IN-SITU SOAKING TEST ON THE DISTURBED LOESS SITE AT LANZHOU METRO, GANSU PROVINCE, CHINA
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摘要: 由于受长期地表降水与排水下渗、前期施工、拆迁等加卸载作用及车辆交通荷载的扰动影响，城市拆迁场地土体的特性与处于原始地形地貌和地层分布的土体情况有所不同。目前尽管已经发表了大量黄土浸水试验的成果，但基本都是在原状黄土场地进行，而在这类扰动场地黄土中开展浸水试验的研究尚不多见。在兰州东岗轨道交通车辆段建设场地进行了累计观测时间超过100天的试坑原位浸水试验。结合室内土工试验和现场测试结果，讨论了该扰动场地黄土浸水产生沉降变形的特征。结果表明：该扰动场地浸水发生沉降变形的时间发展过程具有"缓慢增长-突增-趋于稳定"的特点，其总沉降也远小于既有原状黄土场地的实测结果，应理解为广义的浸水增湿湿陷，其变形包括压缩变形和湿陷变形两部分，二者比例近似为7：3；前期扰动导致的较低的孔隙比和试坑开挖造成的卸荷是其总变形量较小的原因，但是其浸水沉降变形增长过程中突增的湿陷变形和土层空间分布不均匀引起的差异沉降值得引起注意。研究结果对于进一步加深对黄土湿陷变形与水稳定性的理解，选择扰动场地黄土地基处理和防排水措施具有一定的参考价值。Abstract: The underlying soil under the engineering construction on the levy and removing sites in cities is quite different from the soil on the sites with primitive landform and strata distributions due to the disturbing influence of loading and reloading caused by long-term water seepage from precipitation and drainage, previous construction & demolition, traffic loading and so on. Although there are a lot of published researches on the in-situ soaking test for loess sites, most of which are for the intact loess sites, very little research has been devoted to the disturbed loess sites. An in-situ soaking test on the loess test pit were carried out on the construction site of car depot of rail transit in Donggang, Lanzhou and the observation last for over 100 days. Combined with the laboratory experiments and the in-situ test, the settlement deformation patterns due to the soaking of the loess at this disturbed site were discussed. The results indicate that the characteristics of the settlement deformation of the loess site can be generalized as the process of 'slow increasing-sudden increasing-tending to be stable', and the total settlements are much less than those obtained from other similar studies, which can be interpreted as the broadly-defined humidifying collapsibility including the compressive deformation and collapsible deformation with the approximate proportion of 7:3 between them. The relatively low void ratio caused by previous disturbances and unloading resulted from excavation of test pit are the main reasons that the total settlements are quite small, but much attentions should be paid to the sudden collapsibility settlement during the development of settlement deformation due to soaking and differential settlement due to uneven distribution of soil strata. The result would help to comprehend the collapsible deformation and water stability of loess and provide reference to select the measures of foundation treatment and waterproof & drainage for loess site.
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Key words:
- Lanzhou /
- disturbed site /
- loess /
- in-situ soaking test
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图 4 单层灌水体积和累计灌水体积计算值随深度变化
Figure 4. The irrigation amount in each single layer and the total amount vs.time
图 7 深标点埋深深度与最大沉降速率出现时间的相关关系
Figure 7. The correlativity between the burial depth of the deep monitoring points and the occurrence time of the maximum settlements
图 9 浅标点三维沉降分布图
Figure 9. The three-dimensional settlement distribution of the surface monitoring points
图 10 圆心面积均布荷载作用下圆心下附加应力随深度衰减
Figure 10. The additional stress under the center of a circular uniform load vs.depth
表 1 试验场地黄土物理力学参数汇总表
Table 1. The physical and mechanical parameters of loess in the test site
深度/m 密度/(g/cm3) 含水率/% 液限/% 塑限/% 塑性指数 液性指数 颗粒比重 初始孔隙比 饱和度/% 粘聚力/kPa 内摩擦角/(°) 标贯击数 自重湿陷系数 2 1.65 7.6 28.1 18.6 8.5 0.8 2.70 0.76 26.9 61.86 30.25 26 0.025 3 1.65 8.4 30.3 19.9 10.4 -0.92 2.71 0.78 29.2 63.23 26.65 26 0.034 4 1.6 8.9 25.8 16.8 9.0 0.44 2.70 0.84 28.7 71.71 30.49 24 0.026 5 1.65 10.5 25.9 16.8 9.1 -0.28 2.70 0.81 35.1 95.29 31.6 23 0.030 6 1.7 12.2 25.7 16.8 9.0 0.42 2.70 0.78 42.0 76.42 32.22 27 0.027 7 1.7 13.1 25.5 16.7 8.8 -0.83 2.70 0.80 44.4 74.54 29.68 20 0.047 8 1.85 17.3 25.6 16.7 8.9 0.33 2.70 0.71 65.5 79.25 27.34 19 0.049 9 1.9 21.3 26.7 17.2 9.5 0.09 2.70 0.73 79.4 99.8 25.00 22 0.045 10 1.95 23.0 27.0 17.3 9.7 -0.04 2.70 0.71 88.2 92.46 36.61 19 0.037 11 1.9 21.9 26.8 17.2 9.6 0.2 2.70 0.73 80.5 74 27.03 17 0.025 12 1.92 22.3 26.6 17.1 9.4 -0.15 2.70 0.72 83.6 80.47 26.83 16 0.034 
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表 2 深标点和浅标点位置最终沉降量汇总表
Table 2. The summary of the monitoring points and the related total settlements
序号 浅标点编号 灌水结束沉降量/mm 观测结束沉降量/mm 灌水结束沉降量占总沉降比值/% 深标点编号 埋设深度/m 灌水结束沉降量/mm 观测结束沉降量/mm 灌水结束沉降量占总沉降比值/% 1 Q1 96 105 91.4 S1 6 73 72 101.4 2 Q2 207 215 96.3 S2 7 70 77 90.9 3 Q3 226 236 95.8 S3 8 84 84 100.0 4 Q4 261 268 97.4 S4 9 76 75 101.3 5 Q5 260 268 97.0 S5 5 86 84 102.4 6 Q6 280 288 97.2 S6 4 97 100 97.0 7 Q7 370 381 97.1 S7 12 86 81 106.2 8 Q8 66 70 94.3 S8 11 78 82 95.1 9 Q9 51 61 83.6 S9 10 98 85 115.3 10 Q10 47 58 81.0 S10 3 80 83 96.4 11 Q11 79 92 85.9 S11 2 92 88 104.5 12 Q12 55 69 79.7 注：浅标点埋设深度统一为自然地面以下2.6 m，试坑表面以下0.3 m。
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表 3 各测点最大沉降速率及其对应时间
Table 3. The maximum settlement velocities and their corresponding time
深标点编号 埋深/m 最大沉降速率/mm 最大沉降发生时间/d 占总沉降比值/% 浅标点编号 最大沉降速率/mm 最大沉降速率发生时间/d 占总沉降比值/% 湿陷变形占总变形比例/% S1 6 15 23 80.6 Q1 32 26 84.8 30.5 S2 7 13 11 74.0 Q2 65 26 80.5 30.2 S3 8 11 11 42.9 Q3 81 26 88.6 34.3 S4 9 12 12 48.0 Q4 87 26 96.3 32.5 S5 5 12 10 65.5 Q5 75 26 95.5 28.0 S6 4 10 15 78.0 Q6 110 26 94.4 38.2 S7 12 15 14 56.8 Q7 109 25 66.9 28.6 S8 11 14 13 56.1 Q8 17 27 100 24.3 S9 10 10 13 62.4 Q9 16 26 60.7 26.2 S10 3 12 6 44.6 Q10 16 26 72.4 27.6 S11 2 11 20 88.6 Q11 32 28 78.3 34.8 Q12 16 23 52.2 30.5
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