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23-105468-Geotechnical Investigation and Geologic Hazard Analysis-11-9-23
15365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 • (425) 449-4704 • FAX (425) 449-4711 Earth Solutions NW LLC Geotechnical Engineering, Construction Observation/Testing and Environmental Services October 24, 2023 Updated October 26, 2023 ES-9258 John Stevenson dba Off the Porch 7001 Seaview Avenue Northwest, Suite 160, PMB 43 Seattle, Washington 98117 Subject: Geotechnical Investigation and Geologic Hazard Analysis Proposed Slide Repair 3620 Southwest Dash Point Road Federal Way, Washington Greetings: As requested, Earth Solutions NW, LLC (ESNW) has prepared this geotechnical investigation and analysis of a recent landslide that occurred at the subject property. The subject site is located at 3620 Southwest Dash Point Road, approximately 525 feet northeast of the intersection between Southwest 309th Street and Southwest Dash Point Road, in Federal Way, Washington (see Plate 1 – Vicinity Map). The property consists of King County parcel number 661350-0030 and totals approximately 1.07 acres. The site is currently developed with a single-family residence and associated infrastructure improvements that are positioned within the southeastern property area. The remainder of the site is comprised of a hillslope feature which descends to the margins of Puget Sound. Approximately 105 feet of elevation change occurs across the entire property area. Landslide Activity A landslide occurred at the site in December 2022 and was initiated as the result of a water line break. The slide resulted in the creation of a large washout feature that carried soil, concrete, wood, and other debris downslope and to the base of the surrounding descending slope areas. An existing bulkhead (rockery) at the base of the descending slope areas (and at the margins of Puget Sound) was also displaced as a result of the slide debris. The attached Plate 2 (Boring Location Plan) illustrates the approximate path of the landslide and relative positioning of the existing residence located above (and immediately adjacent) to the area of landslide activity. We understand the project is pursuing remediation of the slide area in the direct vicinity of the existing residence. The proposed remediation measures include the construction of a soldier pile wall, long-term erosion control / slope stabilization measures, stability improvements for the existing residence, and reconstruction of yard and patio areas. John Stevenson dba Off the Porch ES-9258 October 24, 2023 Page 2 Updated October 26, 2023 Earth Solutions NW, LLC Subsurface Conditions An ESNW representative observed, sampled, and logged the advancement of two soil borings within accessible areas of the lot on August 28 and 29, 2023. The borings ranged in depths between about 61.5 to 91.5 feet below the ground surface (bgs) and were performed using a drill rig and operators retained by our firm. The approximate locations of the borings are illustrated on the attached Boring Location Plan (Plate 2). Please refer to the attached exploration logs for a more detailed description of subsurface conditions. Representative samples collected at the boring locations were analyzed in general accordance with the Unified Soil Classification System (USCS) and the United States Department of Agriculture methods and procedures. Neither topsoil nor fill was encountered at the boring locations during the August 2023 explorations. The following native soil conditions were generally encountered at each boring location: B-1: Soils to a depth of about 60 feet were primarily characterized as silty sand and poorly graded sand (USCS: SM and SP, respectively). It should be noted that local lenses of silt- dominated soils were generally encountered within the silty sand and poorly graded sand units. The upper approximately five feet of existing grades were generally encountered in very loose condition. Medium dense to dense soil conditions were encountered from depths of about 5 to 35 feet bgs and dense to very dense soil conditions were encountered from about 35 feet to 60.5 feet. At a depth of approximately 60.5 feet bgs, native soils were observed transitioning to very stiff to hard silt (USCS: ML). This condition generally continued to the terminus of this boring, which occurred at about 91.5 feet bgs. B-2: Native soils were primarily characterized as silty sand and poorly graded sand (USCS: SM and SP, respectively) to the terminus of the boring, which occurred at about 61.5 feet bgs. Medium dense soil conditions were generally encountered to a depth of about 30 feet bgs. Thereafter, dense to very dense soil conditions were encountered at the terminus of the boring. The in-situ moisture content of the native soils was generally characterized as moist. However, local areas of damp conditions (near the surface) or wet to saturated conditions (near areas of exposed groundwater) were also encountered. A review of a local geologic map resource suggests that the site area and adjacent slope are underlain primarily by advance outwash deposits (Qga). These soils are characterized as sand and pebble to cobble-sized gravels. In general, the soil texture of the native silty sand and sands appear like advance outwash sands (Qgas) which consist of fine to medium-grained sand with silt and gravel. The underlying silt appears to be representative of Lawton Clay deposits (Qgalc) which are characterized as massive silt, clayey silt, and silty clay. The referenced WSS resource suggests that most of the site is underlain by Alderwood and Kitsap soils while the southwest most site corner is underlain by Indianola loamy sand (Map Unit Symbols: AkF and InC). The Alderwood Kitsap association is found in moraine and till plains and is typically derived from basal till while the Indianola series is found in eskers, kames, and terrace landforms and is derived from sandy glacial outwash. Based on the encountered conditions, native soils appear to be representative of outwash soils overlying Lawton Clay like deposits. John Stevenson dba Off the Porch ES-9258 October 24, 2023 Page 3 Updated October 26, 2023 Earth Solutions NW, LLC Moderate to heavy perched groundwater seepage was exposed intermittently at depths between about 30 feet to 70 feet bgs during the August 2023 fieldwork. Groundwater elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. Groundwater seepage rates and elevation are generally higher during the winter, spring, and early summer months. Geologically Hazardous Areas Evaluation We understand that the Federal Way Municipal Code (FWMC) recognizes and defines areas susceptible to erosion, landslide, seismic activity, or other geologic events as geologically hazardous areas (GHA). Based on our review of the site soil and groundwater observations and readily available topographic information, the adjacent hillslope feature located within the northern site area generally meets the FWMC criteria to be considered a potential erosion and landslide hazard area. Our evaluation of each potential site GHA and applicable mitigation recommendations are provided in the following sections. Erosion Hazard Areas Chapter 19.05.070.1 of the FWMC defines an erosion hazard as areas that have a moderate to severe or severe to very severe rill and inter-rill potential due to natural processes. Soils associated with severe erosion potential are the Alderwood-Kitsap (AkF) series, which has been mapped within the confines of the subject site. On this basis, the project area may be considered an erosion hazard per the FWMC. Per Chapter 19.145.240, buffers are generally not required for erosion hazard areas. However, proposed development (or in this instance slide remediation efforts) in the area should not result in an increase of surface water discharge or sedimentation beyond the predevelopment conditions, decreased slope stability, or adversely impact other critical areas. In our opinion, the current proposed remediation plan will not result in increased runoff or discharge or adversely impact current slope stability characteristics or adjacent critical areas. Landslide Hazard Areas Chapter 19.05.070.2 of the FWMC defines landslide hazards based on soil and groundwater conditions, slope inclinations, previous and current stability characteristics, or a combination thereof. Based on our review, the northern site slope meets the FWMC criteria of a potential landslide hazard based on present gradients and soil and groundwater conditions. Per Chapter 19.145.230 a standard buffer of 50 feet is typically applied to the top, toe, and sides of the landslide hazard area. However, the buffer can be altered and potentially reduced based on the sensitivity of the landslide hazard area provided it does not create an increase in the potential slide hazard. Based on our evaluations, the proposed remediation plan incorporating soldier pile support to restore the landslide area and protect the existing residence will reestablish local slope stability conditions. Furthermore, the intended remediation work will improve erosion control and face stability of the downgradient portions of the slope through the placement of anchored wire mesh (Tecco Mat) and vegetation. On this basis, it is our opinion that no buffer be assumed for the remediation activities. If typical buffer restrictions were imposed, the slide area would essentially be left un-mitigated. John Stevenson dba Off the Porch ES-9258 October 24, 2023 Page 4 Updated October 26, 2023 Earth Solutions NW, LLC Discussion Based on our review and geotechnical investigation, the proposed remediation activities including soldier pile wall placement, anchored Tecco Mat placement, and slope revegetation will satisfy the intent, values, and standards applied by the FWMC for project areas containing GHAs. On this basis, it is our professional opinion that the proposed remediation and slope restoration plan is considered an acceptable approach for reestablishing and maintaining local stability conditions and erosion control measures within the subject slide area. Slide Evaluation To our understanding, the subject slide event was triggered because of a broken water line that discharged water along the slope surface. It should be noted that the slide was not the result of naturally occurring processes, and to our understanding, no indications of slope instability had been noted before the slide. This condition is generally corroborated through our review of local mapping resources, lidar data, and aerial photographs of the area. The induced movement resulted in the creation of a large washout feature and carried soil, deck and patio elements, and other debris down gradient and was ultimately deposited at the base of the slope. The slide also displaced an existing rockery that serves as a bulkhead at the shoreline. Based on our evaluations, the slide initiated within the medium dense silty sand to poorly graded sand unit. It is unclear if, or to what extent, the denser silty sand and sand and silt-dominated soils were mobilized during the event. However, surficial exposures of these units can be seen along the exposed slope face, particularly from the base of the slope. Since the event, it appears that no further mass soil movement has occurred. Localized riling is apparent along the slope face and is likely attributed to rainfall and the absence of vegetation along the slide scarp. Proposed Remediation Remediation activities will include the construction of a two-tier soldier pile wall, placement of a Tecco mesh and reinforced turf mat, and other localized stability improvements. A brief description of each proposed remediation is provided in the following: Solider Pile Wall: Two rows of soldier pile walls are proposed and will be constructed in a tiered condition. Retained heights of the wall system will generally be 15 feet or less. Geofoam backfill will be utilized behind the walls to restore grades in the area, where necessary. The soldier pile wall will intend to provide local stability to the lost yard space and adjacent residence. Tecco Mesh: A Tecco mesh system will be installed and anchored to the slope face at the base of the soldier pile wall and extend downslope to the 50-foot OHWM. Remediation beyond the placement of the Tecco mesh is not proposed in the area. Reinforced Turf Mat: Within the 50-foot OHWM, a reinforced turf mat is currently proposed. The mat intends to provide erosion protection measures for the slope face and would allow for the planting of native vegetation. John Stevenson dba Off the Porch ES-9258 October 24, 2023 Page 5 Updated October 26, 2023 Earth Solutions NW, LLC Slope Stability Modeling Slope stability was performed using GeoStudio 2023 Slope/W software to evaluate global stability characteristics of the subject hillside in the post-slide condition and demonstrate local stability characteristics of the direct area of proposed remediation (soldier pile wall). Soil strength parameters were chosen based on our experience with similar deposits and published data associated with both the referenced Tubbs document and the WSDOT Geotechnical manual. Soil (or “material”) unit geometry and location were modeled based on the encountered soil condition and field observations. Some geometry has been inferred. Each stability analysis and associated design parameters are provided in the following sections. Post-Slide Event The global stability of the entire slope feature is provided in the post-slide event analysis. The modeled section extends for the southern property line (abutting Southwest Dash Point Road) and extends through the slope and slide body to the beach. A seismic coefficient (Kh) of 0.21 was used in this model and equates to approximately one-third of the modified peak ground accelerations (PGAm) and was derived using the slope height scaling factor discussed in the referenced NCHRP report. This was adopted under the assumption that the slope could accommodate minor deformations while still maintaining global stability during a seismic event. As suggested by the models, a factor of safety (FOS) of 1.12 during a static condition and FOS of 0.80 during a seismic condition was generated by the model. Based on the modeled factor of safety, the existing slope is stable in the current condition and configuration, however, is generally considered to be below local FOS standards. The output suggests that the existing slope could experience deformation or soil movements during a seismic event given that the calculated FOS is below 1.0. Local Evaluation The local evaluation analysis provides local stability of the proposed soldier pile wall and the immediate surrounding area. The modeled section is the same as the post-slide event, however, the slip-surface entry and exit points have been adjusted to evaluate the direct area of the proposed remediation, rather than the entire hillslope. This was modeled as such given that the proposed remediation is intended to establish local stability for the residence and yard area, not the larger hillslope feature. A seismic coefficient (Kh) of 0.32 was used in this model and equates to approximately one-half of the modified peak ground accelerations (PGAm). The soldier pile wall was modeled with a shear force capacity of 100 kips, spaced eight-feet on center, and embedded approximately 15 feet. These conditions are generally representative of the soldier pile wall configuration that is depicted on the referenced topographic survey sheet. As suggested by the model, a FOS of 1.86 during a static condition and FOS of 1.12 during a seismic condition was generated by the model. These FOS values are generally consistent with local standards of practice. John Stevenson dba Off the Porch ES-9258 October 24, 2023 Page 6 Updated October 26, 2023 Earth Solutions NW, LLC Soldier Pile Wall Design Based on the findings of our investigation, soldier pile wall construction for purposes of stabilizing (and restoring) the scarp and related deep cavity produced by the landslide is considered a viable approach for the project. To minimize the overall exposed wall height, and to better contour to the surrounding grade, the wall structure will be constructed as a two-tier wall positioned approximately as shown on Plate 2 of this report. Plate 4, provided as an attachment to this report, specifies the recommended criteria for design of the soldier pile wall. As such, for purposes of structural design, please refer to the design values presented on Plate 4. As necessary during the soldier pile wall design, the geotechnical engineer should coordinate with the structural design team to ensure overall design objectives for restoration (and stabilization) of the slide scarp are satisfied. In any case, the geotechnical engineer should perform a final review of the structural design and wall alignments to confirm appropriate application of the recommended design values. It should be noted that subsequent to the soldier pile wall construction, areas of the slope immediately below the new wall structure will be stabilized with an anchored wire mesh (Tecco). In our experience, such stabilization methods are effective in securing the slope face while also allowing for the reestablishment of vegetation. Additional Remediation Additional items included with the overall scope of the project include underpinning the existing foundation nearest to the edge of the slide scarp. The intent of the underpinning will be to mitigate any potential foundation settlements related to the adjacent areas of displacement caused by the landslide. Based on recent discussion with the contractor and structural designer, an underpinning plan has been developed (and approved) and will be implemented in the near future. We understand project plans also include restoring the existing rockery bulkhead “in-kind” utilizing existing, salvageable materials that are present in the area. The project intends to excavate the displaced rockery and reestablish the existing keyway in general alignment with areas of the rockery that were undisturbed. In our opinion, reconstruction of the rockery in the manner proposed will reestablish the values and functions of the bulkhead to the pre-slide event condition. Limitations The recommendations and conclusions provided in this report are professional opinions consistent with the level of care and skill that is typical of other members in the profession currently practicing under similar conditions in this area. A warranty is not expressed or implied. Variations in the soil and groundwater conditions observed at the exploration locations may exist and may not become evident until construction. ESNW should reevaluate the conclusions in this letter if variations are encountered. Additional Services ESNW should have an opportunity to review the final designs concerning the geotechnical recommendations provided in this evaluation. ESNW should also be retained to provide testing and consultation services during the earthwork phase of construction. John Stevenson dba Off the Porch ES-9258 October 24, 2023 Page 7 Updated October 26, 2023 Earth Solutions NW, LLC We trust this letter meets your current needs. Should you have questions, or if additional information is required, please call. Sincerely, EARTH SOLUTIONS NW, LLC Chase G. Halsen, L.G., L.E.G. Raymond A. Coglas, P.E. Project Manager Senior Principal Engineer Attachments: Plate 1 – Vicinity Map Plate 2 – Boring Location Plan Plate 3 – Cross Section A-A’ Plate 4 – Soldier Pile Wall Pressure Diagram Slope Stability Outputs Boring Logs Grain Size Distribution cc: Soundview Consultants, LLC Attention: Racheal Villa 10/26/2023 John Stevenson dba Off the Porch ES-9258 October 24, 2023 Page 8 Updated October 26, 2023 Earth Solutions NW, LLC References: Limited Topographic Survey, prepared by Lanktree Land Surveying, Inc., as marked-up by TerraFirma Drilling, dated May 26, 2023 Chapter 19 of the Federal Way Revised Code iMap GIS database, maintained by King County, Washington Coastal Atlas Map, maintained by the Washington State Department of Ecology Geologic Map of the Tacoma 1:1,000,000-scale Quadrangle, Washington, prepared by Eric J. Schuster, et al., dated November 2015 Washington State Department of Transportation Geotechnical Design Manual, dated February 2022 Geotechnical Properties of Geologic Materials, prepared by Jon W. Koloski, Sigmund D. Schwarz, and Donald W. Tubbs, dated 1989 Seismic Analysis and Design of Retaining Walls, Buried Structures, Slopes, and Embankments, Report 611, prepared by the National Cooperative Highway Research Program (NCHRP), dated 2008 Geologic Information Portal (GIP), maintained by the Washington State Department of Natural Resources (DNR) Geotechnical Engineering,Construction Observation/Testing and Environmental Services Drawn MRS Checked CGH Date Oct.2023 Date 10/03/2023 Proj.No.9258 Plate 1 Earth Solutions NWLLCEarthSolutionsNWLLC EarthSolutions NW LLC Vicinity Map Afrasiabi Residence Federal Way,Washington Reference: King County,Washington OpenStreetMap.org NORTH NOTE:This plate may contain areas of color.ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black &white reproductions of this plate. SITE Federal Way Plate Proj.No. Date Checked DrawnEarthSolutionsNWLLC GeotechnicalEngineering,ConstructionObservation/TestingandEnvironmentalServicesEarthSolutionsNWLLCEarthSolutionsNWLLCBoringLocationPlanAfrasiabiResidenceFederalWay,WashingtonNORTH LEGEND Approximate Location of ESNW Boring,Proj.No. ES-9258,Aug.2023 Subject Site Existing Building Slide Area NOTE:This plate may contain areas of color.ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black &white reproductions of this plate. NOTE:The graphics shown on this plate are not intended for design purposes or precise scale measurements,but only to illustrate the approximate test locations relative to the approximate locations of existing and /or proposed site features.The information illustrated is largely based on data provided by the client at the time of our study.ESNW cannot be responsible for subsequent design changes or interpretation of the data by others. 0 2 0 4 0 8 0 Sc ale in Feet1"=4 0 ' MRS CGH 10/25/2023 9258 2 B-1 B-1 B-2 Driveway Lot 4 Lot 2 S .W . D A S H P O IN T R O A D Puget Sound 20 30 40 50 60 70 80 90 100 10 40 50 60 70 80 90 100 10 Soldier Pile Walls Slide “Runout” (Revegetate) Anchored Teccoo Mat with Vegetation Approximate Slide Scarp Displaced Rockery Bulkhead (To Be Repaired) A A’ Plate Proj.No. Date Checked DrawnEarthSolutionsNWLLC GeotechnicalEngineering,ConstructionObservation/TestingandEnvironmentalServicesEarthSolutionsNWLLCEarthSolutionsNWLLCCross-SectionA-A’AfrasiabiResidenceFederalWay,WashingtonNOTE:This plate may contain areas of color.ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black &white reproductions of this plate. NOTE:The graphics shown on this plate are not intended for design purposes or precise scale measurements,but only to illustrate the approximate test locations relative to the approximate locations of existing and /or proposed site features.The information illustrated is largely based on data provided by the client at the time of our study.ESNW cannot be responsible for subsequent design changes or interpretation of the data by others. NOTE:The stratification lines shown on this cross section represent the approximate boundaries between soil types.The actual transitions may be either more gradual or more severe.They are based on our interpretation of the subsurface conditions encountered at the individual test locations and our judgement and experience.ESNW cannot be responsible for the interpretation of the data by others. 0 1 0 2 0 4 0 Sc ale in Feet1"=2 0 ' 0 1 0 2 0 4 0 Sc ale in Feet1"=2 0 ' Vertical Scale Horizontal Scale MRS CGH 10/20/2023 9258 3 LEGEND SILT (ML) Silty SAND (SM) Poorly Graded SAND (SP) Landslide Debris (Infered) Beach Deposits Perched Groundwater Seepage 0 20 40 60 80 100 120 ELEVATION(FEET)B-2 11 13 22 28 28 14 53 117 50/6" 63 59 58 B-1 (80 S.) 11 16 19 18 40 27 32 39 110 34 53 36 3 3 31 45 23 27 23 29 ????? ?? ? ? ? ?? ?? ? ? ? ?? ?? ?? ???????? ? ? ? ????? ? Slide AreaConcreteRetaining Wall (Existing) Displaced Rockery Bulkhead A A’ Proposed Soldier Piles (Approximate) Geofoam Light Weight Fill Tieback ? ?? ? 10' Puget Sound Drawn CAM Checked CGH Date Oct.2023 Date 10/24/2023 Proj.No.9258 Plate 4 Geotechnical Engineering,Construction Observation/Testing and Environmental Services Earth Solutions NWLLCEarthSolutionsNWLLC EarthSolutions NW LLC Soldier Pile Wall Pressure Diagram Afrasiabi Residence Federal Way,Washington SCHEMATIC ONLY -NOT TO SCALE NOT A CONSTRUCTION DRAW ING Light Weight Backfill Slide Scarp Bonded Zone 3 kips/ft. 10' 20'Max.Soldier Pile 18'Max. 5'Min. 175 pcf 100 psf35pcf Tieback NOTES: •Structural Engineer to Design Soldier Pile Section and Tiebacks Based on Above Pressure Diagram. •Geotechnical Engineer Must Review and Approve Final Pile Design Plans. 1 5 'U n b o n d e d 1.12 Distance 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300Elevation0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 Color Name Unit Weight (pcf) Effective Cohesion (psf) Effective Friction Angle (°) Piezometric Surface Beach Deposits 100 0 28 2 Concrete Retaining Wall 150 Dense to Very Dense Silty Sand and Poorly Graded Sand 125 100 38 1 Landslide Debris 100 0 26 2 Medium Dense Silty Sand and Poorly Graded Sand 125 25 34 3 Very Stiff to Hard Silt 120 500 30 1 Post-Slide Condtion: Static 10/16/23, 10:17 AM Afrasiabi Residence file:///C:/Users/chase.halsen/Desktop/Project Files/9258/Slope Stability/Post Slide Condition/Pre-Existing Condition - Afrasiabi Residence.html 1/8 Afrasiabi Residence Report generated using GeoStudio 2023.1.2. Copyright © 2023 Bentley Systems, Incorporated. File Informa on File Version: 11.05 Created By: Chase Halsen Last Edited By: Chase Halsen Revision Number: 63 Date: 10/16/2023 Time: 10:16:57 AM Tool Version: 23.1.2.11 File Name: Pre-Exis ng Condi on.gsz Directory: C:\Users\chase.halsen\Desktop\Project Files\9258\Slope Stability\ Last Solved Date: 10/16/2023 Last Solved Time: 10:17:00 AM Project Se ngs Unit System: U.S. Customary Units Analysis Se ngs Afrasiabi Residence Descrip on: Pre-Exis ng Condi on Kind: SLOPE/W Analysis Type: Morgenstern-Price Se ngs Side Func on Intercolumn force func on op on: Half-Sine PWP Condi ons from: Piezometric Surfaces Apply Phrea c Correc on: No Use Staged Rapid Drawdown: No Unit Weight of Water: 62.430189 pcf Slip Surface Direc on of movement: Le to Right Use Passive Mode: No Slip Surface Op on: Entry and Exit Cri cal slip surfaces saved: 1 Op mize Cri cal Slip Surface Loca on: No Tension Crack Op on: (none) Distribu on F of S Calcula on Op on: Constant Convergence Geometry Se ngs Minimum Slip Surface Depth: 0.1 Minimum Slip Surface Volume: 35.314667 ³ 10/16/23, 10:17 AM Afrasiabi Residence file:///C:/Users/chase.halsen/Desktop/Project Files/9258/Slope Stability/Post Slide Condition/Pre-Existing Condition - Afrasiabi Residence.html 2/8 Number of Columns: 30 Factor of Safety Convergence Se ngs Maximum Number of Itera ons: 100 Tolerable difference in F of S: 0.001 Under-Relaxa on Criteria Ini al Rate: 1 Minimum Rate: 0.1 Rate Reduc on Factor: 0.65 Reduc on Frequency (itera ons): 50 Solu on Se ngs Search Method: Root Finder Tolerable difference between star ng and converged F of S: 3 Maximum itera ons to calculate converged lambda: 20 Max Absolute Lambda: 2 Materials Medium Dense Silty Sand and Poorly Graded Sand Slope Stability Material Model: Mohr-Coulomb Unit Weight: 125 pcf Effec ve Cohesion: 25 psf Effec ve Fric on Angle: 34 ° Phi-B: 0 ° Pore Water Pressure Piezometric Surface: 3 Dense to Very Dense Silty Sand and Poorly Graded Sand Slope Stability Material Model: Mohr-Coulomb Unit Weight: 125 pcf Effec ve Cohesion: 100 psf Effec ve Fric on Angle: 38 ° Phi-B: 0 ° Pore Water Pressure Piezometric Surface: 1 Very S ff to Hard Silt Slope Stability Material Model: Mohr-Coulomb Unit Weight: 120 pcf Effec ve Cohesion: 500 psf Effec ve Fric on Angle: 30 ° Phi-B: 0 ° Pore Water Pressure Piezometric Surface: 1 Landslide Debris Slope Stability Material Model: Mohr-Coulomb Unit Weight: 100 pcf Effec ve Cohesion: 0 psf Effec ve Fric on Angle: 26 ° 10/16/23, 10:17 AM Afrasiabi Residence file:///C:/Users/chase.halsen/Desktop/Project Files/9258/Slope Stability/Post Slide Condition/Pre-Existing Condition - Afrasiabi Residence.html 3/8 Phi-B: 0 ° Pore Water Pressure Piezometric Surface: 2 Beach Deposits Slope Stability Material Model: Mohr-Coulomb Unit Weight: 100 pcf Effec ve Cohesion: 0 psf Effec ve Fric on Angle: 28 ° Phi-B: 0 ° Pore Water Pressure Piezometric Surface: 2 Concrete Retaining Wall Slope Stability Material Model: High Strength Unit Weight: 150 pcf Slip Surface Entry and Exit Le Type: Range Le -Zone Le Coordinate: (0.7513, 109) Le -Zone Right Coordinate: (124.175, 64) Le -Zone Increment: 25 Right Type: Range Right-Zone Le Coordinate: (128.41763, 59.96136) Right-Zone Right Coordinate: (229, 6) Right-Zone Increment: 52 Radius Increments: 4 Slip Surface Limits Le Coordinate: (0, 109) Right Coordinate: (247.55, 6) Piezometric Surfaces Piezometric Surface 1 Coordinates X Y Coordinate 1 0 59 Coordinate 2 148 43.03333 Piezometric Surface 2 Coordinates X Y 10/16/23, 10:17 AM Afrasiabi Residence file:///C:/Users/chase.halsen/Desktop/Project Files/9258/Slope Stability/Post Slide Condition/Pre-Existing Condition - Afrasiabi Residence.html 4/8 Coordinate 1 180.695 6 Coordinate 2 211.3 6 Coordinate 3 247.55 6 Piezometric Surface 3 Coordinates X Y Coordinate 1 0 79 Coordinate 2 68 73 Geometry Name: 2D Geometry Se ngs View: 2D Element Thickness: 1 Points X Y Point 1 0 109 Point 2 34.4 109 Point 3 34.4 101 Point 4 63.8 100 Point 5 66.3 95 Point 6 76.3 90 Point 7 91.3 85 Point 8 99.4 80 Point 9 110.65 75 Point 10 118.95 70 Point 11 123.35 65 Point 12 128.35 60 Point 13 137.1 55 Point 14 140.85 50 Point 15 145.05 45 Point 16 152.55 40 Point 17 155.65 35 Point 18 161.9 30 Point 19 165.65 25 Point 20 170.65 20 Point 21 201.9 15 Point 22 211.3 10 Point 23 211.3 6 Point 24 247.55 6 Point 25 0 74 10/16/23, 10:17 AM Afrasiabi Residence file:///C:/Users/chase.halsen/Desktop/Project Files/9258/Slope Stability/Post Slide Condition/Pre-Existing Condition - Afrasiabi Residence.html 5/8 Point 26 64 68 Point 27 125 63 Point 28 159 33 Point 29 0 45 Point 30 185 0 Point 31 0 0 Point 32 211.3 0 Point 33 247.55 0 Point 34 34 109 Point 35 34 101 Regions Material Points Area Region 1 Medium Dense Silty Sand and Poorly Graded Sand 25,26,27,11,10,9,8,7,6,5,4,3,35,34,1 3,187.3 ² Region 2 Dense to Very Dense Silty Sand and Poorly Graded Sand 27,12,13,14,15,16,17,28,29,25,26 3,992.9 ² Region 3 Very S ff to Hard Silt 29,28,18,19,20,30,31 6,651.5 ² Region 4 Landslide Debris 20,21,22,23,32,30 520.88 ² Region 5 Beach Deposits 23,24,33,32 217.5 ² Region 6 Concrete Retaining Wall 2,34,35,3 3.2 ² Slip Results Slip Surfaces Analysed: 5301 of 6890 converged Current Slip Surface Slip Surface: 5,469 Factor of Safety: 1.12 Volume: 1,322.5307 ³ Weight: 162,808.49 lbf Resis ng Moment: 8,512,298.7 lbf·