The Mark at Eugene January 6, 2026 <br />Geotechnical Investigation and Seismic Hazard Study 7 Project No.: 2251077 <br />Eugene, Oregon Landmark Construction, LLC <br />Demolition of Existing Structures <br />Demolition of the existing structures is required as part of the planned construction. <br />The demolition should include the removal of any concrete slabs, foundations, or <br />below-grade walls or vaults. Based on anecdotal information, we understand the <br />existing structure adjacent to Hilyard Street has a below-grade basement. Therefore, <br />we anticipate deep excavations will be required to remove the foundations. Due to <br />the close proximity to the existing streets, the required demolition and excavations <br />are expected to require temporary shoring. It is the contractor’s responsibility to <br />provide the necessary cut slopes, benching, or shoring as required by Oregon OSHA <br />(OR-OSHA). The shoring system is typically selected and designed by the contractor. <br />Design earth pressures will depend on the type of shoring system that is selected. <br />As with any shoring system, care should be taken to ensure the excavation does not <br />impact adjacent structures or infrastructure. The appropriate earth pressure diagrams <br />for the shoring system will depend on the shoring method. We can provide earth <br />pressure diagrams for the selected method and additional consultation or review, if <br />necessary. <br />The presence and condition of any fill underlying the existing building should be <br />confirmed by a Foundation Engineering representative during construction. In <br />addition, the subgrade stabilization as well as documentation of removal of all <br />unsuitable soil and placement and compaction of approved fill will require inspection <br />and documentation throughout the work. <br />We understand that reuse of crushed concrete from the demolition work may be used <br />for structural fill as part of the backfill. All backfill should consist of well-graded, <br />relatively clean, crushed granular fill that is free of any organics, debris, or deleterious <br />materials. All granular fill should be placed and compacted in lifts as recommended <br />herein. <br />Existing On-Site Fill <br />The conditions encountered in BH-2, and the test pits suggest the previous buildings <br />in the landscaped area near the center of the site were demolished and the <br />excavations were backfilled with crushed gravel. The crushed gravel appeared to be <br />relatively dense and free of debris. This material is suitable for reuse, provided the <br />surface is compacted and capped with a minimum of 6 inches of Base Aggregate, as <br />defined in the Recommendations section of this report. <br />High Plasticity Clay <br />Laboratory testing and field observations indicate the presence of potentially <br />expansive, high plasticity clay across portions of the site. The expansive soil was <br />encountered at typical depths of ±7.5 to 25.0 feet. The clay is typically stiff with <br />medium potential for shrink/swell with moisture changes. It appears that the bulk of <br />the clay is not expected to experience significant seasonal moisture change due to <br />the depth of the stratum. Therefore, these soils are expected to experience very <br />minor swelling and shrinking due to seasonal changes in moisture content.