1018 14TH ST 2023-02-09 - Laserfiche WebLink

SHANNON&WILSON,INC. In our opinion,the trenching could be accomplished with conventional excavation equipment. If sloping trench side walls are not feasible,trench boxes could potentially be used if the deadman anchor is located above the groundwater table. Trench boxes are designed to provide passive protection for workers in the trench, but the trench boxes provide poor contact with the trench sidewalls; therefore, movement of the ground adjacent to the trench is likely. Deadman trench backfill should be densely compacted. Where soft or unsuitable cohesive soils are encountered at the base of the deadman anchors,the soils could be improved by pushing 6-inch-minus quarry spalls with a backhoe or trackhoe bucket into the underlying soft soils until a firm subgrade is established. In our experience, 2 to 3 feet of quarry spalls are typically sufficient to improve the subgrade in the soft, cohesive soils. Where unsuitable cohesionless soils are encountered and the groundwater level is at least 3 feet below the excavation bottom, the soils could be improved using a vibratory plate compactor. 5.5 Backfill Material and Compaction We understand that contaminated soil from behind the bulkhead at Segment A will be excavated and removed from the site. Excavations should be backfilled with structural fill meeting the WSDOT Standard Specification for Select Borrow (Section 9-03.14[2]) or City of Everett (City) equivalent. If compaction is strictly monitored and the work is performed during dry weather months (July through September) Common Borrow (Section 9-03.14[3]) or City equivalent could be used. Backfill should be placed in horizontal lifts and compacted in accordance with the WSDOT Standard Specifications, Method C of Section 2-03.3(14)C. As discussed in Section 3.2, the groundwater likely fluctuates with the level of the tide. We anticipate that the excavations on site may extend below the groundwater level. To backfill portions of the excavation that are below water, we recommend using a material meeting either the WSDOT Standard Specification for Ballast(Section 9-03.9[1])or a Gravel Backfill for Walls (Section 9-03.12[2]). To prevent segregation of the gravel backfill, it should not be allowed to fall through the water as it is placed. Instead, the backfill should be released from an excavator bucket or clamshell at the bottom of the excavation. For the drainage material directly behind the walls, we recommend using a material that meets WSDOT Standard Specification for Gravel Backfill for Drains (Section 9-03.12[4]) or City equivalent. 21-1-21761-003-R 1 f.docx/wp/c1p 21-1-21761-003 20