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Bus <br /> The lateral pressure caused by a surcharge load, such as a traffic load, should be incorporated <br /> in the wall design. This lateral pressure may be computed by multiplying the coefficient of earth <br /> ' pressure by the surcharge pressure. <br /> The normal groundwater levels at this site are anticipated to be above the bottom of the proposed <br /> walls. Therefore, water pressure needs to be included in the wall designs. However, if possible <br /> and economically feasible, it is recommended that all the walls at this site be designed and <br /> constructed with an effective sub-drainage system in order to remove any transient water that <br /> ' may enter the soil. Additionally, it is recommended that the permanent walls be backfilled with <br /> well graded sand or gravel, in order to minimize any lateral pressures that may be exerted on <br /> ' the walls, and to help provide drainage. <br /> CORROSION CONSIDERATIONS <br /> Based on our past experience with soil conditions in this area, it is our judgment that the cohesive <br /> natural soils are slightly to moderately corrosive to buried steel. Therefore, all buried utilities of <br /> different metallic construction should be carefully isolated from each other using dielectric <br /> ' connections, or similar methods to minimize corrosion problems. All mechanical connections <br /> should be carefully coated with coal tar epoxy paint, or a similar coating suitable for underground <br /> ' applications. Further, any metal extending into the ground may also require cathodic protection. <br /> The corrosive nature of the soils does not, in our judgment, extend to concrete corrosion. <br /> Therefore, we recommend the use of conventional Type 1 Portland Cement. However, all steel <br /> in concrete structures extending below grade, should receive a maximum amount of concrete <br /> cover to avoid contact with corrosive soils. Further, project specifications should detail <br /> densification practices for the concrete to assure that it is a dense mass with a low permeability. <br /> Geotechnical Exploration for Sanitary Pipeline <br /> New Vulcan Waterline Pipeline, Decatur, Macon County, Illinois <br /> SKS Project No. 12-418885 Page 7 <br />