6617 ASSOCIATED BLVD AMAZON Geotech Report 2022-10-25

• • r—\KLEINFELDER • 8 ght People.RightSoh,rbns. • ��.. • below existing grade or 12 inches below the finished subgrade elevation, whichever is deeper. The exposed subgrade be proof-rolled with heavy construction equipment (e.g. loader or smooth-drum roller) to disclose areas of soft and yielding material. Where soft and yielding material is observed, it should be overexcavated and replaced as • structural fill. After proof-rolling and/or prior to placement of fill, the subgrade should be • scarified to a depth of 6 to 8 inches, moisture conditioned, and compacted to at least 95 percent of the maximum dry unit weight. The proof-rolling should extend beyond the proposed improvements a horizontal distance of at least 2 feet. • • It is also common to encounter wet, unstable soils upon removal of site pavements or flatwork • as a result of subsurface moisture becoming trapped beneath relatively impervious asphalt • concrete or Portland Cement Concrete (PCC) surfaces, particularly adjacent to landscape •I areas. Pumping/wet subgrade conditions are likely to be encountered and the subgrade may • need to be stabilized. The contractor should be prepared to stabilize the subgrade prior to the • start of grading activities so that significant delays in construction do not occur. The contractor should also provide unit pricing for stabilizing subgrade at the time of the bid. Subgrade • stabilization options are provided below. • 4.5.3 Unstable Subgrade Conditions • • As discussed above, it is common to encounter wet, unstable soils upon removal of site • pavements or flatwork as a result of subsurface moisture becoming trapped beneath relatively ,• impervious asphalt concrete or PCC surfaces. Additionally, should grading be performed during or following periods of rainfall, the moisture content of the near-surface soils will also be • significantly above the optimum moisture content. Pumping subgrade conditions may be • encountered during site grading activities, and the subgrade may need to be stabilized. These • conditions could seriously impede grading by causing an unstable subgrade condition. Typical remedial measures include the following: •• • Drying: Drying unstable subgrade involves disking or ripping wet subgrade to a depth of • approximately 18 to 24 inches and allowing the exposed soil to dry. Multiple passes of the equipment (likely on a daily basis) will be needed because as the surface of the soil • dries, a crust forms that reduces further evaporation. Frequent disking will help prevent the formation of a crust and will promote drying. This process could take several days to t several weeks depending on the depth of ripping, the number of passes, and the • weather. • • 20203884.001A/SEA20R110164 Page 19 of 28 June 1, 2020 • ©2020 Kleinfelder •