SITE INVESTIGATION

Site Investigation

Site Investigation

Introduction

The importance of geology in the planning of tunnels is stressed, as is the significance of the vast uncertainty and risk that exist in underground projects. Fortunately, in spite of the inherent uncertainty and risk, geotechnical investigations for tunnels are largely successful. Geotechnical information can be invaluable in both the decision of the general corridor and the specific alignment of a tunnel project. An overall perspective and broad guidelines are given for planning and conducting geotechnical investigations for tunnels.

Role Of Geotechnology In Planning

Each tunnel project is unique! This paper provides broad-based guidelines for the conduct and use of site investigations for planning and design of tunnels. It provides an overall approach or perspective rather than cookbook solutions. Inflexible rules or cookbook solutions often work for some situations in design of civil works but not in geotechnical investigations. This paper, which is intended for owners, as well as the planners, engineers and contractors, concentrates primarily on the aspects of geotechnical issues and investigative methods, which are important to tunnelling. Much of this paper is based on tunnelling practice in the United States but the concepts and procedures are applicable worldwide with appropriate modifications for local conditions and methods. For the tunnel designer and builder, the rock or soil surrounding a tunnel is effectively a construction material. Think of it this way; when the excavation is made, the strength of the surrounding ground keeps the hole open until the tunnel supports are installed. Moreover, even after the supports are in place, the ground, through arching, continues to provide a substantial percentage of the total load-carrying capacity.

Geotechnical engineering is a discipline of civil engineering that deals with soil, rock and underground water, and their relation to design, construction and operation of engineering projects. It is also sometimes called soils engineering, ground engineering or geotechnics as it is closely related to engineering geology. Nearly all civil engineering structures are supported on or built into the ground, and thus require at least geotechnical engineering

Coastal engineers are concerned with engineering problems in the coastal environment. They design and maintain harbours, marinas, and coastal structures such as breakwaters, seawalls, and jetties. They are also concerned with the control of erosion, the study of waves and currents and their effect on coastal structures and with pollution of the coastal waters.Ocean engineers are involved in the design of offshore structures. They study the way wind and waves, climate, currents and earthquakes affect a structure and its foundation. The geology along a tunnel alignment plays a dominant role in many of the major decisions that must be made in planning, designing, and constructing a tunnel. Geology dominates the feasibility, behavior, and cost of any tunnel. Although difficult to appreciate, the engineering properties of the geologic medium and the variations of these properties are as important as the properties of the concrete or steel used to construct the tunnel structure. In a tunnel, the ground acts not only as the loading mechanism, but also ...