Geotechnical Engineering Report Country Ridge Subdivision Strawberry Lane Richland, Washington Prepared for: Pahlisch Homes, Inc. 210 SW Wilson Avenue, Suite 100 Bend, Oregon 97702 November 17, 2020 PBS Project 66265.000 4412 S CORBETT AVENUE PORTLAND, OR 97239 503.248.1939 MAIN 866.727.0140 FAX PBSUSA.COM Geotechnical Engineering Report Country Ridge Subdivision Strawberry Lane Richland, Washington Prepared for: Pahlisch Homes, Inc. 210 SW Wilson Avenue, Suite 100 Bend, Oregon 97702 November 17, 2020 PBS Project 66265.000 Prepared by: 11/17/2020 11/17/2020 Clint Nealey, PE Shaun Cordes, LG, LEG Geotechnical Staff Engineer Project Engineering geologist Reviewed by: Ryan White, PE, GE (OR) Principal/Geotechnical Engineering Group Manager © 2020 PBS Engineering and Environmental Inc. 4412 S CORBETT AVENUE, PORTLAND, OR 97239 . 503.248.1939 MAIN . 866.727.0140 FAX . PBSUSA.COM Geotechnical Engineering Report Country Ridge Subdivision Pahlisch Homes, Inc. Richland, Washington Table of Contents 1 INTRODUCTION ........................................................................................................................................... 1 1.1 General ........................................................................................................................................................................................... 1 1.2 Purpose and Scope ................................................................................................................................................................... 1 1.2.1 Literature and Records Review ................................................................................................................................ 1 1.2.2 Subsurface Explorations ............................................................................................................................................. 1 1.2.3 Field Infiltration Testing .............................................................................................................................................. 1 1.2.4 Soils Testing .................................................................................................................................................................... 1 1.2.5 Geotechnical Engineering Analysis ........................................................................................................................ 1 1.2.6 Report Preparation ....................................................................................................................................................... 1 1.3 Project Understanding ............................................................................................................................................................. 2 2 SITE CONDITIONS ........................................................................................................................................ 2 2.1 Surface Description ................................................................................................................................................................... 2 2.2 Geologic Setting......................................................................................................................................................................... 3 2.2.1 Regional Geologic Setting ......................................................................................................................................... 3 2.2.2 Local Geology ................................................................................................................................................................. 3 2.3 Subsurface Conditions ............................................................................................................................................................. 4 2.4 Groundwater ................................................................................................................................................................................ 4 2.5 Infiltration Testing ..................................................................................................................................................................... 4 2.6 Critical Areas – Geologically Hazardous Areas .............................................................................................................. 5 2.6.1 Landslide Hazard ........................................................................................................................................................... 5 2.6.2 Erosion Hazard ............................................................................................................................................................... 6 2.6.3 Seismic Hazard ............................................................................................................................................................... 6 2.6.3.1 Fault Surface Rupture ................................................................................................................................. 6 2.6.3.2 Seismically Induced Landslides ............................................................................................................... 6 3 CONCLUSIONS AND RECOMMENDATIONS .............................................................................................. 6 3.1 Geotechnical Design Considerations ................................................................................................................................. 6 3.2 Shallow Foundations ................................................................................................................................................................ 7 3.2.1 Minimum Footing Widths and Design Bearing Pressure .............................................................................. 7 3.2.2 Footing Embedment Depths .................................................................................................................................... 7 3.2.3 Footing Preparation ..................................................................................................................................................... 7 3.2.4 Lateral Resistance .......................................................................................................................................................... 7 3.3 Floor Slabs .................................................................................................................................................................................... 8 3.4 Seismic Design Considerations ............................................................................................................................................ 8 3.4.1 Code-Based Seismic Design Parameters ............................................................................................................. 8 3.4.2 Liquefaction Potential.................................................................................................................................................. 8 3.5 Temporary and Permanent Slopes ..................................................................................................................................... 8 3.6 Ground Moisture........................................................................................................................................................................ 9 4 CONSTRUCTION RECOMMENDATIONS ..................................................................................................... 9 4.1 Site Preparation .......................................................................................................................................................................... 9 4.1.1 Proofrolling/Subgrade Verification ........................................................................................................................ 9 4.1.2 Wet/Freezing Weather and Wet Soil Conditions ............................................................................................. 9 4.1.3 Compacting Test Pit Locations .............................................................................................................................. 10 November 17, 2020 i PBS Project 66265.000 Geotechnical Engineering Report Country Ridge Subdivision Pahlisch Homes, Inc. Richland, Washington 4.2 Excavation ................................................................................................................................................................................... 10 4.3 Structural Fill .............................................................................................................................................................................. 10 4.3.1 On-Site Soil .................................................................................................................................................................... 11 4.3.2 Imported Granular Materials .................................................................................................................................. 11 4.3.3 Base Aggregate ............................................................................................................................................................ 11 4.3.4 Foundation Base Aggregate ................................................................................................................................... 11 4.3.5 Trench Backfill..............................................................................................................................................................