Introduction to the maintenance of the penetration tester—quickly save this for future reference!

The standard penetration tester is widely used in our daily lives, yet people are often unclear about its purpose and functions. So, how exactly is the standard penetration tester used? Here’s an introduction for you.

　　1. First, use the drilling tool to drill to a depth 0.15 meters above the elevation of the test soil layer, and remove any residual overburden soil. During the hole-cleaning process, avoid disturbing the test soil layer. When testing in soil layers below the groundwater table, the water level inside the borehole should be higher than the groundwater level to prevent sand influx and borehole collapse. If necessary, install casing or use mud to protect the borehole wall.

　　2. Before using the penetration depth gauge, tighten the drill rod joints and carefully insert the penetrometer into the borehole, taking care to avoid impact with the bottom of the hole. Pay attention to maintaining the vertical alignment of the armor-piercing projectile, the drill rod, and the guide rod. A guiding device should be added above the borehole to ensure that the center of the perforating hammer applies force precisely at the center.

　　3. Use the automatic hammer-drop method: Once the penetration tester has driven 0.15 meters into the ground at a rate of 15 to 30 blows per minute, begin recording the number of blows required to penetrate an additional 0.1 meter. The cumulative number of blows for a 0.3-meter penetration depth shall be taken as the standard penetration count. Record both the penetration depth and the conditions observed during the test. If a dense soil layer is encountered and the number of blows required to penetrate 0.3 meters exceeds 50, do not force further penetration; instead, record the penetration depth at which 50 blows were reached.

　　4. Rotate the drill rod, then remove the penetration tester. Take soil samples from the sampler for identification, description, and recording, and measure their length. Carefully package and number the soil samples for testing.

　　What are the precautions for using a penetrometer? Here’s more information for you.

　　1. The penetration tester should be sent for inspection at regular intervals. If the armor-piercing bullet boot has cracks or crush marks, and the length of a single crack exceeds 5 mm or the cumulative length of all cracks exceeds 12 mm, the penetration tester should be replaced.

　　2. The device used to control the drop distance should be adjusted regularly to ensure the accuracy of the drop distance.

　　3. Regularly inspect the degree of bending in drill rods, using the total length of the drill rod as the standard, and remove any bent sections or drill rod joints that do not meet the required coaxiality.

　　The working principle of the penetration tester, a concrete strength testing instrument, is based on the penetration resistance principle outlined in the U.S. ASTM Standard C 803-82. A steel measuring pin is driven into the concrete through a loaded compression spring. By measuring the depth to which the pin penetrates, the concrete’s strength can be determined. The penetration depth of the pin is inversely proportional to the concrete’s strength—meaning the deeper the pin penetrates, the lower the concrete’s strength; conversely, the shallower the penetration, the higher the concrete’s strength. Extensive measurements were conducted in the laboratory on cylindrical and cubic specimens with various mix proportions, yielding a wealth of data. On this basis, a relationship curve between concrete strength and penetration depth was established. Practical experience has shown that the testing accuracy of this instrument fully meets the requirements of national standards. After using the penetration tester for a period of time, the rear cover should be unscrewed, and some mechanical grease applied to the decompression bearing. This will make it easier to turn the adjusting nut. Additionally, the product should not remain hooked for extended periods; the working spring should be released as soon as possible. Do not casually discharge explosive substances or disassemble the main unit, as this could affect its service life and testing accuracy. Also, handle the penetration depth gauge with care and protect the probe from damage or breakage. The statutory metrology authority should calibrate the penetration tester at least once a year. The above is an introduction to this instrument; we hope it proves helpful to you.