Regaining of strength over time in remoulded clays

Abstract

Regain rate of strength in remoulded clays with time has been investigated and evaluated in this study. The clays loose much of the original strength after disturbance, especially in quick clay where the strength after disturbance drops to less than 0.5kpa depending on its sensitivity. Thereafter the structure of remoulded clays is rebuilt to a more stable and rigid one than the original structure. During this process a regain of strength is established overtime, but this process is affected by several factors and takes long time. In principle, these factors can be divided into two types; factors that are related to the mineralogical composition of clays, and the type of bonding between particles in the soil-water system.The second type of factors affecting the regain of strength is the surrounding conditions such as, climate, stress history and stress distribution, the thixotropic action, reconsolidation and water pressure.

This study is conducted through experimental work with wide variations in the surrounding conditions and methodologies of testing. The experimental work is composed of field experiment in Tiller and laboratory small scale experiment on clay samples from Tiller.

A new electrical vane shear test device, developed in the geotechnical laboratory in NTUN, was utilized to measure the strength of remoulded clays in the field. This apparatus is accurate and sensitive to measure the resistance in remoulded clays.

The search includes also a real case study to evaluate the regain of strength in remoulded quick clay under natural conditions during installation of two tubular sheet piles in a quick clay zone. This work includes field and laboratory tests on remoulded quick clay after 1 year.

From this study, the important findings were:

- The clay recovered its strength, or even regain more than the original strength, but the required time is extensive, in terms of years.- The time required to recover the original strength is varying depending on the specific boundary conditions after disturbance. Summary of the work as well as recommendation for further work has been presented and discussed.

Key words: sensitive clay, remoulding, electrical vane test device, regain of strength.