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June 73,2023 <br />HWA Project No. 2022-188-2 1 <br />fine-grained alluvial soils. Additionally, existing plans call for the grade to be raised <br />approximately 2 feet in this area. <br />This area is not planned to support any structures and therefore over-excavation in this area is not <br />desirable from an economic standpoint however it would eliminate the potential development of <br />dips and sags in pavement placed to support composting activities and minimize future <br />maintenance costs. Alternatively, consideration could be given to smaller areas of over- <br />excavation where heavy equipment like the trommel screen or grinder will be parked for years at <br />a time, thereby minimizing the need for re-leveling of the equipment and pavement repair. <br />Localizedremoval of settlement prone soils may result in the need for wedge lifts of HMA to be <br />installed periodically between the fill supported equipment pads and surrounding pavement areas <br />that remain underlain by alluvial soils. <br />Partial over-excavation notwithstanding, we recommend that after subgrade preparation is <br />conducted as described in Section 4.ll.l below. The pavement section should consist of and be <br />constructed as described in Sections 4.I 1.2 through 4.11.6, below. <br />4.10 Urrr,Irtps <br />4.10.1 Bedding and Pipe Support <br />We currently do not have information regarding proposed utility corridors or proposed invert <br />elevations. However, due to the presence of soft, compressible subgrade soils we anticipate that <br />sewer systems that convey gravity flow may develop dips or bellies if supported directly on <br />compressible subgrade soils. To limit the possibility of developing dips and bellies, over- <br />excavation of compressible materials could be performed. If over-excavation is not desired, <br />consideration should be given to designing the pipelines with increased fall that will allow for <br />proper function of the pipes after as much as 6 inches of settlement occurs along the sewer line. <br />Flexible connections allowing for rotation and resistance to pulling apart should be constructed <br />at the points where the pipe transitions of areas with compressible soils to areas where <br />compressible soils have been over-excavated. Non-settlement sensitive utilities such as <br />electrical, communication, gas and water can be installed without over excavation provided the <br />type of pipe and pipe connections can accommodate future settlement. <br />Utility piping and conduits should be designed with sufficient pipe penetration into manholes <br />and pull boxes such that they do not pull out as the ground settles. The connections should be <br />constructed with access vaults to allow for easy access and replacement when needed. <br />If over-excavation of compressible materials is selected, it will be necessary to over-excavate the <br />unsuitable material down to coarse granular native subgrade and backfill with pipe bedding <br />material. In wet conditions, 1-inch minus gravel or permeable crushed rock or similar approved <br />granular fill may be used to backfill the over-excavatedportion of the trench. Alternatively, the <br />2022-188-21 KCTS - Final Geotechnical Report T4 HWA GEOSCIENCES INC