A Tragic and Unpredictable Station Cavern Collapse During Construction of a Metro, Despite Extensive Drilling Investigations
In January of 2007, seven people in a S(a)o Paulo street, four of them in a small bus, were suddenly sucked into falling soil and saprolite, from a street elevation about 20 m above a metro station cavern of 19 m span and 40 m length. Despite the evidence of four surrounding and one central borehole, and six more boreholes around the adjacent station shaft, the assumed mean rock cover of just 3 m above the 20 m deep cavern arch, proved locally to be more than 10 m in error, due to a buried ridge of rock running high above the cavern arch, with one fateful low point exactly where drilled on the cavern centre-line. Seven lanes of adjacent highway and twin railway lines prevented viable seismic refraction, and a consistent drilling result had not proved this to be necessary. Due to the assumed low rock cover, heavy lattice girders, embedded in 40 cm of S(fr) were used as temporary support. The feet of the lattice girders were founded on broad ‘elephant’ footings. Due to the unknown adverse loading from a wedge-shaped, clay-bordered, giant ridge of rock and saprolite, weighing some 15,000 tons, all forms of temporary support would eventually have failed. Post-collapse, painstaking, police-supervised excavation of the entire 20 by 20 by 40 m of collapsed materials, taking some 15 months, finally revealed large remnants of the arch and wall support, crushed and folded beneath the fallen gneiss, amphibolite, saprolite, sand and soil.
N.R.Barton
Nick Barton & Associates, Oslo
国际会议
香港
英文
1-5
2009-05-19（万方平台首次上网日期，不代表论文的发表时间）