Preliminary Geotechnical Assessment Based on Dynamic Cone Penetrometer (DCP) Testing in West Lombok Housing Development Areas

The high number of residential developments along the Mataram-Gerung Bypass Road risks structural failure due to uncompacted alluvial subgrade on former agricultural land. The purpose of this study was to analyze California Bearing Ratio (CBR) and assess the subgrade bearing capacity, serving as a preliminary geotechnical assessment for residential construction planning. In-situ Dynamic Cone Penetrometer (DCP) testing was conducted at six measurement points to a depth of 1000 mm. In addition, the subsurface stratigraphic profile was characterized based on soil samples, cross-referenced with regional geological maps. The penetration value (DCPI) was then converted into a CBR percentage using Harison’s (1987) empirical correlation, while the mechanical soil parameters (qd, qu, and qall) were estimated using the Dutch Formula approach and Portland Concrete Association modification with a Safety Factor of 3. The results showed that the CBR value varied from 4.07% to 14.67%. Points B2 is categorized as Poor Subgrade (CBR 4.07%), point A2 and C2 as Medium Subgrade (CBR 6.95%–7.68%), and points A1, B1, and C1 as Good Subgrade (CBR 13.24%–14.67%). The bearing capacity estimation analysis produces dynamic penetration resistance (qd) values ​​of 216.91–574.86 kPa, ultimate bearing capacity (qu) of 64.97–151.76 kPa, and allowable bearing capacity (qall) of 21.66–50.59 kPa. Although some points have CBR in the good category, the overall qall value of the study area remains low and below the safe threshold for shallow foundations. Geotechnical recommendations include excavating and replacing topsoil with selected compacted fill material.