1 Introduction The degree of compaction is one of the most important internal indicators of the quality of roadbed projects. Only by fully compacting the roadbed can the strength and overall stability of the roadbed be ensured, and the extension and extension of the roadbed can be ensured. The service life of the road. The main testing methods for on-site compaction testing of roadbed include sand filling method, ring knife method, nuclear method, water bag method and other testing methods. According to the actual construction conditions and the owner's requirements, the sand filling method is mainly used to test the roadbed compaction on the Shiman Expressway. This article combines engineering practice to briefly analyze and discuss some issues in roadbed compaction testing. 2 Basic Principles of Sand Filling Method The basic principle of sand filling method (standard method, but not suitable for compaction testing of materials with large holes or large pores such as stone-filled embankments) is to use particle sizes of 0.30 to 0.60mm or 0.25 to 0.50mm for cleaning. Clean uniform sand is freely dropped into the test hole from a certain height. The volume of the test hole is measured according to the principle that its unit weight remains unchanged (that is, standard sand is used to replace the aggregate in the test hole), and the volume of the test hole is measured according to the content of the aggregate. The measured dry density of the sample can be derived from the amount of water. 3 Selection of sand filling barrel and indoor calibration 3.1 Select sand filling barrel according to the maximum particle size of the aggregate (1) When the maximum particle size of the sample is less than 15mm and the thickness of the measurement layer does not exceed 150mm, a small sand filling barrel with φ100mm should be used Barrel test. (2) When the maximum particle diameter of the sample is equal to or greater than 15mm, but not greater than 40mm, and the thickness of the measurement layer does not exceed 150mm, but does not exceed 200mm, a large sand filling cylinder with a diameter of 150mm should be used for testing. (3) If the maximum particle size of the aggregate reaches 40mm ~ 60mm or exceeds 60mm, the diameter of the sand filling tube and on-site test hole should be 200mm. The φ150mm sand filling tube is commonly used on construction sites. Its measuring depth is 150mm, and its measured compaction is only the compaction of this 150mm. However, the thickness of the on-site compaction layer is often around 200mm, and generally the degree of compaction is relatively high in the compacted surface layer, which is difficult to ensure downwards. Therefore, aggregates containing more gravel on mountainous sites should use large sand filling tubes with a diameter of 200mm. Testing is advisable. 3.2 The impact of the accuracy of indoor sand measurement calibration on the degree of compaction (1) The impact of the sand surface height and the total weight of sand in the sand storage cylinder on the sand density in the "Highway Geotechnical Test Procedures" (JTJ 051-93) The height and quality of the inner sand are clearly specified. The distance between the height of the sand in the cylinder and the top of the cylinder does not exceed 15mm. The reason is that sand with different sand surface heights has different falling speeds, so the density of the sand poured into the calibration tank is also different, which directly affects the density of the measuring sand. . Therefore, the height of the sand surface in the sand storage cylinder must be strictly controlled; in addition, the mass of the sand in the cylinder must be accurate to 1g. This quality is maintained during each calibration and subsequent tests. Because during calibration, as long as the total weight of the sand is the same, that is, the self-weight of the sand is the same, obviously its falling speed can also remain consistent, thereby improving the accuracy of measuring sand. Practice has proved that during on-site testing, the height and weight of the sand surface in the sand storage tube were consistent with those during indoor calibration, which greatly improved the accuracy of the detection data. (2) The influence of the depth of the calibration tank on the density of the measured sand. The test results show that for every 1 cm decrease in the depth of the calibration tank, the sand density decreases by approximately 1.2. It can be seen that the different depths have a greater impact on the sand density. Therefore, the depth of the on-site test hole should be as consistent as possible with the depth of the indoor calibration tank. (3) The influence of the particle gradation composition of sand on the density of measured sand. Sand with different particle sizes has different gradations and obviously different densities. Therefore, standard sand (0.30~0.60mm) must be used for measuring sand during each test. or 0.25~0.50mm), and the sand must be kept clean and dry. It can be seen from the above that the height of the sand surface of the sand storage tube, the total weight of the sand, the depth of the calibration tank, the particle composition of the sand, etc. all affect the density of the measured sand to a certain extent. Whether the sand density calibration is accurate or not will also affect the detection accuracy of roadbed compaction. Therefore, before conducting roadbed compaction testing, the calibration work cannot be ignored and must be given sufficient attention. 4 Precautions for on-site testing 4.1 During on-site testing, the height and weight of the sand surface in the sand storage tube should be consistent with those during indoor calibration. 4.2 Try to use the substrate as much as possible to ensure test accuracy. 4.3 Try to make the detection surface as smooth and flat as possible.
After the on-site test, check whether there is any sand leakage between the bottom plate of the sand filling tube, the base plate and the ground. If so, clean it out separately and call its mass. This part of the mass should be deducted when calculating the density. 4.4 The recycled measuring sand must be sieved, washed, dried, and left for sufficient time before next use to make it consistent with the clean, dry and moist conditions at the time of calibration. 4.5 On-site moisture content detection was compared with the drying method and the alcohol method (free liquid surface appears in the submerged aggregate and burned three times). The result did not exceed 1%, which proved to be feasible. However, it should be noted that the purity of the alcohol used must reach 95%. Low-quality alcohol will not only fail to burn fully but will turn into water, affecting the test results. 4.6 The depth of the test pit should be as close as possible to the depth during calibration, the pit walls should be straight, and the diameters of the upper and lower openings should be equal to avoid being larger at the top than smaller at the bottom or smaller at the top and larger at the bottom. Reposted on China Paper Download Center