Characteristics of groundwater seepage with cut-off wall in gravel aquifer. I: Field observations

Y.-X. Wu, S.-L. Shen, Y.-S. Xu, Zhenyu Yin

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90 Citations (Scopus)

Abstract

© 2015, Canadian Science Publishing. All rights reserved.This paper presents a case history of the leakage behavior during dewatering tests in the gravel strata of an excavation pit of a metro station in Hangzhou, China. The groundwater system at the test site is composed of a phreatic aquifer underlain by an aquitard and a confined aquifer with coarse sand and gravel. The sandy gravel stratum has very high hydraulic conductivity. The maximum depth of the excavation is 24mbelow the ground surface, which reaches the middle of the aquitard strata, where the thickness of the clayey soil is insufficient to maintain the safety of the base of the excavation. To understand the hydrological characteristics of gravel strata, single-and double-well pumping tests were conducted, where a cut-off wall was installed 43 m deep with its base penetrating 2 to 3 m into the aquifer. Test results show that this partial cut-off of the aquifer cannot effectively protect the base of the excavation from the upward seepage force of the groundwater during excavation. Therefore, a new cut-off wall (second phase) was constructed to a depth of 54mto cut off the confined aquifer. A second pumping test was conducted after the construction of the second phase cut-off wall, and test results show that this full cut-off combined with dewatering can control groundwater effectively during excavation. This finding indicates that when a deep excavation is conducted in a confined aquifer with high hydraulic conductivity, determination of the depth of the retaining wall should be based on three factors: the stability of the base, the upward seepage stability, and settlement control.
Original languageEnglish
Pages (from-to)1526-1538
Number of pages13
JournalCanadian Geotechnical Journal
Volume52
Issue number10
DOIs
Publication statusPublished - 1 Jan 2015
Externally publishedYes

Keywords

  • Cut-off walls
  • Deep excavation
  • Dewatering
  • Gravel strata
  • Pumping test
  • Settlement

ASJC Scopus subject areas

  • Civil and Structural Engineering

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