DRAFT <br />designed to resist buoyancy, which is commonly accomplished by increasing the thickness <br />of the base slab and/or by extending the base slab beyond the sidewall of the structure. <br />The forces resisting uplift would include the weight of the structure and the buoyant <br />weight of the backfill material placed directly over the portion of the base slab that extends <br />beyond the wall of the structure. We recommend evaluating the uplift resistance of <br />structural fill using a buoyant unit weight of about 60 pcf. If additional uplift resistance is <br />required, the use of ground anchors installed through the base slabs could be considered. <br />5.6.2 Subdrainage <br />In areas where embedded structures will be designed as fully drained structures, <br />permanent subdrainage systems should be provided to reduce hydrostatic pressures and <br />the risk of groundwater entering through embedded walls and floor slabs. Typical <br />subdrainage recommendations for embedded structures are shown on Figure 5. The figure <br />shows perimeter subdrains to drain embedded walls and a layer of free-draining, clean, <br />drain rock beneath concrete floor slabs, which is drained by a system of underslab <br />drainpipes. All groundwater collected by the subdrainage system should be drained by <br />gravity or pumped from sumps. If the water is pumped, an emergency power supply <br />should be provided to prevent flooding in the event of a power loss. If the perimeter wall <br />drains and underslab drain system are routed to the same location, check values or other <br />measures should be utilized so that water collected in the wall drains is not allowed to <br />enter the drain-rock section beneath the floor slabs. <br />5.7 Seismic Considerations <br />5.7.7 Site-Response and Design-Acceleration Parameters <br />We understand seismic design for the project is being completed in accordance with the <br />2019 OSSC and ASCE 7-16. As part of our investigation, we completed a site-specific <br />seismic-hazard evaluation and site-response analysis for the project, the results of which <br />are provided in Appendix B. As discussed in Appendix B, the results of these analyses were <br />used to develop recommended ground motions for design purposes. <br />A site-specific site-esponse analysis was completed for the project using nonlinear total <br />stress analysis (TSA) procedures, which are described in more detail in Appendix B. The <br />site-specific response analysis consists of three primary components: 1) review of U.S. <br />Geological Survey (USGS) Probabilistic Seismic Hazard Analysis (PSHA) to support <br />selection of target response spectra at the base of the soil column; 2) selection and scaling <br />of ground-motion acceleration time histories to match the target response spectra over <br />the period range of interest; 3) one-dimensional site-response modeling to evaluate the <br />site-specific influence of subsurface conditions on the resulting ground-surface response <br />spectra; and 4) calculation of the surface-to-base response spectral ratios (i.e., ratios of the <br />surface response spectra values to the input motion response spectra values) quantifying <br />GRI #6497-A - 2.MO Indoor Football Practice Facility Page 19 <br />August 26, 2021 <br />