FLH PDDM Chapter 9 - Eastern Federal Lands Highway Division

9.4.D. Earth Retaining Structures. (continued)Subsurface:Shear strength and consolidation properties of foundations materials.Shear strength and unit weight of backfill.Structural and Geotechnical:Design life (minimum service life) - normally 75 years.Safety factors for overturning, sliding, and stability of temporary slopes.Allowable foundation bearing pressure and minimum embedment depths.Maximum tolerable differential settlement.MSE internal design requirements.External loads.Drainage requirements.Backfill requirements.Facing requirements.In addition, the Notebook provides guidance on information and requirements which should be included insupplier prepared designs and plans.The bid advertisement period shall be extended from 30 to 45 days, or longer, if the Project Managerdetermines projects with alternative bids and Contractor designed walls require additional bid preparation time.One advantage of the development of the FLH Guidelines for the Design of Retaining Wall Systems is thereduction or elimination of the need to review and analyze complex proprietary wall systems under tightcontractual time constraints. The Project Manager should insure that special contract requirements areincluded in projects which prohibit submission of value engineering change proposals (VECPs) which proposeto change the basic wall system alternatives permitted. This restriction is possible since the use of the designguidelines insures that all suitable wall systems have been considered and are included in the contract.However, VECPs may be permitted on the components of the wall systems, such as facing and connectiondetails.The contract specifications shall identify the procedures for the FLH review of designs and working drawingssubmitted by the Contractor, similar to the bridge process for reviewing and approving falsework drawings.The information which will be required from the Contractor for review of wall submittals shall be specifiedin the contract, along with the amount of time required for FLH reviews. The contract should includeprovisions for additional time needed to permit the working drawings to be reviewed by the A&E firm whichdid the original design, if appropriate. The specifications shall define when the time count begins for both thereview of initial submissions, and for subsequent reviews when changes are required. The contract shallspecify the number of sets of drawings needed by FLH.The pay unit for contractor designed alternative walls shall be identified. The impacts of alternative wall typeson the units of measurement should be considered if a common measurement, such as wall face area is used.If alternative wall systems require different pay item measurements, alternative bid items shall be required.The contract shall include a method for adjustment of quantities for field changes if a lump sum payment isused.9 - 86