2000 TOWER ST INDEX HALL 2023-12-29

A& •R ENGINEERING 4.2 EXCAVATION AND SLOPES In order to achieve construction subgrade elevations, we anticipate cuts of three to five feet deep may be needed. Our comments and recommendations concerning excavations are presented below. Soil Conditions Based on our explorations, we anticipate that site excavations will encounter medium dense to dense gravelly silty sand. In our opinion, these soils can be readily excavated with conventional earth -working equipment. Groundwater Conditions At the time of exploration (March 2021), groundwaterwas encountered at 4.2 feet below ground surface (bgs). Because our explorations were performed during an extended period generally wet weather, these observed groundwater conditions may closely represent the yearly high levels; somewhat lower levels probably occur during the summer and early fall months. Ideally, the excavations would be performed during the summer or early fall, when groundwater levels will tend to be at a yearly low. Dewaterine We anticipate that the excavation can be adequately dewatered by means of a series of internal ditches, sump holes, and pumps. In all cases, the specific design of a dewatering system should be completed by the contractor using groundwater level data appropriate for the time of earthwork. Temporary Slopes and Excavations Configuration and maintenance of safe working conditions, including temporary excavation stability, is the responsibility of the contractor. All applicable local, state, and federal safety codes should be followed. Temporary excavation should either be shored or sloped in accordance with Safety Standards for Construction Work, Part N, Washington Administrative Code WAC) 296-155-650 through 66411. The soil type classification and maximum inclination based on Part N of the Safety Standards for Construction Work, WAC 296-155-66401 and 66403 is provided below. Soil Unit WAC Soil Type Maximum Inclination Vashon Till Deposits Type C 1 K H:1 V Safety Considerations The stability of temporary excavation slopes is a function of many factors, including soil type, soil density, slope inclination, slope height, the presence of groundwater, and the duration of exposure. Generally, the likelihood of slope failure increases as the cut is deepened and as the duration of exposure increases. For this reason, we recommend the contractor maintain adequate slopes and/or setbacks. Temporary slope safety should remain the responsibility of the contractor, who is continually present at the site and MP ENGINEERING, PLLC MPGEOTECH.00M