Geotechnical investigation and assessment of potential building damage arising from ground movements: CrossRail

Abstract

One of the largest geotechnical survey and site investigations ever carried out in London, costing approximately £3 million, was undertaken prior to the design of the underground sections of CrossRail. This paper outlines the procurement, management and technical aspects of this survey, the application of the results to the prediction of ground movements arising from tunnelling and the design of building protective works.

Integrated InSAR monitoring and structural assessment of tunnelling‐induced building deformations

“…The hydrogeology of the London area is mainly controlled by two aquifers, commonly referred to as the upper and lower aquifers. The piezometric surfaces are at approximately zero Ordnance Datum (OD), that is, 5–6 m below the ground level, and between −40 and −50 m OD, respectively 9 . Due to the different ground features and groundwater conditions, diverse tunnelling methods were adopted.…”

“…Evaluating the settlement impact to buildings and structures is a primary concern for the construction industry, and large budgets are usually allocated to (i) monitor building deformations and (ii) estimate the potential building damage. 7,9 Traditional monitoring techniques utilise established ground-based instruments such as precise levellings, electrolevels, tape extensometers, displacement gauges and robotic total stations. 8,10,11 These instruments enable the inspection of sparse points on the structure, providing a direct measurement of their displacement over time.…”

“…Depending on the construction material, the building stiffness and the foundation typology, tunnelling‐induced settlements can affect adjacent structures with a different level of severity. Evaluating the settlement impact to buildings and structures is a primary concern for the construction industry, and large budgets are usually allocated to (i) monitor building deformations and (ii) estimate the potential building damage 7,9 …”

Multi-Temporal InSAR Structural Damage Assessment: The London Crossrail Case Study

“…Tunneling was primarily through the London clay and Lambeth Group layers, resulting in settlements with the typical characteristics of tunneling in soft ground. In the region two aquifers are present, with piezometric surface at approximately zero Ordnance Datum (OD) and between −40 m and −50 m OD, respectively [37].…”

“…Compensation grouting was adopted in several locations along the tunnel route and near the stations to minimize ground settlements. The 14 selected buildings are located directly above, or in close proximity to, the tunnel track (Figure 1), and therefore were potentially at risk of being damaged by the tunnel-induced settlement [37].…”