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25 SECTION 3 GEOTECHNICAL REPORTS FEASIBILITY EVALUATION All properties shall be evaluated for feasibility. For that evaluation a site plan showing the location and dimensions of the property is necessary. The site plan should be of sufficient detail to outline existing topography and proposed grading. It is not necessary to provide information on existing topography in flatland areas (less than 4 percent surface relief). Excavations for slopes, basements, etc. should be identified on the Feasibility map. A detailed Feasibility evaluation should be performed for properties with flaws that would affect the design process; i.e., necessitate design around a defect. Adverse conditions could be active faults, nuisance water disposal and large preexisting landslides. Since these conditions entail different geotechnical investigation techniques they are considered as separate issues in the following text. A project may have more than one adverse condition and the analysis would be a combination of the following: Active Fault Potential 1. Prior to the design phase, a fault study must be prepared on properties within an Alquist-Priolo Special Studies Zone and those outside that zone which may be affected by the trace of an active fault. The fault study should be along the following outline: 1.1. A photo lineament study should be performed. A map should be prepared that shows all possible lineaments. Scale of the map will be dependent upon size of the property and detail and expression of the lineaments. 1.2. The consultant is encouraged to discuss the findings of the photo-lineament analysis with the reviewer. 1.3. Any Alquist-Priolo Special Studies Zones limits shall be shown on a base map with a minimum I" = 2,000' scale. 1.4. A fault trenching program should be implemented to evaluate all suspect fault features. 1.5. Relative age dating of soils and geomorphic features by a qualified soil and geomorphic stratigrapher may be necessary on a case by case basis depending upon the site conditions. 1.6. Continuous faults that have insufficient soil cover to allow age assessment and are structurally associated with active fault regimes will be considered active. Correlation of these fault conditions between tracts may be performed on a case by case basis. 1.7. Active faults identified by the consultant shall be located by a registered land surveyor and shown on the geologic or fault map which utilizes the final grading plan. ---PAGE BREAK--- 26 2. Nuisance Water Disposal 2.1. During the feasibility phase, tracts in impermeable soil/bedrock areas or high groundwater locations will be evaluated for effectiveness of drywell disposal of nuisance water. The feasibility of the nuisance water drywells will be substantiated by on-site percolation tests. The nuisance water evaluation will be in general conformance with the guidelines covered in Section 5, Nuisance Water Management. 3. Large Landslides 3.1. Evaluation of large landslides will be performed in the feasibility phase of tracts in hillside (slopes steeper than 5:1) areas. Where landslides are present or suspected, sufficient subsurface exploration will be required to determine the basic geometry and stability of the landslide mass and the required stabilization measures. Gross stability studies and pseudostatic analyses must indicate calculated safety factors of at least 1.5 and 1.1 respectively. DESIGN PHASE After a project is considered feasible it should go to the geotechnical design phase. This phase requires a thorough geotechnical study for review. The design geotechnical study is based on the grading or construction plan to be used for earthwork or construction. A geotechnical report should be prepared that considers pertinent soils engineering, geologic and hydrogeologic conditions. It would present recommendations including but not necessarily limited to site grading criteria, collapsible soil distribution and treatment, foundation design, slope stability for cut and fill slopes 10 feet or higher, lateral earth pressure, and location and effects of nuisance water. In some cases these questions would have to be answered, at least in part, during a feasibility stage investigation. Following are general minimum guidelines for this phase of tract development. 1. Grading Plan 1.1. The tract grading plan shall be at a minimum scale of 1" = 40'. Smaller projects shall have a scale suitable to define grading and foundation parameters. All grading plans shall be on a 24" x 36" sheet of 3 mil mylar. 1.2. The first sheet of the grading plan shall be wet ink signed, sealed and dated by both the tract geotechnical consultants and the civil engineer. 1.3. Building setbacks from recognized active faults shall be clearly identified on the grading plan. Special foundation zones shall be shown on the grading plan or identified in the grading notes. 1.4. Cut/fill lines shall be shown on the grading plan. 1.5. The locations of proposed structures, surface and subsurface drainage facilities, paved surfaces, drywells, etc., shall be clearly shown on the grading plans. ---PAGE BREAK--- 27 GEOTECHNICAL REPORT The geotechnical report shall consider all applicable and pertinent earth conditions at the site. The relationship of the site to the regional geologic framework shall also be discussed. The geotechnical report shall, at a minimum, consider and present the following general requirements where applicable: 1. Geologic map and cross sections shall be prepared in all bedrock areas. The geologic base map should be the final grading plan. The cross sections should be oriented to best demonstrate site geologic structure. If desired an additional larger scale map may be used to illustrate site geology. 2. All subsurface exploration locations should be shown on a map that utilizes the final grading plan as a base. They may be shown on the geologic map. 3. All subsurface explorations shall have a descriptive log. The log shall, at minimum, provide ground surface elevation, the depth of all samples, unified soils classification, depth to ground water (if encountered), all geologic measurements and description of all encountered materials. 4. Sufficient geologic measurements taken from explorations, photo lineaments, outcrop or referenced studies should be shown on the geologic map to define the geologic structure of the project. 5. The site earth materials and geologic structure shall be discussed. 6. Regional geology shall be discussed. 7. Rippability shall be considered. 8. Large rock disposal and handling shall be discussed. 9. Seismicity of the region and site should be evaluated. 10. The geotechnical report shall consider slope stability. 10.1. This applies to deep-seated stability of natural, cut and fill slopes. Surface stability infinite saturated slope within 3 feet of the face) of slopes should be calculated for all slopes greater than 10 feet high. All graded slopes should be at a ratio of 2:1 or flatter. All slopes should have a calculated safety factor of 1.50 or greater under static conditions. Pseudostatic analysis with at least 1.1 safety factor may be required. The consultant should provide recommendations for control of erosion/surficial deterioration for graded slopes with low cohesion near surface soil or bedrock geologic structure. Any geologic structure bedding, joints, fault surfaces etc.) should be Utilized in the stability analyses. utilized in the stability analyses should be derived from laboratory tests on the material that is considered for hypothetical failure. Representative geologic cross section(s) shall be developed for all slopes that have geologic structure and are analyzed for slope stability. Laboratory testing for shear strength should be performed on water saturated samples. ---PAGE BREAK--- 28 11. The geotechnical report shall discuss and present soils engineering parameters. The minimum guideline requirements for soils engineering studies are as follows: 11.1. Each site must have a soils engineering study. 11.2. Soils engineering studies shall be based on adequate and sufficient laboratory testing which should consist of; but not necessarily be limited to, soil compressibility; shear strength; dry density and optimum moisture content; and expansion potential. 11.3. The potential for soil collapse must be evaluated. 11.4. Subsurface explorations for the soils engineering report should be shown on a plan with a scale sufficient to describe their location (not necessarily a 1" = 40' scale). 11.5. Recommendations for soil removal, foundation design, retaining wall design, slope stability (deep and surficial), compaction requirements and any other pertinent soils condition should be presented. 11.6. Liquefaction potential should be considered where applicable. 12. The geotechnical report shall consider rising water potential as it affects the proposed development. 12.1. Rising water is any water that daylights as seepage, springs or flows at the earth surface. It can be the result of landscape watering, natural rainfall and runoff or rising ground water table. It generally occurs after grading when geologic structure in combination with artificial fill and landscape water produce daylighting of subsurface water. 12.2. All areas of fill over low permeability bedrock shall be evaluated for rising water potential. 12.3. Any geologic boundary (i.e. faults, formational contacts, etc.) shall be evaluated for rising water. 12.4. Subdrains shall be designed and specifications presented for control of rising water. They should be discussed and described in the geotechnical report and shown on the grading. 13. The geotechnical report shall include an analysis of nuisance water drywells. Minimum report guidelines are as follows: 13.1. Permeability of soils and bedrock should be determined by on-site percolation tests. 13.2. The percolation tests should take into account the interval where nuisance water will be discharged. Testing outside the injection zone is not applicable. 13.3. Barriers to ground water flow should be identified by subsurface exploration. ---PAGE BREAK--- 29 13.4. Depth to bedrock and ground water should be determined. This can be achieved by reference documents in deep alluvial or ground water areas. 13.5. The subsurface effects of nuisance water injection shall be determined by the consultant. This includes potential for soil hydroconsolidation and daylighting (rising) water on and off site. 13.6. Mounding potential of discharged water should be determined. 13.7. The appropriate City guidelines should be utilized for design, construction and testing of the drywell (refer to Section 5 for further guidelines). 14. Site grading details and specifications shall be in the geotechnical report and on the grading plan. Typical items that would be discussed includes, but is not limited to, the following: 14.1. Buttress key dimensions shall be indicated in the report and shown on the grading plan. 14.2. All subterranean drainage devices shall be shown on the grading plan. 14.3. Cut slopes converted to fill may require subdrains. 14.4. Filled major canyons require subdrains. 14.5. Subdrain material specifications shall be in the report. 14.6. Subdrain design volume of filter material, pipe specifications, etc.) should be shown in the report. 14.7. Fill placement specifications should be presented and field guidelines for approval of over-excavation bottoms given. 14.8. The grading plan to be used for earthwork should be reviewed by the geotechnical consultant for conformance to their recommendations. 15. The grading plans submitted to the City should be wet ink signed and sealed by the design geotechnical consultant(s). FINAL REVIEW After the design review approval, the tract may commence with grading. A final review shall be performed after grading and submitted to the City. Requirements of this phase are in the following sections. 1. General in-grading review guidelines are: 1.1. The City Inspectors will provide regular in-grading inspections, as needed. If desired, the consultant of record may contact the City Engineering office to schedule a site visit by the appropriate City professional or consultant. 1.2. In-progress grading (interim) may be prepared by the consultant for review. These reports would discuss the grading progress and any changes from the original design. Changes in design to be reviewed by the City. ---PAGE BREAK--- 30 1.3. Major design changes should be reviewed by the geotechnical consultant and recommendations submitted for approval with plan revisions to City Engineering. 2. After grading, a final geotechnical report shall be submitted for review. It shall, at a minimum, contain the following information: 2.1. A general description of the grading operations and encountered conditions. Deviations from the design report shall be identified and explained. 2.2. Where necessary, a geologic map shall be provided which shows the as-built geologic conditions. It shall include mapping of faults, geologic contacts and bedding attitude measurements. 2.3. Subdrain locations shall be shown on the as-graded map. 2.4. Buttressed slopes shall be shown on the grading plan. If conditions other than those anticipated by the design report were encountered during grading, stability calculations should be presented in the report. 2.5. Over-excavated lots shall be identified in the report. 2.6. Final recommendations for expansive soils and soluble sulfates shall be in the report. 2.7. Final foundation design recommendations shall be in the report, including seismic design criteria. 2.8. Depth of soil over-excavation shall be in the report. 2.9. Results of laboratory and field tests. 2.10. Plan showing locations of soils test. 2.11. Certification of lots by the Soils Engineer (GE/RCE) 3. A separate letter shall be prepared that identifies the lots on which soils investigations will be required for future additions. 4. For additional information and guidelines on preparation of Geotechnical Reports refer to the City of Palmdale Guidelines For Preparation of Geotechnical Reports, Prepared by: GeoDynamics, Inc. July 2006.