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D6172 – Standard Test Method Technical Guide
The ASTM D6172/D6172M-18 standard provides a definitive framework for determining volumes of bulk materials such as stockpiles, landfills, and borrow pits. Unlike fully automated digital methods, this test method specifically relies on direct operator compilation using photogrammetric procedures to generate contours or cross sections from stereo aerial imagery. Adherence to the standard ensures consistent, auditable volume calculations grounded in classical survey principles.
🗺️ Scope and Core Definitions
The scope of D6172 covers site preparation, technical procedures, quality control, and equipment specifications. It mandates two distinct volume computation approaches: the Contour Test Method (Sections 8.1.1 / 9.1) and the Cross-Section Test Method (Sections 8.1.2 / 9.2). A critical distinction is that this standard does not encompass Digital Terrain Model (DTM) software procedures, although a task group has been established to develop a separate method for DTM procedures that will address conventional survey, GPS, and other data collections.
The standard defines essential terminology used throughout the photogrammetric process:
| 🟦 Term | 📏 Definition |
|---|---|
| Base Map | A map showing the soil surface of the site used for material storage, including control monument locations, values, and surface elevations. |
| Ground Control | Surveyor-provided XYZ values of targets or specific points near the project area necessary to scale and level the stereo model. |
| Check Point | Targeted points within the stockpile area used to check the accuracy of the photogrammetry; elevations are established by ground surveying. |
| Stereo Model | The overlapping area covered by two adjacent aerial photographs used to create measurement observations. |
⚙️ Technical Procedures and Quality Assurance
Executing a successful volume determination under D6172 requires strict adherence to procedural hierarchy. Initially, a base map must establish the existing soil surface and control monument values. Ground control targets must be accurately surveyed near the project area. Within the stockpile itself, check points are placed at various distinct elevations to serve as an accuracy check for the photogrammetric model. The stereo operator—a person who is trained and competent—makes quality measurement observations using a stereo instrument. All equipment must have valid calibration forms/reports from federal agencies or equipment manufacturers.
The use of a check panel is specified for the sole purpose of marking a point on the surface of the stockpile to verify the setup of the stereo model, while check points validate overall accuracy.
💡 Best Practice from the Standard: Check points should be evenly spaced at various different elevations in the stockpile, with their elevations established by precise ground surveying to ensure the most reliable accuracy verification.
⚠️ Critical Exclusion: The use of Digital Terrain Model (DTM) software and procedures to create contours or cross sections for volume calculation is NOT encompassed in this test method. D6172 relies entirely on direct operator compilation from stereo instruments.
📐 The Two Volume Computation Methods
D6172 explicitly permits only two methods for calculating the final volume, both requiring direct operator input. The Contour Test Method requires the operator to compile elevation contours representing the current surface of the bulk material. The Cross-Section Test Method requires the operator to compile cross sections along defined baselines.
| 📏 Feature | 🔄 Contour Method (8.1.1 / 9.1) | 📐 Cross-Section Method (8.1.2 / 9.2) |
|---|---|---|
| Primary Product | Contour map of the stockpile surface | Set of vertical cross-section profiles |
| Computation Basis | Planimetric area between contours and the base surface | Average end area method applied between successive sections |
| Material Handling | Best for gently sloping or flat stockpiles | Best for long, linear, or irregularly shaped stockpiles |
| Units Requirement | Values stated in SI or inch-pound units are regarded separately. Each system shall be used independently, and values from the two systems shall not be combined. | |
Practitioners must also carefully account for peripheral material, which is material existing within the site that is above the recognized base but outside the obvious stockpile perimeter.
❓ Frequently Asked Questions
🔍 What is the fundamental difference between the Contour and Cross-Section methods?
The Contour Method compiles an entire elevation contour map of the stockpile, with volume calculated from the area between contours and the base level. The Cross-Section Method compiles a series of vertical slices along defined baselines, with volume calculated by the average end area method between these slices.
💡 Why does D6172 explicitly exclude Digital Terrain Modeling (DTM) software?
This standard is written specifically for “direct operator compilation” using a stereo instrument. At the time of its development and adoption, DTM procedures had not yet been standardized for this specific test method. A separate task group has been established to develop a companion standard for DTM procedures.
⚡ How are “Check Points” and “Check Panels” used to ensure accuracy?
A check panel is a target specifically used to verify the setup of the stereo model. Check points are broader targets within the stockpile area used to check the overall accuracy of the photogrammetry. Both serve distinct roles in the quality control chain and must be validated against ground survey data.
📌 What constitutes a valid “Base Map” under this standard?
The base map must show the soil surface of the site used for material storage. It must include the location and values of control monuments and surface elevations. This map serves as the foundational reference plane for calculating the volume of material above the natural ground.