09-25-2013 Council Agenda - Laserfiche WebLink

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2.3 Geotechnical Summary Chosen Valley Testing was hired to prepare a Geotechnical Engineering Report to determine the existing road cross - section. This included pavement thickness, aggregate base thickness, and subgrade soil type. Twenty -seven soil borings were taken on area streets. Exhibit 7 provides a summary of the soil borings while Exhibit 8 provides a map of the soil boring locations. 2.31 Soil Conditions A variety of soil conditions were encountered through the various soil borings taken from the neighborhood streets. The following is a summary of the commonly found existing soil profiles as described in the Design Phase Geotechnical Report submitted by Chosen Valley Testing and dated October 12, 2012. 1) 13 of 27 borings o Bituminous pavement thicknesses vary from 2 to 8 inches. o No defined aggregate base currently in place. o Sub -grade materials are generally sandy with a little silt and gravel material. 2) 9 of 27 borings o Bituminous pavement thicknesses vary from 2 to 8 inches. o No defined aggregate base currently in place. o Sub -grade materials are generally sandy with intermixed silt and clay material. 3) 5 of 27 borings o Bituminous pavement thicknesses vary from 5 to 7 inches. o No defined aggregate base currently in place. o Sub -grade material is mostly silts and clays. Groundwater was not observed in any of the borings; however areas of moist soil were noted which can indicate areas susceptible to perched groundwater. Existing bituminous thicknesses vary from 2 to 8 inches, with an average thickness of 5 inches. The streets in the project area were originally constructed in the 1960's. The streets were subsequently overlaid and seal- coated as pavement conditions deteriorated. The placement of an overlay, as well as the seal- coating of the project streets, represented a short-term pavement surface correction. As was noted in the geotechnical report, a lack of a defined aggregate base was seen throughout the project area. It appears from the data provided in the geotechnical report that the sub -grade had not been modified to provide proper support for the original pavement section, contributing to the pavements deterioration over the years. Sub -grade soils mostly consisted of natural sands, with some being silty or clayey in nature. These materials are generally suitable for pavement support when accompanied with an engineered aggregate base. Areas of silts and clays were noted in the geotechnical report to be present in the northeastern area of the project, including portions of Burr Street, Highway Drive, Hendry Place, and Sunrise Drive. These materials are generally not suitable for pavement support and are more susceptible to frost. Infiltration rates should generally be moderate to high within the project area, given the poorly graded sands present in the majority of the project area. This infiltration capacity makes the neighborhood a good candidate for rainwater gardens. 7 17