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Bechtel’s Impact Report

Stability of Excavations in Karst for Deep Underground Stations of Lines 1 and 2 of Riyadh Metro Project

Authors: Dino Sarac, Joan Aranda Gelabert, and Alwalid Alekrish

Geology of Riyadh area comprises surficial soils over a sequence of sedimentary rocks, bedded Limestone and Limestone breccia. Construction of deep underground stations was carried out in vertical excavations which required support in soils, completely weathered rock and cavities. The excavations were free standing in highly weathered to fresh rock. The support measures for soils and completely weathered rock included flattening of the excavation, gravity walls, soil nails or anchors and shotcrete and secant pile walls with anchors. Selection of the support measures depended on site constrains and soil or completely weathered rock properties. Cavity types encountered included empty cavities, infilled cavities and karstic systems. Support systems for excavations through cavities depended on cavity type, cavity size and risk profile.

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