Key words: 30cm mixed slag +20cm crushed stone +4cm lime soil. From mid-March to early June, I had the honor to practice in Tianjin Avenue Project in Tanggu District, Tianjin. Based on my knowledge and understanding of subgrade engineering of Tianjin Avenue project during my internship, according to the sequence of engineering construction, I wrote a paper by analyzing the key points in subgrade construction. 1. Tianjin Meteorological Hydrogeology Tianjin is located in the warm temperate zone of the northern hemisphere, on the east coast of Eurasia at mid-latitude, with distinct seasons, in the transitional zone of continental maritime climate, and belongs to semi-humid monsoon climate. Spring is dry and windy, and the temperature is changeable; In summer, the temperature is high and wet, and the rain and heat are economical; In autumn, the sky is high and the clouds are light, and the wind is sunny; Winter is cold and dry, with little rain and snow. Annual average temperature 1 ~ 12℃, July average temperature 25.9℃, 1 month average temperature -5℃, extreme minimum temperature -2 1℃, extreme maximum temperature 40.3℃. The annual average rainfall is 652.5mm, the daily maximum rainstorm is 304.4mm, and the maximum snow depth is 29 mm The rainfall in spring and autumn accounts for 10% and 14% of the whole year respectively. Summer is rainy season (flood season) from mid-June to mid-September, with an average rainy day of about 34 days, accounting for more than 73% of the annual precipitation; The blood volume in winter accounts for 1% ~ 3% of the whole year. Tianjin is located in the lower reaches of Haihe River, which is the largest water system in northern China. This project runs from north to south, passing through the center of the plate. There are three first-class rivers such as Yongding River, Zhong Ting River and Ziya River, and three second-class rivers such as Longhe River, Hong Zhong Old Road and South Canal. There are many irrigation and drainage channels along the line. Two. Overview of Tianjin Avenue Project Tianjin Avenue connects Xiaobailou Business District in the center of Tianjin and Yujiapu and Xiangluowan Business Districts in Binhai New Area. It is an urban expressway, starting from Jingu Interchange in the outer ring in the west and reaching Central Avenue in the east, with eight lanes in both directions, with a designed driving speed of 80 km/h. Material requirements (1) subgrade fill 1. Gravel soil and sandy soil with good gradation should be used as fillers first. Peat, silt frozen soil, strong expansive soil, organic soil and soil with soluble salt content exceeding the allowable value shall not be directly used for filling subgrade. 2. This project is located in the frozen area, and it is forbidden to directly fill subgrade with untreated silt. When other fine soil is used, the CBR of subgrade filler should meet the requirements. In addition, fine-grained soil with liquid limit greater than 50% and plasticity index greater than 26 shall not be directly used as subgrade filler. 3. It is forbidden to use swamp soil, peat and silt, and soil with roots, stumps, perishable substances or organic matter content exceeding 5%, chlorine salt content exceeding 3% and carbonate content exceeding 0.8%. 4, the central median and green belt fill according to the requirements of green backfill filling. 5. Fine-grained soil should be broken as much as possible, and the particle size should not be greater than15 mm.. (2) Gravel 1, excluding plant residues, garbage and other sundries. 2. The maximum particle size should be less than 30mm, the crushing value should not exceed 30%, and the strength should not be less than 15MP (unscreened gravel). 3. The particle composition of crushed stone shall meet the requirements of 2# gradation in clause 2.2. 1.6 of JTJ034-2000. For the convenience of construction, 10 ~ 30 mm coarse aggregate, 5 ~ 10~30mm medium aggregate and 0 ~ 5 mm fine aggregate of stone chips should be adopted ... 3. The strength of gravel used for gravel cushion treatment of pond subgrade should not be less than 15MP (unscreened gravel), and the maximum particle size should be less than/kloc-. The selected materials passing through 20mm sieve holes shall not exceed 30% of the total, and the selected materials passing through 0.075mm sieve holes shall not exceed 10% of the total. (3) Steel-plastic two-way geogrid 1, which should be in the form of convex nodes to ensure firm connection, has the following performance requirements: longitudinal tensile strength ≥80KN, transverse tensile strength ≥80KN, expansion ratio ≤3%, joint peeling force ≥350N 2, and in order to minimize the number of overlapping times, the width of steel-plastic two-way geogrid should not be less than 4m. (4) Lime 1, and hydrated lime or quicklime powder should be used for lime; There should be no undissolved quicklime particles in the slaked lime, and the lime grade should be above Grade III. 2. If quicklime is used, the content of available calcium oxide and magnesium oxide in calcareous quicklime should be greater than 70%; If hydrated lime is used, the content of available calcium oxide and magnesium oxide in calcareous hydrated lime should be greater than 50%. 3, lime dosage = lime quality/dry soil quality, lime block should be fully digested for 7 ~ 10 days before use. Hydrated lime should maintain a certain humidity, and dust or excessive moisture agglomeration is not allowed. Hydrated lime should pass through a sieve with the aperture of 10mm and be used as soon as possible. (5) cement 1, cement should meet the requirements of national technical standards, and 42.5MPa ordinary portland cement, slag portland cement or pozzolanic portland cement should be adopted. (6) Soil curing agent 1. The soil curing agent is liquid powdery soil curing agent Ropong EN- 1 (concentrated solution), and the dosage of concentrated solution of curing agent is 0.0 14%, or determined according to the experiment. 2. The technical performance index of the soil curing agent shall conform to the current industry standard "Soil Curing Agent" CJ/T3073, and the solid content of the solution shall not be greater than 3%, and there shall be no precipitation or flocculation. (seven) water should be drinking water or water with PH greater than or equal to 6. Four. Construction Procedure (I) Overall Treatment Scheme for Subgrade Surface As this project is located in wet areas such as paddy fields and reeds, the surface turf, tree roots, humus, garbage and sundries should be removed before subgrade filling, and the subgrade should be roughly leveled and rolled 30cm after surface cleaning, and the compactness should meet the design (90%) requirements. If the degree of compaction cannot be met, 5% plastering can be used; If the lime content of 0 ~ 50cm still cannot meet the requirement of compactness, 50cm gravel cushion should be replaced to speed up the construction progress. When the filling height of subgrade is less than the total thickness of pavement and subgrade, the surface soil of subgrade should be overbreak and backfilled and compacted by layers, and the treatment depth should not be less than the bottom surface of subgrade. The area where the project is located is plain landform, and the soil is clay or silty clay, with rich groundwater and high soil water content. The subgrade of the whole line is in wet and medium wet state, and the surface layer of subgrade needs to be treated according to the actual situation before subgrade filling. 1, road section with filling height greater than 2m (the distance from the lowest point of subgrade to the surface after surface cleaning): After the surface is leveled, the road section exposed to groundwater shall be aired, and temporary drainage ditch shall be set to discharge the surface water. After the bulldozer is unloaded, it will be filled with 30cm mixed slag, and rolled for 3-4 times with a roller above 12t, and then a bidirectional geogrid will be laid, which will be covered with lime soil layer (20cm thick, 5% \). Continue to fill layered compacted lime soil (5% lime, increase the lime content to 8% if it can't meet the compactness and strength requirements of the corresponding horizon) to 80cm below the top surface of subgrade. For the road section of roller that can't bear more than 12t, increase the thickness of mixed slag, and the compactness and strength of each layer can meet the design specification requirements. 2. Road section with filling height greater than 1.3m and less than 2m (the distance from the lowest point of bed to the ground after surface clearing): After the ground is leveled, the road section exposed to groundwater shall be aired, and a temporary drainage ditch shall be set to drain the surface water. After the bulldozer is discharged, 40cm mixed slag is filled, and it is rolled by a roller for 3-4 times 18t or more, and then a bidirectional geogrid is laid, and the geogrid is covered with lime soil layer (20cm). 5% lime) 2m, continue to fill layered compacted lime soil (5% lime, increase ash to 8% if it can't meet the compactness and strength requirements of the corresponding horizon) to 80cm below the top surface of the roadbed, and increase the thickness of mixed slag for the road section of the road roller that can't bear more than 18t, so that the compactness and strength of each layer can meet the design specification requirements. 3. Road section with filling height less than 1.3m (the distance from the lowest point of the back road bed to the ground surface): the ground surface continues to be excavated to the height of 1.3m on the top surface of the road bed, and the accumulated water on the ground surface will be drained, then 30cm mixed slag will be discharged by bulldozer and filled, and it will be rolled for 20cm times with a roller above 18t, and then the gravel will be filled continuously in two directions (. When the filling thickness of mixed slag is large, it should be filled and compacted by layers, each layer is 20 ~ 25 cm. 2. When filling mixed slag, the water content should be strictly controlled. If the water content is large, it should be dried properly before rolling. In addition, mixed slag with high soil content should be avoided. If the materials with large soil content enter the site, they should be piled up first, and then mixed with other mixed slag with small soil content and filled into the subgrade. 3. The strength of the mixed slag shall be no less than 15MP, and the maximum particle size shall be less than 150mm. The materials passing through the 20 mm sieve hole shall not exceed 30% of the total amount, and the materials passing through the 0.075 mm sieve hole shall not exceed 10% of the total amount. Large-particle slag stones should be filled in the lower part and small-particle slag stones should be filled in the upper part to ensure the flatness of the mixed slag top. 4. Pay attention to the drainage of the base tank in rainy days to prevent the mixed slag from being crushed under the condition of excessive water content. 5. In order to prevent the foundation from being compacted due to excessive disturbance, vibration rolling is strictly prohibited during the rolling process of the road roller. But at the same time, in order to ensure the compactness of the filler, the transverse joints should overlap 50cm during the rolling process to ensure no pressure leakage and even rolling, and the rolling times should be strictly controlled at 4 times. The requirements for crushed stone packing and mixed slag rolling are the same. (3) Gravel packing is 1. Because the thickness of gravel filling is only 20cm, the elevation of the top surface of mixed slag should be strictly controlled to prevent mixed slag from invading the scope of gravel filling and reduce the thickness of gravel filling. 2, gravel packing particle size should be controlled within 5cm, the total throughput of 0.075mm does not exceed 65438+/-00% of the total, and the grading is good, without sundry. 3. The strength of gravel used shall not be less than 15MP (unscreened gravel). 4. Gravel with large particle size is filled in the lower part and gravel with small particle size is filled in the upper part to ensure the smoothness of the top of the gravel (the error is less than 2cm). (4) Laying steel-plastic two-way geogrid 1. It is forbidden to contain strong acidic and strong alkaline substances in the fillers directly contacted by geogrids. 2. The laying of geogrids in general sections should be perpendicular to the direction of embankment axis, and the geogrids in the subgrade treatment section at the bridgehead should be laid along the direction of embankment axis. 3. The connection between geogrids shall be firmly bound with plum-blossom nylon fasteners, with the overlapping length not less than 30cm and the spacing not more than 3 grids. 4. After the geogrid is laid, it should be filled with seasoning in time to avoid long-term exposure to the sun, and the time interval between laying and filling should not exceed 48 hours. 5. Measures should be taken to avoid damage to geogrids during construction, and repair or replace them in time. 6. Geogrids shall be laid level, straight, smooth and tight, close to the bearing layer, and shall not be twisted and folded. 7. The first layer of filler on the geogrid should be leveled and rolled by light machinery, and all vehicles and construction machinery are only allowed to drive along the embankment. 8. When laying geogrids, the length of not less than 2m shall be reserved on both sides of the embankment, which shall be folded back and covered on the compacted fill level, and the exposed part shall be covered with soil. 9. The mixed slag layer is roughly flat and dense, and the large stones should be pressed into the lower soil as far as possible or picked up manually to avoid the stones rotting the geogrid. 10. The grader should pay attention to the cutting strength when leveling the gravel. Found geogrid, immediately closed. Someone must keep an eye on the scene at ordinary times, and problems will be dealt with manually in time. (5) The subgrade construction and filling requirements are 1. Generally, subgrade section filling treatment (1) The subgrade must be filled by layers and rolled by layers. The maximum compaction thickness of each layer shall not exceed 20cm (the compaction thickness can be increased appropriately after the compaction mechanical energy ensures the compaction degree and is qualified by the field test), and the compaction thickness of the last layer on the top surface of the road bed shall be 20cm (in case of special circumstances that do not meet the design requirements, the minimum compaction thickness shall not be less than 10cm). (2) The water content should be controlled within 2% of the optimum water content for compaction. (3) Each side of subgrade filling width is 30cm wider than the design width of filling layer, the compaction width is not less than the design width, and finally the slope is nailed. (4) The subgrade surface should have 2% ~ 4% outward cross slope to prevent water accumulation. In order to prevent subgrade slope from being washed by rain, temporary drainage dam and drainage facilities are required to be set two meters away from the downhill foot of subgrade when subgrade is filled. (5) Centralized soil borrowing is prohibited in the range of 10m outside the land requisition line. (6) It is forbidden to be used as a construction access road within the scope of subgrade filling. (7) The subgrade filling should be uniform and dense, and the transverse slope of the top surface of subgrade should be consistent with the transverse slope of road arch. (8) The compactness, minimum strength and maximum particle size of subgrade filler shall not be less than the requirements in Table 1. Compactness of subgrade, Table 1 Item Classification Compaction Degree (%) (heavy compaction standard) Maximum particle size of filler (cm) Minimum strength of filler (CBR)% Upper subgrade bed of embankment (0 ~ 30cm) ≥ 96 108 Lower subgrade bed (30 ~ 80cm) ≥ 96 105 Upper embankment. ≥ 93 153 zero fill excavation subgrade (9) subgrade filling height The minimum filling height of subgrade must ensure that the stability is not affected by groundwater, surface water, capillary water and frost heaving. This project is an urban road, and the minimum filling height of subgrade design should be greater than the critical height of subgrade in wet or moderately wet state. According to the underground water level revealed by drilling along the line (drilling time is the most unfavorable season in June) and the critical height of subgrade in wet and moderate wet state in Ⅱ 4 area, the minimum filling height of subgrade is shown in Table 2. Under moderate humidity, Table 2 Name of Minimum Fill Height in Wet State Hole Location ZK48 ZK49 ZK50 ZK5 1 Aperture Elevation 2.25 1.9 1.35 2.55 Static Water Level Buried Depth (m) 1.3 0.9 1.75. 0.80 design elevation of wet subgrade (m) 3.90 3.95 3.60 3.75 wet fill height (m)1.62 2.02 2.221.17 design elevation of wet subgrade (m) 3.20 3.25 2.90 3.05 wet fill height (. 8+0.55 0.5 2. Treatment of special subgrade section (1) The subgrade filling section of the bridgehead approach section is in a medium wet state. After the existing ground is cleared and leveled, the subgrade soil is backfilled, and then 20cm soil curing agent is used to cure lime soil (5% lime) +20cm soil curing agent cement lime soil (2% cement +3% lime) below the top surface of subgrade. (2) Treatment of subgrade in pond section ○ 1 The route shall be dammed, pumped, dredged and leveled at the place where it crosses large ponds and ditches, and then compacted mixed slag (20cm ~ 30 cm per layer is appropriate) shall be filled in layers to below the top surface of subgrade 100cm. After the steel-plastic two-way geogrid is laid, 20 cm gravel should be filled, and lime soil should be filled in layers above the gravel. Ponds, ditches and other slopes should be stepped, with a height of 0.4m and a width of ≥0.6m, and steel-plastic two-way geogrids with a width of ≥ 1.6m should be laid at the opening. ○2 When the route crosses a large pool, before filling the mixed slag cushion and laying the geogrid, the dam between the pools should be leveled to ensure the integrity of the subgrade. (3) Treatment of subgrade at bridge head ○ 1 According to geological conditions, fill height and construction period, the treatment method of reinforced soil piles (cement mixing piles) and lime soil (8%) is adopted, and the reinforced soil piles are arranged in plum blossom shape. The slope within the lateral arrangement range of reinforced soil piles shall be at least 1.0m beyond the toe of the approach slope. 2 After the pile is completed, the pile head shall be chiseled 50cm, and the top of the pile shall be paved with 30cm gravel cushion, then with geogrid, and finally with 30cm gravel cushion. A. 3 bridgehead processing range control in 50 m.. According to the adverse settlement before and after the treatment, 8% lime soil is used as embankment filler within 50m near the bridge head (except for the backfilling of abutment back), and the filling filler shall be compacted in layers, with the degree of compaction reaching 90%. Backfill of abutment adopts 14% lime-soil layered rolling. (6) The lime-soil filling construction shall be carried out in accordance with the "four sections" and "eight processes". The "four stages" are "paving area, drying and mixing area, leveling and rolling area and applying for curing", and the "eight processes" are "paving, drying, dust removal, mixing, leveling, rolling and curing". The specific construction technology is as follows: 1. Before the test calibration, the natural water content and liquid plastic limit of soil should be determined by taking field soil samples, and the standard compaction test should be carried out to determine the best water content and maximum dry density. 2, measuring lofting survey group accurately released the road centerline. 3. When filling the embankment, use excavators and loaders to load the soil into dump trucks and transport it to the filling subgrade. According to the width of subgrade, the volume of dump truck and the thickness of loose paving, make a grid with lime sprinkling line to determine the unloading position of each truck soil to ensure the thickness of filling soil. 4. After coarse paving of plain soil, the elevation should be determined according to the virtual paving coefficient. If the post-bid can't reach the design value after considering the virtual paving coefficient, measures should be taken in time to remedy it. After meeting the requirements, it is necessary to turn over the soil and roll it with a plow and a rotary tiller. Check the water content of soil before plastering, and plaster it in time when it is close to the optimal water content. 5. Lime paving: After the plain soil is leveled and compacted, the squares are paved according to the eyeliner of 5× 10m, and the amount of lime required for each square is evenly distributed manually in proportion. When applying ash, ensure that there are no impurities and undigested ash blocks in the lime soil. 6. Road mixer mixing: After lime paving is completed, it must be mixed with road mixer for more than 2 times. The mixing depth shall be checked by the personnel behind the road mixer at any time, and the mixing depth shall be 5 ~ 10 mm below the top surface of the road bed, so as to ensure that there is no plain soil interlayer, uniform mixing, consistent color, and no ash clusters and stripes. The water content and ash dosage of the mixture should be tested, and the water content should be controlled at the optimal water content. 7. Leveling and rolling: track and control the elevation with grader and level gauge. When the elevation and transverse slope meet the requirements of the specification, first stabilize the pressure with vibratory roller, then vibrate twice, then roll it with 18 ~ 2 1t roller for three times, and roll it from the shoulder to the center of the road. When rolling, the wheel tracks overlap 1/2 wheel width, and the shoulder should be pressed 2 ~ 3 times more. It is forbidden for the roller to turn around or brake suddenly on the completed or rolling section to ensure that the surface of lime soil is not damaged. If the phenomenon of "spring" appears in the rolling process, measures such as digging and filling or mixing lime or cement should be taken to deal with it. Before the roller is rolled, the grader shall be used for final leveling again, so as to make it longitudinal and comfortable and the road arch meet the design requirements. The final leveling should be carried out seriously, and the local higher parts must be scraped off and the road surface swept away. The local low-lying areas will not be patched up, but they can be handled when paving the lower layer. 8. Test and detection: After the completion of the first section of subgrade, the tester shall test and detect the pavement shape, compactness and ash dosage. In a timely manner, after passing the self-inspection, report to the supervision engineer for acceptance. After the acceptance, proceed to the lower construction. Measurement frequency of shape management and inspection method of specified value of quality standard items, vertical elevation (mm) of frequency+5 ~-20, thickness (mm)- 10 ~-25, width of 26 points (1500 ~ 2000m2) not less than design value, and flatness (1 2000m2). Every 200 linear meters, 2 places, each continuous slope 10 foot (%) +0.5, -0.5 per 100 linear meter, 3 places I sent are word documents, some formats are definitely incorrect, please modify them yourself.