Construction Dewatering Means and Methods Presentation

Construction Dewatering

Getting Your Project on Firm Ground……Before It Starts

Introduction

• David Giles– Co-Founder/Managing Partner: TerraFirma Earth

Technologies, Ltd.

• Overview of Construction Dewatering– Giving guidance to those directly or indirectly

involved in the planning, design, supervision, construction and operation of dewatering systems.

Topics of Discussion

• Construction Dewatering– What is it?– Why do it?

• The Consequences of Improper Dewatering• Design Considerations• Subsurface Investigations and Soil Borings• Methods of Groundwater Control• Case Studies

Dewatering: What is it?Intercepting/minimizing groundwater seepage from entering an

excavation.

Depressing the piezometric water surface to a point below the excavation.

Dewatering: Why do it?

Short Term Objectives(Temporary Systems)

• Intercept Seepage– Increase slope stability– Prevent loss of material

• Reduce lateral/uplift pressure

• Improve the excavation and the backfill characteristics of the excavation to allow construction to proceed in a safe and eficient manner

Long Term Objectives(Permanent Systems)

• Reduce or eliminate lateral and/or uplift pressures

• Achieve waterproofing objectives

Improper Dewatering

The Consequences• Blows, Rendering Excavation Subgrade

Unstable• Boils/Piping, the Creation of Voids Rendering

Slopes and Subgrades Unstable• Excavation Support Systems Rendered Unstable• Future Settling• Lost Time• Decreased Worksite Safety• Increased Cost

Improper Dewatering

The Consequences• Blows, Rendering Excavation Subgrade Unstable• Boils/Piping, the Creation of Voids Rendering

Slopes and Subgrades Unstable• Excavation Support Systems Rendered Unstable• Future Settling• Lost Time• Decreased Worksite Safety• Increased Cost

Improper Dewatering

Rio Grande River Crossing, Albuquerque, NM

Improper Dewatering Proper Dewatering

42” Gas Pipeline, Blythe, CA


• The Origins of Dewatering• Construction Dewatering

– What is it?– Why do it?


Design Considerations

Dominant Considerations• Location and Geologic Environment• Size and Depth of Excavation• Groundwater (Piezometric) Level• Soil & Aquifer Characteristics (Hydraulic Conductivity)• Proposed Excavation Method and Excavation Support• Proposed Schedule• Proximity to Existing Structures, Potable and/or Irrigation

Wells, Potential Sources of Recharge• Nature of any On/Off-site Contamination

Depth to Water & the Piezometer


Dominant Considerations• Location and Geologic Environment• Size and Depth of Excavation• Groundwater (Piezometric) Level• Soil & Aquifer Characteristics (Hydraulic Conductivity)• Proposed Excavation Method and Excavation Support• Proposed Schedule• Proximity to Existing Structures, Potable and/or Irrigation

Wells, Potential Sources of Recharge• Nature of any On/Off-site Contamination

Hydraulic Conductivity (K)

“K” can simply be defined as the ease at which water moves through soil.

More specifically defined by D’Arcy’s Law

Q=KA(h/L) Q = Quantity of Water Flow K = Permeability of Soil A = Cross-sectional Area h = Friction Loss in Distance L

Estimating PermeabilityVisual Classification (USCS)Soil Classification Hydraulic Conductivity(USCS) gpd/ft2 μ/secClay (CL) .02-.0002 .1-.0001Silt (ML) 1-2 .5-1Clayey Sand (SC) 2-20 1-10Silty Sand (SM) 20-100 10-50Well Graded Sand ( ) 20-2000 10-1000Uniform Sand (SP) 100-4000 50-2000Well Graded Gravel (GW) 1000-6000 500-3000Uniform Gravel (GP) 4000-20000 2000-10000Open Work Gravel 20000+ 10000+

J. Patrick Powers


Dominant Considerations• Location and Geologic Environment• Size and Depth of Excavation• Groundwater (Piezometric) Level• Soil & Aquifer Characteristics (Hydraulic Conductivity)• Proposed Excavation Method and Excavation Support• Proposed Schedule• Avoiding Undesirable Side Effects

– Proximity to Existing Structures, Potable and/or Irrigation Wells– Nature of any On/Off-site Contamination


Dominant Considerations• Location and Geologic Environment• Size and Depth of Excavation• Groundwater (Piezometric) Level• Soil & Aquifer Characteristics (Hydraulic Conductivity)• Proposed Excavation Method and Excavation Support• Proposed Schedule• Avoiding Undesirable Side Effects

– Proximity to Existing Structures, Potable and/or Irrigation Wells, and potential sources of recharge

– Nature of any On/Off-site Contamination

Subsurface Investigations

Typical Bore Log for Pump House, Fulton, Arkansas

Dewatering Methods

• Open Pumping• Pre-Drainage

– Wellpoints– Deepwells– Eductors

• Methods of Cutoff– Soil Bentonite– Interlocking Steel Sheet Pile– Concrete Caisson

Open Pumping

Favorable Conditions:• Dense, Well Graded Soils, Some Cementation/Cohesiveness• Firm Clays, Few Sand/Silt Lenses Unconnected Hydraulically• Hard Fissured Rock• Low Dewatering Head• Remote Source of Recharge• Open Cut, Relatively Flat Slopes, Minimal Depth Below GW

Table• Steel Interlocking Sheet Pile, Concrete Caisson

Dewatering Methods• Open Pumping• Pre-Drainage


• Methods of Cutoff– Soil Bentonite– Interlocking Steel Sheet

Pile– Concrete Caisson

Vacuum Wellpoints

Key System Components:• Vacuum Pump• Suction Header• Wellpoint• Swingjoint• Discharge Pipe

Traditional Rotary Lode Vacuum Wellpoint Pump 8”, Diesel Driven

Accessories: wellpoint, swingjoint, header pipe

Vacuum Wellpoints

Vacuum WellpointsFavorable Conditions:• Wide Ranging Soil Types• Impervious Clay/Rock At or Near Subgrade• Highly Stratified Soil• Wide Ranging Permeability• Remote or Proximate Sources of Recharge• Excavations <= 20’; Greater than 20’ requires the use of multiple stages• Rapid Drawdown Required

Dewatering Methods




Deepwells

Key System Components:• Well Assembly

– Well Screen\Casing– Filter Media

• Pump Assembly– Submersible Pump\Motor– Discharge Column Pipe

• Pump Control Panel• Electrical Distribution• Discharge Pipe

Deepwells

12” SDR 26 Well Screen

24” Sch 40 Stainless Steel Well Screen/Casing

Deepwells

20 HP Submersible Pump and Motor

Deepwells

DeepwellsFavorable Conditions:• Sands and Gravels Extending

Well Below Subgrade• Uniform Soil• Moderate to High

Permeability• Open Cut or Vertical/Shored,

Excavations of Any Depth• Long Draw Down Times

Acceptable

Dewatering Methods




Eductor SystemKey System Components:• Well Assembly

– Well Screen/Casing– Filter Media

• Eductor Assembly• High Pressure

Recirculation Pump• Supply/Return Headers• Recirculation Tank• Discharge Pipe

Eductor System

Eductor Body

Eductor System

Eductor Wellhead and Headers

Eductor SystemFavorable Conditions:• Silty and Clayey Sand• Highly Stratified Soil• Impervious Clay/Rock At or

Near Subgrade• Low Permeability Soils• Excavation Depths Not

Limited• Rapid Draw Down Times

Required

Dewatering Methods




Cut-Off WallFavorable Conditions:• Impervious Clay/Rock At or

Near Subgrade• Proximate Sources of

Recharge• Close Proximity to Existing

Structures• Close Proximity to

Contamination Plume• Properly Designed Cut-off

Wall can Function as Ground Support

Materials Utilized…– Soil Bentonite– Cement/Bentonite– Concrete Caisson– Interlocking Steel Sheet Piling

Stop seepage into an excavation, where excavation encroaches upon or penetrates an impervious stratum

Cut-Off Wall

Soil Bentonite Mixing Station and Trenching Activities


• The Origins of Dewatering• Construction Dewatering

– What is it?– Why do it?


Case Studies• San Juan Chama Drinking Water Project (SJCDWP)

– Install (2) two 54” Pipelines under the Rio Grande River• Bayport Terminal Complex – Port of Houston

– Container Loading/Off Loading Facility– Cruise Ship Terminal

• Denver Justice Center, Down Town Denver• Environmental Retrofit Program – Luminant Generation• US 93 Wickenburg Bypass• Beaver Dam Road Reconstruction Project• Trinity Rural WSC Water Treatment Plant

Dimensions– Length 1100 ft– Width 110 ft– Depth 26 ft

Excavation Type: Open CutGeology: Typical River Deposits (Well Graded Sands, gravel, cobbles, boulders)Depth to Water: at surface


(Installing Dual 54” WL Beneath the Rio Grande River)

San Juan Chama Drinking Water Project

General Contractor: AUI, Inc.


System Description

Deep Wells: 12” (30” BH), Spaced Approximately 50 – 75 ft apart, extending 75 ft bgs

62 Deep Total

Powered by 20 hp, 600 GPM Each

Initial Flow Rate: Measured at approx 12,000 GPM (10 – 12 running at any one time

Results: Dropped Water 5 ft Below Pipe Subgrade


Portable Coffer Dam Construction


Completed Portable Coffer Dam Construction


Drilling Operation


Drilling Spoils


Setting of the 12” Well Materials


Gravel Packing the Well


Filter Media


Well Development

Pump Setting



Common Discharge Piping/Manifold


Lateral Seepage AlongCemented Cobble Layer

Pipe Installation – Successfully Dewatered Excavation

Pipe Laying Activities – Ideal Conditions



Finished Excavation

Well Removal/Abandonment



Breach of Portable cofferdam

Breach of Portable Coffer Dam


Bayport Terminal – Port of Houston

• Dimensions– Length 2100ft– Width 200ft– Depth 62ft (-) 56 msl

Excavation Type: Open CutGeology: Beaumont Formation (Clays, Sands, Silts)

Depth to Water: 13’ BGS (+) 3 msl


General Contractor: Zachry Construction Corporation

System Description Deep Wells: 8” (30”

BH), Spaced Approx. 75 ft apart, extending 80 ft bgs

Sand Drains: 2” (6” BH) – 2 between ea. pumping well

65 Deep Wells Total 130 Sand Drains Powered by 5 hp, 60

GPM EA Initial Flow Rate:

Estimated at approx 3600 GPM (10 – 12 running at any one time

Results: Dropped Water 45 ft from its original level



Deepwell and Sand Drain Detail


Drilling of Sand Drains – Mud Rotary Method


Drilling of Deepwells – Bucket Auger Method


Night Time Drilling and Well Placement


Gravel Packing the Deepwell


Pump Assembly, Pre-Wiring


Pumping Setting


Pump Setting Discharge Installation


Completed Well Heads (rigid/flexible)


Completed – Dewatering System


Excavation Beneath Deck, Between Drilled Piers


Discharge

Design Considerations:Dimensions

– Length 250 ft– Width 250 ft– Depth 28 ft

Excavation Type: H-Pile and Wood Lagging

Geology: well graded sands, gravel, cobbles, boulders over lying a steeply sloped “Blue Shale”

Depth to Water: 20 ft bgs

General Contractor: Hensel Phelps Construction Company

Case Study: Denver Justice Center, Down Town Denver, Colorado

General Contractor: Hensel Phelps Construction Company


General Contractor: Hensel Phelps Construction


• Deep Wells: 12” dia. (30” BH), spaced approximately 75 ft apart, extending 60 ft bgs

• 10 Deep Wells Total• Powered by 10 hp, 250 GPM

Each• Initial Flow Rate: Estimated

at approx 2500 GPM• Results: Dropped water

several feet below subgrade in the deep alluvium.

System Description

Drilling Activities


Pump Setting and Wiring Activities


Well Head Completion and Discharge Assembly Operations


Completed Well Head and Discharge


Completed Well Heads and Discharge Manifold


Discharge Water & Baffled Settling Tank


Baffled Settling Tank & Final Discharge Point


Excavation During Demo Phase, Prior to Dewatering


Completed Excavation Following Successful Dewatering


Excavation Subgrade & Excavation Support Wall


Design Considerations:


Excavation Type: Combination Vertical Shoring, Open Cut

Geology: Man placed fill (fine sand, dense) to 18ft bgs. Intermediate concrete “mud” slab from previous construction 10 ft bgs


General Contractor: Fluor Enterprises, Inc

Case Study: Environmental Retrofit Program, Luminant Generation Facility, Rockdale, TX

General Contractor: Fluor Enterprise, Inc



• Vacuum Wellpoints• Approx. 1200 ft perimeter• Approx. 180 wellpoints

extending to 18 ft bgs (top of natural clay)

• 2 primary wellpoint pumps, electrically driven

• 2 stand by wellpoint pumps, diesel driven

• Anticipated initial flow of 1800 gpm; anticipated steady state flow of 900 gpm

System Description

Existing Conditions – Prior to Dewatering/Excavation.



Slab Removal– Prior to Dewatering/Excavation.

Specialty Drilling Rig – Designed/Built by TerraFirma and Duramast


Water Supply and Custom Designed and Built Self Jetting Head.


Wellpoint and Flexible Riser Pipe (2” HDPE).


Self Jetting and Sanding Activities


Pump Testing and Completed Wellpoint Installation


Completed Wellpoint and Header Pipe Installation


Completed Wellpoint, Header Pipe, and Wellpoint Pump Installation



Completed Excavation Following Successful Dewatering



Excavation Type: Sloped, Open Cut

Geology: Alluvium material, primarily unconsolidated silt, sand, and gravel: underlain by a confining layer of conglomerate sandstone.

Depth to Water: 5ft Below River Bed

General Contractor: Markham Contracting, Inc

Case Study: US 93 Wickenburg Bypass (Soil Cement Scour Protection)Wickenburg, AZ

General Contractor: Markham Contracting, Inc

Case Study: US 93 Wickenburg BypassWickenburg, AZ


• Deep Wells: 12” dia. (34” BH), spaced approximately 60 ft apart, extending 60 ft bgs

• 33 Deep Wells Total• Powered by 20 hp, 600 GPM


at approx 6000 GPM• Results: Dropped water

several feet below subgrade in the deep alluvium.

System Description


Hassayampa River Bed – Existing Bridge


Drilling Operations

42” x 10’ Surface Casing


Biopolymer Mixing Station – Borehole Stability and Fluid Loss


Drilling OperationsBiopolymer Slurry / Surface Casing


Well Setting Activities (glue and screw)


Borehole Development – Fresh Water Injection

Drilling Operations (thru biopolymer)


Gravel Packing Operation

Water Displacement During Gravel Placement


Well Development – Reverse Air


Pump Setting Activities – 20 hp Pumps, 800 GPM


Completed Well Head

Connection at HDPE Manifold


Discharge Manifold Assembly


Completed Installation – East Abutment


Discharge – East Abutment (est. 6500 gpm)


The New Local Watering Hole


The Other Local Watering Hole


Excavation Following Successful Dewatering


Dimensions– Length 1200 ft– Depth 12 ft

Excavation Type: Open Cut

Geology: Erratic silt, clay, sands and gravels.


General Contractor: WSU, Inc

Case Study: Beaver Dam Road ReconstructionVail, CO

General Contractor: WSU, Inc

Case Study: Beaver Dam Road ReconstructrionVail, CO

• Sump Wells: 12” dia. (30” BH), spaced approximately 200ft apart, extending 15-25 ft bgs

• 9 Sump Wells Total• Powered by 2 hp, 40 GPM


at approx 250 GPM


System Description


Beaver Dam Road – Prior to Excavation/Dewatering


Well Drilling at Base of Beaver Dam Road


Drilling Activities

Boulder Removal


Drilling Operations

Placement of Well Materials


Gravel Packing Activities


Well Development – Traditional Airlift


Drilling Activities – Boulder Removal


Well Placement Gravel Packing the Well


Excavation Following Successful Dewatering

Discharge Settlement Tank

Final Discharge Point – Adjacent Beaver Creek


Scenery – Main Lift, Vail Ski Resort


Dimensions– Length 165 ft– Width 120 ft– Depth 12 ft (16 ft @

Decant Pump Station)

Excavation Type: Open CutGeology: Upper clayey soils,

fine to silty sands, confining clay layer 20 ft bgs.


General Contractor: RM Dudley Construction

Case Study: Trinity Rural Water Supply Co. – Water Treatment Plant, Trinity, TX

• Vacuum Wellpoints

• 60 Wellpoints: 1 ½”, Spaced approximately 10 ft c. to c. extending 18-22 ft BGS

• Powered by Vacuum Wellpoint pump, electric primary, diesel backup

• Flow Rates: Measured at approx 150 GPM

• Results: Ongoing


System Description

Dewatering Layout – Plan View


Pre-Drilling Activities


Jetting Activities


Jetting and Gravel Packing Activities


Header Pipe Completion


Primary and Stand By Wellpoint Pumps - Discharge to The River


Discharge


Thank You

Reference Material:• Driscoll, Fletcher G. Groundwater and Wells, Second Edition. St. Paul: US

Filter/Johnson Screens, 1986

• Powers, J Patrick. Dewatering – Avoiding Its Unwanted Side Effects. New York: American Society of Civil Engineers, 1985

• Powers, J Patrick. Construction Dewatering: New Methods and Applications, Second Edition. New York: John Wiley & Sons, Inc., 1992

• Todd, David Keith. Groundwater Hydrology, Second Edition. New York: John Wiley & Sons, Inc., 1980

Construction Dewatering Means and Methods Presentation

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