ABSTRACT:

The intention of this paper is to present the construction method used to build the underground road crossing, that is a part of the revamping project of "Praa XV", in the city of Rio de Janeiro, and discuss the monitoring results obtained through instrumentation data. An alternative construction method was proposed and successfully executed, allowing reduction of embedded lengths of diaphragm walls and avoiding the need for temporary support. This innovative method distinguishes itself from the original design by using jet-grouting and introduces the following features: smaller and thicker diaphragm walls, temporary support elimination, no need of ground water level lowering and reduction of the bottom slab thickness. In this alternative diaphragm walls constituted the retaining wall, while the columns of jet-grouting were disposed as to form the support.

INTRODUCTION

To provide the revamping of "Praa XV", located in Rio de Janeiro downtown, it was built an underground crossing for vehicle passage. The square area covering 50 thousand square meters of esplanade was totally re-built in order to create a large playground for the population. Basic design of the underground crossing set up the execution of a trench, with variable width as shown in Figure 3 and 5.5m excavation executed through the inverted method, which consists of excavating under the ground slab, that would support the retaining wall. Such diaphragm walls 60 cm thick, besides the fact that they have been used to retain the soil, it would also be used as complementary foundation for ground slab; barrettes would be used as central supports. The design, also provided internal water pumping of the excavation, using a deep wells system in other to avoid base failure in the existing sand layer 16.5 meter deep. The bottom slab served as uplift slab supported by diaphragm walls and barrettes.

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