1215 W MUKILTEO BLVD 2017-07-28 - Laserfiche WebLink

` April 29,2015 HWA Project No.2014-162-21 soils, where encountered. The amount of perched water will likely vary seasonally with higher water level readings during the wet winter months and lower water level readings during the dry summer months. DESIGN RECOMMENDATIONS General Our evaluation of the existing rockeries suggests that the rock comprising the terraced structures has deteriorated to the point that surface spalling has occurred. This deterioration appears to be a result of the poor quality of rock used during the initial construction of the rockeries. We anticipate that further deterioration and spalling of the individual rocks will result in a collapse of the rockery if preventative action is not taken. Our subsurface explorations indicate that the soils along the western edge of the subject property are glacially consolidated and possess high shear strength and cohesion. These soils are known to be capable of standing unsupported at near vertical configurations for long periods of time. The predominate slope failure mechanism in these glacially consolidated soils consists of near surface sloughing due to weathering of the exposed face. To protect these type of slopes from weathering, they are often faced with rockeries. Based on the results of our subsurface explorations and analyses we believe that the native soils are self-supporting in the their current configuration but will be subject to mechanical weathering and near surface sloughing if the exiting rockeries continue to deteriorate. We recommend that the existing lower rockery be demolished and replaced with a new rockery constructed to the specifications provided below. Our inspection of the existing 4 foot tall cast in place concrete retaining wall suggests that it is in good condition and shows no signs of distress or deformation. This structure should remain in place and be protected during reconstruction of the rockeries. If the recommendations provided below are followed, the proposed rockery reconstruction will result in a net increase in the stability of the exiting slope and will have no adverse effect on the stability of the adjacent properties. Seismic Considerations Earthquake loading for the Lorentz Rockery Replacement Project was developed in accordance with the 2012 International Building Code (IBC), which requires above-grade structures be designed for the inertial forces induced by a "Maximum Considered Earthquake" (MCE), which corresponds to an earthquake with a 2% probability of exceedance (PE) in 50 years (approximately 2,475 year return period). The relevant probabilistic spectral response parameters were developed using the United States Geological Survey's website. 2014-162 Letter Report 4 HWA GEOSCIENCES INC.