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22-100688-Geotechnical Report-5-26-2222-100688 RECEIVED aye x52022aazx E O .L H 2401 1 nth Ave E CONSULTANTS, INC. Seattle, Washington 98102 (425) 747-5618 November 11, 2021 JN 21445 Campus Green II HOA c/o Property Concepts 5622 California Avenue S.W. Seattle, Washington 98136 Attention: Alyssa McGlothlin via email. al�ssaCc r®yertVconce�atsinc.net Subject: Geotechnical Engineering Report Stabilization of Settling Foundations 527 South 323rd Street, Unit 18-D Campus Green II Condominiums Federal Way, Washington On November 2, 2021, the undersigned principal geotechnical engineer met with you and representatives of the Campus Green II HOA to observe the subject unit located in the northeastern portion of the complex. The owner of the unit was also present during this meeting, as well as Kris Smith of Sejant Construction and Dennis Titus of CG Engineering. The owner had reported indications of cracking in her ceiling and the southern wall of her master bedroom, and was concerned that foundation settlement was occurring. Cracks are evident in the east and south perimeter foundations of the unit, confirming that at least some excessive differential settlement has occurred. Near the southwest corner of the unit, where interior settlement was evident, the southern foundation wall appears to have deflected outward. At this location, the foundation wall retains approximately 4 feet of backfill that would have originally been placed to reach the level of the interior floor slab. The interior slab appears to have undergone varying amounts of settlement since the building was constructed in approximately 1979, indicating that the fill was not well compacted when it was placed. We understand that surface drainage issues, including clogged gutters, have occasionally resulted in water being discharged near the perimeter foundations of the building. The condition of the downspout pipes carrying water away from the building is not currently known, but will be assessed in the near future. From geologic maps, and our previous work on other projects in the vicinity, we know that the site is underlain by dense, glacially -compressed soils. Conclusions and Recommendations The observed foundation settlement is the result of the footings originally having been constructed on poorly -compacted fill or loose, native soils. Over time, these loose soils have consolidated. This process can be sped up by water infiltrating into the loose soils, which can be the result of groundwater or improperly -functioning drainage elements. GEOTECH CONSULTANTS, INC. Campus Green 11 HOA November 11, 2021 A 21445 Page 2 As we discussed at the time of our site meeting, the most important immediate activity is to complete a camera inspection of the various drain lines around this portion of the building. This includes the buried downspout pipes as well as the pipes that connect the surface catch basin located alongside the concrete sidewalk to the east of this unit. Any clogs should be flushed out, and leaking pipes should be entirely replaced with new smooth wall pipe, preferably PVC. Clean - outs should be provided in any new pipes to aid with flushing of clogs. The settled portions of the foundation should be underpinned using 2-inch-diameter pipe piles driven to refusal in dense soil alongside the foundation wall. The piles would then be structurally tied to the foundation to prevent further settlement. These piles are driven using portable jackhammers, allowing the piles to be installed close to the footing, even under a roof overhang. The spacing between the piles will be determined by the project engineer, based on the estimated design loading on the footing. The piles should extend at least one pile beyond the visible cracks in the east and south foundations. The outward deflection of the tall portion of the south foundation wall is likely due to the fact that the wall would not have been designed to retain the approximately 4 feet of backfill at this location. This is not uncommon in older structures, where tall, lightly -reinforced foundation walls were backfilled with more than one to 2 feet of soil. The outward deflection can also be related to excessive settlement of the footing, which appears to have been placed on loose soils. This wall movement is causing deflection and cracking in the interior wall of the master bedroom that is supported on this foundation wall. In addition to underpinning this portion of the foundation with pipe piles, we recommend that helical anchors be installed through holes cored in the wall to provide lateral support for the backfill loads. Recommendations for helical anchors Pipe Piles Due to the site access limitations, the pipe piles will need to be installed using hand -carried equipment. A 2-inch-diameter pipe pile driven with a minimum 90-pound jackhammer or a 140- pound Rhino hammer to a final penetration rate of 1-inch or less for one minute of continuous driving may be assigned an allowable compressive load of 3 tons. Extra -strong steel pipe should be used. The site soils are not highly organic, and are not located near saltwater. As a result, they do not have an elevated corrosion potential. Considering this, it is our opinion that standard "black" pipe can be used, and corrosion protection, such as galvanizing, is not necessary for the pipe piles. Subsequent pipe sections should be connected together using threaded or slip couplers, or by welding. If slip couplers are used, they must fit snugly into the ends of the pipes. This can require that shims or beads of welding flux be applied to the couplers. Helical Anchors Helical anchors consist of single or multiple helixes that are rotated into the ground on the end of round or square metal shafts. These anchors can be used to support both compression and tension loads, but their lateral capacity is negligible due to the relatively small diameter of the metal shafts. The design capacity of single helix anchors is the allowable soil bearing capacity on the helix area. Multiple -helix anchors are typically assumed to have a design capacity equal to the sum of the allowable bearing capacity on each helix, if they are separated more than three helix diameters. Buckling of the shaft may limit the design load, and we recommend that the shaft be analyzed for buckling assuming no lateral soil support, as the installation of the anchor will disturb the soil in the vicinity of the shaft. GEOTECH CONSULTANTS, INC. Campus Green 11 HOA November 11, 2021 A 21445 Page 3 The minimum diameter of a single helix anchor is 8 inches. The ultimate capacity of the anchor in tension or compression can be estimated roughly by multiplying the installation torque by 10. We recommend that the helix be installed at least 5 feet into the dense native soil. A typical anchor capacity for an anchor with an 8-inch helix on the lead section is 8 kips. The anchors should be installed by a specialty contractor familiar with design and installation of chance systems. The contractor can assist with refining the anchor design and details and estimating, capacities for different soil and anchor conditions. The anchors should be installed to a sufficient torque to empirically equal 200 percent of the allowable design anchor capacity. Please contact us if you have any questions regarding this letter, or if we can be of further assistance. Em Respectfully submitted, GEOTECH CONSULTANTS, INC. Marc R. McGinnis, P.E. Principal 111 /gym 1 GEOTECH CONSULTANTS, INC.