Groundwater Dewatering
Groundwater Dewatering
(OP)
I am looking for a simple (relatively simple) method to approximate the dewatering rate for an unconfined aquiferwhere sheet pile (cofferdam) is used to provide flow cutoff (minimize flow). SHeet pile and well point system do not fully penetrate aquifer.





RE: Groundwater Dewatering
Suggest you look in CIRIA Report entitled Control Of Groundwater In Excavations (can't remember the report number - possibly 113 or 133 ?). Alternatively books by Harry Cedergren.
Regards
Ginger
RE: Groundwater Dewatering
Thank you for the response. Please forgive my ignorance, but what does CIRIA stand for and how can I get information/reports from CIRIA?
Best Regards,
VR1963
PS. I have not found simple/practical solutions for estimating flow rate/drawdown relationship for unconfined aquifers where an excavation being pumped results in substantial vertical flow (resulting from partial penetration) and partial flow exclusion is used (i.e. sheet pile). I have used finite difference models to solve but will continue to look for more practical solutions. Thanks again for your help.
RE: Groundwater Dewatering
You can find CIRIA at www.ciria.org.uk
Hope this is of use
Regards
Ginger
RE: Groundwater Dewatering
Thanks for your help
RE: Groundwater Dewatering
RE: Groundwater Dewatering
Has anyone experienced this problem? If you have, how did you resolve this dilemma?
I turned to MODFLOW, the USGS Finite Difference computer code. However, I do not have much field data to verify its effectiveness. I only have one site where I used it and dewatering was completed. Other sites where I used it have not started to dewater. For the one site where dewatering was completed, the estimated dewatering rate was about 40 percent higher than the actual rate. This I attribute to poor hydraulic conductivity data provided by the client.
I am looking for field data to perfect this approach. If you send me data, I will forward you a copy of a manual that I am working on that describes procedures and solution methods using MODFLOW.
RE: Groundwater Dewatering
Could you characterize the soil conditions including thickness of strata?
Also, what is the depth of excavation and depth of sheet pile embedment relative to the ground surface?
Where is the top of the water or water table relative to the ground surface?
RE: Groundwater Dewatering
The following is a problem description:
Total Aquifer Thickness: 200 ft, Unconfined
Hydrogeologic Unit 1: Sand w/K = 1000 ft/day and 40 ft thick
Hyd. Unit 2: Limerock w/K = 500 ft/day and 50 ft thick
Hyd. Unit 3: Limerock/Sandy Limerock w/K = 300 ft/day
Depth to water = 5 ft below grade
Excavation depth 15 ft below grade
Required drawdown = 12 ft ( 2ft below bottom of excavation)
Sheet pile driven to 25 ft below grade all sides
Excavation: L shaped w/100ft long sides & 50 short sides
25% of the recovered groundwater will be recharged 25 feet away from excavation parralel to long side of L to minimize drawdown at adajacent facility.
Required:
Pumping rate at startup and at steady state
Spatial/temporal distrubution of water table
Radius of influence (R @ 0.1 ft drawdown)
Solution should address different hyd. unit K values, partial penetration, and flow exclusion (sheet pile)
I look forward to your reply.
RE: Groundwater Dewatering
thanking u
hariharanath.k
Design engineer,
L&T, ECC,
Manappakkam
Chennai-89.
India.
RE: Groundwater Dewatering
Dewatering at this depth suggests that you are constructing a tunnel, a shaft or a deep basement or highway cutting?
If it is a tunnel or a shaft and you are looking to dewater the rock, then generally only deep well pumping will do. This is on the assumption that the mass permeability of the rock is great enough to let you dewater it. If the overlying soils are water bearing then you may wish to consider a second set of wells with pumps suited to the permeability of this material.
If it is a cutting then perhaps the cheapest way of dewatering is to let the water flow in naturally and sump pump it away from the base of the excavation. Don't forget to check slope stability under these conditions. A deep basement will probably need a ring of deep wells or one central well if you can get enough drawdown in order to keep your basement dry.
Regards
Andy Machon
Andy@machona.freeserve.co.uk
RE: Groundwater Dewatering