DCPZP-2018-00233 - Laserfiche WebLink

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Subsurface Exploration and Foundation Evaluation Proposed Golden Oil Refueling Station Stoughton, Wisconsin PSI Project No. 0092822 Page 11 Utility Construction In general, the on-site soils can be used for support of utility lines. However, some undercutting of soft, loose, or otherwise unsuitable soils, in conjunction with the placement of crushed stone or other suitable granular backfill may be necessary to establish a stable working mat and/or bearing subgrade. Substantial difficulty with the stability of utility trenches and underground storage tank excavations should be expected due to the presence of granular soils across the site, especially in the presence of water. The use of shoring, bracing, or trench boxes will be required. Additionally, excavations encroaching upon or extending below the groundwater or perched zones can become substantially unstable when the confining effect of the overburden is removed. An adequate dewatering effort and bracing of sidewalls may be required. Utility construction should be performed in accordance with "The Standard Specifications for Sewer and Water Line Construction" for the State of Wisconsin. It is recommended that well graded granular soils such as those specified in Tables 37 and 39 of the Standard Specification for Sewer and Water Construction be utilized as backfill in utility trenches to reduce the potential for consolidation and settlement of the backfill. All fill soils must be properly placed and compacted under engineering controlled conditions to provide suitable support for overlaying structures and roadways. Silty and clayey soils, and wet granular materials are not recommended for use as backfill within utility trenches due to the substantial difficulty of obtaining proper compaction in confined areas. Substantial importing of suitable fill will likely be required. As with all excavation work, all open cut trenches must be properly shored and braced as required by applicable federal and state OSHA codes, and as necessary to protect life and property. CONSTRUCTION CONSIDERATIONS Groundwater Control Groundwater was encountered in most of the borings at depths of about 6 to 13 feet (El. 872.1 to El. 869.0) at the time of the exploration. On the basis of the observations, some difficulty with groundwater may be experienced during excavation work in at least some areas on this site. If excavations extend only a few inches or so below the groundwater, it is expected that filtered sump pumps or other conventional means may suffice to control the groundwater. However, for deeper excavations (such as utilities or underground storage tanks), or for substantial perched zones, prolonged dewatering with a series of sumps or well points and high capacity sump pumps, or other more comprehensive means may be necessary to facilitate construction. Since the foundation materials are subject to softening when exposed to free moisture, every effort should be made to keep excavations dry. Discharge water from roof drains should be directed away from the building, and the site grading direct runoff to catch basins, so that the potential for the softening of the foundation and pavement subgrade soils is reduced.