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HomeMy WebLinkAboutRe: Engineering field report Jesse Struve From: Jesse Struve Sent: Friday, March 08, 2013 8:48 AM To: Melanie Curtis Subject: 20130308 4731 North Shore Drive Melanie, The only comment I have regarding this is the applicant needs to submit an engineering review to determine the stability of the slope. Since the house encroaches on the bluff setback, the engineering review will need to address if the slope is stable and can handle the additional loadings resulting from the house and deck. It will need to be signed off by an registered, professional engineer. Jesse Struve, PE Director of Public Works/City Engineer City of Orono (952) 249-4661 - Direct (952) 249-4616 - Fax www.ci.orono.mn.us 1 CARL ANDQRSON QNG NQQRNG 1625 SOUTH SECOND AVENUE - ANOKA, MINNESOTA 55303 OFFICE AND CELL PHONE: 612 518 5317 ENGINEERING FIELD REPORT Client: Rodney Colson Site: 4731 North Shore Drive Colson Custom Homes Orono, MN 18001 Highway 7 Ste 1, Minnetonka, MN Date of Report: March 21, 2013 Site Visit: March 16, 2013 Background: You are planning to build a single family home at 4731 North Shore Drive in Orono, MN. It is my understanding that bluff setback variances have or will be granted by the city of Orono and that Orono city officials have requested an engineering review of the stability of the slope given the additional loadings from the house and deck. You provided a survey prepared by Lot Surveys Company showing the location of the planned house on the lot, plus the topography of the lot as expressed by contour lines and the location of the bluff line. An excerpt from their survey is reproduced here at a scale of 1 inch equals 40 feet. The locations of four soil borings augured in May of 2007 have been added to the survey, figure 1. m �1• 6 4 Unimproved ,5treet 4$ ..e ��$ ,. r 921 S 36'00'00'W 150.00 _�,--Q�•9aI rao ' u Ck rf .✓' 2 2 L arri Y n ., Ir I : r —J, b �1 TN2v 't Tl E 1! av I ' w i 3 0 10 20 30 40 504W Fe Feet Figure 1 —Topographic survey of 4731 North Shore Drive Geotechnical Observations: The soil borings were made by me in 2007 to examine soil conditions along the alignment of what was then a proposed tram to serve both properties — 4731 and 4725. The soil borings were located from the base of a cribbed earthen platform, and down the slope along the property line. Logs of the soil borings are given below. Test Elev. 963, Test Elev. 955, Test Elev. 945, Test Elev. 935, hole 1 3' toward hole 2 13' toward hole 3 26' toward hole 4 39' toward lake* lake* lake* lake* Black Black 0' to BlackBlack 0' to 2' clay 0' to 2' clay topsoil 1.5clay topsoil 0' to 1' clay topsoil topsoil Tan lean 2' to 3' 1'Tan lean 1.5' to Tan lean Tan lean 2' to 3' clay clay 3' clay to 3' clay * Distances were measured horizontally from the toe of the cribbed platform. The test holes consistently showed black clay topsoil, somewhat organic, underlain by tan colored lean clay. The tan lean clay is undisturbed glacial till and was found to be quite stiff. The map below shows the subject property outlined in light blue on an aerial photograph. Also superimposed on the map are the boundaries of soil types taken from the April 1974 edition of the Soil Survey of Hennepin County Minnesota. The soil type names have been updated to conform to more current editions of said soil survey. ,it y -14 IF Z ^: ,,f ` . . y Figure 2— Soil boundaries around 4731 North Shore Drive The subject property lies within a soil mapping unit named Lester- Kilkenny complex. These soils are competent for home construction and provide adequate soil bearing quality for single family structures such as the one you are considering for this site. These soil units were formed from glacial moraine consisting of glacial till which is an undifferentiated mix of sand, silt and clay. Locally, Lester— Kilkenny soils are lean clay and clay loam. The physical locations of the soil boundaries are somewhat approximate however because the soil unit is surrounded by similar units differing only by the degree of surface slope, they can be expected to be accurate for soil composition. An exception shown on the map is an area named Tadkee depressional complex which consists of muck over beach sand over till. This soil type is a minor part of the site and will not be an influence on house or deck foundations. Findings and Assessment: House Footings: The planned structure will be a full basement walkout. According to the survey, the lowest basement floor elevation is set for 967.6 feet. Assuming an additional 4.5 feet below floor for frost protection in the walkout area, footings will be set at elevation of about 963 feet. The survey also shows a proposed ground elevation at the rear of the house at 967.1 feet in an area where interpolation between contour lines indicates that the existing ground surface is presently at elevation 965 feet. A geotechnical inspection will be required of the footing trenches during excavation to locate competent bearing soil. Some trenches may not reach through the topsoil and depending upon the geotechnical inspection, some footings may require deepening or corrective filling. The lean clay can be expected to provide adequate soil bearing capacity for single family residential dwelling footings, designed for clay. Deck Footings: From conversations with you in the field, it is understood you have access to construction equipment that allows for installation of auger piles. It is recommended that this equipment be utilized to install deck pier foundations. This will minimize soil disturbance. The installation of the augured piers should be inspected by a geotechnical engineer during installation. Recommendations: All excavations will require silt fencing to prevent down slope erosion protection. The rear yard fill in the walkout area should be immediately protected after excavation, with commercial netting and straw. Your engineer and surveyor should design all runoff discharge from the new house, yards, walks and driveways. The use of rain gardens or small retention ponds may be adviseable, and can be readily designed for one or both sides of the proposed structure with minimal grading. With careful attention to slope protection during and after construction, it is my opinion that existing soils at this site have sufficient stability to allow construction of a home at the site indicated on the Lot Surveys Company certificate without the risk of loss of support due to slope collapse. I hereby certify that this report was prepared by me ,++ ►,, ++ +'Ri ' and that I am a duly Licensed Professional Engineer �'` r ' ''r�'� • w �.•.........0 under the laws of the State of Minnesota. -o _ AL Carl E. Anderson, P. E., P. G. ...... '••• .r'�t����. �'�� °°�••'°' � 0 'J . ©F M1Nl�'. Registration Number 10736 '�:i,Fiy;t++` '��,a,,,,++'