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�f Section 5.0 Engineering Analyses and Recommendations ■ Location of the Wet Pit-The temporary excavation must provide that the stability of the wet pit is maintained during construction. For example, excavation of the soil surrounding the northern half of the wet pit only may cause sliding and/or overturning instability due to lateral earth and hydrostatic pressures acting on the southern half. Since the base of the wet pit is about one #, foot higher than the base of the south wall, the excavation should be executed and maintained such that it does not undermine the wet pit. �. a Existing Pipes-The limits of the excavation should not interfere with the existing pipes,which have to remain in service during construction. Furthermore,the impact of installation-induced vibrations and excessive lateral deformations on the existing pipes should be considered in the design and the selection of the support system. ■ Existing Structures-The existing south pump station wall is known to be in poor condition and we do not know the condition of the wet pit walls. Removal of the soil and external hydrostatic forces within the temporary excavations will s.. remove lateral support while the internal hydrostatic pressure will remain. Considering the above,we recommend an internally braced shoring system, such as interlocking steel sheet piles. Detailed recommendations for such a system are presented in the following section. 5.4 Design Recommendations 5.4.1 Temporary Shoring Location and Depth The temporary shoring limits should encompass the wet pit entirely to avoid instability, or the wet pit should be braced during construction. To form a relatively groundwater cut-off,the shoring should extend to at least Elevation 46 to provide +� about 5 feet of embedment into the stiff clay layer below the bottom of the proposed excavation. .. To stop groundwater flow into the excavation from the sandy layer,the cutoff will need to extend along the south side of the pump station and also along the wet pit,if necessary. Different alternatives (sheet piles, ground freezing, grouting) to control the L* groundwater flow into the excavation at these locations were evaluated. In our opinion, grouting is the most appropriate alternative. Among the different grouting methods,jet grouting is likely to be the most efficient one. Jet grouting consists of erosion of soils by high water pressure and simultaneous ejection of cement grout to replace eroded soils. The jet grouting,however,will need to be carefully executed to avoid damaging the two 6-inch-diameter pipes. CDM Camp Dry&McKee Inc 5"3 Q:U5=9268-GEO-T4-Repartl mksidO Pump station,dcc A.r