A tunnel located in the loess and different stone quality, variable geological section, in order to smoothly remove the cave water, the pavement grass-roots level will be designed into a drainage structure, to ensure the quality of pavement drainage grass-roots level engineering, is to ensure that after the work of the operation of one of the important factors of safety.
Tunnel lining adopts elastic anti-drainage design, and waterproof board, geotextile and ring and longitudinal soft permeable pipe are set up between the initial support and the second lining; the pavement base layer adopts 15cm cement stabilized graded gravel as the permeable layer, so that infiltration water in the tunnel enters into the cement stabilized graded gravel base layer through vertical seepage, then seeps into the longitudinal gravel layer, and enters into the longitudinal concrete drainpipe to be discharged.
Cement concrete surface drainage base layer (cement stabilized open-graded gravel)
The back arch is filled with C10 schist concrete concretes and covered with clean 1-2cm gravel layer to form a drainage ditch back arch C25 concrete
Tunnel Drainage System Schematic Diagram1Technical Principle and Characteristics of Cement Stabilized Open-Graded Gravel Permeable Base LayerCement stabilized open-graded gravel is used to drain the water through the tunnel, and then the water can flow into the longitudinal concrete pipe, and then into the longitudinal concrete pipe to drain. The cement stabilized open-graded gravel is made of graded gravel without or with less than 4.75mm particle size, and mixed with a certain ratio of cement. Reasonable group distribution ratio is chosen to improve the bearing capacity of permeable grass-roots level and to meet the drainage function. The construction method, process, mechanical equipment and other aspects of the general pavement grass-roots level is the same. Pavement permeable grass-roots level should have a strong bearing capacity, good drainage effect, wide adaptability features, in the tunnel project has a good value of promotion.
1.1 Advantages of cement stabilized open-graded gravel permeable grass-roots level
(1) The gravel aggregate without cement treatment is prone to segregation in construction paving, and is not easy to be compacted in crushing, and also is prone to deformation under the action of construction machinery;
(2) Stabilized continuous graded gravel is relatively dense, and the coefficient of permeability after cement treatment K< 300m / d, can not meet the drainage design specifications;
(3) cement stabilized open-graded gravel that can meet the drainage requirements, but also to meet the strength requirements.
1.2 Drainage and strength of cement stabilized open-graded gravel
(1) The permeability coefficient of cement stabilized open-graded gravel is controlled between 1000m/d and 6000m/d, and the drainage effect should satisfy the drainage design requirements;
(2) Mixing a certain proportion of cement to make the aggregate mix uniformly and under mechanical compaction to achieve compactness, and the strength of the no-limit to meet the strength and bearing capacity requirements. strength and bearing capacity requirements.
2, cement stabilized open-graded gravel ratio
Design of cement stabilized open-graded gravel and large-hole gravel concrete is the basic difference between the components of the ratio and molding specimens are different. Big hole gravel concrete ratio to concrete strength requirements for ratio design, molding specimens using 150 × 150 × 150mm test mold, take 28 days strength for strength verification standards. The cement stabilized open-graded gravel ratio based on the design strength, while meeting the drainage requirements, using Ф150×150mm mold, molding specimens to take 7-day unconfined compressive strength and water permeability test as a verification standard.
How to choose gravel gradation, mixed with how much cement, in order to meet the grass-roots bearing, drainage dual function requirements, is critical.
2.1 Selection of materials
(1) cement: ordinary silicate cement P.O32.5 should be preferred, the initial setting time is more than 3h, the final setting time is less than 6h, and other indicators in line with the current national cement standards;
(2) crushed stone: should be selected clean, hard gravel, crushed value should not be greater than 30%, the largest particle size of 20cm, and shall not exceed the thickness of 2/3 of the layer, 4.2%, 4.3%, and the maximum particle size should not be greater than the thickness of the layer. Layer thickness of 2/3, 4.75mm particle size content should not be greater than 10%, aggregate grading should meet the requirements of water permeability (permeability coefficient should not be less than 300m/d)
(3) water: drinking water or other water sources qualified by the test 2.2 Component ratio selection component ratio design, the following influencing factors should be taken into account: according to the design of permeability coefficient (k=1200m/d), select the appropriate gradation, the design of the water permeability coefficient (k=1000m/d). According to the design permeability coefficient (k=1200m/d), select the corresponding graded gravel, gravel technical indicators should be in line with the current national standard.
Cement, gravel according to the design of the trial proportion of mixing, according to the inorganic binding material stabilized soil compacting method of heavy-duty type, to find out the ρ dry max and the optimal moisture content W value.
According to the specification of the grass-roots compaction requirements (98%), to determine the specimen dry weight ρ dry = ρmax × 0.98. Known optimal water content W, to find the wet weight. Know the volume of the test mold to get, calculate the mass of the specimen. Preparation of specimens 9 or 13 specimens as a group. The 7-day unconfined compressive strength as the selection of the optimal fit ratio index.
(5) Calculate the material mix ratio and the amount of cement per m3 mixture, known: W value, n value; Calculate the cement: gravel: water combination ratio, and then according to ρ dry max calculate the amount of each party.
3, cement stabilized open-graded gravel quality control
3.1 test section of the tunnel pavement grass-roots level is 15cm thick, cement stabilized gravel permeable layer permeability coefficient is required to ≥ 300m/d, the maximum particle size of the gravel is less than 25mm, the design strength of 4Mpa.
(1) the main construction machinery and construction methods: YZ18JC road roller and 750L forced mixer, 6 sets of 1m3 transportation trucks, an air rammer, manual leveling.
(2) construction process: YZ18JC roller static compression once, micro-vibration four times, and finally static compression once, requiring no wheel tracks after rolling.
3.2 Quality control of cement stabilized open-graded gravel permeable grass-roots level
3.2.1 Quality control of construction preparation
(1) Raw materials and machinery preparation is strictly in accordance with the design of the laboratory ratios for the construction of the site control of sand, gravel and cement and other raw materials should be in accordance with the specification requirements. The use of forced concrete mixing machine, mixing capacity can not be less than 750L.
(2) construction sampling and elevation control in the accurate measurement of the baseline, on both sides of the cable trench with an ink line marking out the top of the grass-roots level elevation and elevation of the cement concrete pavement line, as the construction of the construction personnel and loose pavement coefficient of the control basis.
(3) clean up debris, installation of drainage pipes in the paving mixture must be cleared before the original ground debris, with water to the floating turbid cleaning, will be discharged out of the sewage hole, to prevent sewage soaked into the center of the drainage ditch. Center drain must be designed to play a good drainage holes in the precast concrete round pipe installation in place, the pipe is covered with clean 1-2cm of gravel.
3.2.2 Construction quality control of the actual amount of cement should be higher than the design amount of about 0.5 ~ 1.0%, the water content should be greater than the optimal water content of 1 ~ 2%. In order to prevent the mixture from segregation, the funnel mouth should be added skewer.
Transportation vehicles will be mixed mixture to the scene, according to the loose paving thickness marking line for paving, leveling, with a three-meter straightedge horizontal scraping, more push less make up, hanging line to adjust the cross-slope. The length of the paving section is controlled by time, generally within 2h, according to the mixing and transportation capacity, the paving length of the project is about 15m. Paving a good section of rolling a section, rolling according to the order from the sides to the middle, two wheels staggered 1/3, with 18T roller steady pressure 1-2 times, and then micro-vibration 3 ~ 4 times; in a section of construction compaction, the transverse construction joints into a straight seam, in order to be connected with the construction of the subsequent section of the road.
Construction process to choose a representative point, using sand filling method to detect the compaction, to meet the specification requirements to stop rolling. Grinding termination of the compaction test is shown in Table 4. construction to record the number of grinding, loose paving coefficient, grinding time, in order to summarize, improve.
3.2.3 Post-work quality testing (1) permeability comparison test in the case of permeability test conditions do not have, with reference to the asphalt pavement permeability test measured permeability coefficient K, with the same ratio, the gradation of the aggregate is different on the permeability coefficient and strength of the impact is greater, in particular, the content of 4.75mm a most prominent.
(2) choose 100m as a test section, according to the laboratory type with the selection of the best ratio, mixture by mixing, transportation, paving and leveling, rolling, with a three-meter ruler to detect the flatness index, in line with the design requirements.
(3) in the permeable grass-roots test section drilling four Ф10 × 10cm cylindrical core samples, core sample integrity is good, strength to meet the design requirements.
4. Conclusion
The test section proves that the cement stabilized open-graded gravel permeable layer, the use of conventional test and inspection methods, the construction machinery and equipment investment is not much, can reduce the cost of the project, the indicators to meet the grass-roots level strength and permeability requirements. It is worth to popularize the application in the tunnel grass-roots level of highway and other grass-roots level with drainage requirements.
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