RELATING THE FIELD AND LABORATORY CALIFORNIA BEARING RATIO (CBR) OF STABILISED ROAD BASE

Abstract

Road base materials may not comply with the stipulated minimum load-bearing capacity, especially those of soft soil deposits with high clay and silt contents. An effective and potentially economical solution is the stabilization of the in situ poor soils instead of the conventional remove-and-replace approach, especially for low-cost subsidiary and private roads leading to agricultural land with heavy tonnage traffic. This paper examines the California Bearing Ratio (CBR) of stabilized soils for an existing site, with comparisons made between field and laboratory tests of the treated soil samples. With 3% stabilizer admixed per dry weight of the soil, rolled and pounded to at least 95% of compaction degree, 5 samples were tested in situ and the laboratory. The field measurements differed from laboratory results within the range of 30-60%, an observation attributed to the ideal compaction attained with the laboratory sample’s preparation procedure and condition. Laboratory measurements recorded approximately 55-88 kPa for the bottom face (5.0 mm penetration), and 90-105 kPa for the top face penetration (2.5 mm penetration). The corresponding unconfined compressive strength of the 3% binder-treated sample was 3.2 MPa, with a distinct rather linear climb of the stress-strain plot before sudden rupture at the peak, typical of a hard and brittle material under compression. Summarily, the stabilized road base was found to sustain traffic loads of up to 5 tonnes while complying with the CBR requirement of at least 50%. Variations between laboratory and field measurements were mainly due to the controlled sample preparation method adopted in the former.