CECW-ED

Regulation No.1110-2-8152

Department of the ArmyU.S. Army Corps of Engineers

Washington, DC 20314-1000

ER 1110-2-8152

31 August 1994

Engineering and Design

PLANNING AND DESIGN OF TEMPORARY COFFERDAMS AND BRACED EXCAVATIONS

Distribution Restriction StatementApproved for public release; distribution is unlimited.

DEPARTMENT OF THE ARMY ER 1110-2-8152U.S. Army Corps of Engineers

CECW-ED Washington, DC 20314-1000

RegulationNo. 1110-2-8152 31 August 1994

Engineering and DesignPLANNING AND DESIGN OF TEMPORARY COFFERDAMS

AND BRACED EXCAVATIONS

1. Purpose

This regulation provides directives for procedures to befollowed while planning and designing temporaryconstruction for cofferdams and unwatered excavationson major civil works projects. The objective is to pro-vide criteria and guidance for providing safe workingconditions and life protection, optimizing cost versusrisk of damage, maintaining navigation, and securing theintegrity of permanent structures during the use of tem-porary unwatered cofferdams and excavations on majorcivil works projects.

2. Applicability

This regulation applies to all HQUSACE elements,major subordinate commands (MSC), districts, labora-tories, and field operating activities having civil worksresponsibilities.

3. References

a. Required references.

(1) Clean Water Act, Sections 402 and 404.

(2) TM 5-818-5, Dewatering and Groundwater Con-trol for Deep Excavations.

(3) ER 1110-2-101, Reporting of Evidence of Dis-tress of Civil Works Structures.

(4) ER 1110-2-1150, Engineering and Design forCivil Works Projects.

(5) EM 1110-2-1902, Stability of Earth and Rock-Fill Dams.

(6) EM 1110-2-2300, Earth and Rock-Fill Dams--General Design and Construction Considerations.

(7) EM 1110-2-2503, Design of Sheet Pile CellularStructures, Cofferdams and Retaining Structures.

(8) CWGS 02411, Metal Sheet Piling.

b. Related references.

(1) ER 5-7-1(FR), Project Management.

(2) ER 1105-2-100, Guidance for Conducting CivilWorks Planning Studies.

(3) ER 1110-2-1200, Plans and Specifications forCivil Works Projects.

(4) ER 1110-2-1461, Design of Navigation ChannelsUsing Ship-Simulation Techniques.

(5) ER 1130-2-306, Navigation Lights, Aids to Navi-gation, Charts, and Related Data, Policy, Practices andProcedures.

(6) EM 385-1-1, Safety and Health RequirementsManual.

(7) EM 1110-2-1605, Hydraulic Design of Naviga-tion Dams.

(8) EM 1110-2-1908, Instrumentation of Earth andRock-Fill Dams.

(9) EM 1110-2-2504, Design of Sheet Pile Walls.

(10) EM 1110-2-2906, Design of Pile Foundations.

(11) ETL 1110-2-338, Barge Impact Analysis.

ER 1110-2-815231 Aug 94

4. Scope

a. Construction cofferdams used in this context aretemporary structures, in which collapse or inundationcan result in a potential risk to life or that exceed10 percent of the project cost for the permanent struc-tures, used to facilitate construction of major civil worksprojects. Temporary construction cofferdams includesheet pile structures, cellular cofferdams, movable cof-ferdams, slurry walls, braced and unbraced excavations,tie-back walls, and embankments that can be unwateredfor construction of permanent hydraulic structures insidethe cofferdam area. Major civil works projects arethose that involve construction of, or alterations to,navigation, hydropower, or multipurpose dam projects orother similar hydraulic structures.

b. Recognizing that the cost of cofferdams and theassociated dewatering can be a large percentage of thefinal project’s cost, innovative techniques such as reus-able cofferdams, in the wet construction, and incorpo-ration of the cofferdam into the permanent constructionshould be investigated.

5. Policy

Construction cofferdams on major civil works projectsshall be planned, designed, reported, approved, speci-fied, and inspected by the government in the same man-ner as for permanent project features. Constructioncofferdams shall be designed or reviewed by engineersexperienced in this area. Use of experienced consultantsin this specialized field should be considered for impor-tant cofferdam structures. Performance specificationsfor contractor-furnished dewatering systems can bedeveloped based on the government’s design and asso-ciated criteria. For uniformity in bidding, contract plansand specifications will include the major features devel-oped from the approved criteria and design. Alternatecontractor-proposed designs will meet the approvedgovernment design criteria and will be reviewed andapproved by the government. Deviation from thispolicy will be made only in consultation with andapproval by CECW-E.

6. Planning

The results of the necessary investigations and studiesmade for the purpose of planning and designing con-struction cofferdams will be reported in the feasibility

report and appropriate design memoranda in accordancewith ER 1110-2-1150.

a. Feasibility phase. The feasibility report mustinclude the results of the studies of the type and geome-try of cofferdams, construction procedures, and diver-sion plans, including alternate schemes investigated.The general features of the construction cofferdam,including layout, materials construction sequence, num-ber of stages, degree of protection, cofferdam height riskanalysis, and economic studies, along with the recom-mended plan, must be reported. Coordination with navi-gation interests, local interests, and sponsoring agenciesmust be conducted and reported. Sufficient informationon the hydrologic, stream flow, scour, and sedimentationcharacteristics, and the topographic, geologic, and soilsfeatures, including the effect on dewatering, must bepresented to support the general features of thecofferdam.

b. Construction procedure and diversion plan -feasibility phase. The results of the following inves-tigations and studies, proposed design criteria, andpreliminary design of the construction cofferdams mustbe reported in the feasibility report on the constructionprocedure and diversion plan.

(1) Geotechnical. Sufficient foundation and embank-ment investigations will be conducted to adequatelydetermine the strengths, permeability, and other founda-tion and embankment characteristics affecting the integ-rity of the cofferdam. Weak or fault zones beneath thecofferdam that may cause sliding or overturning risksmust be identified. Excavations for permanent struc-tures must be planned to prevent the undermining ofcofferdam foundations, particularly in weak rock forma-tions or where weak seams underlying the cofferdamwill be exposed by the excavation. Sources of cell filland embankment material shall be identified and engi-neering properties evaluated for use in the cofferdamand embankments. Adequate space must be providedbetween the cofferdam and structural excavation toaccommodate relief wells, piezometers, or strengtheningdevices such as toe buttresses and foundation anchors ifthey are necessary. Also, sufficient area should beprovided to accommodate construction activities andaccess. Estimated amounts for cofferdam dewateringand care of water must be determined.

(2) Hydraulic/hydrology. Design studies and eco-nomic evaluations must be conducted for constructionstaging and diversion alternatives. Risk-based analysis

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procedures must be used to determine the most econom-ical diversion plan. This plan will minimize hazards tothe construction activity, downstream development, andupstream swellhead effects on flood protection, land use,or infrastructure. Effects on river environment andnavigation will be determined from studies to determineflow directions, velocity patterns, and tendencies forsedimentation and scour, including probabilistic analysisof discharges and river stage. Elevations for top ofprotection must be determined from risk-based analysisprocedures. Guidelines for risk-based analysis proce-dures can be obtained from CECW-EH. Directives willbe provided in a future engineer regulation. Hydraulicmodels can be used for the design to determine thesequence of individual cell construction, effects of scourand sedimentation during construction, and closuregeometry and sequencing. The hydraulic model canalso be used to assist in the design of scour protectionfor individual and partially completed cells and currentdeflector structures used during the installation of cells.Effects on navigation during intermediate cofferdamconstruction and closure can also be determined. Theresults of these studies and designs must be reported inthe feasibility report or design memorandum.

(3) Coordination with navigation or sponsoringagencies. For cofferdams used to construct navigationprojects, close coordination must be maintained withnavigation interests. The views of navigation interestsare a valuable asset while planning cofferdam stagingthat may affect navigation. Towboat pilots could givedesign input when shown the hydraulic navigationmodel with model towboats to demonstrate constructionstaging alternatives. Costs of interference factors to thenavigation industry due to temporary constructionshould be fully evaluated and reported in the feasibilityreport. Requirements for temporary construction oflocal protection projects should be coordinated with thesponsoring agency to ensure that items such as neces-sary real estate are obtained.

(4) Structures. During cofferdam design and eco-nomic studies, the following factors should be consid-ered: type and availability of cofferdam material (i.e.,sheet pile, walers, anchors, and tie-backs), erosion pro-tection, source of cell fill or embankment material,flooding provisions, rate of construction, constructiontechniques, and navigation requirements. Items to beconsidered are braced, anchored, or tied-back sheet pilewalls, slurry trench walls, soldier pile and lagging, andsingle wall cofferdam. If applicable and feasible, cof-ferdam planning and design must include provisions for

construction access, equipment storage, heavy cranesand machinery, and work areas around and on top of thecofferdam. The baseline design must be performed insufficient detail to develop quantities and cost estimatesrequired for feasibility reports.

(5) Hazardous, toxic, and radioactive waste(HTRW). During the reconnaissance phase, potentialHTRW in the construction area must be thoroughlyexplored. Mitigation measures and costs must bereported in the feasibility report.

(6) Section 402 and Section 404, Clean Water Act.Construction of cofferdams generally requires removalor placement of fill materials in the river. Necessary402 and 404 permits must be reported in the feasibilityreport. Necessary permits must be scheduled andobtained before construction.

7. Design

Design guidance for cellular cofferdams is contained inEM 1110-2-2503. The design of earth cofferdams willbe in accordance with the applicable provisions ofEM 1110-2-1902 and EM 1110-2-2300. Guidance forthe design of unwatering and groundwater control sys-tems for deep excavations is contained in TM 5-818-5.Limited guidance is available in official publications fordesign of braced excavations, soldier pile lagging, andconcrete slurring trench walls. Industry standards andexpert consultation should be used in these instances. Inaddition, the following items should be included:

a. Sheet piling tolerances.

(1) Interlocks. If the analysis indicates that the sheetpiling cofferdam cells have significant hoop tension, theinterlock tolerances may be critical to provide theneeded tensile strength. Since there is no AmericanSociety for Testing and Materials (ASTM) specificationfor tolerances on interlock dimensions, it may be neces-sary to specify the interlock tolerances in the contractdocuments. The sheet piling should be gauged to ensuredimensional requirements at the mill, and governmentinspectors should also gauge a representative number ofsheets at the jobsite.

(2) Camber and sweep. Tolerances for camber andsweep can affect the ability to construct sheet pile cells.These tolerances should be studied and the requirementsincluded in the contract documents.

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b. Cold formed sheet piling. Cold formed sheetpiling is not appropriate for use on cellular constructioncofferdams. Difficulties in maintaining in-plane plumbtolerances and the propensity to drive the sheets out ofthe interlocks, coupled with the greater tendency ofmigration of water and materials through the loose fit-ting interlocks, render the use of cold formed sheetpiling inappropriate for cofferdam applications.

c. Effective section modulus. In cases where thesheet piling is subjected to high bending stresses, theeffect of transverse stresses and the width-to-thicknessrelationship shall be evaluated to ensure the desiredcapacity of the section in bending.

8. Construction

Construction cofferdams must be constructed by thecontractor in accordance with the government-preparedplans and specifications. The contractor will, however,be afforded the opportunity to recommend changes bythe value engineering incentive provisions of the con-tract. For any deviations from the plans and specifica-tions, the value engineering proposal must be submittedfor approval of the district’s engineering division priorto acceptance of the proposal.

a. Plans and specifications. The project plans andspecifications must include the results of the design insufficient detail for the bidders to evaluate all construc-tion techniques, scour protection provisions, deflectorstructures, cofferdam rewatering, and instrumentationand surveillance requirements. The contract documentsmust fully and clearly cover surveillance requirements,instrumentation, and construction conditions requiringspecial attention to protect permanent works and founda-tions. Additional provisions such as interlock size toler-ances and camber and sweep tolerances are contained inCWGS 02411. Reference to design investigations suchas pile driving tests, pump tests, and design memoran-dum will be listed in the plans and specifications, andthese documents will be made available to the biddersprior to bidding. Environmental conditions, such asweather, river stage frequency, wind conditions, andtemperature, should be considered in the design andstated in the specifications under the conditions underwhich the contract is to be performed.

b. Care and diversion of water. The cofferdamand diversion are site-specific. Each project usually hasfeatures which make it difficult to set forth a specific

design that will be the most economical for a specificdewatering contractor. Thus, performance specificationsfor care and diversion of water are preferred. However,a government design for the unwatering system must beperformed to determine the performance requirements tobe included in the contract. If necessary, a plan forflooding, rewatering, and subsequent unwatering of thecofferdam will be developed in the plans andspecifications.

c. Quality construction. The safety and integrity ofthe cofferdam depends, to a large extent, on quality con-struction fostered by active cooperation and communica-tion between the design team, the quality assuranceengineers, and the contractor’s supervisory and qualitycontrol staff. To ensure conformity with the designintent and that safe, quality construction practices areachieved, the engineers of record from the design teamwill review the contractor submittals and be involved inengineering during construction. The engineers ofrecord should conduct frequent field visits to monitorand discuss the construction with the quality assurancestaff. In accordance with the contractor’s quality con-trol plan, the engineers of record should be involved inthe preparatory and initial phase meetings. Engineeringinstructions to the field describing the design principles,design intent, assumptions, and construction proceduresrequired to achieve the design must be prepared andfurnished to the project office prior to start of con-struction. Partnering concepts are useful in fosteringcommunication and resolving disputes that disrupt thesuccessful quality construction of cofferdams. Membersof the partnering team should consist of engineering,construction, and contractor representatives.

d. Cofferdam instrumentation and surveillance.Requirements for contractor surveillance and operationof the cofferdam must be clearly stated in the contractdocuments. Movement monitoring procedures, alarmsystems, personnel escape facilities, flood warning andflooding criteria, foundation drainage provisions, scoursurveys, and other essential aspects of surveillance andoperation must be thoroughly stipulated and enforced.Tolerable redline criteria for such items as movementmonitoring, water levels, and uplift pressures will beincluded in the instructions to the field. An emergencyresponse team should be formed from the engineering,construction, and operations staff for decisionmakingactions in response to emergency situations. In addition,the contracting officer must maintain an effective, con-tinuous monitoring and evaluation program to ensuresafety and stability. A specific plan of action must be

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prepared should the cofferdam become endangered byovertopping or structural and foundation distress.

e. Report of distress. To maintain a file of lessonslearned, cofferdam failures that result in flooding, lossof life, unresolved project delays, or significant eco-nomic loss must be reported to CECW-E according toER 1110-2-101 with proposed or actual correctiveactions.

9. Deviations

In general, deviation from the policy for planning,designing, constructing, and operating construction

cofferdams will be approved only for local protectionworks, pumping plants, and relocation facilities.Authority may be granted for the design of a construc-tion cofferdam by the construction contractor wherethere is no potential for major damage or significantdelays in project benefits resulting from cofferdamfailure. This authority may also be granted for a majorproject only upon assurances that the construction sche-dule will provide ample design and review time toensure a competent, safe design. All requests forassigning cofferdam design responsibility to the con-struction contractor must be submitted in the feasibilityreport.

FOR THE COMMANDER:

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