MANF - 1514480 - Laserfiche WebLink

Home Browse Search

FRO?l : TERRA FIRMA GEOTECHNICAL PHONE NO. : 541 367 8178 Jut. 50 1999 02: 19PM P03 James Grlffiths Excavating, Inc. Berger Residence July 30, 1999 Page 2 The slope was covered with plastic sheeting at the time of the site visit. Terra Firms did not directly observe the slope face. Observations at the top of the slope indicated no tension cracks or seffiement. Minor drying cracks were observed on the slope face outs]de the area covered with plastic sheeting. Conclusions and Recommendations Lon;I Term Slope Stability. The county's concerns regarding the placement of loose soil on a steep, vegetated slope are in general valid. The presence of the fill on the slope is undesirable with respect to the long-term stability of the stope The decomposing vegetation will, within e period of about one to five years, result in the development of a weak, inclined surface on which the overlying soil will be predisposed to slip. in order to fill this slope successfully, the ~ooss fill should be removed, the original slope face stripped of vegetation and topsoil, and the slope face benched to prepare it for permanent filling. The slope dimensions will require retention. However, it will not be feasible to simply increase the height of the existing retaining wall without also reinforcing it structurally. A new retaining system would probably be required at the toe of the slope, The height and position of the new wall would depend in part on the desired appearance of the finished grading. In general, a single wail about eight feet high, located immediately adjacent to the existing wall, or a series of two or three Iow wails spaced a suitable distance apart, would be appropriate. Wails more than four feet high and walls with sloping backfill surfaces must be engineered. The walls could be constructed of concrete, boulders, reinforced fill faced with architectural stone, or soldier piles and lagging. Cottage block with unreinforced fill will not be adequate for the purpose. Terra Firms is qualified and available to design boulder walls, reinforced fill walls, and pile walls, and to provide soil characteristics to a structural engineer to design reinforced concrete walls. Sh~)d; Term Slope Stability. The presence of the loose fill on the slope face does not appear to pose an immediate threat to the stability of the slope or the structure. However, the steepness of the slope and the presence of the fill pose a moderate risk that some type of failure might develop during periods of high moisture. The potential risk to the house is partly mitigated by the setback and depth of the structure's east footing, and by the inherent rigidity of most manufactured homes which enables them to withstand a greater amount of displacement from ground movement than a comparable, site~built home. Terra Firma's primary recommendation is for the homeowner to progress toward a permanent solution in the form of retaining walls and regraded slopes this year if funding and construction schedules allow. If the project, including design, permiffingl and construction, cannot be completed before the end of October of this year, the construction phase should be postponed until next summer. The stability of the slope over the coming winter can be substantially improved by reducing the opportunity for surface water to infiltrate the slope. The slope face should be covered with an intact plastic sheet from the end el~ October through next May The sheet should extend over the top of the existing retaining wall. The sheet must be securely anchored at all edges using tires, rocks, sandbags, or other suitably heavy weights. Weights should also be spaced about 10 to 15 feet apart across the sheet. Periodic inspection of the sheet should be made throughout the winter. Rips or holes should be promptly patched with