Geotech Rport
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Office Locations ALASKA Anchorage Juneau Fairbanks Ketchikan Kodiak Palmer GEOTECHNICAL REPORT CITY OF MONTROSE ARIZONA SOUTH HILLCREST EXTENSION Tempe Tucson E. NIAGARA TO E. OAK GROVE MONTROSE, COLORADO COLORADO Denver Montrose Grand Junction MONTANA Billings Bozeman Butte Great Falls Helena Miles City March 10, 2017 NORTH DAKOTA Dickinson OREGON Bend Portland WASHINGTON Redmond Seattle WYOMING Gillette Lander Laramie Sheridan Prepared for: Scott Murphy City of Montrose 433 South 1st Street Montrose, CO 81401 TABLE OF CONTENTS 1.0 Introduction ............................................................................................................. 1 2.0 Construction Plans .................................................................................................... 1 3.0 Site Conditions ......................................................................................................... 1 4.0 Geologic Setting ....................................................................................................... 3 5.0 Geologic Hazards ..................................................................................................... 3 5.1 Runoff & Erosion ................................................................................................... 3 5.2 Flooding ............................................................................................................... 3 5.3 Shallow Groundwater ............................................................................................ 4 5.4 Expansive and Compressible Soil ............................................................................ 5 6.0 Soil Characteristics ................................................................................................... 5 6.1 Field Evaluation .................................................................................................... 5 6.2 Laboratory testing ................................................................................................. 6 7.0 Pavement Design ..................................................................................................... 7 7.1 Traffic Analysis ..................................................................................................... 7 7.2 Equivalent Single Axle Loading (ESAL) Calculation ................................................... 8 7.3 Soil Sample Classification ....................................................................................... 8 7.4 Subgrade Support Characteristics ........................................................................... 8 7.5 Road Section Selection .........................................................................................10 8.0 Recommendations ...................................................................................................11 8.1 General Design Criteria .........................................................................................11 8.2 Site Preparation and Grading ................................................................................11 8.3 Concrete .............................................................................................................12 8.4 Pavement Section ................................................................................................13 8.5 Concrete Flatwork ................................................................................................13 8.6 Excavation and Shoring ........................................................................................13 9.0 Closing Considerations .............................................................................................15 9.1 Standard of Care and Interpretation of Subsurface Data ..........................................15 9.2 Use of This Report ...............................................................................................15 9.3 Retention of Samples ...........................................................................................16 10.0 Additional Services ..................................................................................................16 APPENDIX A - Project Maps ................................................................................................ A APPENDIX B – Test Pit Logs ................................................................................................ B APPENDIX C - Laboratory Results ........................................................................................ C City of Montrose South Hillcrest Extension geotech report.docx Project #7122.74681.01 Page i 1.0 INTRODUCTION DOWL conducted an evaluation of shallow subsurface and site conditions on February 1, 2017 along the general alignment of the southerly extension of Hillcrest Drive from E. Niagara Road to E. Oak Grove Road (hereafter referred to as the “Hillcrest Extension”) for the City of Montrose to provide an evaluation and design of a roadway. The evaluation consisted of a site reconnaissance, excavating five test pits, logging and testing of materials found, and analysis of available data. This report presents the findings of our evaluation and our geotechnical engineering recommendations for site preparation, management of drainage, and pavement design. 2.0 CONSTRUCTION PLANS The proposed Hillcrest Extension will be roughly 2,800 feet long (0.5 miles) and will be designed and constructed in accordance with the City’s Standards and Specifications (May 2012), the American Association of State Highway and Transportation Official’s Geometric Design of Highways and Streets (2011), and the Federal Highway Administration’s Manual on Uniform Traffic Control Devices (2012). For the “northern reach” portion of the alignment (e.g. north of the undeveloped agricultural fields where a road already exists), the City has requested four (4) alternatives to be presented in the 30% design phase of this project that include (1.) leave as-is; (2.) limited pedestrian improvements (i.e., 8-foot wide sidewalks); (3.) addition of bike lanes; and (4.) full corridor re-build (i.e., City’s 80-foot wide template). The “southern reach” will use an 80-foot template (back of walk to back of walk) containing a center turn lane, two through lanes, detached sidewalks, curb, gutter and bike lanes on each side of the road. The roadway will be designed with a design speed of 40 mph unless approved otherwise. 3.0 SITE CONDITIONS The Hillcrest Extension is located in the southeast portion of the City of Montrose, east of Highway 550 (South Townsend St), between E. Niagara Road and E. Oak Grove Road, as seen on the Vicinity Map (Map 1, Appendix A). The Site Plan (Map 2, Appendix A) is a Google Earth image with the approximate locations of the test pits indicated. The following photographs were taken of the site on January 25, 2017 to show the general site conditions. Photo 1. View south along the existing Hillcrest Drive which accesses the Sunrise Creek development. The white painted line at the bottom of the image is located at the stop sign for the intersection with E. Niagara Road. City of Montrose South Hillcrest Extension geotech report.docx Project #7122.74681.01 Page 1 of 16 Photo 2. View south along the east side of the bridge that crosses the Montrose Arroyo. Note the three drain pipes that allow water to drain under the primitive dirt road. A house is located to the left of the wall on the left side of the photograph. Photo 3. View south from the northern end of the irrigated field near the middle of the project area. Note the manhole for the stormwater drain system that extends south to E. Oak Grove Road. Note the linear depression in the field where snow is collecting, which is caused by settlement of the fill over the stormwater line. Photo 4. View north from the southern end of the general alignment, immediately north of E. Oak Grove Road. An irrigated field is to the left (west) and an undeveloped and unirrigated parcel of land is located to the right of the fence seen in the upper right portion of the photograph. City of Montrose South Hillcrest Extension geotech report.docx Project #7122.74681.01 Page 2 of 16 According to the USGS Montrose East topographic quadrangle, the site is at an average elevation of 5,860 feet. As seen in the above photographs, the terrain is generally flat-lying with a very gentle slope (<2%) down to the northwest. The Montrose Arroyo flows to the northwest across the northern portion of the project area, as seen on the Site Plan (Map 2). The southern two-thirds of the alignment contains irrigated agricultural fields and undeveloped land, while the northern one-third contains the existing Hillcrest Drive, residences, and a bridge that crosses the Montrose Arroyo. 4.0 GEOLOGIC SETTING According to the Geologic Map of the Montrose East Quadrangle (CGS Open-File Report 07-02 by Noe et al, 2007), the Hillcrest Extension is located on Quaternary alluvial mudflow (Qamf) deposits. These are fine-grained alluvial slopewash deposits that eroded off of the outcrops of Mancos Shale (“Adobes”) located at the valley margin to the east. These soils are extensive valley fill deposits found east of the Uncompahgre River throughout the Montrose area. They are typically composed of clay, silt and fine sand, with variable amounts of salts such as gypsum and calcite. When saturated, they are typically weak and compressible (hydro- compactive) and when dry or moist they can be moderately expansive. Underlying this valley fill is Mancos Shale at variable depths. The Mancos Shale