A simple and precise borehole extensometer

Burland, J. B.; Moore, J. F. A.; Smith, P.D.

doi:10.1680/geot.1972.22.1.174

Cited by 27 publications

(5 citation statements)

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“…The monuments and the top of all tubings have been levelled to first-order accuracy with reference to a deep-seated bench mark. The in-depth settlements magnetic equipment (Burland et al 1972 level in the trench fell to levels lower than in the excavation phase. Also, the excavated material was placed too close to the margin opposite to the instrumentation, causing failure of the bank on July 19.…”

Section: Instrumentation and Execution Of The Trial Trenchmentioning

confidence: 80%

Site investigations for unretained excavations in a soft peaty deposit

Sandroni¹,

Silva²,

Pinheiro³

1984

Can. Geotech. J.

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As part of an urbanization scheme, artificial islands are being created on the swampy land around the Itaipu lagoon, close to Rio de Janeiro. The islands are being formed by hydraulic filling with sand and their periphery consists of retaining walls resting on sand cushions. The very soft local soils pose settlement and stability problems in execution and operation.A site and laboratory investigation program, involving several types of triaxial, consolidation, and in-situ vane tests, has been carried out and is described. A full-scale instrumented settlement fill has been built and is mentioned. An instrumented 5 m deep trial trench has been carried out and monitored during the excavation stage which took 5 days and during a 45 day long repose stage. In both these stages failure was avoided by keeping water inside the trench at its original level. Finally, failure was induced by pumping water out of the trench. The observations at the trial trench are presented and discussed in some detail.

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Section: Instrumentation and Execution Of The Trial Trenchmentioning

confidence: 80%

Site investigations for unretained excavations in a soft peaty deposit

Sandroni¹,

Silva²,

Pinheiro³

1984

Can. Geotech. J.

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“…A comprehensive set of displacement and strain measurements to be made in the neighbour hood should increase our understanding of ground behaviour in the London area, and will enable a check to be kept on the design and safety of the project. A new magnetic borehole extensometer (Burland, Moore & Smith 1972) will be used to measure the vertical displacements beneath the car park as it is excavated, and the horizontal displacements of the walls will be measured by a remote-reading borehole inclinometer.…”

Section: Eformations Of the Ground Around Britannic H Ouse L Ondonmentioning

confidence: 99%

A Discussion on the measurement and interpretation of changes of strain in the Earth - The use of ground strain measurements in civil engineering

Ward

Burland

1973

Phil. Trans. R. Soc. Lond. A

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Strains of the ground are of increasing importance in civil engineering for as projects get larger the strains they induce often exceed the natural strains. For the engineer to ensure the safety and stability of a structure and its surroundings he must be able to predict and, if need be, control the strains. Our approach is to measure the deformations in specific cases and to use the information to gain a better understanding of ground behaviour, to determine parameters of the ground to use in prediction and to check the safety and design of the project. It demands simple and sensitive instruments that can be used reliably under rigorous field conditions. Examples of recent studies are given.

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“…However, grout reported in the literature is perceived as a filler material with a non-universal consistency. Burland et al (1972) described the grout surrounding the access tube of a magnetic extensometer as a soft flexible material capable of preventing borehole collapse. For soft ground, grouting boreholes after installation of extensometers with thick bentonite slurry is suggested (Burland et al 1972).…”

Section: Introductionmentioning

confidence: 99%

“…Burland et al (1972) described the grout surrounding the access tube of a magnetic extensometer as a soft flexible material capable of preventing borehole collapse. For soft ground, grouting boreholes after installation of extensometers with thick bentonite slurry is suggested (Burland et al 1972). Marsland and Quarterman (1974) reported that borehole extensometers are typically backfilled with soil or grout of a similar strength to that of the surrounding soil.…”

Section: Introductionmentioning

confidence: 99%

On the Evaluation of Settlement Measurements Using Borehole Extensometers

Bayoumi

2010

Geotech Geol Eng

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Borehole extensometers are commonly utilized in field monitoring programs to measure settlement. In order to secure the targets of the extensometer, the borehole is typically backfilled with cement-bentonite grout. In the absence of standards for grout mix designs and due to non-universality of the properties of the backfilling grout, the accuracy of settlement furnished by borehole extensometers may be questionable. A preliminary parametric study was conducted to investigate the influence of grout stiffness on settlement measurements using borehole extensometers. The finite element program ABAQUS was used to model a borehole extensometer installed in an isotropic homogeneous elastic soil layer of a finite depth subjected to a uniform surface surcharge. Effect of the grout-soil elastic moduli ratio, soil/grout interface parameters (friction angle and shear strength), and extensometer embedment depth were investigated. Soil/grout interface behavior was assumed to comply with the elastic-perfectly plastic Coulomb friction model. The mechanism of measuring settlement using borehole extensometers was studied. The numerical study revealed that minimum errors in settlement can be obtained if the grout-soil elastic moduli ratio is made equal to about 1.0. Depending on the grout-soil moduli ratio, larger grout/soil interface friction angle and interface shear strength are generally associated with smaller settlement errors. Compared to fully embedded extensometers, partial embedment yields smaller settlement errors for grout-soil moduli ratio significantly above unity.

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A simple and precise borehole extensometer

Cited by 27 publications

References 0 publications

Site investigations for unretained excavations in a soft peaty deposit

Site investigations for unretained excavations in a soft peaty deposit

A Discussion on the measurement and interpretation of changes of strain in the Earth - The use of ground strain measurements in civil engineering

On the Evaluation of Settlement Measurements Using Borehole Extensometers

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