Monitoring Program for Cement Grouting of Underground Karst Cavities

Abstract

A total of eight ground-surface subsidence was detected in a residential suburb. The subsurface failure cases in the suburb were investigated in detail after their development. Results of the investigations indicated that the geological profile in this suburb consists of overburden soil which is underlain by limestone bedrock. It was concluded that raveling of the overburden soil into the underlying Karst cavities was the main cause of ground-surface subsidence development. Filling the Karst cavities with cementitious grout was chosen as a treatment measure for the cavity problems. Before and during the grout works for filling the Karst cavities, continuous monitoring of elevations in some selected points at critical locations were considered as essential tool to detect any slight movement or change that may be evaluated and considered a warning for larger movements or cavity and ground-surface subsidence formations. The continuous monitoring program was based on two major elements; dilapidation survey of selected high risk locations, ground surface movement and the measurement of water levels for determining water fluctuations. Dilapidation was achieved through topographical site surveys including houses, utilities and general surveys along with a set of pictures illustrating important features. Station points were set all over the site and their elevations were checked regularly. Regular periodic evaluation of
elevations, water-table levels and crack-meter readings were used as tools to evaluate the impact of the grouting works. Status of existing structures was checked regularly using crack-meters along with water-table levels through available piezometers. This paper contains description of the conducted dilapidation and topographical survey. Results of the monitoring program of the grouting works and their impact on the ground-surface subsidence is also presented in this paper.