In the common practice of geotechnical design, the state of soil is considered fully saturated, while recent examples show the importance of the consideration of unsaturated conditions as well due to the location of the groundwater table at deeper levels. However, it is problematic to design a foundation and calculate bearing capacity as the internal stress in unsaturated conditions needs to be quantified. The mechanics of unsaturated soils are critical in geotechnical engineering, especially when the case of the foundation design is required. This study aims to investigate the influence of suction on the shaft capacity of pile foundations based on the data obtained from in situ and laboratory testing. The three modified methods (i.e., modified α, β, and λ) were implemented in this study in order to calculate the shaft capacity of the pile foundation incorporating unsaturated soil mechanics principles. In addition, the effect of varying matric suction on shaft capacity was discussed. The results of obtained changes show the importance of rain infiltration in the design of piles in unsaturated conditions. It can be concluded that the most conservative method is found to be the modified β method in designing pile foundations incorporating the suction changes due to rainwater infiltration. However, cost optimization shall be considered while choosing the method for the design. As for the increase in GWT, the modified $\lambda$ method depicted the most conventional behavior. The possible rain infiltration decreases matric suction, mostly in the upper layers.

Pagar Alam and its surrounding area are located in the Bukit Barisan Mountain Rang, thus, the topography is hilly and mountainous. National Road segments passing the area often experience slope failure, which causes distraction to the transportation of people and goods. Past observations showed that slope failures are related to frequent and prolonged rainfall. This paper presents the results of a numerical study on the mechanism of rainfall-induced slope failures in Pagar Alam. The study aimed to identify the critical rainfall scenario triggering slope failures. Data observation indicates that even though wet season started in October, most slope failures occurred between January and April. Thus, initial moisture is required to start the mechanism of failure. The transient pore-water pressure was assessed using SEEP/W while the slope stability was evaluated using Slope/W. The analysis showed that the critical rainfall scenario is a combination of antecedent and major rainfall. The duration of the antecedent rainfall is influenced by the slope angle.

Recycled concrete aggregate, that are easily found from destruction waste materials, has been used in the construction industry as an alternative for coarse aggregate component in concrete or as backfilling material in retaining structure. This paper presents the results of study on the use of the recycled concrete aggregate in the design of a newly developed sustainable retaining wall i.e., Geobarrier system (GBS). The GBS system was developed based on capillary barrier to limit water infiltration into the backfill soil while vegetative cover is used as provisions of the sustainable construction concept. Two types of concrete aggregate are used as components of capillary barrier i.e., fine and coarse aggregate. Laboratory test result shows the recycled concrete has similar mechanical and hydraulic properties as the natural aggregate; thus, can be used as alternative material. Stability and deformation analyses were carried out for 4 m high wall with 70^o inclination. Results indicate that the retaining wall meet the requirement of the code of practice according to Eurocode 7 in terms of Factor of safety. Deformation analysis shows that the maximum deformation was only 4.5 mm at the bottom of the GBS wall.