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| ANALYSIS OF RESIDUAL STRESS ON PILE-BASE POST GROUTING PILE |
| ZOU Jian1，2，ZHANG Zhongmiao1，2，LIN Cungang1，2 |
| (1. Institute of Geotechnical Engineering，Zhejiang University，Hangzhou，Zhejiang 310027，China；2. Key Laboratory of Soft Soils and Geoenvironmental Engineering，Ministry of Education，Zhejiang University，Hangzhou，Zhejiang 310027，China) |
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Abstract Theoretical analysis and field tests on pile-base post grouting pile were carried out to study the generation and dissipation of residual stress and their effects on bearing behaviour of pile. Generation and dissipation of residual stress were observed for a long time by means of embedding earth pressure cells at pile tip and reinforcement stress gauges at pile shaft. The observation results show that during pile-base post grouting，high pressure grout produces a bidirectional force inside the confined spaces of pile tip，where the pile tip and pile tip soil are preloaded. Because of the bidirectional force，pile tip soil is preloaded and there will be negative friction along the bottom of pile shaft. However，within 24 hours after grouting，the permeation and pressure filtration of injected grouts will lead to the decrease of this bidirectional force and the dissipation of residual stress. 24 hours later，the residual stress remains at a constant value. So before loading test，there are still negative friction along the bottom of pile shaft and the pile tip soil is preloaded. By preloading the pile tip soil and not changing the value of side friction resistance，the existence of residual stress can improve tip resistance；and thereby enhances the ultimate bearing capacity of post grouting pile as well. If the residual stress was neglected and the reading of reinforcement stress gauges was taken as zero reading assumption，the side friction resistance of pile will be overestimated and its tip resistance will be underestimated.
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Received: 02 April 2010
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2011, Vol. 30 
