Finite Element Analysis of Sampling Disturbance in Clay Soils

Bendahgane, Mohamed (1989) Finite Element Analysis of Sampling Disturbance in Clay Soils. MSc(R) thesis, University of Glasgow.

Abstract

The work presented in this thesis describes a numerical (Finite Element Method) analysis of sampling disturbance in clay soils during the sampling operation. Of all sampling methods, block sampling appears to disturb soils least but this method is extremely tedious and is restricted to shallow depths. For this reason thin walled sampling is the usual choice for most practical purposes although soils may be grossly distorted both during the sampling process itself and the subsequent laboratory testing. The major objective of this study is to improve existing finite element analyses of sampling disturbance of clays during sampling. An investigation into the parameters having the greatest effects on sampling disturbance has been carried out. These parameters include the effect of sampler geometry, roughness of the sampling tube and soil stress history. Atotal stress analysis using the Von Mises criterion was carried out as well as an effective stress analysis using a critical state elastoplastic model. From the analysis of the results it is shown that the rough thick walled tubes cause the greatest downdrag on samples during penetration and in general yielding of the soil initiates close to the sampler tip and propagates along both sides of the sampling tube and into the soil below the sampler. Eventually, the yield zone reaches the central part of the sample ahead of the sampling tube. Maximum pore water pressures devlop close to the sampler tip which suggests that during subsequent delays before testing water would migrate from the sides to the central portion of the sample. The results of this investigation also show that highly overconsolidated clays are more susceptible to disturbance than lightly overconsolidated clays. Further work in this area is needed and it is suggested, among other recommendations, that instrumented test on carefully controlled sampling operations should be carried out in the future.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Keywords: Civil engineering, Soil sciences
• Date of Award: 1989
• Depositing User: Enlighten Team
• Unique ID: glathesis:1989-77958
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2020 15:46
• Last Modified: 30 Jan 2020 15:46
• URI: https://theses.gla.ac.uk/id/eprint/77958