DRAFT <br />completed at the adjacent Hatfield-Dowlin Complex, and we anticipate similar conditions <br />could be encountered at the site. Groundwater seepage, running-soil conditions, and <br />unstable excavation sidewalls or subgrades, if encountered during construction, may <br />require dewatering of the excavation and sidewall support. The impact of these conditions <br />can be reduced by completing excavations during the summer months, when groundwater <br />levels are lowest, and by limiting the depths of the excavations. <br />We anticipate groundwater inflow in shallow excavations, if encountered, can generally be <br />controlled by pumping from sumps established within the excavations. Although not <br />currently planned, deeper excavations will likely require dewatering using wells or well <br />points depending on the actual depth and groundwater levels at the time of construction. <br />If groundwater is encountered in excavations, we recommend overexcavating the base of <br />the excavations and installing a granular working blanket consisting of relatively clean, <br />free-draining material such as 2- to 4-inch, open-graded crushed rock to facilitate <br />groundwater management by pumping from sumps and provide a working surface for <br />construction activities. Depending on the conditions disclosed during excavation, use of a <br />geotextile fabric beneath the crushed rock may be appropriate. The need for and required <br />thickness of the granular working blanket will depend on the actual conditions exposed in <br />the excavations and the effectiveness of the contractor's dewatering efforts and must be <br />evaluated based on observations during construction. However, for preliminary planning <br />purposes, our experience indicates the required thickness of the granular working blanket <br />may be on the order of 12 inches. <br />5.3.3 Open-Cut Excavations <br />The inclination of temporary excavation slopes will depend in part on the composition and <br />relative consistency/density of the soils, groundwater conditions encountered at the time <br />of construction, and the contractor's ability to control these conditions. In this regard, we <br />anticipate temporary excavation slopes can be cut in the range of 1 H:1 V to 1.5H:1 V if <br />groundwater levels are maintained at least 2 feet below the bottom of the excavation. <br />Flatter slopes may be necessary if seepage conditions are encountered. Some minor <br />amounts of sloughing, slumping, or running of temporary slopes should be anticipated <br />shortly after excavation, particularly if groundwater seepage occurs. A blanket of relatively <br />clean, well-graded, crushed rock such as 2- to 4-inch-minus crushed rock placed against <br />the slopes may be required to control these conditions. The thickness of the granular <br />blanket should be evaluated based on actual conditions but would likely be in the range <br />of 12 inches to 24 inches. <br />In our opinion, the short-term stability of temporary slopes will be adequate if surcharge <br />loads due to construction traffic, vehicle parking, material laydown, etc., are maintained a <br />horizontal distance equal to the height of the slope away from the top of the open cut. <br />GRI #6497-A - 2.MO Indoor Football Practice Facility Page 11 <br />August 26, 2021 <br />