Conceptual modelling for the design of groundwater control systems

Abstract

Groundwater control is required to allow excavations and tunnels to be formed in stable and workably dry conditions below groundwater level. Representative and relevant conceptual models are an essential requirement for the successful development of groundwater control schemes. Prior to construction, conceptual models can aid the planning of ground investigations to help select borehole depths, borehole locations, and hydrogeological testing methods. During construction the effectiveness of groundwater control techniques will vary with different hydrogeological conditions and the hydraulic conductivity of the strata. A sound conceptual model reduces the risk of designs being developed using inappropriate approaches to groundwater control. Common misconceptions include the assumption of a single aquifer (where multiple aquifers and aquitards exist) and cases where significant transmissive zones (which may act as aquifers) are not identified. Other errors include assuming that groundwater levels reported during site investigations are representative of maximum levels that may occur during construction, or not considering the risk of external impacts caused by groundwater control methods. A suggested framework to produce better models is: problem-solution-technology-impacts. This framework can avoid some of the common misconceptions that have resulted in problems during the design and implementation of groundwater control schemes.Thematic collection: This article is part of the Ground models in engineering geology and hydrogeology collection available at: https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology

The changing nature of groundwater control for temporary works

“…For example, Figure 4a illustrates a ground profile where lowering the groundwater levels in a sandy gravel (typical of the River Terrace Deposits in London) could result in the underdrainage of the overlying soft silty clay (of alluvial origin), with a risk of surface settlement and the potential to impact adjacent structures (if present). A case in which similar pumping from a coarse granular layer below alluvial clays and peat resulted in settlement damage to buildings in the vicinity is reported by Powrie (2014), and discussed in Preene (2020).…”

“…Each groundwater control technique has a specific range of application, particularly in relation to the permeability of the ground (Figure 3a and 3b). There are examples of groundwater control measures being ineffective when applied in the wrong conditions (Preene, 2020).…”