Performance of high-capacity tensiometer in constant water content oedometer test

M Wijaya,E C Leong

doi:10.1186/s40703-016-0027-6

M Wijaya, E C Leong

Open Access

https://doi.org/10.1186/s40703-016-0027-6

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Abstract

Matric suction is one of the stress-state variables which governs the behaviour of unsaturated soils. In order to evaluate the effect of matric suction on the behaviour of unsaturated soil under constant water content condition, rapid measurement of change in matric suction during the test is required. High-capacity tensiometer can be used to rapidly measure the change in matric suction of unsaturated soil. In this paper, an oedometer apparatus was modified to incorporate a high-capacity tensiometer to investigate the compression behaviour of unsaturated soil under constant water content condition. The design of the oedometer apparatus was described. Two soils which are kaolin FP grade (commercial kaolin which has a fine grain size) and residual soil from Bukit Timah Granite were used to evaluate the performance of the high-capacity tensiometer. The results showed that kaolin paste is helpful in improving the contact condition between the soil specimen and high-capacity tensiometer. The equilibrium time of the high-capacity tensiometer was about 10 min. Evaporation effect reported by other researchers was not observed with the high-capacity tensiometer. The change in matric suction due to loading and unloading was accurately captured by the high-capacity tensiometer.

Highlights

Matric suction is one of the stress-state variables which governs the behaviour of unsaturated soils
Kaolin FP grade and residual soil from Bukit Timah Granite were used to evaluate the performance of the High-capacity tensiometer (HCT)
A modified base plate was constructed in order to incorporate the HCT into the oedometer apparatus to measure the pore-water pressure of the unsaturated soil specimen

Summary

Background

The properties of unsaturated soils such as shear strength, volume change and permeability are different from those of saturated soils due to the presence of matric suction s which is the pore-water pressure (uw) referenced to the pore-air pressure (ua). Under constant water content condition, the pore-air pressure of the soil specimen ua is at atmospheric condition It is possible for the soil specimen to dry due to evaporation during the test [9]. The purpose of attaching the HCT at the bottom of the oedometer is to minimise the effect of evaporation on the HCT which is apparent in the test results of Jotisankasa et al [9] and to improve the contact condition between the HCT and the soil specimen as the soil specimen is loaded Both Jotisankasa et al [9] and Tarantino and De Col [23] used two tensiometers installed in the top load cap of their modified oedometer apparatuses.

20 Kaolin

Conclusion