11831 AIRPORT RD WHOLE SITE FILE Geotech Report 2022-10-25

If a permanent facing is constructed in front of the soldier piles that is designed to resist the lagging pressures described above and timber lagging is used for temporary support,then we recommend that the temporary timber lagging be sized using the procedures outlined in the Federal Highway Administration's Geotechnical Engineering Circular No. 4. The site soils are best described as competent soils. The recommended lagging thicknesses (rough-cut) are presented in Table 9 below as a function of soldier pile clear span and depth. TABLE 9.TEMPORARY TIMBER LAGGING THICKNESS(ROUGH-CUT)FOR SOLDIER PILE WALLS Recommended Lagging Thickness(rough-cut)for Clear Spans of: Height(feet) 5 feet 6 feet 7 feet 8 feet 9 feet 10 feet 0 to 25(competent soils) 2 inches 3 inches 3 inches 3 inches 4 inches 4 inches Drainage A suitable drainage system should be installed to prevent the buildup of hydrostatic groundwater pressures behind the soldier pile and lagging wall. It may be necessary to cut weep holes through the lagging in wet areas. Seepage flows at the base of the excavation should be contained and controlled. Drainage should be provided for permanent below grade walls as described in the"Wall 1 and 2 Cast-in-place Walls"section of this report. Construction Considerations Temporary casing or drilling fluid may be required to install the soldier piles where: • loose fill is present; is the native soils do not have adequate cementation or cohesion to prevent caving or raveling; and/or • the soldier pile extends below perched or static groundwater levels. We recommend that the concrete be placed into the drilled shafts using a tremie pipe or hose to deliver the concrete to the bottoms of the shafts. Cobbles and boulders are frequently encountered in glacially deposited soils and were encountered in some of the borings. The contractor should be prepared to remove cobbles and boulders during drilled shaft construction and should be prepared for difficult and/or very dense drilling conditions, consistent with conditions encountered in many of the borings. Signal Poles Design Considerations Based on the conditions encountered in the explorations, subsurface soils likely consist of a variable fill thickness overlying medium dense to very dense native sand and gravel. For the intersection at SR 527 and SR 524, we assume that the fill is medium dense and underlain by glacially consolidated deposits. For the intersection at SR 527 and 164th Street SE,we assume that the fill is medium dense and underlain by medium dense sand and gravel. In the nearby vicinity of the 128th Street SE improvement area, subsurface soils likely consist of a variable fill thickness overlying medium dense to dense native sand and gravel. Along Airport Road,subsurface soils likely consist of loose to medium dense granular fill underlain GEOENGINEERS April 14,2017 Page 18 File No.2095-032-00