Development of deformation of enclosure wall during dewatering in a leaky aquifer
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摘要: 依托某基坑开挖前抽水试验,利用ABAQUS建立有限元模型,探讨了复杂越流含水层中基坑抽水引发围挡变形的发展规律。研究发现：当基坑内外存在水力联系时,受弱透水层影响,基坑抽水过程中各土层围挡两侧孔压差值(ΔP)先增大后减小最后趋于稳定,从而导致基坑围挡发生同样规律的变形（即,增大后再减小最后趋于稳定）。而当基坑内外无水力联系时,基坑抽水导致的各土层围挡两侧孔压差值(ΔP)将单调增大并很快趋于稳定,此时,基坑围挡变形不再出现前述先增大后减小的规律,而同样表现出单调增大的规律。Abstract: The finite element model is established to investigate the development of deformation of enclosure wall during dewatering in a leaky aquifer by using ABAQUS on the basis of a practical pre-excavation dewatering test. The results show that when there is hydraulic connection between the inside and outside of a foundation pit, under the influences of an aquitard, the difference of pore pressure at both sides of enclosure wall (ΔP) increases first, then decreases, and finally tends to be stable during the pumping. As a result, the deformation of enclosure wall first increases, then decreases and finally becomes stable. However, when there is no hydraulic connection between the inside and outside of the foundation pit, ΔP increases monotonously and tends to be stable soon. The deformation of enclosure wall no longer first increases and then decreases, but increases monotonously.
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Keywords:
- leaky aquifer /
- foundation pit dewatering /
- wall deformation /
- numerical simulation
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图 3 基坑内外水位变化实测值与计算值对比
Figure 3. Comparison between computed and measured water level drawdowns
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图 4 抽水结束后基坑北侧地连墙侧移实测与计算值对比
Figure 4. Comparison between computed and measured wall deformations at north side of foundation pit after pumping
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图 5 孔压特征点示意图
Figure 5. Layout of monitoring points for pore water pressure during numerical simulation
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图 6 坑内外水力连通下围挡两侧孔压差值随抽水时间变化
Figure 6. Time-history curves of ΔP of foundation pit hydraulically connected with outside
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图 7 坑内外水力连通下围挡不同深度侧移随抽水时间变化
Figure 7. Time-history curves of wall deformations at different depths of foundation pit hydraulically connected with outside
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图 8 坑内外无水力连通下围挡两侧孔压差值随抽水时间变化
Figure 8. Time-history curves of ΔP without hydraulic connection between inside and outside of foundation pit
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图 9 坑内外无水力连通下围挡不同深度侧移随抽水时间变化
Figure 9. Time-history curves of wall deformations at different depths without hydraulic connection between inside and outside of foundation pit
表 1 土层分布及其物理力学参数
Table 1 Soil distribution and its physical and mechanical parameters
土层 土性 H/m γ/(kN·m-3) K0 w/% e Es/MPa c'/kPa φ'/(°) Kh/(m·d-1) Kv/(m·d-1) E/MPa Vs/(m·s-1) Aq0 粉黏 10 19.1 0.58 30.4 0.85 7.4 17 25 0.03 0.003 43.5 152 AdІ 粉黏 15 19.3 0.61 28.7 0.81 6.8 18 23 0.025 0.001 56.3 172 AqІ 粉土 19 20.2 0.44 21.7 0.62 17.4 10 34 0.2 0.1 137.6 266 AdІІ 粉黏 22 19.9 0.56 25.1 0.71 8 19 26 0.006 0.001 118.6 246 AqІІ 粉土 24.5 20.4 0.44 22.3 0.55 14.6 8 34 2.5 0.5 151.8 278 粉土 29.5 20.6 0.41 20.9 0.58 15.9 8 36 1 0.2 153.3 278 粉黏 32.5 20.3 0.56 23.6 0.66 8.6 17 26 1 0.16 128 253 粉砂 35.5 20.6 0.40 16.3 0.52 18.9 7 37 3 0.6 178.5 300 AdⅢ 粉黏 37 20.5 0.56 20.7 0.6 9.5 19 26 0.02 0.004 152.1 274.5 AqⅢ 粉土 41 20.7 0.44 18.2 0.54 19.9 10 34 3 0.9 214.5 328 AdⅣ 粉黏 47 20.3 0.55 22.1 0.64 10.3 18 27 0.0005 0.0001 198.4 315 AqⅣ 粉砂 50 20.6 0.38 17.5 0.53 25.3 7 38 3.5 1.5 257 360 注：H为层底埋深；γ为土的天然重度；K0为静止土压力系数；w为含水率；e为初始孔隙比；Es为压缩模量；c'为黏聚力；φ'为内摩擦角；Kh为水平渗透系数；Kv为竖向渗透系数；E为弹性模量；Vs为剪切波速。 
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