7.2 Sitework, Soil Mechanics, Excavation & Grading

7.2 Sitework, Soil Mechanics, Excavation & Grading

Earthwork and subsurface engineering form the physical base upon which all structural building systems rely. In West Virginia's mountainous and geologically diverse terrain—characterized by steep slopes, fractured bedrock, clay shale formations, and high groundwater tables—a comprehensive understanding of site preparation, utility damage prevention, soil mechanics, compaction physics, volume mathematics, and erosion control is vital for every general building contractor.

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1. Site Preparation & West Virginia 811 Utility Locating

Before initiating earth-disturbing activities, a contractor must execute site preparation and clear statutory utility notifications.

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|                  WEST VIRGINIA 811 STATUTORY NOTIFICATION FLOW              |
|                                                                             |
|   [STEP 1: PRE-MARKING]                                                     |
|   - Contractor marks proposed excavation boundaries with WHITE paint/flags. |
|                                     |                                       |
|                                     v                                       |
|   [STEP 2: NOTIFY WV 811 (WV CODE §24C-1)]                                  |
|   - Call 811 or submit electronic locate ticket.                            |
|   - MINIMUM TIMEFRAME: 48 HOURS prior to digging (excluding weekends/hols). |
|                                     |                                       |
|                                     v                                       |
|   [STEP 3: UTILITY LOCATORS RESPOND]                                        |
|   - Facility owners mark underground lines using APWA Uniform Color Code.   |
|                                     |                                       |
|                                     v                                       |
|   [STEP 4: TOLERANCE ZONE HAND-DIGGING]                                     |
|   - Maintain 24-inch safety tolerance zone on either side of markings.      |
|   - Must hand-dig, vacuum excavate, or use soft-digging techniques.         |
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West Virginia Code §24C-1 (Underground Facilities Damage Prevention Act):

• Mandatory 48-Hour Notice: Every contractor planning excavation, demolition, trenching, or grading must notify the West Virginia 811 one-call system at least 48 hours (excluding Saturdays, Sundays, and legal state/federal holidays) prior to initiating work.
• White Lining: Excavators are required to pre-mark the perimeter of the proposed excavation zone with white paint, stakes, or flags before the utility locator arrives.
• Tolerance Zone: Excavators must exercise reasonable care and maintain a safety clearance tolerance zone—typically 24 inches (2 feet) from the outer edge of the marked utility on both sides. Mechanical excavation equipment is strictly prohibited within this tolerance zone until the facility is exposed safely by hand digging, air/water vacuum excavation (potholing), or soft probing.

APWA Uniform Utility Color Code System:

| Marking Color | Utility Infrastructure Type | | :--- | :--- | | | RED | Electric power lines, cables, conduit, and lighting cables | | YELLOW | Natural gas, oil, steam, petroleum, or gaseous materials | | ORANGE | Communication, telephone, cable TV, fiber optics, and alarm/signal lines | | BLUE | Potable drinking water systems | | GREEN | Sewers, storm drains, and sanitary drain lines | | PURPLE | Reclaimed water, irrigation, and slurry lines | | WHITE | Proposed excavation boundaries and trench limits | | PINK | Temporary survey markings, reference stakes, and boundary points |

Clearing, Grubbing, and Topsoil Stripping

• Clearing: Removal of all surface vegetation, trees, brush, and structures down to natural grade.
• Grubbing: Complete excavation and removal of tree stumps, roots greater than 1.5 inches in diameter, and organic debris to a minimum depth of 12 to 24 inches below subgrade.
• Topsoil Stripping & Stockpiling: Organic topsoil (A-horizon loam, typically 4 to 8 inches deep) lacks structural bearing capacity and must never be used beneath building foundations, slabs, or structural pavements. It must be cleanly stripped and stockpiled in designated spoil areas, surrounded by silt fence, and stabilized with temporary seed/mulch for subsequent finish landscaping.

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2. Soil Mechanics & Engineering Classification

Soils are categorized under the Unified Soil Classification System (USCS - ASTM D2487) based on particle grain size distribution and plastic consistency:

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|                        SOIL PARTICLE GRAIN SIZE SPECTRUM                    |
|                                                                             |
|   BOULDERS     COBBLES       GRAVEL          SAND           SILT & CLAY     |
|   > 12"        3" - 12"      3" to #4        #4 to #200     Passes #200     |
|                              (4.75 mm)       (0.075 mm)     (< 0.075 mm)    |
|   |-----------|------------|---------------|--------------|-----------------|
|   <------------------ COARSE-GRAINED -------------------> | FINE-GRAINED >  |
+-----------------------------------------------------------------------------+

Grain Size Thresholds:

• Boulders: Rock fragments greater than 12 inches (300 mm) in diameter.
• Cobbles: Rock fragments between 3 inches (75 mm) and 12 inches (300 mm).
• Gravel (Coarse / Fine): Particles passing a 3-inch sieve and retained on a No. 4 sieve (4.75 mm).
• Sand (Coarse / Medium / Fine): Particles passing a No. 4 sieve and retained on a No. 200 sieve (0.075 mm / 75 microns).
• Fines (Silts & Clays): Particles passing through a No. 200 sieve.

Cohesionless vs. Cohesive Soils:

• Cohesionless (Granular) Soils (Sand & Gravel): Soil particles lack internal molecular cohesion and derive structural shear strength entirely from internal friction and particle interlocking. They drain freely, consolidate rapidly under mechanical load, and settle quickly upon load application.
• Cohesive Soils (Clay & Silty Clay): Fine-grained soils where microscopic platy particles possess internal electrostatic molecular bonds. They exhibit high plasticity, possess low hydraulic permeability, drain very slowly, and undergo long-term time-dependent consolidation settlement when loaded.

Atterberg Limits & Soil Plasticity (ASTM D4318):

Fine-grained soils transition through distinct physical states as their moisture content varies:

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|                             ATTERBERG LIMITS PHASES                         |
|                                                                             |
|        SOLID        SEMI-SOLID           PLASTIC                LIQUID      |
|   +--------------+--------------+-----------------------+---------------+   |
|   0% Moisture                   ^                       ^                   |
|                          PLASTIC LIMIT (PL)      LIQUID LIMIT (LL)          |
|                                 |<--------------------->|                   |
|                                    PLASTICITY INDEX                         |
|                                      (PI = LL - PL)                         |
+-----------------------------------------------------------------------------+

• Liquid Limit (LL): The moisture content percentage at which soil transitions from a plastic state to a viscous liquid state.
• Plastic Limit (PL): The moisture content percentage at which soil transitions from a semi-solid state to a moldable plastic state (the moisture level where soil crumbles when rolled into a 1/8-inch diameter thread).
• Plasticity Index (PI): The numerical difference between the Liquid Limit and Plastic Limit: $\text{PI} = \text{LL} - \text{PL}$ Engineering Significance: Soils with $\text{PI} > 20$ are classified as highly plastic clays subject to severe volumetric shrink-swell cycles upon wetting and drying, requiring chemical stabilization (lime/cement) or complete undercut and replacement beneath foundations.

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3. Presumptive Soil Bearing Capacities (IBC Table 1806.2)

In the absence of a site-specific geotechnical engineering investigation with laboratory testing, the International Building Code provides presumptive load-bearing values for foundation design:

[!NOTE] Standard Penetration Testing (SPT): Geotechnical engineers determine subsurface bearing strata using the Standard Penetration Test (ASTM D1586), driving a 2-inch split-spoon sampler 18 inches into the ground using a 140-pound hammer falling 30 inches. The N-value is the number of hammer blows required to drive the sampler through the final 12 inches.

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4. Soil Compaction Mechanics & Proctor Testing

Compaction is the mechanical process of densifying soil by expelling air voids through rolling, tamping, or vibrating. Achieving maximum density requires placing soil at its Optimum Moisture Content (OMC).

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|                          PROCTOR COMPACTION MOISTURE CURVE                  |
|                                                                             |
|   DRY DENSITY (pcf)                                                         |
|          ^                                                                  |
|          |                      PEAK: Maximum Dry Density (MDD)             |
|          |                              (e.g., 125 pcf)                     |
|          |                                   *                              |
|          |                                *     *                           |
|          |                             *           *                        |
|          |                          *                 *                     |
|          |                       *                       *                  |
|          |                    *                             *               |
|          +-------------------------------------------------------->         |
|          0%                        OPTIMUM MOISTURE          MOISTURE %     |
|                                     CONTENT (OMC)                           |
|                                     (e.g., 11.5%)                           |
+-----------------------------------------------------------------------------+

Standard Proctor vs. Modified Proctor Comparison:

Jobsite Compaction Specifications:

• Structural Fill / Building Pads: Must be compacted to a minimum of 95% of Maximum Dry Density (MDD) determined by Modified Proctor (ASTM D1557) within $\pm 2%$ of Optimum Moisture Content (OMC).
• Non-Structural Fill / Landscaped Areas: Typically compacted to 85% to 90% of Standard Proctor density.
• Lift Thickness Limits: Structural fill must be placed in loose horizontal lifts not exceeding 6 to 8 inches (uncompacted) prior to rolling with smooth drum vibratory rollers (for granular soils) or sheepsfoot/padfoot tamping rollers (for cohesive clay soils).
• Field Verification: Measured on-site using a Nuclear Density Gauge (ASTM D6938) or the Sand Cone Method (ASTM D1556).

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5. Earthwork Volume Calculations: Bank, Loose & Compacted Yards

Earthwork volume expands and contracts across three physical states:

+-----------------------------------------------------------------------------+
|                        THREE STATES OF EARTHWORK VOLUMES                    |
|                                                                             |
|   [BANK CUBIC YARDS (BCY)]       In-situ, natural undisturbed ground before |
|                                  excavation. (Density = 100%)               |
|              |                                                              |
|              |  EXCAVATION (+ SWELL %)                                      |
|              v                                                              |
|   [LOOSE CUBIC YARDS (LCY)]      Excavated material loaded in dump trucks;  |
|                                  air voids expand volume.                   |
|              |                                                              |
|              |  COMPACTION (- SHRINKAGE %)                                  |
|              v                                                              |
|   [COMPACTED CUBIC YARDS (CCY)]  Material placed and mechanically rolled    |
|                                  in structural fill. Air voids eliminated.  |
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Volume Transformation Formulas:

$\text{Loose Volume (LCY)} = \text{Bank Volume (BCY)} \times (1 + \text{Swell \%})$ $\text{Compacted Volume (CCY)} = \text{Bank Volume (BCY)} \times (1 - \text{Shrinkage \%})$ $\text{Required Bank Volume (BCY)} = \frac{\text{Required Compacted Volume (CCY)}}{1 - \text{Shrinkage \%}}$ $\text{Truck Haul Loads} = \frac{\text{Total Loose Volume (LCY)}}{\text{Truck Volumetric Capacity (LCY)}}$

Typical Earthwork Soil Properties:

Practical Step-by-Step Earthwork Calculation:

Problem: A contractor must excavate a commercial basement measuring 120 feet long, 60 feet wide, and 10 feet deep. The in-situ soil is dense clay with an estimated swell factor of 30% ($S_w = 0.30$). If highway dump trucks have a hauling capacity of 16 Loose Cubic Yards (LCY), calculate the total bank volume, loose volume, and number of truckloads.

1. Calculate In-Situ Bank Volume ($V_{\text{BCY}}$): $V = 120\text{ ft} \times 60\text{ ft} \times 10\text{ ft} = 72,000\text{ cu ft}$ $V_{\text{BCY}} = \frac{72,000\text{ cu ft}}{27\text{ cu ft/cu yd}} = 2,666.67\text{ BCY}$

2. Calculate Loose Haul Volume ($V_{\text{LCY}}$): $V_{\text{LCY}} = 2,666.67\text{ BCY} \times (1 + 0.30) = 2,666.67 \times 1.30 = 3,466.67\text{ LCY}$

3. Calculate Required Truck Haul Cycles: $\text{Truckloads} = \frac{3,466.67\text{ LCY}}{16\text{ LCY/truck}} = 216.67 \rightarrow 217\text{ truckloads}$

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6. Groundwater Control & Site Dewatering Systems

Uncontrolled groundwater compromises soil shear strength, destabilizes trench slopes, and prevents proper compaction.

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|                       EXCAVATION DEWATERING SYSTEMS                         |
|                                                                             |
|   [SUMP PUMPING]             [WELLPOINT SYSTEMS]      [DEEP WELL PUMPS]     |
|   - Shallow trenches / pits  - High water table       - Deep excavations    |
|   - Perforated barrels       - Vacuum header pipe     - Submersible pumps   |
|   - Surrounded by washed     - 2" riser pipes @ 3-6'  - Drilled into deep   |
|     #57 stone.                 OC around perimeter.     aquifers (> 25').   |
+-----------------------------------------------------------------------------+

• Sump Pumping: Simplest method. Perforated sump basins surrounded by crushed stone are placed in low collection pits, and submersible trash pumps discharge water away from the excavation. Limited to shallow depths with low water influx in cohesive or gravelly soils.
• Wellpoint Systems: A continuous series of small-diameter (1.5" to 2") perforated riser pipes driven or jetted into permeable sandy soils at 3- to 6-foot intervals around the excavation perimeter. Risers connect to a common suction header pipe evacuated by a high-capacity vacuum pump. Effective for lowering water tables up to 15 to 18 feet in a single stage.
• Deep Wells: 12- to 24-inch perforated casings drilled 25 to 100 feet deep with individual submersible turbine pumps. Ideal for dewatering deep, large commercial excavations in permeable strata.
• Trench / French Drains: Perforated collector pipes embedded in washed stone and wrapped with non-woven geotextile filter fabric, installed along building perimeters to capture and divert shallow perched groundwater.

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7. Erosion & Sediment (E&S) Control & WV DEP NPDES Regulations

Under federal Clean Water Act mandates and state environmental statutes, the West Virginia Department of Environmental Protection (WV DEP) Division of Water and Waste Management strictly regulates construction stormwater runoff.

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|                  WV DEP NPDES CONSTRUCTION STORMWATER RULES                 |
|                                                                             |
|   DISTURBANCE THRESHOLD:   Land disturbance >= 1.0 ACRE (or part of a       |
|                            common plan of development)                      |
|                                                                             |
|   MANDATORY SUBMISSION:    Stormwater Pollution Prevention Plan (SWPPP)     |
|                            filed with WV DEP before ground disturbance.     |
|                                                                             |
|   CORE BMP CONTROLS:       - Stabilized Construction Entrance (AASHTO #1)   |
|                            - Silt Fence (Wire-backed, entrenched 6"x6")     |
|                            - Sediment Traps & Basins (< 35% capacity clean) |
|                            - Stabilization: Seed/mulch within 7 DAYS        |
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Primary Best Management Practices (BMPs):

1. Stabilized Construction Entrance (Pad): Installed at all points of ingress and egress to prevent tracking mud onto public paved roadways. Must consist of AASHTO No. 1 coarse crushed aggregate (2" to 3.5" stone), a minimum of 6 inches deep, at least 50 feet long (30 feet for single lots), and placed over a non-woven geotextile separation fabric.
2. Silt Fence (Sediment Barrier): Synthetic woven geotextile fabric attached to metal or hardwood posts spaced no more than 6 feet apart. The bottom 6 inches of the fabric must be buried in a continuous 6" x 6" trench backfilled with compacted earth to prevent undercutting (blowouts). For heavy slopes, wire-mesh backing is mandatory.
3. Sediment Traps & Basins: Engineered settling ponds sized to retain runoff from contributing drainage areas. Accumulated sediment must be removed when the basin reaches 50% of its design capacity (or 35% under specific WV DEP local watershed rules).
4. Rock Check Dams: Small stone dams (using 4" to 8" rip-rap) placed across temporary drainage ditches or swales at calculated intervals to reduce flow velocity and settle suspended soil particles.
5. Site Stabilization Timelines: Temporary or permanent soil stabilization (mulching, hydromulch, or seed) must be applied to denuded areas within seven (7) calendar days after reaching final grade or after construction activities have temporarily ceased.