Information on the most widely used ASTM standards within the materials testing industry
Model: UTR1072-PL1, ASTM D5731
Rock point load tester (also commonly called the rock point load testing instrument) is a portable geotechnical testing device developed according ASTM D5731 Standard Test Method for Determination of the Point Load Strength Index of Rock and Application to Rock Strength Classifications. Its core principle is to conduct tests using concentrated point load splitting. The device applies a concentrated load to rock specimens using a pair of spherical cone heads, quickly determining the rock point load strength index, and through standard conversion formulas, obtains key mechanical parameters such as uniaxial compressive strength, tensile strength, and strength anisotropy coefficient of the rock. China Geological Survey Institute of Prospecting Technology Research.
General Introduction
Rock point load tester (also commonly called the rock point load testing instrument) is a portable geotechnical testing device developed according ASTM D5731 Standard Test Method for Determination of the Point Load Strength Index of Rock and Application to Rock Strength Classifications. Its core principle is to conduct tests using concentrated point load splitting. The device applies a concentrated load to rock specimens using a pair of spherical cone heads, quickly determining the rock point load strength index, and through standard conversion formulas, obtains key mechanical parameters such as uniaxial compressive strength, tensile strength, and strength anisotropy coefficient of the rock. China Geological Survey Institute of Prospecting Technology Research.
Point load tester places a rock specimen between two spherical conical platens, applies a concentrated load to the specimen until failure, and then calculates the point load strength of the rock based on the failure load. The point load strength can serve as an indicator for rock strength classification and rock mass weathering classification, and can also be used to evaluate the degree of anisotropy of rock strength and estimate other related strengths such as uniaxial compressive strength and tensile strength.
The point load strength test apparatus is suitable for all types of regular or irregular rocks, which can be either drilled cores or rock blocks taken from outcrops, exploration pits, adits, or tunnels. This test determines the point load strength of the rock in its natural state.
Key Features
Rock specimens are placed between two spherical conical hard inditors, and a concentrated load is applied at a constant speed through a hydraulic system, generating tensile stress concentration between loading points, ultimately causing the specimen to split and fracture along the loading line. Record the ultimate load P and the spacing between loading points D at the moment of specimen failure, and calculate the point load intensity index Is; Based on sample size correction, the standard point load strength index Is(50) is obtained.
Then, based on the industry-common conversion factor (k value 20~25), the uniaxial compressive strength of the rock σc, and at the same time, it can calculate rock strength anisotropy indicators to determine strength differences caused by rock joints and bedding.
Determining the mechanical parameters of rock foundations
Detects rock point load strength index Is(50), quickly converts uniaxial compressive strength and tensile strength, compensates for the shortcomings of standard uniaxial compressive strength tests in the field, and provides basic mechanical data for engineering design. The Institute of Exploration Technology of the China Geological Survey is designed to provide basic mechanical data.
Rock mass mass grading and weathering assessment
Based on strength indicators, rock mass grades are classified, the degree of rock weathering is identified, and weak interlayers from intact rock masses are widely used in rock mass quality evaluation systems such as RMR and Q systems.
Detecting rock strength anisotropy
Tests were conducted along the vertical and parallel bedding/joint directions of the rock samples, calculating anisotropy coefficients to evaluate the impact of bedding, foliation, and fractures on overall rock stability.
ASTM D5731 Standard Test Method for Determination of the Point Load Strength Index of Rock and Application to Rock Strength Classifications
1. Grouping of Specimens
Divide rock specimens that are visually distinguishable and have roughly similar engineering geological characteristics into the same group. If the rock is anisotropic (such as sedimentary and metamorphic rocks with obvious bedding or foliation), further subdivide them into subgroups with loading parallel or perpendicular to the bedding. Each group should contain about 15 specimens.
2. This test can use core samples, regular, or irregular rock block samples. The dimensional requirements for different shapes of specimens are as follows:
2.1 For radial tests on cores, the specimen's diameter-to-length ratio should be greater than 1.0.
2.2 For axial tests, the specimen's diameter-to-length ratio should be equal to or less than 1.0.
2.3 For irregular rock block samples, the length (L), width (W), and height (h) should preferably satisfy L ≥ W ≥ h. The specimen height (h) is generally controlled between 0.5 and 10 cm to meet the requirements of the test instrument's loading system; in addition, the rock surface near the loading point should be leveled.
3. The water content of specimens can be chosen according to requirements: natural water content, dried state, saturated state, or other water content states.
3.1 Dried specimens: dried at 105–110°C for 12 hours.
3.2 Saturated specimens: first immerse the specimens gradually in water, by 1/4, 1/2, 3/4, and 4/4 portions of the specimen height, with each portion submerged for 6 hours (if the specimen height is very small, it is acceptable to use 1/2 or the whole portion). Then allow free water absorption for 48 hours, followed by saturation using boiling or vacuum suction methods.
Main parameters
| Spherical end curvature of cone | r = 5mm |
| Cone apex angle | 60° |
| Cone material | high-quality steel, hard |
| Maximum working pressure of jack | 50-100 MPa |
| Maximum range of force sensor | 100 kN |
| Axial stroke | Greater than 100 mm |
| Built-in battery | capable of continuous field operation |
| Display type | digital display |
| Weight | 32kg |
Frequently Asked Questions
Rock Point Load Test Equipment Test Steps
1. Install the specimen
Before installing the specimen, first check whether the upper and lower loading cones of the point load attachment are accurately aligned. Then place the specimen in the testing machine so that the loading cones closely contact the shortest side of the specimen, making sure that the contact point coincides as much as possible with the center of the specimen. If it is necessary to determine the strength of structural planes (bedding, foliation, joints, etc.), ensure that the line connecting the two loading points lies within the same structure.
2. Loading
After the specimen is installed, apply pressure manually and load slowly to cause specimen failure. Apply load at a uniform rate until the specimen fails.
3. Describe the characteristics of specimen failure
A normal specimen failure surface should pass through both the upper and lower loading points simultaneously. If the failure surface passes through only one loading point, resulting in local failure, this test is invalid and should be discarded. The description of the failure surface should also include whether it is flat or curved.
4. Measure the dimensions of the failure surface
After the specimen fails, the dimensions of the failure surface must be measured. The measured dimensions include the distance D between the upper and lower loading points and the average width Wf perpendicular to the line connecting the loading points, with a measurement error not exceeding ±0.2 mm.
5. Repeat the test
Repeat steps 1-4 for the remaining specimens.
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