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iIMIN, <br />•R ENGINEERING <br />4.4 LIQUEFACTION POTENTIAL <br />Soil liquefaction results from loss of strength during cyclic loading, such as imposed by earthquakes. Soils <br />most susceptible to liquefaction are clean, loose, saturated, uniformly graded sand below the <br />groundwater table. Empirical evidence indicates that silts and low plasticity clays (fine-grained soils) are <br />also potentially liquefiable, though this phenomenon is commonly referred to as cyclic softening. When <br />seismic ground shaking occurs, the soil is subjected to cyclic shear stresses that can cause excess <br />hydrostatic pressures to develop. If excess hydrostatic pressures exceed the effective confining stress <br />from the overlying soil, the soil may undergo deformation. If the soil consolidates or vents to the surface <br />during and following liquefaction, ground settlement and surface deformation may occur. <br />The subject site is underlain by medium dense to dense siltysand (Vachon Till). Based on these conditions, <br />in our opinion, the liquefaction potential of the site is relatively low and design considerations related to <br />soil liquefaction are not necessary for this project. <br />4.5 BUILDING FOUNDATIONS <br />Based on the subsurface conditions encountered at the site and our understanding of the planned <br />development, it is our opinion that shallow conventional isolated or continuous spread footings may be <br />used throughout the site provided they are founded on the undisturbed native soil or on properly <br />compacted structural fill placed directly over these soils. The following comments and recommendations <br />are presented for purposes of footing design and construction. <br />Footing Depths and Widths <br />For frost and erosion protection, exterior footings should be embedded at least 18 inches below adjacent <br />outside grade, whereas interior footings need extend only 12 inches below the surrounding slab surface <br />level. To minimize post -construction settlements, continuous (wall) and isolated (column) footings <br />should be at least 18 and 24 inches wide, respectively. <br />Bearing Pressures <br />We recommend that all footings bear on the undisturbed Vachon Till deposits or on properly compacted <br />structural fill placed directly over these soils. Footings that bear on properly prepared native or structural <br />fill subgrades can be designed for the following maximum allowable soil bearing pressures for static <br />loadings: <br />MP ENGINEERING, PLLC MPGEOTECH.COM <br />