Instrumentation for monitoring the effectiveness of retaining wall design

Abstract

Large excavation in urban areas can affect the foundations of existing structures close to the excavation. To eliminate this interacting effect, an effective retaining wall must be erected and its performance must be monitored continuously using proper instruments. This study established instrumentations monitoring process on a retaining wall design assessment dealing with a critical historical structure that require too many sensitivity element to be protected critically. Museum textile ages 120 years was constructed in 1896 is categorized as "Bangunan Warisan" was build up with no foundation detail. Without proper monitoring, failure on the structural, geotechnical movement, hairline cracks and several more can easily occurs. This study aims to determine the effectiveness of secant pile retaining wall design through instrumentation monitoring. Two ground investigations, comprising a total of 28 boreholes, with in-situ testing and soil sampling was performed on the site in the summer of 2014, by a local Contractor, Maxi Mekar Sdn Bhd. Finite element (FE) analyses using computer software "PLAXIS" used for modelling the excavation sequences in order to estimate the ground deformation around the excavation and the performance of the secant pile wall. Inclinometer installed in the secant bored pile wall to monitor the wall deflection, magnitude, direction and rate of lateral movement of the soil. The ground surface settlement marker is used to monitor ground movement at specific locations. Building settlement marker of the simple wall plug used to monitor the vertical movement of the structure. The BeanDevice® AX-3D Xrange been used 24 hours to monitor the vibration caused by the construction activities in nearby structure and vicinity. Through the total ground settlement contour, five monitoring point (within museum textile adjacent area) addressed as established ground settlement limitation points. The critical wall maximum ground deformation, props forces and response of wall for critical sections are summarize based on the ground settlement and structure established limit summarize by Finite Element (FE) analyses using computer software "PLAXIS". The cumulative monitoring data for ground settlement markers are within 2.4mm to 6.9mm, Building Tiltmeter are from 1:2455 to 1:12808 ratio, Building settlement markers are 0.3mm to 1.4mm, Inclinometer within 1.29mm to 4.03mm in A and B direction and Vibration monitoring in between 0.37mm/s to 0.5mm/s. Based on instrumentation data analysis collected on daily basis from February’16 until August’16, the instrumentation readings was monitored against three trigger levels namely Alert, Alarm and Action levels for individual instruments on the instrumentation schedule. It can be concluded that all the monitoring data are within the design limit. The design considered as successful by meeting this limit. It is recommended to extend the monitoring stage up to completion of the excavation at B4 level in order to get critical view on the overall design wether within the spesified limit or not.