Retaining Wall Knowledge Quiz

Q1. Field Boring & Sampling Specifications Boring Quantity & Location: A minimum of two soil borings must be performed per site, and they must be drilled directly within the footprint of the proposed structure Minimum Boring Depth: Borings must extend to a minimum depth of 5 feet or until they reach "auger refusal" on non-shrink/swell geologic strata Footing Clearance: The soil investigation must reach at least 12 inches below the bottom of the recommended footing depth (unless auger refusal is hit first) 1 .

Q2. Laboratory Testing Guidelines Testing Standards: Laboratory testing must include at least one set of index parameters performed using ASTM test procedures or another County-approved method Strict Classification Restriction: ASTM unified soil classification is NOT acceptable as a test standard for the purposes of the County's expansive soils policy

Q3. Soil Boring Location and Depth Guidelines Boring Quantity & Placement: A minimum of two soil borings must be drilled per site, and they must be positioned directly within the footprint of your proposed structure Exact Boring Depth: Test borings must go to a minimum depth of 5 feet, or until they reach "auger refusal" on non-shrink/swell geologic strata Footing Clearance: The borings must extend at least 12 inches below the recommended footing depth (unless the drilling equipment hits auger refusal first) Targeted Sampling: The engineer must retrieve a soil sample representing the "poorest" observed soil quality on the lot This sample must be taken specifically from the zone 0 to 12 inches below the proposed bottom of the footing to be used for laboratory testing

Q4. Geotechnical Report Requirements The final report submitted to the County to secure your permit must include: Bore Logs: Detailed soil bore logs of all bore holes or test pits investigated on your property Scaled Site Sketch: A scaled sketch of your site identifying the exact locations of each bore hole or test pit, documenting the precise layout of the parcel Tabulated Lab Data: A clear tabulation of all laboratory test results A Licensed Stamp: The signature and professional seal of the licensed individuals who performed or supervised the field testing, lab work, and final report compilation

Q5. Basic Development Plan Requirements (All Walls) The City requires one copy of a Basic Development Plan, which must clearly delineate: Dimensions and shape of your property lot 1 Adjoining streets and roads adjacent to your lot lines 1 Precise location of the proposed retaining wall on your property 1 Total height and length of the proposed retaining wall 1 A section or profile view showing the exact relationship of the unbalanced fill to your retaining wall 1

Q6. Advanced Design Plan Requirements (For Walls Requiring Building Permits) If your wall height requires a formal building permit (over 2 feet of unbalanced fill in the City) and building plans are triggered (over 4 feet in height), the drawings must also include: Strict Scale: A minimum scale of 1/4 inch = 1 foot, with all physical dimensions clearly labeled 4 Structural Sections: Wall elevations and multiple structural cross-sections showing construction details Material Specs: Clear specifications for your construction materials, backfill material, and compaction requirements Soil & Slope Profile: The bearing capacity of the foundation soil, along with the actual ground slope at both the top and the toe of the retaining wall Drainage Details: The specific method of drainage engineered behind the wall Safety Barriers: Guardrail locations and design details for any retaining wall system 30 inches or higher where pedestrian traffic protection is applicable Multi-Property Access: If the retaining wall extends across multiple properties, the drawings must describe the provisions made for physical access and future maintenance of the wall

Q7. Timber Retaining Wall Drainage Requirements Perforated Drain Pipe: You must install a 4-inch diameter perforated drain pipe along the full length of the wall’s base, which must outlet to daylight Gravel Envelope: The drain pipe must be embedded in gravel and completely wrapped in filter fabric. For timber walls, this gravel core must measure 12 inches wide by 24 inches high Backfill Material: Clean crushed stone backfill must be placed behind the wall to within 12 inches of the top of the timber structure Subgrade Prep: If the foundation soil beneath the wall footing consists of soft clay, you are required to place 4 to 6 inches of crushed stone under the footing first

Q8. Masonry Retaining Wall Drainage Requirements Perforated Drain Pipe & Outlets: You must install a minimum 4-inch diameter perforated drain pipe along the full length of the wall Unlike timber walls, masonry walls allow two options for discharge: the pipe can either outlet to daylight at each end OR discharge water through cast-in-place weep holes spaced at 8 feet on center 1 Gravel Envelope: The gravel surrounding the pipe must be wrapped in filter fabric, but the envelope is smaller than a timber wall's, measuring 12 inches wide by 12 inches high 1 . Subgrade Prep: Just like timber, if you encounter soft clay under the concrete foundation, you must lay down a 4-to-6-inch bed of crushed stone before pouring your footing

Q9. Concrete Masonry Retaining Walls (48" Height) For a block wall that retains 48 inches of soil, the reinforcement requirements are as follows 1 : Footing Width (W): Must be a minimum of 63 inches wide Vertical & Dowel Bars (O-bars): #4 rebar spaced at 16 inches on center (#4@16") Note: You can substitute the O-bars and corresponding footer dowels with a single, full-height bar of equal size and spacing Horizontal Footing Bars (P-bars): #4 rebar spaced at 30 inches on center (#4@30") running horizontally through the footing Footing Cross-Bars: #3 bars spaced at 12 inches on center (#3@12") placed perpendicular to the P-bars Bond Beams: You must construct a reinforced bond beam at the top course of blocks and at every other intermediate course below it, with each bond beam containing 2 #4 bars laid horizontally

Q10. 🎥 Explainer Video Storyboards Concept A: "The Invisible Force: Understanding Hydrostatic Pressure" Format: 2D or 3D Animation (2–3 minutes) Target Audience: DIYers and property owners. Visual Story: Start with a beautiful yard and a newly built retaining wall. Rain starts falling. Show a wall without drainage bowing, cracking, and ultimately sliding forward. Key Message: Retaining walls don't just hold back dirt; they hold back water. Proper drainage is the single most important factor in wall longevity. Concept B: "What is a 'Deadman' Anchor?" Format: "How-To" Style Live-Action or Schematic Animation (90 seconds) Target Audience: Handymen and novice builders. Visual Story: Show a timber retaining wall being stacked course-by-course using 6x6 southern pine (AWPA UC4A treated for ground contact) 2 Highlight the common mistake: simply stacking wood like a Jenga tower. Introduce the "Deadman"—a 6-foot timber running perpendicular to the wall, extending deep back into the structural backfill, secured with a 30-inch cross plate Animate how the weight of the compacted backfill soil sits directly on top of this cross plate, anchoring the wall and preventing it from tipping over. Detail the layout: placed 8 feet on center and staggered across intermediate courses (excluding the top and bottom buried courses)

Q11. 📊 Educational Infographics Concept A: "Anatomy of a Compliant Retaining Wall: Timber vs. Masonry" Visual Layout: A side-by-side, high-contrast cross-sectional diagram comparing a typical timber wall and a concrete masonry (block) wall. Timber Wall Key Callouts: Fasteners: 60d hot-dipped galvanized spikes spaced at 24 inches on center and staggered, penetrating at least 2 inches into the base member 3 Staggered Joints: A callout showing joints staggered by a minimum of 3 feet, 6 inches between courses to prevent vertical weak lines Gravel Wrap: A shaded 12" x 24" gravel pocket wrapped in filter fabric around the pipe Masonry Wall Key Callouts: Footing Keyway: The 1" x 4" keyway or roughened joint connecting the concrete footing to the starting block course Reinforcement: Steel dowels and vertical O-bars lapped a minimum of 20 inches 6 Bond Beams: Horizontal steel placement featuring two #4 bars inside specialized bond-beam blocks at the top course and every other intermediate course Drainage: Highlight the option of weep holes spaced at 8 feet on center Concept B: "The Geotechnical Dirt: Understanding Expansive Clay" Visual Layout: A microscopic/macro hybrid infographic explaining shrink-swell soils. Sections: Swell Action: Micro-clays absorbing water like tiny sponges, causing the ground to heave up multiple inches in winter rains Shrink Action: Clay drying and cracking in summer heat, creating structural voids 9 .

Q12. 📋 Step-by-Step Checklists & To-Do Lists Concept A: The "Post-Pour & Backfill" Inspection Checklist This checklist is designed for site managers and owners before backfill material is laid: [ ] Validate Cure Time: Verify that concrete or grout has cured for at least 7 days before backfilling is permitted against concrete or masonry structures [ ] Set Equipment Buffer: Mark out a physical boundary tape indicating that compactors and heavy machinery must maintain a distance from the wall equal to the wall's height [ ] Check Joint Spacing: Confirm that vertical control joints are placed no more than 20 feet on center and that expansion joints are installed at every fourth control joint [ ] Verify Subgrade Material: If soft clay is present under the footing, ensure a 4-to-6-inch bed of crushed stone has been placed and compacted underneath [ ] Measure Lap Lengths: Ensure all lapped steel reinforcement bars overlap by at least 20 inches

Q13. 🛝 Slideshow Presentation Outline Title: "Building for the Long Haul: Engineering Soil and Concrete Retaining Systems" Slide 1: Title & Overview Visual: Cross-section blueprint of a retaining wall. Concept: Introducing the structural principles of earth-retaining systems. Slide 2: The Hazard of Expansive Soils Data Point: Expansive soils cause billions in structural damage in the U.S. every year—more than hurricanes, tornadoes, and earthquakes combined Concept: Why understanding the "shrink-swell" index of clays is vital to foundation design. Slide 3: Timber System Architecture Data Point: Standard specifications for structural timber walls—using 6x6 southern pine (grade #2 or better) treated with UC4A preservatives 2 Concept: Using structural deadmen and staggered joints to distribute earth pressure. Slide 4: Masonry and Solid Poured Concrete Data Point: Requiring 3,500 psi concrete 3 , lapping steel rebar by 20 inches 7 , and using ASTM C90 concrete masonry units Concept: Selecting between block systems (using integrated bond beams) 6 and solid cast-in-place concrete walls. Slide 5: The Golden Rule of Drainage Data Point: Highlighting the requirements for a 4-inch perforated pipe and filter-fabric gravel wraps Concept: Eradicating hydrostatic load, preventing backfill clay saturation, and handling soft clay subgrades

Q14. 🧩 Interactive Quizzes Topic: "Are You Ready to Build? The Structural Integrity Test" How long must concrete or grout cure before you can backfill soil against a masonry wall?

Q15. Why Standard Details Do Not Apply A sloped backfill introduces a slope surcharge, which drastically increases the lateral soil pressure and hydrostatic forces pushing against the back of the wall compared to a standard flat yard 1 Because the standard typical details are engineered only for level earth, they cannot safely accommodate this extra weight

Q16. General Material & Strength Specifications [ ] Steel Yield Strength: Ensure all reinforcing steel complies with ASTM A615 and has a minimum yield strength of 60,000 psi (Grade 60) [ ] Concrete Masonry Units (CMUs): Verify that all concrete masonry blocks comply with ASTM C90 [ ] Mortar Standard: Confirm that the mortar conforms to ASTM C270 [ ] Foundation Concrete: Ensure the concrete footing has a minimum compressive strength of 3,500 psi at 28 days and complies with ACI 318 [ ] Corrosion Protection: Verify that all horizontal joint reinforcement, ties, and other accessories are corrosion-resistant

Q17. Footing and Keyway Reinforcement [ ] Footing Width (W): Check that the minimum footing width matches the design height (H) of the wall 5 : For H = 24 inches: Footing width W must be at least 39 inches For H = 36 inches: Footing width W must be at least 48 inches For H = 48 inches: Footing width W must be at least 63 inches [ ] Horizontal Footing Bars (P-bars): Verify that P-bars are placed in the bottom of the footing according to the wall height 5 6 : For H = 24 inches: #4 bars spaced at 48 inches on center For H = 36 inches: #4 bars spaced at 48 inches on center For H = 48 inches: #4 bars spaced at 30 inches on center [ ] Footing Cross-Bars: Verify that horizontal cross-bars of #3 rebar are spaced at 12 inches on center perpendicular to the footing length [ ] Keyway or Rough Joint: Confirm that the top of the concrete foundation footing has a 1" x 4" keyway or is sufficiently roughened along its full length to bind with the block wall

Q18. Vertical & Dowel Reinforcement (O-bars) [ ] Vertical Wall Bars (O-bars) & Footing Dowels: Verify vertical steel placement matches the scheduled height 5 6 : For H = 24 inches: #4 bars spaced at 56 inches on center For H = 36 inches: #4 bars spaced at 32 inches on center For H = 48 inches: #4 bars spaced at 16 inches on center [ ] O-Bar Substitution Option: Dowels and O-bars may be substituted with a single, full-height bar of the same size and spacing [ ] Minimum Lap Length: Ensure all overlapping vertical rebar segments have a minimum lap length of 20 inches 4 [ ] Rebar Clearance: Confirm vertical steel is positioned to maintain a 3-inch minimum clearance from the soil-facing edge of the concrete footing

Q19. Horizontal Bond Beam Reinforcement [ ] Bond Beam Placement: Ensure a horizontal bond beam is constructed at the top course and at every other intermediate course below it 5 [ ] Bond Beam Steel: Verify that each bond beam contains two #4 rebar segments running horizontally [ ] Block Selection: Confirm the use of specialized bond beam units, such as slotted units or blocks with sections removed, to accommodate horizontal steel prior to grouting 6

Q20. Reinforcement Positioning & Grouting Controls [ ] Vertical Rebar Tie-Holds: Use wire loops installed directly into the bed joints before the mortar sets to securely anchor and position vertical steel prior to pouring grout [ ] Grout Stop Barriers: Verify that metal lath or similar material is placed over un-grouted cores directly beneath bond beams to prevent grout from filling unintended block cavities 7 [ ] Curing Limit: Do not allow backfilling against the masonry wall until the concrete and grout have cured for at least 7 days

Q21. "The 7-Day Curing Rule: Why Rushing Backfill Destroys Walls" Visual Hook: A split-screen time-lapse. On the left, a contractor backfills soil against a freshly mortared concrete block wall on Day On the right, the contractor waits until Day 7 1 . Key Code Point: Highlight the strict safety code prohibiting backfilling against masonry or concrete retaining walls until at least 7 days after placing concrete or grout

Q22. "Timber Wall Physics: Spikes, Joints, and Staggers" Visual Hook: A close-up 3D assembly animation of a timber retaining wall, resembling a puzzle coming together piece-by-piece. The Story: Demonstrate the critical "interlocking" details that prevent timber walls from splitting apart. Zoom in on: Joints staggered by a minimum of 3 feet, 6 inches between courses 60d hot-dipped galvanized spikes driven into pre-drilled holes, showing them penetrating at least 2 inches into the log below The spacing rule: Spikes placed at 24 inches on center and staggered, with 2 spikes securing each timber end and corner Key Code Point: Standard structural integrity relies entirely on correct fastener density and joint spacing to prevent vertical weak lines 2

Q23. "The 5-Foot Boring Test: Battling Expansive Clay" Visual Hook: An animated drill rig boring into a residential lot, showing the different layers of soil beneath the surface. The Story: Explain how expansive "shrink-swell" clays expand when wet and shrink when dry, causing billions in damage Walk the viewer through a code-compliant geotechnical test: Drilling a minimum of two borings within the structure's footprint Going to a minimum depth of 5 feet (or 12 inches below the planned footing) Extracting the "poorest" quality soil sample from the first 12 inches below the footing for lab testing Key Code Point: Showing how proper lab testing prevents foundation movement by confirming soil characteristics before a single shovel of dirt is moved 5