Development of Innovative Plate Load Testing Equipment for In-Situ Saturated Clays Soils

Abstract

This study proposes a method of gradually loading plate load on-site using lever arms to squeeze out pore water from clayey soils, allowing the soil to settle. Several types of tests were conducted, including a conventional field plate load test (CFPLT), a numerical field plate load test (NFPLT) and an innovative field plate load test (IFPLT) proposed in this study. Three trial pits with soils of varied engineering properties were studied using CFPLT, which employed the use of a heavy jack for load application, the NFPLT test using PLAXIS and an IFPLT, which employed a lever arm to magnify the applied static load. Disturbed soil samples collected from these trial pits were tested for index properties while the undisturbed soil samples were tested using the undrained triaxial compression test (UTCT) and laboratory consolidation tests. The results of the index properties classified these three clay soils as silt of low plasticity (ML) for clay from site 1, and clay of low plasticity (CL) for clay from site 2 and 3. The cohesion and angle of internal friction from the UTCT recorded cohesion values were 28, 29 and 37 kN/m2 for sites 1, 2 and 3, respectively, while the angle of internal friction values were 13, 8 and 6◦ for sites 1, 2 and 3, respectively. The plate load testing using the three methods showed similar graph pattern except that the allowable load occurred at approximately 350 kN/m2 for the CFPLT and 150 kN/m2 for the IFPLT. The high value of bearing capacity in CFPLT is due to the short period of time taken to load from a jack, which allowed the test to be completed within a short period of time. The ultimate bearing capacities computed from the laboratory test have values of 315.0, 231.0 and 270.0 kN/m2 for sites 1, 2 and 3, respectively. These values agree closely with the bearing capacities obtained for CFPLT but higher than the values recorded for the IFPLT. This is probably due to the long period of sustained loading during testing, which allowed for dissipation of pore water during each loading. Settlements obtained using the IFPLT were close to 25 mm, which is recommended as minimum settlements for building structures BS 8004, 1986.