B3 Field mapping

Abstract

Reconnaissance surveys are usually carried out to establish the main topographical, geological and engineering criteria that will influence the selection and design of a new alignment (e.g. Brunsden et al. 1975) or the key issues that need to be addressed in the case of a road improvement project (environmental and social impact reviews also form critical elements of these surveys). Reconnaissance surveys also allow validation of the desk study interpretations, and provide field information that can then be used to calibrate the desk study outputs. The use of reference conditions to assist in classifying ground conditions originated as an aid to the management of construction contracts in complex/unknown ground conditions (CIRIA 1978). The technique can be used to define the expected engineering parameters and extent of each difficult ground condition, which can then be built into the contract documents. If the ground conditions encountered during construction are different at any particular location to those anticipated, a price adjustment can be made based on the rates provided in the contract for the reference condition actually found. More recently, the technique has been used to assist in the classification of anticipated ground conditions for project feasibility study and design purposes (Baynes et al. 2005; Fookes & Baynes 2008), and is a logical follow-on from terrain modelling and classification (Sections B2.4 & B2.5). By grouping together geological or combined geological-terrain units with approximately similar ground conditions, the technique can be used in the prediction of soil and rock profiles for earthworks schedules and preliminary estimates of quantities. The ground conditions exposed in excavations during construction can be highly variable and sometimes confusing in mountain terrain, and reference condition mapping developed from terrain modelling and classification can help to explain and clarify these variations. The technique can therefore also provide a rationale for …