Calculation method of dewatering settlement in saturated loess stratum
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摘要:
在周边环境复杂的地下工程建设中，合理地预测和评价降水对周边环境的影响是控制工程可行性的关键性问题。目前，基于分层总和法的工程降水沉降计算方法主要取决于经验系数的选择，取值过于笼统, 不能完整反映层厚和土性变化的影响，预测结果与实际情况相差较大。为相对合理、准确地预测黄土降水沉降，在分析饱和黄土物性沉积状态的基础上，提出用孔隙比（e）和液性指数（IL）反映降水过程中黄土失水的可变性和能变性的思路，同时提出失水敏感性指标，建立了饱和黄土地层降水沉降实用化计算方法e-IL法，并开展了多个场地的沉降验证。研究成果表明：（1）饱和黄土视其上覆压力和地下水作用方式的不同，可形成欠压密饱和黄土和压密饱和黄土，两类饱和黄土物性和工程降水沉降差异较大；（2）影响降水沉降变形的主要物性指标是孔隙比和液性指数，可分别反映饱和黄土的可变性和能变性，即失水敏感性；（3）6个场地的计算与实测结果对比表明，黄土地区工程降水沉降主要发生在大孔隙结构依然存在的欠压密饱和黄土层中。考虑失水敏感性的降水分层沉降计算e-IL法，能够全面反映饱和黄土降水沉降规律，可为黄土地区降水工程的设计和施工提供可靠的理论依据。
Abstract:In the construction of underground engineering with complex surrounding environment, reasonable prediction and evaluation of the influence of precipitation on the surrounding environment is a key problem to control the feasibility of the project. At present, the calculation of dewatering-induced settlement using the layered summation method heavily relies on empirical coefficients, leading to significant variability in predictions and deviations from actual observations. To predict the precipitation settlement of loess reasonably and accurately, based on the analysis of the physical properties of saturated loess, the void ratio and liquid index were introduced as key indicators to characterize both deformation potential and the deformation’s difficulty in the dewatering process. The practical calculation method of dewatering settlement of saturated loess stratum was established, and settlement verification was carried out at multiple sites. The results show that depending on the overlying pressure and groundwater action mode, saturated loess can form uncompacted saturated loess and compact saturated loess. The physical properties and dewatering settlement deformation of the two types of loess are different. The main physical property indexes affecting dewatering deposition deformation are the porosity ratio and liquid property index in the initial state, reflecting the deformation potential and the difficulty of deformation of saturated loess, respectively. The comparison between the calculation and measurement of six sites shows that the dewatering subsidence in the loess area mainly occurs in compact saturated loess where the macroporous structure still exists. The proposed e-IL method, incorporating void ratio and liquid index, effectively captures the settlement behavior of saturated loess. This study provides effective technical method for designing and constructing dewatering engineering in the loess area.
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Key words:
- saturated loess /
- dewatering settlement /
- void ratio /
- liquid index /
- deformation potential /
- deformation difficulty
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表 1 西安地区水位降深范围内特征土层物性指标统计表
Table 1. Statistical table of index of characteristic soil layers within the scope of water level drop in Xi’an
特征土层 e IL $ \varphi_{\mathrm{w}i} $ 欠压密饱和Qp3黄土 0.85～1.10 0.77～1.20 0.67～1.32 压密饱和Qp3黄土 0.74～0.76 0.22～0.64 0.16～0.49 饱和Qp3古土壤 0.73～0.91 0.29～0.51 0.23～0.46 欠压密饱和Qp2黄土 0.75～0.84 0.66～0.89 0.50～0.74 压密饱和Qp2黄土 0.70～0.75 0.21～0.58 0.27～0.44 饱和Qp2古土壤 0.68～0.74 0.15～0.58 0.27～0.43 
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表 2 验证场地位置各特征土层相关参数
Table 2. Range values of each characteristic soil layer at the site location
特征土层 e IL e·IL 欠压密饱和Qp3黄土 0.85～1.01 0.92～1.04 0.84～1.05 饱和Qp3古土壤 0.74～0.80 0.24～0.65 0.18～0.50 欠压密饱和Qp2黄土 0.77～0.79 0.66～0.77 0.51～0.60 压密饱和Qp2黄土 0.69～0.76 0.54～0.75 0.41～0.51
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表 3 现行规范建议方法反算结果
Table 3. Summary of empirical coefficients for backcalculation of current norms and recommended methods
实测沉降量
/mm沉降计算量
（未经修正）/mm反算得到
φw场地1 38.4 92.1 0.42 场地2 86.9 163.1 0.53 场地3 118.8 154.9 0.77 场地4 51.3 144.3 0.36 场地5 53.6 86.7 0.62 场地6 253.0 375.7 0.67
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表 4 典型场地地层信息与验证表
Table 4. Stratum information and verification of typical site
场地编号 特征土层 Es1-2 /MPa Es2-3 /MPa Es3-4/MPa e IL e·IL 预测沉降量/mm 实测沉降量/mm 场地1 欠压密饱和Qp3黄土 4.1 3.5 — 0.910 0.92 0.84 42.5 38.4 饱和Qp3古土壤 6.1 8.2 — 0.764 0.24 0.18 欠压密饱和Qp2黄土 5.2 7.2 9.2 0.778 0.66 0.51 饱和Qp2古土壤 — — — 0.684 0.24 0.16 场地2 欠压密饱和Qp3黄土 4.1 3.5 — 0.910 0.92 0.84 94.1 86.9 饱和Qp3古土壤 6.1 8.2 — 0.764 0.24 0.18 欠压密饱和Qp2黄土 5.2 7.2 9.2 0.778 0.66 0.51 场地3 欠压密饱和Qp3黄土 3.5 6.1 — 0.955 1.04 0.99 103.8 118.8 饱和Qp3古土壤 6.3 8.3 — 0.744 0.44 0.33 欠压密饱和Qp2黄土 5.7 8.1 11.3 0.776 0.77 0.60 场地4 欠压密饱和Qp3黄土 4.1 3.5 — 0.985 0.99 0.98 66.4 51.3 饱和Qp3古土壤 6.1 8.2 — 0.809 0.51 0.41 欠压密饱和Qp2黄土 5.2 7.2 9.2 0.785 0.73 0.57 场地5 欠压密饱和Qp3黄土 6.5 6.1 — 1.008 1.04 1.05 46.3 53.6 饱和Qp3古土壤 3.6 5.2 — 0.748 0.45 0.34 压密饱和Qp2黄土 5.5 7.9 — 0.696 0.75 0.52 粉质黏土 6.8 9.5 13 0.698 0.40 0.28 场地6 欠压密饱和Qp3黄土 4.1 3.5 — 0.845 1.01 0.87 209.3 253.0 饱和Qp3古土壤 6.1 8.2 — 0.771 0.65 0.50 欠压密饱和Qp2黄土 5.2 7.2 9.2 0.768 0.66 0.51 压密饱和Qp2黄土 6.9 10.1 13.5 0.759 0.54 0.41 注：场地1、2、6采用单米预测方法，表中所列数值为对应土层范围内的测试均值；场地3、4、5中所列数值取自于详细勘察报告中的设计参数标准值。—指预测过程中不涉及该参数；Es1-2、Es2-3、Es3-4为不同载荷段内的压缩模量。
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