Engineering behaviour of thanet sand
Research Student: Konstantinos Ventouras
Project Duration: 2002 - 2005
Funding: Greek Government
Background
Thanet sand is a soil stratum that lies deep enough within the central London area not to have been the topic of extensive research until this day, as most foundation works, foundation designs and tunnels have mainly been focused on the London Clay stratum. Recently, as buildings and construction works in general tend to get bigger and heaver and as tunnelling techniques are constantly being improved, Thane....................t
Engineering behaviour of thanet sand
Research Student: Konstantinos Ventouras
Project Duration: 2002 - 2005
Funding: Greek Government
Background
Thanet sand is a soil stratum that lies deep enough within the central London area not to have been the topic of extensive research until this day, as most foundation works, foundation designs and tunnels have mainly been focused on the London Clay stratum. Recently, as buildings and construction works in general tend to get bigger and heaver and as tunnelling techniques are constantly being improved, Thanet sand has attracted increasingly larger scientific interest.
Objectives
The primary aim of this research is to try and identify the engineering behaviour of Thanet sand. This has been attempted by subdividing and examining separately the influencing factors on the soil behaviour into three main groups; the effect of structure within the soil, the effect of site location that the tested soil originated from and the effect of relative depth within the Thanet sand stratum, as Thanet sand is divided into an upper, low silt content, stratum and a lower, high silt content, stratum.
Approach & Apparatus
A series of comparative tests on Thanet sand are being performed using two stress path triaxial cells of different pressure capacities. The medium pressure tests are conducted using a computer controlled hydraulic stress path apparatus (Figure 1), whereas the high pressure tests are conducted using a computer controlled high pressure hydraulic stress path apparatus with a cell pressure capacity of 5MPa (Figure 2). As a supplement to the triaxial experiments, oedometer tests and particle breakage analyses are being undertaken. Also, thin sections have been taken that are then used for a mineralogical analysis.
Outputs
From comparisons of intact and reconstituted samples, structure within Thanet sand does not seem to influence greatly its engineering behaviour, although bender element readings did show a slightly stiffer intact soil response in comparison to the reconstituted soil (Figure 3). The amount of silt content contained within the sand also does not appear to play a part in the soil stiffness whereas it seems to affect the Critical State line in the v-lnp’ plane of the material (Figure 4) and the peak strength, because of the different densities of the soil.
Figures
Figure 1 - Standard pressure system
Figure 2 - High pressure system
Figure 3 - The relationship between Shear Modulus
and mean effective stress.
Figure 4 - Critical state points in v - log(p') space
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