Construction Dewatering Means and Methods Presentation

August 11, 2017 | Author: tfearth | Category: Deep Foundation, Infrastructure, Geotechnical Engineering, Hydrology, Liquids
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Short Description

This presentation was given by David Giles at the University of Houston Cullen College of Engineering....

Description

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

Topics of Discussion • Construction Dewatering – What is it? – Why do it?

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

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

Topics of Discussion

Dewatering: Why do it? Short Term Objectives Long Term Objectives (Temporary Systems) (Permanent Systems) • Intercept Seepage • Reduce or eliminate lateral and/or uplift – Increase slope stability pressures – Prevent loss of material • Achieve waterproofing • Reduce lateral/uplift objectives pressure • Improve the excavation and the backfill characteristics of the excavation to allow construction to proceed in a safe and

Topics of Discussion • Construction Dewatering – What is it? – Why do it?

• The Consequences of Improper Dewatering

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

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

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

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

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

Improper Dewatering

Rio Grande River Crossing, Albuquerque, NM

42” Gas Pipeline, Blythe, CA

Improper Dewatering

Proper Dewatering

Topics of Discussion • The Origins of Dewatering • Construction Dewatering – What is it? – Why do it?

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

Design Considerations

Design Considerations

Design Considerations

Depth to Water & the Piezometer

Design Considerations

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) L

Q = Quantity of Water Flow K = Permeability of Soil A = Cross-sectional Area h = Friction Loss in Distance

Estimating Permeability Visual Classification (USCS)



J. Patrick Powers

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 • Avoiding Undesirable Side Effects • • • •

– Proximity to Existing Structures, Potable and/or Irrigation Wells

Design Considerations

Design Considerations

Design Considerations

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

Subsurface Investigations

Typical Bore Log for Pump House, Fulton, Arkansas

Topics of Discussion

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 •

• • •



Wellpoints Deepwells Eductors

Methods of Cutoff • •



Soil Bentonite Interlocking Steel Sheet Pile Concrete Caisson

Vacuum Wellpoints Key System Components: • • • • •

Vacuum Pump Suction Header Wellpoint Swingjoint Discharge Pipe

Accessories: wellpoint, swingjoint, header pipe

Traditional Rotary Lode Vacuum Wellpoint Pump 8”, Diesel Driven

Vacuum Wellpoints

Vacuum Wellpoints Favorable 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
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