7423 LOWER RIDGE RD 2024-10-25 - Laserfiche WebLink

f • • February 1,2024 Page 2 of 3 Limited Geotechnical Evaluation Soil B..Groundwater Conditions As part of our evaluation,we excavated one hand boring to 6 feet below grade. The hand boring encountered approximately 6 inches of topsoil and vegetation underlain by loose to medium dense, silty-fine to medium..grained sand with gravel (Weathered Glacial Till) which continued to the termination,depth. The soils became medium dense about 5.5 feet below grade. Conclusions and Recommendation Based on our observations,it appears likely that the settlement is likely the result of consolidation of weathered glacial till soils below the affected areas. It appears that the site was inadequately stripped of loose soils during construction. Contributing factors could be downspout leakage into the near surface soils and inadequately designed foundations for the soil conditions. The proposed mitigation utilizing helical anchors with steel connections appears suitable to reduce settlement and support the affected portions of the residence. Based on our observations, we anticipate that helical anchors may extend 5 to io feet(or more)below grade with an average of 7.5 feet. Helical Piers® Helical Piers®may be used to support the foundation systems of the residence. The Helical Piers® could be installed using portable rotary tools,truck mounted rotary tools,backhoe mounted rotary tools,caisson drills,or skid-steer loaders. It is important that the torque output,rotational speed, down pressure capability, and angle control of the installation equipment is compatible with the required foundation system. The pile installation equipment should have adequate torque capacity to prevent refusal conditions at relatively shallower depths that are well above recommended bearing depths or layers. A Helical Pier®consists of an anchor(lead section)with 1, 2,3 or more helical flights on a shaft. The number and diameter of the helices on the anchor are dependent on the soil characteristics of the site and the design loads to be applied to the pier. Based on these parameters the anchor helix configuration is chosen to best fit the site conditions. As the anchor is advanced into the soil extension sections (shaft) are placed on the lead section. The shaft configuration is based on the design loads and anticipated installation torque. The static compression load capacity of a Helical Pier®is the sum of all individual helix capacities below liquefiable soils and in bearing layer. Individual helix static compression capacity is the result of the projected area of the helix,and its bearing pressure. It is recommended that the piers penetrate into relatively dense native soils a minimum of 5 feet, or until refusal whichever is shallower. The bearing layer will be at variable depths below the existing ground surface due to previously natural slope conditions (anticipated to be 5 to io feet (estimated only)). Increased capacity can be obtained with increased penetration,and additional helical flights on the lead section. Helical Pier® installation should be monitored to verify installation torque, and proper embedment into the presumed bearing layer. The Helical Pier®lengths may need to be modified during construction if it is determined that the depth to the bearing layer varies. Helical Pier® anchors are well suited to field adjustments as length can be varied by merely adding or deleting extension sections(shafts)during installation. Monitoring installation torque in the field is used to estimate the anchor compression capacity,and also as a quality control during anchor installation,provided that the anchor is bearing in dense or www.cobaltgeo.com (206)331-io97