Chamber tests for investigating additional internal forces in existing foundation piles induced by excavation

doi:10.3785/j.issn.1008-973X.2019.08.004

Journal of ZheJiang University (Engineering Science)

2019, Vol. 53

Issue (8): 1457-1466 DOI: 10.3785/j.issn.1008-973X.2019.08.004

Civil and Structural Engineering

Chamber tests for investigating additional internal forces in existing foundation piles induced by excavation

De-qi TANG1,2(

),Feng YU1,2,*(

),Xiang-guo HUANG3,Hai-bing CHEN1,2,Tang-dai XIA4

1. Institute of Foundation and Structure Technologies, Zhejiang Sci-Tech University, Hangzhou 310018, China
2. Zhejiang Provincial Engineering and Technology Research Center of Assembly-Concrete Industrialized Buildings, Hangzhou 310018, China
3. Wuhan Municipal Construction Group Co. Ltd, Wuhan 430023, China
4. Research Center of Coastal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China

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Abstract

The lateral displacement of passive soil induced by the excavation of existing buildings has significant impact on the bearing capacity of foundation piles within the pit. The load-bearing characteristics of foundation piles under the lateral movement of the passive soil were investigated through indoor model experiments. Focus was paid on the influences on the pile’s bending moment and shear force of a few factors such as the spacing between retaining and foundation piles, the excavation depth, the axial loading level at the top of the pile and the height of cap restraint. Results showed that under the cantilevered supported excavation condition, the displacement pattern of the passive soil resembled an inverted triangle. The bending moment and the shear force of the foundation pile had several heterogeneous peaks distributed along the pile. Based on this, the foundation pile from top to bottom was divided into three sections, i.e. the excavation-exposed section, the passive-load section and the active-effect section. The smaller the distance between the supporting and foundation piles and the deeper the excavation depth, the greater the bending moment and the shear force induced along the foundation pile. The coupling effect of axial loading and lateral displacement will further increase the bending moment of the foundation pile. The change of the height of the pile top restraint will affect the bending moment and the shear force of the pile. With other conditions being the same, the greater the height of the pile top restraint, the smaller the bending moment and the shear force of the pile. The research results can provide support for the engineering design of underground-storey supplement.

Key words： underground storey supplement model test foundation pile bending moment shear force

Received: 08 June 2018 Published: 13 August 2019

CLC:

TU 473

Corresponding Authors: Feng YU E-mail: 1749569869@qq.com;pokfulam@zstu.edu.cn

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Cite this article:

De-qi TANG,Feng YU,Xiang-guo HUANG,Hai-bing CHEN,Tang-dai XIA. Chamber tests for investigating additional internal forces in existing foundation piles induced by excavation. Journal of ZheJiang University (Engineering Science), 2019, 53(8): 1457-1466.

URL:

http://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2019.08.004 OR http://www.zjujournals.com/eng/Y2019/V53/I8/1457

开挖诱发坑内既有基桩附加内力的模型试验

既有建筑下挖改造引起的基坑被动区土体侧移会对坑内基桩承载性产生重要影响. 通过室内模型试验研究坑内基桩在被动区土体侧移作用下的桩身受力特性，重点分析支护结构与坑内基桩距离、开挖深度、桩顶竖向荷载及承台约束高度对基桩弯矩和剪力的影响. 试验结果表明，在悬臂式支护开挖条件下，被动区土体位移模式呈倒三角形，基桩弯矩和剪力沿桩身分布具有多个异号峰值，桩身自上而下可分为开挖裸露段、被动受荷段和主动作用段. 基桩与支护水平间距越小、基坑下挖深度越大，基桩各部位弯矩和剪力越大，且竖向受荷和桩身侧向变形的耦合效应将使桩身弯矩变大. 桩顶约束高度的改变会对基桩弯矩和剪力产生影响，在其他条件相同时，约束高度越大，基桩弯矩和剪力越小. 研究结果可为地下增层工程的设计提供支撑.

关键词： 地下增层, 模型试验, 基桩, 弯矩, 剪力

Fig.1 Schematic diagram of additional effects on foundation pile induced by underground storey supplement

Fig.2 Schematic diagram of test chamber

Fig.3 Schematic diagram of model pile instrumented with strain gauges

Fig.4 Sketch of underground storey supplement model test

Fig.5 Load-settlement curve for single pile obtained from static load test

Tab.1 Grouping scheme of underground storey supplement model test

Fig.6 Variation of turning angle and displacement at pile top with excavation depth

Fig.7 Distribution of bending moment along supporting pile under different excavation depths

Fig.8 Variation in deflection of supporting pile under different excavation depths

Fig.9 Distribution of bending moment along foundation pile G1 under different excavation depths

Fig.10 Distribution of shear force along foundation pile G1 under different excavation depths

Fig.11 Distribution of bending moment along foundation piles under different distances with excavation depth of 40 cm

Fig.12 Distribution of shear force along foundation piles under different distances with excavation depth of 40 cm

Fig.13 Variation in peak bending moment of piles under different distances

Fig.14 Variation in peak shear force of piles under different distances

Fig.15 Model of foundation piles under existing building subjected to underground storey supplement

Fig.16 Comparison of bending moment of foundation piles with different cap elevations

Fig.17 Comparison of shear force of foundation piles with different cap elevations

Fig.18 Axial force distribution of test piles G2 and G3 along foundation piles under different excavation depths

Fig.19 Effect of axial load on bending moment of foundation pile

Fig.20 Variation in maximum bending moments of test piles


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