Recently, with the continuous improvement of China's highway transportation network, highway engineering construction is steadily advancing towards high quality and long service life. As the foundation of highway structure, the roadbed directly carries the vehicle load transmitted from the road surface, and its compaction quality is directly related to the smoothness, stability, and service life of the highway. As a core indicator for measuring the quality of roadbed compaction, if the compaction degree does not meet the standard, it is easy to cause roadbed settlement, pavement cracking, rutting and other diseases, which affect the safety and comfort of highway traffic and increase the cost of later maintenance.
The compaction degree of highway subgrade refers to the ratio of the dry density of the compacted subgrade soil to the maximum dry density of the soil, reflecting the compactness of the subgrade soil. Its detection and control run through the entire process of subgrade construction, following the core principles of "layered compaction, full process detection, and precise control". Industry experts say that the detection and control of roadbed compaction degree is a key link in the quality control of highway roadbed construction. It is necessary to choose appropriate detection methods and control technologies based on factors such as roadbed filling type, construction technology, geological conditions, etc., to ensure that the compaction degree meets industry standards and lay a solid foundation for the quality of highway engineering.
There are many types of compaction testing techniques for highway subgrade, and different testing methods are suitable for different types of fillers, construction scenarios, and testing needs. The commonly used testing methods mainly include the ring knife method, sand filling method, nuclear density meter method, and core drilling method. Each method has its specific operating process and applicable scope, and must be strictly operated in accordance with the specifications to ensure accurate and reliable testing results.
The ring knife method is the most basic and commonly used compaction degree detection method, suitable for the compaction degree detection of roadbed fillers such as fine-grained soil, silty soil, and clayey soil. It is easy to operate and has low cost, and is widely used in the layered compaction detection of highway roadbeds. During the inspection, the construction personnel need to excavate a test pit at the inspection point, take samples with a ring knife, weigh the total mass of the ring knife and the soil sample, calculate the wet density of the soil sample, and then determine the moisture content of the soil sample through the drying method to finally calculate the compaction degree. During the testing process, it is necessary to ensure that the sampling location is representative, the excavation depth of the test pit is consistent with the thickness of the compacted layer, and to avoid soil disturbance during the sampling process, which may affect the accuracy of the testing results.
The sand filling method is suitable for detecting the compaction degree of roadbed fillers such as coarse-grained soil, sandy soil, and gravel soil. Compared with the ring knife method, its detection accuracy is higher and its applicability is wider. It is one of the most widely used methods for detecting the compaction degree of highway roadbeds. This method involves injecting standard sand into the test pit, calculating the volume of the test pit based on the quality and density of the standard sand, and then combining the quality and moisture content of the soil sample to calculate the compaction degree. During testing, it is necessary to calibrate the density of standard sand in advance to ensure that the excavation of the test pit is neat and avoid problems such as pit wall collapse and sand leakage. At the same time, testing records should be kept to ensure data traceability. During the construction of a highway subgrade, the construction unit used the sand filling method to conduct layered testing on the sandy soil subgrade. At least 3 points were tested every 200 meters to promptly identify and rectify areas with substandard compaction, effectively ensuring the compaction quality of the subgrade.
The nuclear density meter method is a fast detection method suitable for the compaction degree detection of various roadbed fillers. It has the characteristics of fast detection speed, convenient operation, and no damage to the roadbed structure. It is suitable for rapid sampling and quality control during the construction process. This method uses a nuclear density meter to emit radiation to detect the density and moisture content of the roadbed soil, and then calculates the compaction degree. The detection process can be completed in just a few minutes. However, it should be noted that the nuclear density meter needs to be calibrated regularly, and obstacles such as underground pipelines and steel bars should be avoided during testing. At the same time, operators must have corresponding qualifications, strictly follow safety operating procedures, and prevent radiation leakage.
The core drilling method is mainly suitable for the compaction degree detection of the base layer, sub base layer, and cement stabilized roadbed under asphalt pavement. By drilling the roadbed core sample with a drilling rig, the density and moisture content of the core sample are measured, and the compaction degree is calculated. At the same time, the compaction uniformity and structural integrity of the roadbed can be visually observed. This method has high detection accuracy, but the operation is relatively complex and the cost is high. It is usually used for sampling inspection and quality verification of key road sections to ensure that the compaction quality of the roadbed meets the design requirements.
Compared to detection technology, the compaction control technology of highway subgrade is more critical. Its core is to ensure that the compaction of subgrade filling meets the standard requirements through scientific construction control, mainly covering multiple technical points such as filling material selection and improvement, compaction process control, and construction process control.
The selection and improvement of filling materials are the foundation of compaction control, and the properties of roadbed filling materials directly affect the compaction effect. Before construction, it is necessary to conduct tests and inspections on the roadbed filling materials, selecting well graded, high-strength, and stable filling materials such as gravel soil, sandy soil, etc; For fillers with poor compaction performance such as silty soil and clayey soil, improvement treatment is needed. Improvement agents such as lime, cement, and fly ash can be added to improve the grading and compaction performance of the fillers and enhance the compaction degree of the roadbed. In the construction of a rural road subgrade, due to the difficulty of compaction caused by the use of silty soil as the on-site filling material, the construction unit improved the filling material by adding 5% lime, effectively enhancing its compaction performance and ensuring that the compaction degree meets the standard.
Compaction process control is the core of compaction degree control, mainly including the selection of compaction machinery, control of compaction thickness, control of compaction speed and passes, and other key points. Compaction machinery should be selected according to the type of filling material and compaction thickness. For fine-grained soil subgrade, smooth wheel rollers, sheep foot rollers, etc. can be used, while for coarse-grained soil subgrade, vibrating rollers can be used to ensure that the tonnage and vibration frequency of the compaction machinery meet the requirements and can effectively compact the filling material. The compaction thickness needs to be strictly controlled, usually not exceeding 20 centimeters per layer. If the compaction thickness is too large, it can easily lead to insufficient compaction of the subgrade layer, resulting in substandard compaction degree; The compaction speed should be controlled at 2-4 kilometers per hour to avoid insufficient compaction caused by too fast speed and construction efficiency affected by too slow speed.
The number of compaction passes should be determined based on the mechanical properties of the compaction machine, the type of filling material, and the compaction thickness. Generally, a reasonable number of compaction passes should be determined through trial compaction, usually 3-5 times, to ensure that the roadbed filling material is fully compacted. During the construction process, it is necessary to follow the compaction principle of "light before heavy, slow before fast, edge before center", gradually improve the compaction effect, and avoid problems such as local compaction not meeting standards and uneven compaction.
Construction process control is an important guarantee for compaction control, and it is necessary to strengthen the quality control of the entire process of roadbed construction. Before construction, the subgrade base needs to be cleaned and compacted to ensure that the compaction degree of the base meets the requirements, laying the foundation for subsequent subgrade filling and compaction; During the process of roadbed filling, layer by layer filling, layer by layer compaction, and layer by layer testing are required. After each layer of compaction is completed, a compaction degree test must be conducted. Only after passing the test can the next layer of filling be carried out to prevent unqualified areas from entering the next process. At the same time, it is necessary to strengthen the professional training of construction personnel, standardize the construction operation process, and ensure the standardized operation and correct testing methods of compaction machinery.
In addition, the detection and control of roadbed compaction degree also need to consider construction environmental factors. Weather conditions such as rainy days, high temperatures, and severe cold can affect the compaction effect of the roadbed. Construction should avoid rainy days, and the roadbed should be dried after rainy days to ensure that the moisture content of the filling material meets the compaction requirements; In hot weather, it is necessary to sprinkle water in a timely manner to moisturize and prevent the filling material from losing water too quickly and affecting compaction; Anti freezing measures should be taken in severe cold weather to avoid freezing of the filling material and affecting the compaction quality.
The reporter learned that with the continuous upgrading of highway construction technology, intelligent detection and control technology is gradually being applied to the control of roadbed compaction degree. For example, intelligent compaction monitoring equipment can monitor the compaction speed, number of compaction passes, compaction degree and other indicators of compaction machinery in real time, provide timely feedback on problems during the construction process, facilitate construction personnel to adjust construction parameters in a timely manner, and improve the accuracy and efficiency of compaction degree control. Industry experts remind that the detection and control of compaction degree of highway subgrade is a systematic project that needs to run through the entire construction process. Construction units need to strictly implement the quality responsibility system, standardize the detection process, strengthen construction control, and ensure that the compaction degree of the subgrade meets industry standards. In the future, with the promotion and application of intelligent and refined construction technology, the level of compaction detection and control of highway subgrades will be further improved, providing strong support for the high-quality development of highway engineering and helping to create a safe, durable, and comfortable highway transportation network.
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