ABSTRACT:

Unpaved roads built over soft, weak subgrade have been used extensively in the Southeast Asian region as temporary site access roads, forest roads and low volume roads. Trafficking of vehicles on un-reinforced unpaved roads will cause severe rutting and mud-pumping problems especially in the rainy season. In addition, stones will get pushed into the weak subgrade. Geotextiles have been successfully used to improve the overall stability and trafficability of unpaved roads. Placed at the interface of the base layer and the subgrade, geotextiles perform separation, reinforcement, filtration and drainage functions, hence, improving the performance of weak subgrade. This paper presents the performance of geotextiles in the stabilisation of unpaved roads in a laboratory model tracking test. The effect of anchoring and pre-tensioning of geosynthetics is examined. Seven laboratory-tracking tests have been carried out for this purpose: one control test, three composite geotextile tests (un-anchored, anchored and with pre-tensioning) and three non-woven geotextile tests (un-anchored, anchored and with pre-tensioning). During loading, subgrade settlement of each test was carefully monitored. To evaluate the performance of each stabilisation system, rut resistance of each test was evaluated and compared with the performance of the control test.

INTRODUCTION

Unpaved roads built over weak, soft subgrade (less than 3% CBR) are prone to rutting, stone loss and mud-pumping problems. Placing geotextiles at the subgrade-base interface performs the desired separation, reinforcement, filtration and drainage function. Geotextiles when used as separators prevent stone loss into the soft subgrade and minimise base contamination induced by mud pumping. One of the key mechanisms of reinforcement function in geotextiles is the membrane effect. The vertical component of the tension developed in the geosynthetics will distribute the wheel loading over a larger area in the subgrade, avoiding overloading beyond the bearing capacity of the soil.

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