Relation of existing ground water level and the maximum drawdown of groundwater by dewatering
Relation of existing ground water level and the maximum drawdown of groundwater by dewatering
(OP)
I am a structural enginner and hope to seek for some advice on geotachnical concern. In typical strutted cofferdam, dewatering inside the site is required and we need to control the amount of groundwater drawdown outside the site to avoid excessive ground settlement. Does anyone know whether a higher or lower existing ground water level will induce a more critical groundwater drawdown outside the cofferdam due to dewatering?
Thanks so much.
Thanks so much.





RE: Relation of existing ground water level and the maximum drawdown of groundwater by dewatering
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RE: Relation of existing ground water level and the maximum drawdown of groundwater by dewatering
1. Don't dewater the cofferdam to full depth until work inside is ready to begin.
2. As work inside the cofferdam progresses, dewater only as deep as needed for work to proceed safely. Actually, raising the water level inside can improve safety - the distance a worker can fall is reduced (to the water level) and better to fall into water (wearing a life jacket) than onto, say, a concrete footing.
3. At night or on weekends, allow the cofferdam to partially fill. Even a small increase in water level will noticeably reduce groundwater inflow. Obviously, don't do this if the work inside will be harmed by a higher water level. However, never allow the cofferdam to completely fill. Maintaining a higher hydrostatic pressure outside will ensure that the sheeting, wales, struts etc. remain where they are supposed to be.
We did have an unusual situation during construction of an electric generating station that may be of interest. A large, open-ended, existing underground pipeline submerged in groundwater (10 feet inside diameter, 1/4 mile long) needed to be dewatered. Groundwater pumped from the pipe was injected into the (shallow) water table a distance away from the pipe. We approached the appropriate groundwater regulatory authority with this proposal. They had not encountered a request to inject ground water into ground water. After a timely review, approval was given - the work proceeded without complications.
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RE: Relation of existing ground water level and the maximum drawdown of groundwater by dewatering
RE: Relation of existing ground water level and the maximum drawdown of groundwater by dewatering