Analysis of soaking deformation characteristics of large-thickness discontinuous collapsible loess
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摘要:
非连续分布的黄土地层在中国关中平原地区广泛分布，由于其特殊的地层结构，在评价地基湿陷性时自重湿陷量的室内计算值与现场实测值有较大的差异。为此，文章以关中盆地渭河北岸黄土塬地层为研究对象，开展了室内湿陷性试验和现场大型试坑浸水试验，对比了现场与室内湿陷量差异的影响因素。同时在结合数值计算的基础上，分析了现场浸水试验的渗流特征。研究结果显示：场地现场试验和室内试验的自重湿陷量比值小于0.1，产生此差异的原因包括黄土地层的非连续性和不均匀性、室内试验的取样扰动因素以及现场试验的浸水条件差异；黄土的非连续性形成的层拱效应是造成室内试验与现场试验差异的主要原因，其削弱了部分向上传递的变形、阻碍了向下传递的自重应力，同时造成渗流过程的不连续；计算自重湿陷量时，可采用根据地层时代分层的计算方法，该方法可为该地区未来的工程建设提供理论指导。
Abstract:Objective The unique stratigraphic structure of the widely distributed discontinuous loess stratum in the Guanzhong Plain area of China results in significant differences between the indoor calculated values and field-measured values of the self-weight wetting amount for evaluating the foundation’s wetting property.
Methods Indoor wetting tests and large-scale test pit immersion tests were carried out on-site to compare the factors influencing the difference between on-site and indoor wetting amounts, with the loess stratum on the north bank of the Weihe River as the research object.
Results The following results were obtained from the study: (1) The ratio of self-weight wet depressions between field and indoor test was less than 0.1. This discrepancy was due to the discontinuity and inhomogeneity of loess layers, sampling disturbances in indoor tests, and differing immersion conditions in field test. (2) The “layer bow effect” caused by the discontinuity of loess was the main reason for the difference between the indoor and field tests. This effect weakened upward-transmitted deformation, hindered downward-transmitted gravity stress, and caused discontinuity in the percolation process. (3) Stratification calculations for the four test sites showed that most of the gravitational self-wetting in the field tests occurred in the Qp3 soil layer, while the Qp2 loess layer showed large difference between the field-measured and indoor test values. Thus, the Qp2 loess layer has little to no wetting effect.
Conclusion The shape of the saturated zone range obtained through numerical simulation was consistent with the field test results, and the numerical simulation method was more advantageous for observing the experimental results. When calculating wet subsidence by self-weight, a stratification method based on the strata age can be used. For the Qp3 stratum, the correction coefficient method specified in the guidelines was chosen, while the Qp2 loess stratum was determined by an on-site pit immersion test.
Significance The research methodology used in this study provides theoretical guidance for future engineering constructions on the Guanzhong Plain.
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表 1 试验场地黄土物理力学指标
Table 1. Loess physical index of the test site
取土深
度/m地层
岩性含水率/% 天然密度/
(g·cm−3)孔隙比 自重湿
陷系数取土深
度/m地层
岩性含水率/% 天然密度/
(g·cm−3)孔隙比 自重湿
陷系数1 Qp3黄土 18.7 1.49 1.167 0.003 14 Qp2古土壤 8.9 1.44 1.049 0.051 2 Qp3黄土 17.9 1.64 0.948 0.003 15 Qp2黄土 17.1 1.75 0.820 0.016 3 Qp3黄土 16.2 1.43 1.202 0.009 16 Qp2黄土 19.7 1.76 0.850 0.020 4 Qp3黄土 15.0 1.39 1.250 0.018 17 Qp2黄土 12.0 1.42 1.137 0.051 5 Qp3黄土 10.9 1.41 1.131 0.041 18 Qp2古土壤 11.9 1.41 1.151 0.097 6 Qp3黄土 11.3 1.40 1.154 0.057 19 Qp2古土壤 11.9 1.44 1.114 0.105 7 Qp3古土壤 14.3 1.51 1.059 0.033 20 Qp2古土壤 11.3 1.44 1.095 0.081 8 Qp2黄土 10.1 1.52 0.963 0.017 21 Qp2黄土 11.6 1.54 0.964 0.041 9 Qp2黄土 11.0 1.42 1.118 0.040 22 Qp2黄土 20.6 1.68 0.945 0.023 10 Qp2黄土 12.1 1.46 1.081 0.024 23 Qp2黄土 23.3 1.68 0.989 0.021 11 Qp2黄土 15.0 1.68 0.855 0.011 24 Qp2古土壤 19.7 1.86 0.750 0.006 12 Qp2黄土 14.9 1.70 0.838 0.018 25 Qp2古土壤 18.3 1.79 0.798 0.010 13 Qp2古土壤 12.2 1.50 1.027 0.040 26 Qp2古土壤 19.1 1.84 0.761 0.008 
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表 2 数值模拟参数统计表
Table 2. Statistics of the numerical simulation parameters
材料介质 水平渗透系数/（cm∙s−3） 竖直渗透系数/（cm∙s−3） 黄土 2.3×10−4 6.9×10−4 古土壤 1.4×10−4 4.0×10−4
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表 3 考虑地层时代的修正系数β值
Table 3. Values of correction factor β considering stratigraphic age
序号 地层时代 土层厚度
/m现场实测值
/mm室内试验值
/mm修正系数
β数据来源 1 Qp3 7.0 32.3 154.0 0.21 文中试验场地 Qp2 16.0 11.0 556.1 0.02 2 Qp3 16.5 181.7 177.0 1.03 西安市东郊浐河西岸（王庆满等，2022） Qp2 10.0 27.0 351.0 0.08 3 Qp3 15.2 285.4 268.0 1.07 西安地铁6号线项目田家湾站（王庆满等，2022） Qp2 3.3 0 36.0 0 4 Qp3 10.0 380.5 179.0 1.91 西安城际铁路项目咸阳机场附近（杨喆等，2022） Qp2 9.0 0 129.0 0 注：β为现场实测值与室内试验值得比值
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