Control and lowering of ground water.

Construction activities such as deep excavations, slope profiling and compaction are significantly influenced by the presence and elevation of both ground and surface water.   When excavating below the water level, or attempting to compact soil material within close proximity to the water level, compaction difficulties,  delays, disruption and cost increases can be expected if adequate measures are not taken to address the water conditions and adopt suitable dewatering measures.     

In general terms dewatering incorporates measures to lower, cut-off or remove water in the ground to facilitate safe and efficient construction processes associated with excavation and compaction.  Relevant geotechnical site investigations are required to determine the ground model and groundwater parameters that are relevant for the project.  Consideration of the proposed construction works, in relation to the ground and water model, facilitates identification of risks and mitigation measures required to ensure successful project outcomes.

Frequently the issues to be addressed will include inflow of water through the side and base of an excavation, surface water flow down slope and possible base heave due to removal of overburden self-weight.  It is also critical that issues associated with local drawdown and potential settlement of the ground surface are considered where existing structures or infrastructure are adjacent to the project site area.  These issues may only apply in the temporary condition, until permanent works negate the problem, or may be permanent, such as in the case of buoyancy uplift on structures that are below the long term groundwater level, where permanent dewatering will be necessary.  

Having assessed the likely nature of the ground, groundwater conditions and impact on the proposed construction it is possible to assess the nature and degree of dewatering that is required and how that can efficiently be achieved.  Dewatering systems such as wellpoint spears, sump pumps, deep wells, cut off walls and grout curtains can be combined to achieve the required temporary or permanent dewatering results.

CWM has experience in the analysis, design, specification and monitoring of dewatering solutions and can help identify and resolve project challenges associated with construction works that are impacted by surface water inflows or that are located either at or below the groundwater surface.

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