ANALYSIS OF SUBSIDENCE AND RESULTING DAMAGE OVER AN AREA FOR 3 DECADES

摘要

This paper presents an investigation conducted into the cause of collapse and the resulting subsidence and associated damage. The project is located in the East St. Louis area of Illinois. The study consisted of 3 subsurface investigations conducted into the old works over about a 30 year time period and numerous surface investigations. The old works are in the No. 6 Coal Seam in the Illinois Coal Basin which is about 2 m thick, and were mined between the years 1900 to 1925. The depth of the old works is about 60m deep. At the project site there is up to about 50 m of soil overburden.Over the course of the 3 decade investigation period, extensive flooding of the abandoned workings was observed resulting in mine floor softening. Considering the softened floor condition, a bearing capacity of less than one was calculated and appears to be clearly the mode of failure. The paper discusses the floor stratigraphy and rock mechanics properties used in the analysis. The paper also discusses the resulting subsidence events and associated damage. As a result of the damage from one of the subsidence events, a state police headquarters building had to be razed. Also, the measured ground movements of the most recent subsidence are correlated with the rate of damage experienced by the recreational building. This structure exists in the tension zone of the sag subsidence and has consequently been subjected to hogging and tension related damage. The thick soil cover has significantly contributed to the draw zone width which has affected this building. In investigating the subsidence movements and the damage in this building, the measured ground displacements were quantified by angular distortion and compared to the damage over time.