Road and bridge engineering; Road and bridge engineering construction; Subgrade pavement; Subgrade pavement construction; construction technique
With the rapid development of China's economy and the vigorous promotion of urbanization, the demand for highway and bridge engineering construction in China is increasing day by day, and high-level highway and bridge engineering construction needs systematic technical system as guidance and construction means.
Stable subgrade quality and smooth pavement environment are the keys to reflect the quality of highway bridges. However, due to the tight construction period, large engineering quantity and complex construction environment, there are still many problems to be solved in the current construction, which must be strictly controlled.
I. Characteristics and Requirements of Road and Bridge Subgrade Construction
In the whole construction process, due to the influence of natural factors in different seasons, the construction progress is difficult to control; The construction involves a wide range and the project is relatively complicated. Subgrade construction needs to be carried out under any conditions, including climate, topography, geology and other natural factors. The construction period is long, which consumes a lot of time and manpower. Often a project takes about a year to complete, while individual projects take longer and require a lot of investment in funds. The subgrade construction of roads and bridges should be carried out according to the design carefully. On the premise of ensuring the smooth completion of the construction period and quality assurance, raw materials and funds shall be used reasonably according to local conditions, and all indicators shall meet the standards set by the state and relevant departments, so as to save land area and protect ecological environment and resources. Especially in the construction of bridge subgrade, the drawings should be carefully studied according to the construction sequence of bridge structure and the actual arrangement on site to be accurate. Strictly control the construction standards, check whether there is any problem with the template at any time, and do a good job of health preservation. Unless it meets the unified national standards, it is impossible to open it for use.
Second, the problems existing in the construction process of highway bridge subgrade and pavement
1, road surface of highway bridge is uneven.
The smoothness of highway bridge pavement belongs to the main testing part of highway engineering projects. If the operation procedure is not well controlled in the construction, it will accelerate the attenuation of pavement smoothness, lead to accelerated vehicle wear, and make the vehicle unsafe. The reasons leading to the unqualified smoothness of highway bridge pavement are as follows: the smoothness of base is not strictly controlled, and the subgrade pavement fluctuates; The control of pavement construction is weak, the technical level of operators such as pavers and rollers is not high, and the operation methods are improper; Slipping shoes or baseline out of control, etc. All these directly affect the standard of pavement smoothness of highway bridges. To control the pavement smoothness, we must start with the subgrade pavement, strictly control the construction quality of technicians, and ensure that the pavement smoothness of highway bridges reaches the standard.
2. The beam expansion joint is poorly connected with bridge end transition slab.
The difference between abutment settlement and bridge head filling leads to insufficient connection between beam expansion joint and bridge end transition slab, forming a step shape at the interface, which reduces the speed of passing vehicles, can not run the designed full-line speed, affects the safety and comfort of driving, and has a great impact on the bridge. The reason lies in the choice of backfilling materials for abutment back. Using some backfill materials with poor compactness and drainage can not form good compactness, which leads to settlement, thus affecting the connection between beam expansion joints and bridge end transition slab.
3. Subgrade and pavement surface damage
Shortly after the completion of the project, the pavement of highway bridges appeared large-scale, many different degrees of fracture and damage. The reasons are as follows: the smoothness of subgrade and pavement is pursued unilaterally in construction, but the compaction of subgrade is ignored, the material ratio is improper, the quality of matrix asphalt is not up to standard, and the bearing capacity of subgrade and pavement is unevenly distributed due to thermal expansion and contraction caused by high and low temperatures, resulting in excessive deflection and fracture of subgrade and pavement; The shrinkage of subgrade pavement materials causes reflective cracks in asphalt on subgrade surface, which leads to the damage of pavement subgrade; Pavement water seeps into subgrade soil along highway cracks, causing corrosion damage to subgrade and reducing the strength and stability of subgrade pavement. Cracks and fine lines appear in the rolling process, and the catalytic action of sunlight and water erosion makes the surface concrete and asphalt of subgrade and pavement crack and fracture, which greatly shortens the service life of highway.
Three, road and bridge engineering construction technology of subgrade and pavement
1, analysis of control points of base construction
Highway base is generally composed of cement or lime stabilized structure. Therefore, in order to achieve the design strength, we must first ensure the quality of materials and accurately determine the parameters (mixture ratio, sweating, etc.). ) of each component material, with mechanical mixing, and pay attention to the uniformity of mixing. Under appropriate conditions, water reducing agent or other additives should also be added to improve the properties of materials. The smoothness of the base directly determines the smoothness of the completed pavement, so retarding water reducer can be used to extend the initial setting time and provide time for the paving and compaction of cement joints. For example, when the mixing capacity is 300t/h, the paver is used for paving, the speed is 1.5m/min, and the rolling length is designed to be 50m. Real-time compaction, initial compaction with vibratory roller, re-compaction with smooth roller, and final compaction with tire roller. Compared with the steel wheel roller, the tire roller keeps the compressed structural layer in a stressed state for a relatively long time, and the deformation of the structural layer increases with time, so the compaction effect is enhanced.
2. Subgrade filling
Before filling, clear the roadbed, clear the tree heads, roots, weeds, humus soil, soft soil silt and garbage within the roadbed, backfill the tree holes and toilet holes with gravel, and then pay attention to the soil quality. Try to choose soil containing 50% plastic resin, fill it in layers, spread it in layers, compact it in layers, and detect it in layers. The thickness of layering is about 30 ~ 40 cm, and rolling is controlled at the optimum water content. In order to ensure uniform strength and prevent deformation, when using different soils, the joints at the same level are inclined. The following construction errors: no horizontal stratification, accumulated water on the reverse slope, thick stones, many clods and steep slope. Vertical filling is a method of filling along the center line step by step. Pay attention to the compactness of vertical filling and take necessary measures during construction. Choose vibration or hammer ramming, choose sand and gravel packing with small settlement and uniform particle size, and form the embankment at one time with full width. When filling, try to use mixed filling, that is, the lower layer is filled vertically and the upper layer is filled horizontally. If necessary, measures such as foundation reinforcement grouting, reaming or dynamic compaction can be considered to ensure the compactness.
3. Subgrade and pavement drainage
Water is an important factor affecting the stability and strength of subgrade, and subgrade diseases are mostly caused by water erosion. During subgrade construction, attention should be paid to construction drainage to reduce unnecessary losses. Drainage facilities on subgrade surface generally adopt intercepting ditch, side ditch, rapids, falling water and surface drainage pipes, and drainage ditches are reinforced with mortar rubble, or concrete precast slabs can be used. Blind ditch, underground ditch, seepage well and seepage ditch are generally used for subgrade underground drainage. , mainly through seepage drainage. If the water flow is large, add infiltration pipes on the infiltration ditch.
Four. Concluding remarks
With the rapid development of expressway and urban expressways, a large number of highway bridges and urban overpasses have been built. Due to the importance of bridge structural design in various related industries in China, the technology is quite mature. In highway construction, some common quality problems of subgrade and pavement directly affect the performance and operation safety of highway, so subgrade and pavement construction should be carried out in strict accordance with the requirements of specifications, and different concrete measures should be taken for different subgrade projects. Professional and technical personnel should constantly improve their technical level, strictly control and ensure road diseases in all aspects of design, construction and maintenance, build high-quality projects, and maximize road performance and service life.
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