Analysis of an Underground Opening in Jointed Rock

Abstract

The primary objective of the study was to analyze the behavior of an underground rock chamber (Dupont Circle Station) excavated in jointed rock. The chamber was excavated in five stages and was driven in foliated metamorphic rock whose main features consisted of joints, shears and shear zones. The study included the analysis of the rock movements and loads developed around the chamber during the excavation stages. The results were compared directly with field measurements previously collected during the chamber construction to better understand the causes that contributed to support loads and opening stability.

The study was conducted by applying the finite element method to typical geologic cross-sections of the chamber during its excavation stages. The main geologic features of the site were modeled with joint (slip) elements.

The effects that inward movements exerted on the chamber behavior were studied. During the top heading excavation, linings with different modulus were used to study the influence of displacements that occurred prior to as well as after the installation of the actual lining.

The results obtained in this analysis were compared to field measurements collected in the form of extensometer and support strain measurements. For all stages of excavation, the results of this analysis were consistent in major respects with the field measurements.