡率1∶5）
Figure 12. Local safety factors of back silting with different slope heights (slope rate of 1∶5)
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图 13 不同坡高的基槽坡面回淤局部安全系数（边坡坡率1∶7）
Figure 13. Local safety factors of back silting with different slope heights (slope rate of 1∶7)
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图 14 抗剪强度不同时的回淤局部安全系数
Figure 14. Local safety factors of back silting with different shear strengths
表 1 土体物理力学参数
Table 1 Physical and mechanical parameters of soil
土层名称 饱和重度/(kN·m-3) 弹性模量E/MPa 泊松比 固结快剪 c/kPa φ/(°) 淤泥 15.3 4.71 0.40 6.69 8.04 粉砂 20.0 25.20 0.30 8.00 17.70 回淤 12.6 3.00 0.43 1.30 0.70 
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表 2 不同基槽边坡的回淤承载值
Table 2 Load values of back silting for different slopes
(m) 坡高/m 边坡坡率 1∶3 1∶5 1∶7 10 >3 >3 >3 20 >3 >3 >3 30 1.8 >3 >3
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表 3 回淤放坡处理的坡率上限值
Table 3 Upper limit values of desilting slope rate
边坡坡率 南边坡 北边坡 10 m 20 m 30 m 10 m 20 m 30 m 1∶3 1∶1.5 1∶1.5 1∶1.5 1∶2 1∶2.5 1∶3 1∶5 1∶2 1∶2 1∶2 1∶2 1∶3 1∶4 1∶7 1∶2 1∶2 1∶2 1∶2 1∶3 1∶4 注： 回淤放坡坡率与边坡坡率相等时,为将回淤物全部清除。
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