Groundwater Dewatering 1

[VR1963]

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.

 

[Ginger]

VR1963<br>
<br>
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.<br>
Regards<br>
<br>
Ginger

 

[VR1963]

Ginger,<br>
<br>
Thank you for the response. Please forgive my ignorance, but what does CIRIA stand for and how can I get information/reports from CIRIA?<br>
<br>
Best Regards,<br>
<br>
VR1963<br>
<br>
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.<br>

 

[Ginger]

VR1963<br>
<br>
You can find CIRIA at <A HREF="

http://www.ciria.org.uk"

TARGET="_new">

http://www.ciria.org.uk</A>

<br>
<br>
Hope this is of use<br>
<br>
Regards<br>
<br>
Ginger<br>

 

[VR1963]

WOW, thanks for the lead. I am very impressed with CIRIA.<br>
<br>
Thanks for your help

 

lkjhoiu

 

[VR1963]

After several weeks of looking for simplified solutions to dewatering problems, I only found solutions to textbook type problems.&nbsp;&nbsp;Real world problems, where partial penetration and flow exclusion are used, are not easily solved using textbook solutions.&nbsp;&nbsp;<br><br>Has anyone experienced this problem?&nbsp;&nbsp;If you have, how did you resolve this dilemma?<br><br>I turned to MODFLOW, the USGS Finite Difference computer code.&nbsp;&nbsp;However, I do not have much field data to verify its effectiveness.&nbsp;&nbsp;I only have one site where I used it and dewatering was completed.&nbsp;&nbsp;Other sites where I used it have not started to dewater.&nbsp;&nbsp;For the one site where dewatering was completed, the estimated dewatering rate was about 40 percent higher than the actual rate.&nbsp;&nbsp;This I attribute to poor hydraulic conductivity data provided by the client.<br><br>I am looking for field data to perfect this approach.&nbsp;&nbsp;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.<br>

 

[murph]

Could you provide more information on your problem?<br>Could you characterize the soil conditions including thickness of strata?<br>Also, what is the depth of excavation and depth of sheet pile embedment relative to the ground surface?<br>Where is the top of the water or water table relative to the ground surface?

 

[VR1963]

Thank You murph for the reply,<br><br>The following is a problem description:<br>Total Aquifer Thickness:&nbsp;&nbsp;200 ft, Unconfined<br>Hydrogeologic Unit 1: Sand w/K = 1000 ft/day and 40 ft thick<br>Hyd. Unit 2: Limerock w/K = 500 ft/day and 50 ft thick<br>Hyd. Unit 3: Limerock/Sandy Limerock w/K = 300 ft/day<br>Depth to water = 5 ft below grade<br>Excavation depth 15 ft below grade<br>Required drawdown = 12 ft ( 2ft below bottom of excavation)<br>Sheet pile driven to 25 ft below grade all sides<br>Excavation: L shaped w/100ft long sides&nbsp;&nbsp;& 50 short sides<br>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.<br><br>Required:<br>Pumping rate at startup and at steady state<br>Spatial/temporal distrubution of water table<br>Radius of influence (R @ 0.1 ft drawdown)<br><br>Solution should address different hyd. unit K values, partial penetration, and flow exclusion (sheet pile)<br><br>I look forward to your reply.

 

[hari]

i am working for dewatering problem in Maitreya project where i am envisaged to do dewatering for 35m below ground.And unfortunately i am encountering rock at 30m itself. so i am forced to go for both deep well and open dewatering.i would like you to suuggest me a best method to this problem.
thanking u
hariharanath.k
Design engineer,
L&T, ECC,
Manappakkam
Chennai-89.
India.

 

[Ginger]

Hari

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

 

[visitor]

I have a project where we will be excavating 30-35 feet to install a liftstation. My experience at this depth is very limited. Some of my question are how do you determine what is the best method of dewatering? What equipment is need to excavate thru Limerock? What is the best shoring methods? Is this Web Site a location for this kind of Information