3400 RIVERFRONT BLVD Geotech Report 2022-10-25

• • • • • significant repair costs. When the subgrade is wet, site preparation may need to be • accomplished using track-mounted equipment loading into trucks supported on granular haul roads. • • The base rock thickness for pavement and building slab areas is intended to support post- • construction design loads and will not support construction traffic or pavement construction . when the subgrade soil is wet. If construction is planned for periods when the subgrade soil is wet, an increased thickness of base rock will be required. • • Haul roads and working blankets will be required to support construction equipment when the • subgrade is wet of optimum. Based on our experience, at least 12 inches of granular material is required for light staging and at least 18 inches of granular material for haul roads subject to • repeated equipment traffic. The required thickness of working blankets and haul road areas • depends on the contractor's sequencing of a project and the type and frequency of construction • equipment. We recommend that imported granular material for haul roads and working blankets consist of durable crushed rock that is well graded and has less than 8 percent by dry weight • passing the U.S. Standard No. 200 Sieve. Where silt is exposed at the ground surface, a geotextile should be placed on the subgrade before placing the granular material. The granular • material should be placed in a single lift and the surface compacted until well keyed. • As an alternative to placing 12 to 18 inches of granular material, the subgrade can be stabilized • using cement amendment. This recommendation is based on an assumed minimum unconfined • compressive strength of 100 psi and a treatment depth of 12 inches for staging areas and • 16 inches for haul roads. Cement amendment is further addressed in the "Structural Fill" section • of this report. • 6.5 EXCAVATIONS • 6.5.1 General • Excavations will be required for the installation of new footings, utilities, and other earthwork. . Conventional earthmoving equipment in proper working condition should be capable of making the necessary excavations. It is possible that buried construction debris, wood debris, logs, or prior subsurface structures may be encountered by deep excavations, which could result in • difficult digging conditions, trenches being wider than anticipated, and increased amounts of • backfill. • 6.5.2 Utility Trench Excavation • Trench cuts should stand near vertical to a depth of approximately 4 feet in the silt and sand fill • units provided groundwater seepage is not observed in the sidewalls. If seepage is encountered • that undermines the stability of the trench, the sidewalls should be flattened or shored. • Trench dewatering may be required to maintain dry working conditions if the invert elevations of • the proposed utilities are below the groundwater level. Pumping from sumps located within the • trench will likely be effective at removing water resulting from seepage. If groundwater is • present at the base of utility excavations, we recommend placing trench stabilization material at the base of the excavation consisting of 1 foot of well-graded gravel, crushed gravel, or crushed • rock with a minimum particle size of 4 inches and less than 5 percent by dry weight passing the S • G EODESIGN? 15 Polygon-128-01:091615