Geotechnical Engineering Online Library

Rainfall-induced slope failures commonly occur within residual soil slopes. One of the possible systems for slope preventive measure is capillary barrier system. A capillary barrier is a two-layer system of distinct hydraulic properties that is used to prevent water infiltration into the soil below the capillary barrier system by utilizing unsaturated soil mechanics principles. This paper presents the numerical simulation of the capillary barrier system as a slope preventive measure against rainfall-induced slope failures. The capillary barrier was constructed on a slope which experienced several shallow failures due to rainfall. In this study, the capillary barrier system was designed to repair the slope and at the same time to provide preventive measures for further failures due to heavy rainfall conditions of the tropics. The capillary barrier system was constructed using fine sand as the fine-grained layer and granite chips as the coarse-grained layer. Both layers were contained in geocells. The slope was instrumented with tensiometers and piezometers. The tensiometers were installed at different depths from about 0.5 m to 2.0 m below the slope surface. In addition, the adjacent original slope without the capillary barrier system was also instrumented using tensiometers in order to investigate the performance and effectiveness of the capillary barrier system in reducing rainwater infiltration and maintaining negative pore-water pressure in the slope. Results of field measurements from one-year monitoring period and numerical analyses of slope with and without capillary barrier system are presented in the paper. The results of numerical analyses of the slopes with and without capillary barrier system indicated that the capillary barrier system performed well in minimizing rainwater infiltration into the underlying soil layer. In addition, the numerical results showed that the factor of safety of a slope with a capillary barrier system was significantly higher than that of an original slope without the capillary barrier system. The field measurement and numerical analyses results were in good agreement, demonstrating the successful application of unsaturated soil mechanics principles in the design and construction of a capillary barrier system.

The construction of the steel arched Tsakona Bridge, designed to overpass an active landslide, required several temporary projects. Auxiliary steel towers were used for the erection and welding of the arch segments. Most of them had to be founded in the body of the sliding mass. An automated instrumentation and monitoring system was installed on site providing early warning to the engineers in charge in case large displacements were measured. The real-time recording data provided valuable information about the landslide movements. These monitoring results defined the geotechnical and structural design criteria for the deep foundation of the temporary towers. Several 2D and 3D geotechnical and structural models were created to evaluate the sliding effect on the foundation components, finalize their dimensioning and calculate the required reinforcement. The procedure followed for the design of the temporary deep foundation is described based on the criteria devised using the monitoring system, emphasizing on the continuous feedback between the geotechnical and structural design teams. Several key structural design issues required during construction are also presented.

In land scarce Singapore, the development of a comprehensive and efficient underground public transport system is the key to a sustainable transport system. This has resulted in many tunnels being built in densely urbanized areas and at close proximity to buildings and infrastructures. The tunnelling effects on these adjacent structures can be detrimental as problems such as pile settlement and passive loading on the piles could arise. The construction of large scale infrastructure projects such as Circle Line has opened up enormous scope for tunnelling and underground works in Singapore, which offers a great opportunity to study the response of piles to tunnelling. Two case histories are presented and involved the monitoring of 200 buildings located within the influence of tunneling along Circle Line (CCL) 3, 4 and 5. More than 3600 building settlement markers were analyzed and the resulting pile head settlements due to tunnelling were compared with surrounding ground surface movements. The results of the full-scale instrumented piles subjected to the effects of twin tunnel construction on adjacent groups of bored cast in-situ piles are also discussed.