Probe drilling based prediction of rock mass strength, natm-4, Pahang-Selangor raw water transfer tunnel, Hulu Langat, Selangor, Malaysia
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Date
2018-07-01
Authors
Nurfarhana Hassan
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Abstract
Probe drilling in tunnelling is carried out to collect information on the rock mass conditions ahead of a tunnel face. Prior to excavation, geological features are thoroughly studied in order to avoid unexpected difficult ground condition, for example excessive water ingress or tunnel collapse that may cause fatality. Usually, the tunnel jumbo with percussive drill is used for a probe drilling campaign. In this study, probe drilling data was collected from drilling activities recorded at Hulu Langat, Selangor, Malaysia. The observed changes on the drilling characteristic of probe drilling carried out provide us indication on the strength of ground, presence of large cavities, type of rock and the volume of groundwater. The information recorded were interpreted using k-means clustering algorithm to predict the ground condition. Parameters considered are drilling speed and percentages of rock chipping as both play important factors in prediction of ground condition ahead. Both parameters were used to cluster the data and classification of rock strength class. Based on k-means clustering algorithm, range of drilling speed, percentage rock chipping and accuracy was determined for each rock class. Japanese Highway (JH) classification method is used to classified the rock class. Rock class B is defined as a good quality rock, hard and fresh slightly affected by weathering whilst rock class E is defined as very poor to extremely poor-quality rocks and considerably weathered rock mass. By using k-means clustering method, the accuracy prediction was obtained for all rock class B, CI, CII, D and E is 76.2%, 60%, 25,8%, 42.3% and 51.9% respectively whereas prediction from probe drilling for rock class B, CI, CII, D and E is 100%, 30.3%, 36.6%, 84.7% and 85.2% respectively.