Geotechnical Characterization of the Soil along the Banks of the Sagumayon River in the Province of Albay, Philippines

Abstract

The effects of pollution, weather and climate, and societal pressures had changed drastically thephysical characteristics and use of the Sagumayon River, an important river network in the city of Legazpi.This study aimed to obtain relevant geotechnical engineering properties of the soil along the river banks,which could provide an indication of its vulnerability to erosion, settlement, and slope failure. In-situ andex-situ tests conducted in four areas of the river along an 800-m stretch within the Bicol University–MainCampus revealed a granular type of soil, poorly graded sand with silt (SP-SM) of low SPT N-value (from2–20 blows/ ft), friction angle of 27° to 33° and Soil Bearing Capacity of 74 ~ 217 kPa. The riverbank soilsare susceptible to certain modes of erosion, settlement, and slope failure. The soil is comprised of 82% sandand 18% silt. Borehole sites with shallow groundwater table have been found to exhibit high soil moisturecontent values. Structures that will be built on the area should be designed to allow a tolerable, evensettlement of 25 mm and up to 37.5 mm of maximum differential settlement. The study recommends thatthe index properties obtained be used in conjunction with cross-sectional survey data of the river banks toanalyse the stability of the slopes. Remedial measures should be provided to secure against further surfaceerosion. In the design of structures to be built on the area, there is a need to validate the soil properties bydrilling more bore holes to ensure stability of structures.