Innovative Design Of Reinforced Soil Wall On A Steep Slope Subject To Land Slip Risks

This paper presents a case study of an innovative reinforced soil wall (RSW) design on steep slope using site-won material that is not in full compliance with Roads and Maritime Services (RSM) QA specification R57. The steep slope was impacted by a landslip occurred in February 2010. Firstly the local geology and the landslips occurred along the project corridor are briefly described. The key design and material requirements for RSW have been reviewed with respect to the use of site-won material. A detailed strategy is presented on how to deal with the potential risks of using the non-compliance site-won fill material to the specification R57. A comprehensive laboratory testing regime of the site-won material and large-scaled pullout tests of RSW reinforcement were undertaken. With the test results and engineering judgement, the design was proceeded with the following key assumptions/factors: 1) the allowable fines (<75 microns) content of up to 25%, clay (<2.4 microns) content of up to 7%; 2) the use of reduced friction angle of 30 degrees; 3) a 10% reduction in the calculated pullout capacity of reinforcement; and 4) 1.5 times sacrificial allowance as per R57. These were to cater for long term corrosion on steel reinforcement and to ensure longevity and integrity of the RSW. A heavy rainfall in February 2010 resulted in two significant landslips within the project corridor, with the larger one being immediate at the down slope of the reinforced soil wall (RW01). This event required us to carry out an additional geotechnical investigation and landslip remedial works to ensure the long term global stability of RW01. Three dimensional effects were considered in the assessment of the slope instability in the construction stage review.