Groundwater Lowering in Construction

Prior to his death in 1996, Pat Cashman was the leading British exponent of groundwater control for his generation. For more than 40 years, during the growth of soil mechanics into the practice of geotechnical engineering, Pat was responsible—through the organisations he ran, and later as a consultant—for maintaining a practical and straightforward approach to the art of groundwater control. Dr. Martin Preene is a highly experienced geotechnical engineer specializing in groundwater engineering and hydrogeology. Martin has more than 25 years of experience working with contractors and consultants on the design and implementation of dewatering and groundwater control systems. He has worked on major engineering projects around the world, including power stations, road and railway tunnels, dry docks, and open-pit mines. He is widely published on dewatering and groundwater engineering, including papers and industry guidance documents. Dr. Preene is currently a principal at Golder Associates in the UK.

Groundwater lowering: A personal view, P.Cashman


Structure of the rest of the book






History of groundwater theory and practice


Earliest times to the sixteenth century


Renaissance period to the nineteenth century


Progress from a qualitative to a quantitative science


Later theoretical developments


Groundwater modeling


Early dewatering technology in Britain


Practical publications






Groundwater and permeability


Hydrology and hydrogeology


Permeability and groundwater flow


Aquifers, aquitards, and aquicludes


Flow to wells


Aquifers and geological structure


Aquifer boundaries


Using geological structure to advantage


Groundwater chemistry






Groundwater effects on the stability of excavations


Groundwater control—the objectives


Groundwater, effective stress, and instability


Large-scale instability caused by groundwater


Slope instability


Base instability


Localized groundwater problems


Excavations in rock


Surface water problems


Effect of climate and weather






Methods for control of surface water and groundwater


Control of surface water


Methods of groundwater control


Exclusion methods


Dewatering methods


Groundwater control for tunnels and shafts


Use of pumping and exclusion methods in combination






Site investigation for groundwater lowering


Purpose of site investigation


Planning of site investigations


Stages of site investigation


Determination of ground profile


Determination of groundwater conditions


Determination of permeability






Design of groundwater lowering systems


What is design?


Design approach


Development of a conceptual model


Expectations of accuracy


Selection of method and geometry


Estimation of steady-state discharge flow rate


Specification of well yield and spacing


Other considerations


Numerical modeling






Sump pumping


Applications of sump pumping


Pumping of surface water runoff


Pumping sumps


Drainage of side slopes of an excavation


Sump pumping of small excavations


Sump pumping problems


Disposal of water from sump pumping operations


Case history: Sump pumping of large excavation






Wellpoint systems


Which system: Wellpoints or deep wells?


What is a wellpoint system?


Wellpoint installation techniques


Spacing of wellpoints and drawdown times


Sealed vacuum wellpoint system


Wellpoint pumping equipment


Wellpoint installations for trench excavations


Wellpointing for wide excavations


Wellpointing for deeper excavations


Case history: Derwent outlet channel, Northumberland






Deep well systems


Deep well installations


Design of wells for groundwater lowering


Constructing deep wells


Drilling of well boreholes


Installation of well materials


Well development


Installation and operation of deep well pumps


Vacuum deep well installations


Shallow well installations


Case history: Tees barrage, Stockton-on-Tees






Other dewatering systems


Ejectors


Horizontal wellpoints


Horizontal wells


Pressure relief wells


Collector wells


Siphon drains


Electro-osmosis


Artificial recharge systems


Dewatering and groundwater control technologies used for the control or remediation of contaminated groundwater






Methods for the exclusion of groundwater


Principal methods for groundwater exclusion


Geometries of exclusion applications


Steel sheet piling


Vibrated beam walls


Slurry trench walls


Concrete diaphragm walls


Bored pile walls


Grout barriers


Mix-in-place barriers


Artificial ground freezing






Pumps for groundwater lowering duties


Wellpoint pumps


Jetting pumps


Sump pumps


Pumps for deep wells


Sizing of pumps and pipework






Permanent groundwater control systems


Types of permanent groundwater control systems


Objectives of permanent groundwater control systems


Design issues for permanent groundwater control systems


Practical issues for permanent groundwater control systems


Opportunities associated with permanent groundwater control systems


Case history: Govan underground tunnel, Glasgow






Environmental impacts from groundwater control


Why are impacts from groundwater control of concern?


Potential environmental impacts from groundwater control


Impacts from groundwater abstraction


Impacts from groundwater pathways


Impacts from groundwater barriers


Impacts from discharge flows to the groundwater environment


Impacts from discharge flows to the surface water environment


Assessment of potential environmental impacts






Monitoring and maintenance of groundwater lowering systems


Need for monitoring


Monitoring of water levels


Monitoring of discharge flow rate


Other parameters that may be monitored


Data-logging systems


Mechanical factors and automation


Backfilling and sealing of wells on completion


Encrustation, biofouling, and corrosion


Fault finding and problem solving






Safety, contracts, and environmental regulation


Health and safety


Contracts for groundwater control works






The future—a personal perspective by Toby Roberts


Applications and techniques


Communication and monitoring technology


Numerical modeling


Regulation


Where do we go from here?


Next generation of dewatering practitioners






Appendix 1: Estimation of permeability from laboratory data—Loudon method


Appendix 2: Execution and analysis of variable head permeability tests in boreholes


Appendix 3: Execution of well pumping tests


Appendix 4: Design examples


Appendix 5: Estimation of flow rate using V-notch weirs






List of notation


Glossary


List of conversion factors


References