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

Underground Utilities Temporary Shoring The installation of the new underground utilities may require some type of shoring system to support the temporary excavations and maintain the integrity of the surrounding undisturbed soils,to reduce disruption of adjacent improvements and to protect the personnel working within the excavations. Because of the diversity of available shoring systems and construction techniques,the design of temporary shoring is most appropriately left up to the contractor proposing to complete the installation.The following paragraphs present recommendations for the type of shoring system and design parameters that we conclude are appropriate for the subsurface conditions at the project site. The soils within the project area can be retained using conventional trench shoring systems such as trench boxes. The design of temporary shoring should allow for lateral pressures exerted by the adjacent soil, surcharge loads from traffic,construction equipment and temporary stockpiles adjacent to the excavation, etc.Temporary shoring used to support trench excavations typically uses internal bracing such as hydraulic or fixed braces. Temporary trench shoring using internal bracing can be designed using active soil pressures. We recommend that temporary shoring be designed using a lateral pressure equal to an equivalent fluid density of 35 pcf, for conditions with horizontal backfill adjacent to the excavation. If the ground within 5 feet of the excavation rises at an inclination of 2H:1V or steeper, the shoring should be designed using an equivalent fluid density of 55 pcf. For adjacent slopes flatter than 2H:1V, soil pressures can be interpolated between this range of values.Other conditions should be evaluated on a case-by-case basis. These lateral soil pressures do not include traffic or construction surcharges, which should be added separately, if appropriate. Shoring should be designed for a traffic influence equal to a uniform lateral pressure of 100 psf acting over a depth of 10 feet from the ground surface. More conservative pressure values should be used if the designer deems them appropriate.These soil pressure recommendations are predicated upon the construction being essentially dewatered; therefore, hydrostatic pressures are not included. Dewatering Considerations Based on the available subsurface information, most of the proposed excavations will not likely extend below the regional groundwater table. However, perched groundwater will most likely be encountered throughout the site. In general, we anticipate that groundwater seepage in the proposed excavations can be controlled with in-trench pumping from sumps. Temporary Slopes We recommend that temporary unsupported cut slopes greater than 4 feet deep be inclined no steeper than 11/2H:1V. This applies to fully dewatered conditions. Flatter slopes may be necessary if seepage is present on the cut face. Temporary cut slopes should encroach no closer than 5 feet laterally from roadways, pavements, structures or other improvements. Some sloughing and raveling of the cut slopes should be expected.Temporary covering,such as heavy plastic sheeting,should be used to protect these slopes during periods of rainfall. Surface water runoff from above cut slopes must be prevented from flowing over the slope face by using curbs, berms, drainage ditches,swales or other appropriate methods. GEOENGINEERS April 14,2017 Page 24 File No.2095-032-00