Detecting defects in diaphragm walls prior to excavation

Title

Detecting defects in diaphragm walls prior to excavation

 Author

Spruit, R.
Hopman, V.
Van Tol, A.F.
Broere, W.

Faculty

Civil Engineering and Geosciences

 Department

Geoscience & Engineering

 Date

2011-12-31

 Abstract

Recent incidents with leaking diaphragm walls during construction of subway lines in Amsterdam and Rotterdam (Netherlands) have led to reconsideration of the diaphragm wall as a retaining wall construction for deep excavations. In our opinion the joints between the panels are the weak spot. During concrete pouring the concrete should replace the bentonite slurry. If it fails to do so, bentonite inclusions occur (mainly) in the joints. These inclusions are almost impossible to detect with a pumping test or EFT/ERT measurements because the hydraulic resistivity of the inclusion is very high. After excavation however, the bentonite inclusion may become unstable, causing leakage and settlements in de surroundings. Therefor two research projects were initiated at TU Delft, one focusing on optimizing the production process of diaphragm walls and one (as described in this paper) on developing measurement techniques for early (before excavation) detection of defects in the joints. In two projects with deep excavations in the Netherlands, field tests with five different measurement techniques have been carried out. In a scaled test with a known anomaly the basic response of the measurements has been tested. The tested techniques are: Distributed Temperature Profile, Natural Gamma Radiation, Crosshole Sonic Logging (CSL), Single-hole Sonic Logging (SSL) and Direct Conductivity. In this paper the results so far will be presented and discussed. Preliminary conclusions will be drawn. A detailed setup in a diaphragm wall of the most promising method, Cross-hole Sonic Logging, will be shown together with recommendations for the interpretation of the field measurements. An outlook on the upcoming research steps and expected results will be given.

 To reference this document use:

http://resolver.tudelft.nl/uuid:c6b53ce3-8751-482c-b41e-a7481e8c9c19

 Source

FMGM 2011: 8th International Symposium on Field Measurements in GeoMechanics, Berlin (Germany), 12-14 Sept., 2011 FMGMSymposia

 Part of collection

Institutional Repository

 Document type

conference paper

 Rights

(c)2011 Spruit, R., Hopman, V., Van Tol, A.F., Broere, W.
Files
PDF 290361.pdf 1.45 MB
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