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Use and influence of bentonite in bored pile construction

Series/doc. No Report Report PG 3
Year 1977
Abstract The Report explains what bentonite is, how it works, and indicates how construction techniques could, in practice, have significant influence over the final behaviour of a load bearing unit. The introduction of the Report also deals with a variety of subjects; the extraction of bentonite from natural earth deposits, its structure, the stabilising action of the slurry, the effects of suspension contamination, filter cake formation, the displacement of suspension from a borehole by concrete, the technique of placing concrete by tremie, the selection of appropriate concrete mixes for this type of work, and the effects of bentonite on the bond between steel and concrete.
ISBN 9780860170310
Subject(s) Earthworks/foundations/piling/retaining walls
Bearing piles
Civil engineering, infrastructure and public utilities
Bored piles
Supplement Civil & Structural. To subscribe to The Construction Information Service please telephone Customer Care on +44 1344 328300
Publisher CIRIA
Publisher History CIRIA was formerly known as the Construction Industry Research and Information Association. They are a member-based research and information organisation who publish reports and technical papers covering building and civil engineering as well as transport and utilities infrastructure.
Table Of Contents
List of illustrations 7
List of tables 8
Summary 9
1 Introduction 10
2 Bentonite: its use and behaviour in the construction of bored piles 13
2.1 Bentonite material 13
2.2 Bentonite suspension 13
2.3 Specification for bentonite material 15
2.4 Extraction and processing of bentonite 15
3 The stabilizing action of bentonite suspension in a borehole 16
3.1 Caving of an open unsupported borehole 16
3.2 The stabilizing action of bentonite 16
3.3 Filter cake formation 17
3.4 Effect of suspension composition on filter cake formation 19
3.5 The capacity of bentonite suspension to keep detritus in suspension 20
4 Displacement of bentonite suspension by concrete 21
4.1 Pile formation 21
4.2 Displacement of bentonite suspension from the face of the borehole 21
4.3 Displacement of bentonite suspension and detritus from the base of the pile bore 24
4.4 Displacement of bentonite suspension from reinforcing bars 25
4.5 Specification for bentonite suspension 27
4.6 Concrete mix design 29
4.7 Concreting (tremie operation) 31
5 Laboratory tests on the influence of bentonite on skin friction 33
5.1 The contribution of various researchers 33
5.2 Summary 35
6 Effect of bentonite on ultimate shaft friction 37
6.1 Factors affecting the shaft friction of piles 37
6.2 Analysis of the results of pile tests 39
6.3 Results of pile load tests 41
7 Effect of bentonite on base resistance 60
7.1 The displacement of bentonite suspension for a pile base 60
7.2 Case histories 60
7.3 Summary 65
8 Analysis of other pile load tests 67
8.1 Results of tests subjected to further analysis 67
8.2 Results of tests not subjected to further analysis 68
8.3 Summary 68
9 Contract work carried out in the construction of piles and diaphragm wall elements using bentonite suspension 69
9.1 Record of work carried out 69
9.2 Views expressed on the process of forming piles under bentonite 70
10 Conclusions and recommendations 71
Acknowledgements 72
References 73
Appendix 1 78


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