Facilitating drainage run excavations with Wellpoint dewatering

​Hinckley Dewatering

Introduction

PDL was awarded the dewatering works to facilitate excavation and construction of drainage runs across a large development comprising 150 two-storey residential dwellings. An initial overview of the project identified challenging ground conditions, including high groundwater levels and silty sand and silty clay at various levels across the site.

The Works

Following a thorough review of the available information, PDL determined that a double-sided wellpoint system would be necessary to effectively lower the groundwater level. Wellpoints are the dewatering method of choice because of their fast installation rates, adaptability to varied soil conditions and cost-efficiency. The vacuum-induced pumping facilitates groundwater flow to the wellpoints, enabling effective drawdown even in stratified or lower-permeability soils.

The wellpoints are spaced at 2m intervals and positioned to encapsulate the ends of the drainage runs. Over 300 wellpoints have been installed on site with a further 400 wellpoints still to go in. PDL is working closely with groundworkers, strategically leapfrogging pumps and pipework along the drainage runs to ensure excavation progress remains uninterrupted. Installation will continue over the coming month, with PDL collaborating with the principal contractor to resolve challenges and maintain steady progress, keeping the project on schedule.

​Hampshire Dewatering

Introduction

Dewatering was required to facilitate the installation of drainage runs for a new development in Hampshire. Trial pits collapsed due to running sand conditions within a high groundwater table.

The Works

PDL proposed a wellpoint dewatering system to address groundwater ingress during the excavations. Wellpoints were installed to encapsulate the pits and were placed single-sided along the length of the drainage runs. Due to limited information about the strata sequence, the wellpoints were spaced at 1m intervals, with a wellpoint pump installed every 60m to manage potentially high flows.

The installation of the dewatering system, which consists of over 100 wellpoints has been completed, and the system has been handed over to the client. To date, the system is performing as expected, enabling groundworkers to progress with the excavations.