Agenda - Council - 02/10/2015 - Laserfiche WebLink

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3. EXISTING CONDITIONS 3.1 Existing Pavement and Soil Conditions In May of 2014, Northern Technologies, Inc. (NTI) was employed to complete a Geotechnical Evaluation Report for this proposed project. This included completing four (4) soil borings along Garnet Street and 168th Avenue, which included two (2) borings along Garnet Street, and two (2) borings along 168th Avenue. The locations of these borings are shown in the Boring Location Diagram in Appendix C of NTI's Geotechnical Evaluation Report, which is attached in Appendix D. Information obtained from the soil borings was needed to determine existing bituminous pavement and aggregate base thicknesses, subsurface soil conditions, and potential difficulties anticipated during construction, as well as for providing recommendations for excavations, site preparation, engineered fill and compaction, depths of unsuitable soils to be removed, ground water management, and pavement design parameters. The borings terminated at nominal depths of 10 to 20 feet below the existing ground surface. Groundwater was observed in soil borings SB -1 and SB -2 at depths ranging from 17 to 19 feet below existing grade, respectively, corresponding to elevations of 867.4 and 870.0 feet. Based on these recorded water level depths, groundwater is not anticipated to be a significant issue for any work completed with this proposed project, regardless of whether utilities work is included with the project or not. However, excavations extending into sand layers over clay or silt -based soils may encounter perched groundwater which can be effectively controlled by excavating sump pits and removing water from the trenches with pumps. This report therefore assumes that dewatering will not be an issue during construction, and that sump pumps will be sufficient for any necessary dewatering. The soil borings generally indicate that existing bituminous pavement thicknesses along both streets range from 11/2 to 2 inches, that the existing aggregate base thicknesses range from 2 to 3 inches, and that the existing subgrade soils below the pavement sections generally consist of sand (SP), silty sand (SM), clayey sand (SC), and sandy clay (CL). It was also observed that the relative density of the granular fill throughout the project area was generally very loose to medium dense, and that the clay -based fill generally had a medium consistency. Several non -typical conditions were also observed. Fill consisting of sandy clay with trace organics was encountered in soil boring SB -1 ranging from 0 to 2 feet below the pavement section. The silty sand fill was also wet from 2 to 4 feet below the ground surface in boring SB - 2. The underlying native clay below the silty sand fill was generally soft, and soft to medium high plasticity clay (CH) layers were encountered below the previously placed fill in soil boring SB -2 from 11.5 feet to 17 feet below existing grade. The consistency of this material was soft. NTI's report states that the stable non-organic fill and native alluvial soils are generally suitable for supporting utilities construction. However, NTI recommends removing any organic soils and/or unstable clays if encountered below the inverts of any utilities that may be installed with the project. NTI also recommends that the Geotechnical Engineer of Record (NTI) or their designated representative observe all project excavations to determine that any unsuitable soils have been properly removed and that proper bearing support is provided by the exposed soils. Feasibility Report Garnet Street and l681" Avenue Reconstruction City of Ramsey Project No. 13-10 Page 5