Laserfiche WebLink
December 20,2021 <br /> Page 2 of 4 <br /> Limited Geotechnical Evaluation <br /> Soil & Groundwater Conditions <br /> As part of our evaluation,we excavated one hand boring to 6 feet below grade. The hand boring <br /> encountered approximately 6 inches of topsoil and vegetation underlain by approximately 4 feet <br /> of loose to medium dense, silty-fine to medium grained sand with gravel (Weathered Till). This <br /> layer was underlain by medium dense to dense, silty-fine to medium grained sand with gravel <br /> (Glacial Till). <br /> Groundwater was not encountered in the hand boring. <br /> Conclusions and Recommendation <br /> Based on our observations,it appears likely that the settlement is likely the result of insufficient <br /> removal of loose weathered soils prior to foundation placement. There may be areas of fill below <br /> some foundation elements,that could contribute to the settlement. <br /> The proposed mitigation utilizing helical anchors and driven piers with steel connections appears <br /> suitable to reduce settlement and support the affected portions of the residence. Based on our <br /> observations, we anticipate that helical anchors and piers may extend 7 to 15 feet below grade <br /> with an average depth of io feet. <br /> Helical Piers® <br /> Helical Piers®may be used to support the residence. The Helical Piers®could be installed using <br /> portable rotary tools,truck mounted rotary tools,backhoe mounted rotary tools,caisson drills,or <br /> skid-steer loaders. It is important that the torque output, rotational speed, down pressure <br /> capability, and angle control of the installation equipment is compatible with the required <br /> foundation system. The pile installation equipment should have adequate torque capacity to <br /> prevent refusal conditions at relatively shallower depths that are well above recommended <br /> bearing depths or layers. <br /> A Helical Pier®consists of an anchor(lead section)with 1, 2,3 or more helical flights on a shaft. <br /> The number and diameter of the helices on the anchor are dependent on the soil characteristics of <br /> the site and the design loads to be applied to the pier. Based on these parameters the anchor helix <br /> configuration is chosen to best fit the site conditions. <br /> As the anchor is advanced into the soil extension sections (shaft) are placed on the lead section. <br /> The shaft configuration is based on the design loads and anticipated installation torque. <br /> The static compression load capacity of a Helical Pier® is the sum of all individual helix <br /> capacities below liquefiable soils and in bearing layer. Individual helix static compression <br /> capacity is the result of the projected area of the helix,and its bearing pressure. <br /> It is recommended that the piers penetrate into relatively dense native soils a minimum of 3 feet, <br /> or until refusal whichever is shallower. The bearing layer will be at variable depths below the <br /> existing ground surface due to previously natural slope conditions (anticipated to be 7 to 15 feet). <br /> Increased capacity can be obtained with increased penetration, and additional helical flights on <br /> the lead section. <br /> Helical Pier® installation should be monitored to verify installation torque, and proper <br /> embedment into the presumed bearing layer. The Helical Pier®lengths may need to be modified <br /> during construction if it is determined that the depth to the bearing layer varies. Helical Pier® <br /> anchors are well suited to field adjustments as length can be varied by merely adding or deleting <br /> extension sections(shafts)during installation. <br /> www.cobaltgeo.com (206)331-io97 <br />