North Carolina Borrow Pit Sampling Manual Notes

  • Overview of Manual

    • Focuses on procedures for obtaining soil samples from borrow pits and soil stockpiles in North Carolina.
    • Important for ensuring quality fill material for construction projects.

  • Purpose

    • Provides guidance on techniques for soil sampling.
    • Aids in compliance with NCDOT standards and classifications required for construction materials.
    • Essential for assessment of soil suitability for projects.

  • Borrow Pit & Stockpile Definitions

    • Borrow Pit: Area from which soil is excavated for use as fill material.
    • Stockpile: A reserve of soil or aggregate materials stored on site.

  • Importance of Proper Sampling

    • Samples must be representative of the larger whole to ensure reliability in testing results.
    • Poor sampling can lead to unsuitable materials causing structural failure and increased costs.
    • Documentation must be maintained throughout the sampling process.

  • AASHTO Classification System

    • Developed by the American Association of State Highway and Transportation Officials.
    • Soil is classified based on load-carrying capacity (A-1 to A-7).
    • A-1: Excellent
    • A-7: Poor
    • Key tests include gradation, liquid limit, plastic limit, and plasticity index.
    • Liquid Limit: Moisture content where soil transitions from plastic to liquid.
    • Plastic Limit: The moisture content at which soil changes from semi-solid to plastic.
    • Plasticity Index: Determines the range in which soil remains plastic (P.I. = L.L. – P.L.).

  • Soil Terminology

    • Definitions of soil fragments (boulders, cobbles, gravel, and sand).
    • Coarse-Grained Soils: Predominantly gravel and sand.
    • Fine-Grained Soils: Predominantly silt and clay.
    • Importance of using proper terminology for accurate soil identification in boring logs.

  • General Sampling Procedures

    • Obtain a plot plan and approval from property owners.
    • Use of hand auger or power drill for sampling.
    • Each sample should weigh 5-8 pounds and must be distinctly marked for identification.
    • Minimum of two boring samples per acre; careful compliance with established documentation protocols.

  • Sampling Procedures for Contractors and NCDOT

    • Detailed procedures depending on whether contractors or department routinely sample the soil.
    • Both require certified personnel to oversee the processes.

  • Testing and Approving Borrow Sources

    • Samples undergo lab testing to classify soil and ensure compliance with material standards.
    • # Final approval rests with the Resident Engineer based on lab data and a site investigation report.

  • Documentation

    • Boring Logs: Essential for tracking soil types encountered during sampling.
    • Sample Cards: Must accompany soil samples with extensive details (location, type, date).
    • Maintain a detailed site map to visually represent sampling locations.

  • Appendices Overview

    • A: Criteria for borrow materials.
    • B: Summary of select materials.
    • C: Boring log example.
    • D: Sample card examples.
    • E: Soil classification test report examples.
    • F: HiCAMS data entry procedures.
    • G: Stockpile sampling procedures.

  • Glossary of Terms

    • Definitions of critical terms (e.g., cohesion, elasticity, soil profile) used throughout the manual for clarity and understanding.