Analysis of Single Well and Group Wells Pumping Tests for Deep Excavation in Water-rich Sand
-
摘要: 富水砂性地层有着黏聚力低、稳定性差、渗透性强的特点,在该地层中进行基坑施工会面临众多风险。为了探究该地层的水文地质特性,确保基坑施工安全,基于现场抽水试验及三维有限差分反演分析,得出如下结论:(1)本工程第③、⑤1、⑤2、⑤3层水位联系不密切,第④2、⑤t、⑤2层透水性较差,为弱透水层;进行单井试验的⑤1层的影响半径为135 m,第③层的影响半径为52 m;(2)通过群井抽水试验和三维数值模拟反演,测定了主要含水层的包括渗透系数、导水系数以及贮水率在内的水文地质参数;(3)通过分析抽水试验地表沉降监测数据,⑤1层群井抽水引起沉降在抽水结束后可以回弹25%左右,而⑤2层、⑤3层群井抽水沉降回弹约40%左右。各个水位恢复阶段,沉降回弹有明显滞后现象。Abstract: Water-rich sandy strata has the characteristics of low cohesion, poor stability, and strong permeability. Excavation construction in this strata can be risky. Hydraulic characteristics of this strata were studied to ensure the safety of construction. Based on the field pumping test and three-dimensional inversion analysis, the following conclusions are drawn: (1) The hydraulic connection between aquifers ③, ⑤1, ⑤2, and ⑤3 are not strong, and layers ④2, ⑤t and ⑤2 are poorly permeable. The influence radius of aquifers ⑤1 and ③ are 135 m and 52 m, respectively. (2) The hydraulic parameters of the main aquifers, including permeability coefficient, hydraulic conductivity and specific storage, were determined by numerical inversion. (3) The settlement caused by the group-well pumping in aquifer ⑤1 can rebound by about 25%; while the pumping-induced settlement of group-well pumping in aquifers ⑤2 and ⑤3 rebounds by more than 40%. At each stage of water level recovery, there is an obvious time lag of settlement rebound.
-
Key words:
- pumping test /
- hydrogeological parameters /
- radius of influence /
- ground subsidence
-
表 1 试验井结构统计表
层位 井号 井深
/m井径
/mm管径
/mm过滤器
长度/m过滤器
放置深度/m备注 第③层 G3-1 21 650 273 9 11~20 G3-2 21 650 273 9 11~20 G3-3 21 650 273 9 11~20 第④2t层 K1 34 650 273 7 26~33 第④2t、⑤1
混合层K2 38 650 273 11 26~37 K3 42 700 273 15 26~41 兼回灌
试验井第⑤1层 K4 47 650 273 10 36~46 兼回灌
试验井G51-1 42 700 273 5 36~41 G51-2 42 650 273 5 36~41 G51-3 42 650 273 5 36~41 第⑤2、⑤3层 G523-1 57 650 273 7 49~56 兼回灌
试验井G523-2 57 650 273 7 49~56 G523-3 57 650 273 7 49~56 表 2 各含水层静止水位统计信息
地层 井号 井口绝对
标高/m静水位
埋深/m静水位绝对
标高/m第③层 G3-1 +5.89 2.78 +3.11 G3-2 +5.98 2.83 +3.15 G3-3 +6.10 2.92 +3.18 第④2t层 K1 +6.18 4.44 +1.74 第⑤1层 K4 +6.21 4.51 +1.70 G51-1 +5.72 4.09 +1.63 G51-2 +5.85 4.27 +1.58 G51-3 +6.25 4.63 +1.62 第⑤2、⑤3层 G523-1 +5.71 4.30 +1.41 G523-2 +5.89 4.78 +1.11 G523-3 +5.94 4.49 +1.45 表 3 水文地质参数表
层号 土层名称 渗透系数平均值/(m·d–1) 导水系数/(m3·d−1) 贮水率/(10–4·m−1) 水平 垂直 第③1层 粉砂夹粉土 1.1 0.5 5.83 3.2 第③2层 粉砂 2.2 1.1 17.16 8.5 第④2层 粉质黏土夹粉土 0.02 0.004 0.16 0.2 第④2t层 砂质粉土夹粉质黏土 1.2 0.12 4.56 0.1 第⑤1层 粉砂夹粉土 3.0 0.41 38.40 1.8 第⑤t层 粉质黏土夹粉土 0.02 0.002 0.04 0.8 第⑤2层 砂质黏土夹粉质黏土 0.15 0.03 0.60 2.4 第⑤3层 粉砂夹粉土 3.2 0.5 22.40 14.0 -
[1] 施成华,彭立敏. 基坑开挖及降水引起的地表沉降预测[J]. 土木工程学报,2006,39(5):25-32. [2] 吴昌瑜,李思慎,谢 红. 深基坑开挖中的降水设计问题[J]. 岩土工程学报,1999,21(3):92-94. [3] 杨天亮,叶观宝,吕远强. 地面沉降流固耦合模型在深大基坑降水工程中的应用[J]. 工程勘察,2008,(3):27-29, 35. [4] 刘承磊,肖传宁,侯志敏,等. 基于群井抽水试验的基坑降水与地面沉降关系研究[J]. 地下水,2019,44(4):94-96. doi: 10.3969/j.issn.1004-1184.2019.04.038 [5] SHEN S L,XU Y S. Numerical evaluation of land subsidence induced by groundwater pumping in Shanghai[J]. Canadian Geotechnical Journal,2011,48(9):1378-1392. doi: 10.1139/t11-049 [6] 杨 勇,李国敏,窦艳兵,等. 抽取地下水引起地面沉降的研究现状与进展[J]. 工程勘察,2010,38(11):32-37, 91-93. [7] WANG Y Q,WANG Z F,CHENG W C. A review on land subsidence caused by groundwater withdrawal in Xi'an, China[J]. Bulletin of Engineering Geology and the Environment,2018,78(4):2851-2863. [8] 袁 斌,武永霞,廖少明,等. 基于数值模拟的富水砂砾地层深基坑降水方案优化[J]. 工程勘察,2017,45(1):34-39. [9] 刘 林. 黄土场地深基坑降水试验与数值模拟研究[D]. 西安: 西安建筑科技大学, 2012. [10] 方 樟,肖长来,马 喆,等. 大型基坑降水工程弱透水层水文地质参数的计算[J]. 工程勘察,2010,38(4):39-43. [11] 杨建民,郑 刚,焦 莹. 天津站抽水试验数值反演分析[J]. 土木工程学报,2010,43(9):125-130. [12] 钟建文,李 罡,牛 磊,等. 基于抽水试验的参数反演和基坑降水过程数值分析[J]. 工程勘察,2019,47(7):36-41, 72.