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• Gcnyea Homes �� <br /> Hanson Group Project: 4.292 <br /> September 23, 2014 <br /> Page 2 <br /> OBSERVATION AND COMMENTS <br /> 1. Nick Hanson, PE of The Hanson Group perform d a site visit on September 18, 2014 to <br /> verify existing boulder geometry and construction. Tested soils information by Haugo <br /> Geotechnical Services provided on September 2, 2014 was provided for use in the <br /> design of the retaining wall. The Hanson Grou has reviewed the obtained and <br /> provided information and the following is note : <br /> a. The boulders used in the field are fields one and were approximately 24 to 32 <br /> inches wide with an average of 20 inch s in depth. The batter of the walls varied <br /> from 9 inches to 12 inches. The above i formation was also confirmed by <br /> Haugo. Haugo reportedly observed bur al depths of approximately 6 to 8 inches <br /> of the bottom boulders during the bear ng compaction testing. <br /> b. Haugo lists the soil design recommenda ions on Page 3 of their report and are <br /> based on the actual site obtained and I boratory tested soils information. These <br /> soil parameters were the basis for the s ructural stability design of the tiered <br /> retaining wall. <br /> c. It should be noted that draintile could n t be observed by The Hanson Group or <br /> Haugo due to the presence of filter fabr c directly behind the soils. It is reported <br /> by the Builder that each tiered wall had a layer of draintile and drainage medium <br /> directly behind the boulders that daylig ted and were routed into a nearby <br /> pond. Haugo's findings indicated that reas of drainage medium were found at <br /> locations but were inconsistent in locati n and geometry. <br /> 2. The following information is noted in regard to the above observed conditions: <br /> a. A boulder retaining wall of this nature r lies on the self-weight of the boulder <br /> material in conjunction with a slight bat er to resist lateral soil pressures through <br /> gravity. A small amount of passive resi ance is relied upon at the bottom buried <br /> portion at the base. <br /> b. The geotechnical soil properties for uni weight, angle of friction, and bearing <br /> capacity listed in Haugo Geotechnical S rvices report were used for the design of <br /> the wall (refer to this report for all soil i formation). The existing tiered wall was <br /> checked for stability including overturni g, sliding, and bearing capacity failures <br /> based on the lateral pressures of the pr vided soils information. <br /> c. Boulder retaining walls do have the pot ntial for movement from a number of <br /> items including, but not limited to, fros heave, groundwater fluctuation, <br /> improper drainage, creep from prolong d rainfalls, etc. Movement may occur in <br /> this wall as a result of any number of re sons. Boulder retaining walls do have <br /> the ability to accommodate some mino differential movement as a result of <br /> their flexible construction and practices The Hanson Group does not guarantee <br /> that some movement will not occur. <br />