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HomeMy WebLinkAboutGeoTech Review - BLD Engineering / Geo-tech Reports - 5/29/1997 3607544240 023 PO4/04 APR 02 '97 11:23 Bradley-Noble Geotechnical Services A Division of The Bradley Group, Inc. 2401 Bristol Court 5W, Olympia, WA 98502 PO Box 12267, Olympia, WA 98508-2267 Phone 360-357-7883 FAX 360-754-4240 1 April 1997 Mr. Jim Hackman E 40 Merrimount Road Drive Union, Washington 98592 Subject: Reoccupation of your residence and restoration of electrical service at the above site after the recent mass wasting event, Dear Mr. Hackman: When we visited the above site on 22 March 1997 , we observed that a mass wasting event had occurred between your residence and State Highway 106 . This event was actually a mud flow caused by saturation of the loose soils that formed the slope between your residence and the highway. We also observed that a significant flow of ground water was still issuing from the face of the scarp below your deck. We understand that this flow has decreased in volume significantly since the mass wasting event. The nearly vertical scarp face to the north of the deck has a vertical relief of about 25 feet. Soils exposed in the face are dense and highly overconsolidated sands and gravels . We expect that the cause of the slide was the saturation of the soils forming the slope. At some point, the soils in the toe area failed, the soil mass was no longer confined, and the mass wasting event was really more of a mud flow carrying soil and vegetation across the highway and into Hood Canal . The failure continued upslope until competent soils were encountered. From our field observations , we expect that the upslope retreat of the mass wasting event has essentially stabilized for the short term. In the near future you can expect some additional loss of soil from the scarp and possibly loss of foundation support for the deck. 97030501 Page 1 of 3 s �. r 3607544240 023 P02/04 APR 02 '97 11:22 r 97030501 Page 2 of 3 We were on site with your structural engineer who will be preparing engineering drawings for the repair and long term stabilization of the scarp area. We discussed our opinions and recommendations for the type of walls that could be used to provide long-term soil support and ensure that the foundation of your residence is protected. This design work is proceeding in a timely manner, and we are in communication with the engineer. C ,s4cm— Before starting construction of the retaining wall, we CoNc]�� v✓� recommend that you remove those large trees that we identified as danger trees on the slope adjacent to the slide area. These trees are at risk of failure resulting from loss of soil support. They are tall enough to fall across the highway and pose liability risks to you . Also, if these trees fall on their own, wrenching of soil from the slope face could occur which might cause future instability and erosion problems . until the retaining wall is constructed and backfilled, we do not recommend full time occupancy of the structure. While we consider the risk of failure of the structure to be slight, there is always some risk. use of the structure during daylight should be allowed. Restoration of electrical service should be permitted to protect the structure and its contents from moisture damage . The structure should not be occupied during the night when the slope conditions cannot be easily monitored. Likewise, if we continue to have periods of heavy rains, monitoring of the slope should be conducted. If the deck between the structure and the slump scarp begins to experience significant deflection resulting from soil loss then reduced use of the structure would be prudent . It is our opinion that the structure is not now at risk of sliding or experiencing significant damage because of soil movements for a short period of time. Construction of the retaining structure does need to proceed as rapidly as__poss The dense and highly overconsolidated soils in the slump face can stand steeply unprotected for some period of time with only slow erosion occurring. The period that this face is allowed to remain exposed should be minimized to protect the upslope deck and the structure. 3607544240 023 P03/04 APR 02 '97 11:23 97030501 Page 3 of 3 fennot emphasize enough the need to proceed as y as possible with the repairs to the slope and l of the danger trees. We are available to work you, your design team, and your contractor on repairs . Tf you have any questions, please t us at our Olympia office. Cordially, - ---- -- -- _-- BRADLEY-NOBLE GEOTECHNICAL SERVICES David C. Strong Engineering Geologist cc: Mr. Larry Waters Mason County Emergency Services r Bradley-Noble Geotechnical Services A Division of The Bradley Group, Inc. 2401 Bristol Court SW, Olympia, WA 98502 PO Box 12267, Olympia,WA 98508-2267 Phone 360-357-7883 FAX 360-754-4240 29 May 1997 Mr. Harold Hahnenkratt, Associate Engineer MC Squared Incorporated 1235 East 4th Avenue Olympia, Washington 98506 Subject: Soil design values for the gabion retaining wall and buttress fill to be used for the repair and restoration of soil support at the Jim Heckman residence, E 40 Merrimount Road Drive, Union, Washington. Dear Mr. Hahnenkratt: Bradley-Noble has worked with you and the client on various means of restoring soil support to the head of the slump scarp at the Heckman property. From our discussions, the use of a gabion retaining wall and a high quality structural backfill has been determined to be the most cost-effective means of protecting the structure. Soil design values for the native soils are presented. These values are based on the soils exposed in the slide area. We consider these values to be conservative. If higher values are required for the design, then laboratory and field testing would be required. Allowable Soil Bearing Value = 3000 PSF Soil Unit Weight = 120 PCF Active Equivalent Fluid Pressure = 45 PCF Angle of Internal Friction = 35 degrees Coefficient of Friction = 0.45 To reduce the volume of imported structural backfill and allow placement with minimal compactive effort to achieve the required density, we have recommended that the gabion rock used for filling the baskets also be used for the structural backfill . Use of this material offers the project several advantages . It is 97030502 Page 1 of 2 97030502 Page 2 of 2 free draining, will compact easily, the rock will lock together and allow use of a steep backfill slope of at least 1 : 1 that will be stable. If rock meeting the WSDOT/APWA Standard Specification is used, the following backfill soil values may be used for design. Allowable Backfill Bearing Value = 3000 PSF Backfill Unit Weight = 115 PCF Equivalent Fluid Pressure = 30 PCF Angle of Internal Friction = 45 degrees Coefficient of Friction = 0 . 6 We have reviewed the material specified for BACKFILL MATERIAL in your specifications . We concur with the material specified for the project. The Soil Filter material to be placed between the quarry spalls and native soils was recommended by us to be a clean, coarse, crushed rock with no fines . A 5/8-inch to 1 1/2-inch minus crushed rock meeting this requirement is available from Miles Sand and Gravel in Shelton. An alternate material would be crushed rock meeting the BPA Switch Yard Surfacing specification. If we can be of further assistance to you in this project, please contact us at our Olympia office. Cordially, BRADLEY-NOBLE GEOTECHNICAL SERVICES David C. Str ng Engineering Geologist cc : Mr. Jim Heckman