Agenda - Council - 01/26/2016 - Laserfiche WebLink

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3. EXISTING CONDITIONS 3.1 Existing Pavement and Soil Conditions In the fall of 2015, Northern Technologies, Inc. (NTI) was employed to complete a Geotechnical Evaluation Report for this proposed project. This included completing twenty-two (22) soil borings along Andrie Street and 164th Lane, which included fourteen (14) borings along Andrie Street, and eight (8) borings along 164th Lane. 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 a nominal depth of 10 feet below the existing ground surface. Groundwater was observed in soil borings SB -21 and SB -22 at depths of 7 and 8 feet below the ground surface, respectively. Groundwater was not observed in any other soil borings. Based on the recorded water level depths, groundwater is not anticipated to be a significant issue for any work completed with this proposed project. 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. NTI's report therefore assumes that dewatering will not be an issue during construction, and that sump pumps will be sufficient for dewatering, if necessary. The soil borings generally indicate that existing bituminous pavement thicknesses along both streets range from 11/2 to 4 inches, that existing aggregate base thicknesses range from 3 to 7 inches, and that the existing subgrade soils below the pavement section generally consists of sands (SP) and silty sands (SM), with one boring indicating the presence of clayey sands (SC). NTI recommends that the Geotechnical Engineer of Record or their designated representative observe all project excavations to determine that unsuitable materials have been properly removed and that adequate bearing support is provided by the exposed soils. NTI further recommends that compaction of the supporting soils be completed and tested to ensure it meets 95 percent standard Proctor dry density (ASTM D698) which requires observation and testing be performed both prior to and during backfilling operations. Lastly, NTI recommends that all import fill be approved by NTI or the City's representative prior to utilization. NTI also provides new bituminous pavement construction recommendations in their report. NTI recommends reconstructing the bituminous pavement section using 6" of class 5 aggregate base, 2" of bituminous base course, and 11/2" of bituminous wear course. This design meets MnDOT State Aid standards for a 9 -ton pavement section. NTI also recommends that stripping of the existing pavement and aggregate base course should occur immediately prior to subgrade preparation and base aggregate installation to minimize weather -induced instability due to prolonged exposure to the elements. Feasibility Report Andrie Street and 164th Lane Reconstruction City of Ramsey Project No. 16-00 Division C Page 4