This paper presents the processes of investigation, analysis, design, construction and monitoring of a soil nail strengthening work to facilitate a 14.5m deep excavation at an uncontrolled dump site. Pavement distresses on the retained ground were first observed shortly after initial excavation. Compounding with the extreme weather condition and the uncontrolled dumped materials, the distresses became more apparent. Investigation was carried out to probe the causation of the problem. The investigation concluded that the site
was formerly a natural valley with natural stream and without proper land clearing. The development had subsequently leveled the building platform with thick uncontrolled fill, some even over the original soft compressible deposits within the valley. Unfortunately, there was no proper filling and compaction controls over the initial bulk earthworks. The natural drainage, especially the underground seepage, was also not properly addressed. As such, the saturated loose fill had insufficient strength to remain stable after the initial steep excavation. The strengthening strategies were to reinforce the saturated loose fill in-situ with closely spaced soil nails of varying length from 6m to 12m and shotcrete facing, and to freely drain out excessive groundwater from the satura
ted loose fill with subsoil drains. Generally, the excavation surface was finished with shotcrete facing in 4V:1H gradient. At one location, 12m long sheet pile wall with two rows of 18m long soil nail anchorage was used to enhance
the passive resistance of the retained ground, which is seated over the 2m thick original soft deposits almost at the final excavation level. Extensive instrumentation programme had been implemented to monitor the performance of the strengthening solution, validation for the design nail resistance and groundwater variation. From the monitoring results, it was proven that soil nail strengthening technique is suitable for loose saturated fill provided that substantial care is taken during implementation. Construction difficulties, solutions to overcome the problems and lesson learnt will be discussed in the paper.