# Effects of Heavy Rainfall on Shallow Foundations in Bukit Timah Granite in Singapore
###### Abstract  
The increase in rainfall intensities due to climate change affect the entire globe. In particular, Singapore suffers from floods and rising of coastlines. Notably, in the Bukit Timah Region in Singapore, floods are getting more intense, and the region houses multitudes of low-rise constructions with shallow foundations. Damages ranging from physical, in terms of motor vehicle and property damages, to intangible losses such as major traffic delays in both private and public transit were caused by the floods. Few studies have been carried out in Singapore in terms of shallow foundations' response to rainfall events. When rainfall infiltrates into the soil, the bearing capacity and soil stiffness are affected by the change in matric suction. Thus, the impact of heavy rainfall on shallow foundations in Bukit Timah Granite is investigated numerically using SIGMA/W. Fully coupled flow-deformation analysis with unsaturated soil characteristics, e.g., the Soil Water Characteristic Curve (SWCC) and unsaturated permeability functions, were conducted. A range of rainfall intensities, rainfall durations, and applied loadings were investigated to produce a load-settlement curve that was compared against a semi-empirical model to yield reasonable results. The studies showed that the change in matric suction is affected by the rainfall duration, rainfall intensity, initial groundwater conditions, and hydraulic properties of soil, which in turn affects the settlement response heavily. The bearing capacity is evaluated using graphical methods via the load-settlement response curves, and it was found that the reduction in matric suction heavily reduces the bearing capacity of the soil. Combined with the unsaturated residual soils and transient analyses, the discoveries give insight into the assessment of shallow foundations subjected to water infiltration. shallow foundation; bearing capacity; settlement; infiltration; numerical analysis +
Footnote †: journal: Medical  
settlements caused by groundwater level rise, either from floods or heavy rain. This is attributed to the 10% increase in moisture content of clay which increases settlement by 2-3 times [10] and the increase in the degree of saturation that comes with the groundwater table rise [11]. Singapore is a tropical country that experiences monsoon seasons per year with constant heavy rainfall all year round. Singapore is also geographically hilly, with plenty of gentle and steep slopes around the island. Thus, there are numerous studies involving rainfall-induced slope failure. Despite many studies of rainfall events on soil slopes and the impacts on slope stability in Singapore, there are little studies carried out on the response of shallow foundations under rainfall events in Singapore [4; 5; 12; 13; 14; 15]. Globally, laboratory and field studies have been carried out on the impact of rising groundwater level on foundation settlements; these studies generally found that an increase in groundwater level and soil moisture increased soil's deformations and settlements by up to 100% [16]. [PERSON] et al. [17] and [PERSON] et al. [18] simulated field load tests of shallow foundations using finite element methods (FEM) and found reasonable agreement when comparing simulated and field test results. They also concluded that shallow foundations of higher dimensions experience a higher settlement as compared to those of lower dimensions. This size effect can be accounted for by plotting applied loading against normalized settlement curves [19]. Thus, in this study, different sizes of shallow foundations were not considered as a controlling parameter for the load-settlement response. In the same study, the matric suction measured in the field after rainfall was compared against simulated rainfall using a FEM, and was found to be reasonably agreeable. This simulated matric suction was imported to an independent sequential analysis, where the rainfall was simulated first, and the resulting matric suction was used to perform a load-deformation analysis.