According to the technical requirements of the route location, the subgrade is constructed with strip structure, which bears the traffic load transmitted by the pavement and the self-action of water and freezing. Subgrade is an important part of expressway, and the pavement foundation of the main project of expressway runs through the whole expressway, which is connected with bridges and tunnels and bears the traffic load together with the pavement. Its poor construction quality directly affects the service life of expressway. Practice has proved that without a solid and stable subgrade, there is no stable pavement. In order to ensure the quality of subgrade engineering and improve the quality of the whole highway, this paper mainly introduces the construction technology of expressway subgrade for reference by peers. 2. Embankment filling construction 2. 1 Embankment base treatment Before filling, the base treatment should be done well according to the requirements of technical specifications in the bidding documents, and corresponding treatment measures should be taken according to the soil quality, hydrology, planting conditions and filling height of the base, and the access road should be opened. Use bulldozers, graders and excavators to clean up the original trees and plants within the subgrade filling range, and the topsoil removal depth is 10 cm ~ 30cm. Remove topsoil sundries and pile them in the deep ploughed section between the toe line of subgrade at one side of the construction road and the highway boundary markers. The soil should be loosened, destroyed, leveled and compacted, and then passed through paddy fields, ponds and depressions. According to the specific situation, treatment measures such as drainage, replacement, riprap and siltation should be taken. Leveling with a grader, and removing the original surface of the surface with a roller for rolling. Compaction should meet the design and specification requirements. The quality, compactness, elevation and quantity of surface cleaning shall be reported to the supervision engineer for approval. 2.2 Filling test and compaction test of embankment filling. It is suitable for gravel soil, gravel soil and some soils in cohesive silt. These soils have strong internal friction, cohesion and water permeability, reasonable water content space, easy compaction, sufficient strength and stability, and some soils can be used as fillers after softening with water. Particle analysis test; Water content, density and phase density test; Heavy compaction test of soil (to determine good dryness and water content); Soil strength test (value); Test soil mechanical content and soluble salt content. , to ensure that it can meet the requirements of subgrade filling. 2.3 Preparation before construction 2.3. 1 Before the construction is postponed, the traverse, line and leveling points shall be re-measured, and necessary traverse points and leveling points shall be added according to the actual situation on site, and the measurement shall be approved by the supervision engineer. Then according to the drawings, the subgrade line, slope toe, side ditch, cutting slope top, borrow pit, spoil ground and other positions are released. 2.3.2 Earth-filling machines, bulldozers and road graders, especially road graders, shall control the thickness and smoothness of the filling layer. 2.3.3 Before the drainage ditch is set, temporary drainage ditch should be built in combination with permanent drainage facilities, and 4% cross slope should be set, or low ridge should be filled at the edge of the surface to stop water. A drainage trough shall be set every 50m along the line, and the bottom of the trough shall be covered with waterproof cloth or plastered with mortar, so as to keep the subgrade construction site in a good drainage state. 2.4 The construction of the test section should choose the road section with good quality conditions and representative section, and the test section should be constructed around the test section. Construction parameters should be determined: suitable loose laying thickness of the same filler, good mechanical matching, good rolling times of the same compactor, good construction organization, etc. 2.5 Filling operation 2.5. 1 Soil subgrade filling should be paved in parallel layers. The paving thickness of each layer shall be determined according to the type and specification of compaction machinery, and the paving width of each layer shall be greater than 30cm, and exceed the design width of each layer of embankment, so as to ensure the sufficient compaction of the edge of the brush slope embankment. The full width of the embankment should be paved with uniform materials, leveled with a leveler, and the embankment with a cross slope of 2.5.2 of stones and earth-rock mixture should be filled. Earth-rock subgrade can be filled in layers, and the thickness of each layer should be determined according to the type and specification of compaction machinery, and should be greater than 40cm. The full section width of each layer of filler shall be paved continuously, and blasting mixture shall be allowed to be directly filled into the embankment. The particle size of the stone to be filled should be 2.5.3, and the treatment measures of cutting the foundation should be taken to deal with the diseases such as water seepage of cutting the foundation. Effective measures should be taken according to the actual situation, such as replacing and filling, making blind ditches, deepening the depth of side ditches and other areas with strong soil and rock weathering, which must be over-excavated and over-filled. The compaction degree should be 2.6, and the problems that should be paid attention to in subgrade filling. Fillers with the same properties should be filled horizontally in layers and mixed with the filling layer to ensure the uniform strength and permeability of this layer. If filled at the same time, the layers should overlap and connect with each other. 3. Subgrade compaction technology and detection compaction work. The selection and reasonable operation of road roller is an important part of road construction project, which will affect the compaction effect of subgrade. In addition, the comprehensive factor 3. 1 will affect the practical experience of subgrade detection and analysis, and will affect the compaction function of subgrade, rolling machinery, bearing layer strength, moisture content of subgrade soil, etc. According to the requirements of filler performance, choose a reasonable rolling machine. Through the trial paving test section, the loose paving thickness and rolling times, subgrade pre-filling treatment and compaction are determined. To solve the problems of compaction function, rolling technology and bearing layer strength. It is difficult to control the water content of subgrade filler because of the great changes in borrow site, earth-rock type, climate and meteorology. Moreover, it is difficult to compact the subgrade under good water content. The compaction degree must be controlled by the water content and water content of the soil. It should be dried in the air until the water content is good, and then rolled. The project should be continuously operated to reduce rain and exposure to prevent the change of soil water content. In addition, during construction, we should also pay attention to the compaction and filling of some special parts with narrow area (referring to the junction of construction section, the back of building abutment, the back of wall, the place where construction machines and tools arrive, etc.). ), and choose the appropriate filler, using type equipment for rolling, such as flat vibratory roller, hand-held two-wheel roller, etc., the compaction thickness is controlled at 65438+ the water content is strictly controlled. 3.2 Compactor configuration Ten important factors affect the compaction effect of compactor. The good water content of the same soil decreases with the increase of compaction work, and the dry density increases with the increase of compaction. The higher the density of compaction, the same compaction machine should be used in the same yard. Configuration of each construction section: self-weight, vibratory roller, towed cam vibratory roller 3.3 Compaction of subgrade 3.3. 1 Before compaction of earth embankment, it shall be leveled by leveler, and the water content of filler shall be controlled to be better than (determined according to the climate). First of all, the static compaction and vibration of 3.3.2 should be carried out. Before the earth-rock mixed embankment and soil mixture embankment are compacted, the filled stone pores should be leveled with bulldozers on the dense and flat working face, and filled with stone chips. The filler should be separated from the rolling process of the roller, and the gap should be filled with stone or stone chips continuously until the stone is loose and the surface is smooth. According to the regulations, the compaction degree of road base from 80 cm to 150 cm of expressway pavement must be ≥95%. The compaction degree of embankment base is suitable for 93% 3.4 subgrade compaction degree detection and subgrade filling. After each layer is rolled, indicators such as compactness, flatness, line elevation and subgrade width shall be used for testing. All indicators meet the requirements, and the filling layer can be allowed to pass. On-site compaction degree detection of subgrade mainly includes sand filling (universal), ring cutter, coring and water bag detection. 4. Road-bridge crossing section 4. 1 graded coarse-grained filler technical treatment measures to reduce the compressibility of embankment itself. Reduce construction settlement, fill coarse-grained materials with high strength and deformation gradation, crushed stones, gravels, cement lime stabilized sand, low-grade concrete, etc. At the crossing section of the bridge, on the premise of ensuring high degree of compaction, the stiffness and deformation of this part are ensured to be uniform. Crossing 4.2 reinforced earth embankment In order to increase subgrade strength, improve embankment stiffness and reduce subgrade deformation, a certain amount of reinforced materials are filled in the bridge crossing section, and the arrangement spacing of lacing materials is adjusted to stop. Step-by-step settlement at the junction between the subgrade at the back of the bridge and the bridge becomes continuous slope settlement, which makes the cross section of the bridge smooth. 4.3 The reinforced concrete slab is used to reduce the stiffness difference of the crossing part of the bridge. Reinforced concrete slab is set in the subgrade fill in the bridge crossing section, with one end supporting the rigid foundation abutment and the other end simply supported on the sleeper beam, which makes the crossing both rigid and flexible and eliminates the phenomenon of bridge jumping. 4.4 Lightweight materials are used for filling. Fill the bridge subgrade with EPS (polystyrene foam plastic), industrial foam mixed soil (foamed cement mortar), volcanic ash, fly ash, etc. The compression deformation of embankment filler at the back of the bridge is significantly reduced, the vertical load of the foundation is weakened, the horizontal pressure of the abutment structure is reduced, and the settlement of the foundation is reduced. Conclusion: To sum up, this paper mainly analyzes the expressway subgrade construction technology, subgrade compaction quality control means, and analyzes these knowledge, so it is necessary to carry out expressway subgrade construction, and carry out tests and tests. Frontier technology has not been applied to the quality control of expressway subgrade filling project, and its construction quality depends on management, project implementation, summing up experience when problems are found, formulating effective management measures for the whole project, and ensuring the implementation of standardized design, thus improving the quality of highway subgrade construction and the quality of the whole road.
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