Superficial Settlements Caused by a Small Diameter Tunnel Excavated in a Residual Sandy Soil

Abstract

This paper presents a case-history of a shallow, small-diameter tunnel drivcn in the city of São Paulo, Brasil. This tunnel was excavated manually with a shield providing temporary protection for the roof. Final lining consisted of 60 cm-long rings formed by 3 segments of pre-cast concrete.  An instrumentation consisting of surface monuments, borehole extensometers, inclinometers and piezometers was designed in order to assess the efficiency of the construction method in keeping the displacements within tolerable magnitude. The aim of this paper is to present an analysis of the superficial settlements caused by the tunnel excavation. This prediction of tunnel behaviour was carried out through both empirical and semi-empirical methods. ln conclusion, this prediction is compared to the measured displacements.