CLC number: TU473.1

On-line Access: 2013-03-04

Received: 2012-08-20

Revision Accepted: 2013-01-02

Crosschecked: 2013-02-22

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Qian-qing Zhang, Shu-cai Li, Zhong-miao Zhang. Influence of reaction piles on test pile response in a static load test[J]. Journal of Zhejiang University Science A, 2013, 14(3): 198-205.

@article{title="Influence of reaction piles on test pile response in a static load test",

author="Qian-qing Zhang, Shu-cai Li, Zhong-miao Zhang",

journal="Journal of Zhejiang University Science A",

volume="14",

number="3",

pages="198-205",

year="2013",

publisher="Zhejiang University Press & Springer",

doi="10.1631/jzus.A1200210"

}

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%T Influence of reaction piles on test pile response in a static load test

%A Qian-qing Zhang

%A Shu-cai Li

%A Zhong-miao Zhang

%J Journal of Zhejiang University SCIENCE A

%V 14

%N 3

%P 198-205

%@ 1673-565X

%D 2013

%I Zhejiang University Press & Springer

%DOI 10.1631/jzus.A1200210

TY - JOUR

T1 - Influence of reaction piles on test pile response in a static load test

A1 - Qian-qing Zhang

A1 - Shu-cai Li

A1 - Zhong-miao Zhang

J0 - Journal of Zhejiang University Science A

VL - 14

IS - 3

SP - 198

EP - 205

%@ 1673-565X

Y1 - 2013

PB - Zhejiang University Press & Springer

ER -

DOI - 10.1631/jzus.A1200210

**Abstract: **This work presents a new analytical method to analyze the influence of reaction piles on the test pile response in a static load test. In our method, the interactive effect between soil and pile is simulated using independent springs and the shear displacement method is adopted to analyze the influence of reaction piles on test pile response. Moreover, the influence of the sheltering effect between reaction piles and test pile on the test pile response is taken into account. Two cases are analyzed to verify the rationality and efficiency of the present method. This method can be easily extended to a nonlinear response of an influenced test pile embedded in a multilayered soil, and the validity is also demonstrated using centrifuge model tests and a computer program presented in the literature. The present analyses indicate that the proposed method will lead to an underestimation of the test pile settlement in a static load test if the influence of the presence of reaction piles on the test pile response is neglected.

**
**

1. Introduction

In a static load test, the load acted on the test pile is transferred to the soil around the piles with the help of the reaction piles. Since the load applied on the reaction piles leads to an opposite deformation of the test pile, as shown in Fig.

In this work, the correction factor

Based on the results of static load tests conducted using two reaction piles, Poulos and Davis (

This paper presents a new analytical method to analyze the influence of reaction piles on the test pile response in a static load test. In the present method, the interactive effect between soil and pile is simulated by independent springs, and the shear displacement method is also adopted. Furthermore, the influence of the sheltering effect between reaction piles and test pile on the test pile response is taken into account. Two cases presented by Kitiyodom et al. (

This approach can be easily extended to a nonlinear response of a single pile as described in Sections 5 and 6, and the validity of the proposed approach is demonstrated in Section 7. Note that in China, the working piles are often used as the reaction piles, and pile load tests are usually carried out using four reaction piles. Therefore, in this work the test pile diameter is assumed to be identical to the reaction pile diameter. Herein, the influence of the load applied on four reaction piles on the load-displacement response of the test pile is discussed in this paper.

2. Initial pile head stiffness of single pile embedded in a multilayered soil

The general solution of shaft settlement,

The axial force at a depth

A matrix form of Eqs. (

Assume the pile is divided into

The values of

By substituting Eq. (

Using the transfer matrix method, one can obtain the relationship between load and settlement developed at the pile top and end:

The soil stiffness at the pile base,

The pile head settlement,

3. Initial pile head stiffness of an influenced test pile embedded in a multilayered soil

The reaction pile displacement at a given depth below the ground surface,

The displacements of the test pile and reaction pile at a given depth,

A matrix form of Eq. (

Eq. (

Assuming

Assuming the displacement at the pile head

The flexibility of the test pile (reaction pile) due to its loading,

In a pile group with one test pile and four reaction piles,

The reduction in flexibility of test pile (reaction piles) due to loading on reaction pile (test pile), Δ

Eq. (

The reduction in flexibility of the test pile (reaction pile) induced by the effects of pile reinforcement in different soil types due to the adjacent load-free reaction pile (test pile),

The stiffness of the soil around test pile,

Note that for the test pile embedded in a multilayered soil with the influence of four reaction piles, the load applied on the test pile is

4. Comparison of computed results derived from the present approach with that estimated from a computer program, PRAB

Fig.

It can be concluded that even for the case where a pile spacing ratio is adopted as four (in line with recommendations of (JGJ 106-2003)), the correction factor may be 1.28 to 1.33 where 100<

5. Nonlinear response of a single pile embedded in a multilayered soil

Substituting Eq. (

The spring stiffness of the soil around the pile shaft can be calculated as follows:

Substituting Eqs. (

6. Nonlinear response of an influenced test pile embedded in a multilayered soil

The reduction in flexibility of the test pile (reaction piles) due to loading on the reaction pile (test pile), Δ

The reduction in flexibility of the test pile (reaction pile) induced by the effects of pile reinforcement in soil due to the adjacent load-free reaction pile (test pile), Δ

Considering the nonlinear behavior of the soil around the pile shaft, the stiffness of the soil around test pile,

Substituting Eqs. (

7. Comparison of the nonlinear response of the test pile with influence of reaction piles estimated from the proposed approach and centrifuge model test

In this work, the Poisson’s ratio of the soil was adopted as 0.30. Based on the results obtained from the loading test on the single pile, the average shear modulus of the soil was taken as

Comparisons between the measured individual pile displacement and the influenced test pile obtained from the centrifuge model test, as well as that calculated using the present approach along with PRAB (Kitiyodom et al.,

8. Conclusions

The present analyses indicate that the measured pile head stiffness of the test pile is greater than the actual pile head stiffness of the individual pile due to the presence of reaction piles. This leads to an underestimation of the test pile settlement in a static load test if the influence of the reaction piles on the test pile response is neglected.

* Project supported by the China Postdoctoral Science Foundation (No. 2012M521339), and the Independent Innovation Foundation of Shandong University (No. 2012GN012), China

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