6.2. SR 01-13-2003 - Laserfiche WebLink

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City of Elk River STS Project 98934 December 9, 2002 Page 2 Exploration Results Soil Conditions - Our borings penetrated from 2 inches to 4 inches of bituminous concrete pavements. At boring 2, near the southwest intersection of Quinn Avenue and 4th Street, the pavement was underlain by a 6-1/2 inch thick concrete slab. We subsequently delineated the extent of this slab, and found it to be 6 feet wide by 22 feet long, with the long axis being along 4th Street. At boring 6, we found 2 inches of bituminous pavement over 3 inches of aggregate base course, over 3 inches of old bituminous pavement. We did not find a well defined base course layer below the pavement. It appears that some or most of the pavements were placed directly over the native sand or over sand fill. Below the pavement, we penetrated possible fill to depths of 1.5 to 10 feet at borings 3, 4, 5, and 7. The fill consists of a mixture of fine to medium sand and silty sand with variable gravel content. The major native underlying soil type at this site is fine to medium sand. This extends to the 10 foot termination depths of the borings. Standard penetration N-values in the sand range from 4 to 21, representative of a loose to medium dense condition. Groundwater Conditions - We did not encounter free groundwater or saturated soils in our exploration. The groundwater level at this site is more than 10 feet below pavement surface, and should not affect the proposed construction. Analysis and Recommendations The utility line trenches should be bedded in and backfllted with on-site sand or silty sand. This should be placed in 8 to 10 inch loose lifts and compacted to at least 98% of the maximum Standard Proctor dry density, ASTM D-698, up to a level of 3 feet below pavement surface. The uppermost 3 feet of the trench backfill should be compacted to at least 100% of the Standard Proctor dry density. A compacted fine to medium sand or silty fine to medium sand would have an estimated stabilometer R-value of 45. We recommend that this value be used for the pavement thickness design. Construction Considerations - We do not anticipate unusual soil or groundwater conditions for this project. The soil is basically a fine to medium sand with silt and gravel traces. General Qualifications - This report has been prepared to aid in the design of the road reconstruction projects in Elk River. The scope is limited to the specific road projects and locations described herein, and our description of the project represents our understanding of the significant aspects relevant to soil s and foundations. In the event that there are changes in the design or locations of the roadways, the opinions and recommendations contained in this report shall not be considered valid unless STS reviews these changes and modifies or verifies the recommendations of this report in writing. Standard of Care The recommendations and opinions contained in this report are based on our professional judgment. The soil testing and geotechnical engineering services performed for this project have been conducted in a manner consistent with that level of skill and care ordinarily exercised by other members of the profession currently practicing in this area under similar budgetary and time constraints. No other warranty, express or implied, is made.