Key words: 30cm mixed slag 420cm a layer of gravel dust 20cm.

I was lucky enough to go to Tanggu District, Tianjin in early June, and worked as an intern in Tianjin Avenue project room in mid-March. I learned about the project according to the internship materials and analyzed the construction sequence of subgrade construction papers.

1, meteorological and hydrogeological conditions

Tianjin is located in the warm temperate zone of the northern hemisphere, on the eastern coast of Eurasia at mid-latitude, with four distinct seasons, and belongs to the semi-humid monsoon climate between the transitional zones of the marine continent. Spring is dry and windy, and the heating is changeable; Due to the temperature and humidity in summer, rain and heat will be helpful. In autumn, the sky is high and the clouds are light, the sun is shining, and in winter, it is cold and dry, with little rain and snow. Annual average temperature 1 12℃, July average temperature 25.9℃, 1 month average temperature -5℃, -2 1℃, extreme minimum temperature 40.3℃, extreme maximum temperature. The annual average rainfall is 652.5 mm, the maximum daily rainfall is 304.4 mm, and the maximum snow depth is 29 mm. The precipitation in spring and autumn accounts for 10% and14% of the whole year respectively. The rainy season (rainy season) is from June to mid-September in midsummer, with an average rainy day of about 34 days, accounting for more than 73% of the annual precipitation; Winter and blood account for 1% to 3% of the whole year.

Tianjin Haihe River Basin is located in the lower reaches of Haihe River Basin, which is the largest water system in the world. In northern China, the project crosses the central sector of Yongding River, Tinghe River and Ziya River from north to south, and basically forms a drainage and irrigation network system.

II. Overview of Tianjin Road Project

Tianjin Road connects the downtown business district with Xiaobailou Jiabao, Xiangluowan business district and urban expressway in Binhai New Area, and reaches the junction of Jingu Outer Ring Road and Donghuan Avenue in the west, with eight lanes in both directions. The design speed is 80 km/h.

Third, the requirements for materials

(1) dike

1, gravel soil with good gradation should be preferred as subgrade filler, and sand should be selected as filler. Peat, silt, soil, strong expansive soil, soil organic matter and soluble salt content exceeding allowable values should not be directly used for filling subgrade.

2. This project is located in the frozen area, and it is forbidden to use untreated silt subgrade for direct filling. When the CBR of other fine soil subgrade fillers 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 soil and silt contain roots and stumps, and the content of perishable substances or organic matter is more than 5%, the content of chloride ion is more than 3%, and the content of carbonate is more than 0.8%.

4. Backfilling and filling in line with the requirements of central isolation belt and environmental protection.

5. Fine-grained soil is finely ground, and the particle size is greater than 15mm and not greater than.

(2) Sand and gravel

1, excluding sand and gravel plants, garbage and other sundries.

2. The maximum particle size should be less than 30mm, the required value should not exceed 30%, and the fine crushing strength should not be greater than 15MP (unscreened gravel).

3. Gravel particles should meet the requirements of JTJ034-2000 2.2. 1.6 No.2 grading, and the construction is convenient. Three kinds of aggregates should be used: 1030mm coarse aggregate, 5 10mm aggregate and 05mm fine aggregate.

3. The maximum particle size of the pond with less gravel subgrade iron strength less than 15MP (unscreened gravel) should be less than 150mm, and the material passing through the 20 mm sieve should not exceed 30% of the total, and the material passing through the 0.075mm sieve should not exceed 10%.

(3) Bidirectional plastic geogrid

1, the two-way plastic geogrid should be in the form of convex nodes to ensure firm connection. The performance requirements are as follows: longitudinal tensile strength: ≥ 80kn; Transverse tensile strength: ≥80KN.

The expansion rate is less than or equal to 3%, and the peeling strength of nodes is more than or equal to 350 N.

2. At the same time, try to reduce the overlapping mode, and the width of the two-way plastic geogrid shall not be less than 4m.

(4) Lime

1, hydrated lime or quicklime powder should be used; The slaked lime particles cannot be digested, and the lime grade should be Grade III or above.

2. If lime content is adopted, the effective lime content of calcium oxide and calcium hydroxide should be greater than 70%, and if the effective calcium hydroxide content of hydrated lime is adopted, it should be greater than 50%.

3. Limestone ash dosage = mass/dry soil mass, and lime blocks should be fully digested for 7 10 days before use. The digestion of quicklime should maintain a certain humidity, neither producing dust nor being too wet to agglomerate. Lime should be perforated with a 10 mm sieve and used as soon as possible.

(5) Cement

1, cement should meet the requirements of national technical standards, and 42.5 MPa ordinary portland cement, slag portland cement or pozzolanic portland cement should be adopted.

(6) Soil curing agent

1, adopt national highway EN- 1 (concentrated solution), and add 0.0 14% concentrated solution of solidified agent, or 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 be no more than 3%, without precipitation or flocculation.

(7)

There should be water with difficulty in drinking water or with PH greater than or equal to 6.

Fourth, the construction procedure

(1) Overall treatment scheme for subgrade surface

As this project is located in wet areas such as rice and reeds, before subgrade construction, the surface should be cleaned, roots, decomposed soil, garbage and sundries should be planted, and the subgrade should be leveled and rolled for about 30cm. The compactness shall meet the design (90%) requirements. If the required density cannot be reached, the back 5% can be closed for dust removal. If the closed ash of 0.50 cm still can't meet the required degree of compaction, it is necessary to replace the gravel cushion of 50 cm to speed up the progress. while

The construction height of subgrade is less than the total thickness of pavement and subgrade, and the foundation should be overbreak, backfilled, compacted and layered, and the treatment layer should not be less than the surface depth of subgrade.

The plain terrain of the project area, the soil is clay or silty clay, the groundwater is rich, the whole subgrade is wet, and the soil moisture content in wet state is high, so it is necessary to treat the subgrade surface, and the subgrade construction can be carried out according to the actual situation of each side.

1, fill the road with a height greater than 32 19m (from the lowest point in the table on the subgrade):

After the surface is flat and dry, a temporary drainage ditch should be set in the exposed part of the groundwater to drain the surface water, which shows that the discharge pressure of 30 cm mixed slag exceeds 12 ton. After passing through the two-way geogrid bulldozer on the roller for 34 times, the geogrid wraps 32 19 m lime soil (20cm thick, 5% closed ash), and the layered compacted dust (5% closed ash) is continuously filled layer by layer. If the compaction layer and strength requirements are not properly raised to 8% ash), the top surface of subgrade with the thickness of hand-mixed slag below 80 cm cannot bear more than 12 ton, and the degree and strength of compaction layer should be improved to meet the requirements of design specifications.

2. Roads with fill height greater than 1.3m and less than 2m (from the lowest point of the table on the subgrade):

After leveling, the surface is dry, and the exposed part of groundwater should be provided with temporary drainage ditch to drain the surface water. After filling the 40cm bulldozer with mixed slag discharge pressure, the geogrid will not be wrapped with lime soil (20cm thick, 5% closed ash) for 3,265,438+09m65,438+08t, and the filling will be continued with layered compacted lime (5% closed ash). If the compacted layer and the top of subgrade below 8% ash fail to reach an appropriate level, the thickness and strength of the layer should be increased to meet the requirements of the degree described in the design compaction, without the need for 18 ton slag rolling and mixing.

3. The height of the filling part is less than 1.3m (clean the table from the lowest point of subgrade):

The surface should be excavated continuously, descending from the top of bed height 1.3M, excluding surface water. After the surface water is dried, the discharge pressure of the filled mixed 30cm slag exceeds 18t, and it is compacted with bidirectional geogrid to fill 20cm gravel. After mixing slag and crushed stone in the workshop, it will continue for 23 times, and the crushed stone will be repackaged with 2m geogrid. After 34 times, use grader to level the gravel layer, and prepare to fill 18t ash.

(2) mixed slag filling

1, mixed with thick slag filling, layered compaction, appropriate every 2025cm.

2. The filling water content of mixed slag should be strictly controlled, and the one with larger water content should be compressed on the dry side. In addition, excessive mixing of soil and slag should be avoided. If a large amount of soil-bearing materials enter the site, piles should be prepared. After mixing, a small amount of soil and slag should be added to fill the embankment by other methods.

3. The strength of the mixed slag shall be no less than 15MP, and the maximum particle size shall be less than 150mm. Through material selection, the 20mm sieve should not exceed 30% of the total, among which, large-size stones should be filled in the lower slag, and small-size slag stones should be filled in the upper slag to ensure the top slag mixing.

4, pay attention to the foundation pit drainage for a rainy day, in order to prevent too much water mixed with slag.

5. In order to avoid unnecessary nuisance caused by incompressible base plate of production base, vibration rolling is strictly prohibited during rolling. But at the same time, it is necessary to ensure that the density of the treated fillers in the rolling joints should overlap by 50 cm, so it is necessary to ensure uniform compaction without pressure, and the number of rolling passes should be strictly controlled at four times. Slag compacted gravel packing and the same combination are necessary.

(3) Gravel packing

1, because the gravel filling is only 20 cm thick, the elevation of the top surface of the slag should be strictly controlled to eliminate the intrusion into the gravel filling range and reduce the gravel filling thickness.

2. The gravel particle size should be controlled within 5cm, and the total amount of gravel passing through 0.075 mm should not exceed 10% of the total amount, with good gradation and no sundries.

3, the use of less than 15MP (unscreened gravel), gravel strength.

4. Large stones should be filled in the lower part of the small size above the gravel packing to ensure the flatness of the gravel roof (the error is less than 2cm).

(4) bidirectional plastic geogrid laying

1, laying geogrids for storage and packaging, and direct contact with strong acid and alkali substances is strictly prohibited.

2. Ordinary highway geogrids should be laid vertically on the axis of embankment, and the geogrids of bridge subgrade should give up laying the axis of embankment.

3. The connection between geogrids shall be firmly tied with plum-blossom nylon, and the overlapping length shall be not less than 30CM and not more than three spaces.

4. Geogrids should be filled with spices in time to avoid long-term sun exposure. The interval between laying and filling shall not exceed 48 hours.

5. Measures should be taken to avoid damage to geogrids during construction, and any damage should be repaired or replaced in time.

6. The drilling and collision layer of geogrid shall be flat, straight, smooth and compact, and shall be close to the bearing layer, and shall not be twisted or wrinkled.

7. The first layer of geogrid shall be leveled and rolled by light industrial machinery. All vehicles and construction machinery are only allowed to drive along the axis of the embankment.

8. When laying geogrids, the length of each subgrade shall not exceed 2m, and the geogrids shall be wrapped in the exposed part of the application with folded back cover, and then covered with soil.

9. The mixed slag layer is almost flat and dense, and large stones should be trapped underground or artificially as far as possible to prevent the rocks from rotting slightly.

10, when the grader leveled the gravel, pay attention to the strength of the knife and find the geogrid immediately. Usually, someone must pay close attention to the whole site and find the problem manually in time.

(5) Filling subgrade construction requirements

1, subgrade filling treatment

General terms (1) must be filled and compacted by layers. The maximum compaction thickness of each layer shall not exceed 20cm (the thickness can be increased after compaction when the compaction mechanical energy ensures the compaction degree and field test), and the compaction thickness of the last layer on the top surface of subgrade shall be 20cm (in special circumstances, it shall not be less than the minimum compaction thickness 10cm).

(2) The optimum compaction water content should be controlled at 2%.

(3) The designed filling layer width on each side of the subgrade is 30cm, and the compaction width is not less than the designed closure slope.

(4) The subgrade surface should be inclined outward by 2% to 4% to prevent water accumulation. In order to prevent the subgrade slope from being washed away by rain, it is required to set 2m subgrade and the required temporary drainage dam and drainage facilities outside the toe of subgrade slope. It is forbidden to collect soil on the land of every 10 meter at the outer edge of both sides.

(5)。

(6) It is forbidden to use the roadbed of the construction road.

(7) The subgrade filling shall be compacted uniformly, and the top surface of subgrade transverse slope shall be consistent with the road arch.

(8) The sum of subgrade compactness shall not be less than the minimum packing strength in Table 1, but less than the maximum size.

Subgrade compactness, maximum filler strength, maximum filler diameter (cm) and minimum filler strength (CBR)%

Compaction degree (%) (heavy compaction standard) Minimum project area >; Subgrade Subgrade (0.30cm) ≥ 96 1.08.

Subgrade (3080cm) ≥96 10 5

Dike (80 150cm) ≥94 15 4

Next embankment (> 150cm) ≥93 15 3

Zero fill and zero excavation subgrade (0.30cm) ≥96 10 8

Note: This table is a heavy-duty compaction test of compaction degree specified in Highway Geotechnical Test Code (JTJ05 1), and the maximum dry density is calculated.

(9) Ensure that the requirements of filling stability will not be met due to the capillary action and frost heaving of groundwater, surface water and water.

Minimum height of subgrade embankment. This is applicable to urban roads, and the subgrade design should be greater than the minimum height of subgrade fill, which is in a critical height wet state. According to the drilling findings (drilling time is the worst season in June), the groundwater level and Ⅱ 4 subgrade are wet, and the calculation of critical minimum filling height of wet subgrade is shown in Table 2.

Minimum altimeter filled under wet conditions II

When the cave was famous, ZK48 ZK49 ZK50 ZK5 1

The elevation of the orifice is 2.25 1.9 1.35 2.55.

Static water level depth (m) 1.3 0.9 0.7 1.75

Water level elevation (m) 0.95 1.00 0.65 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 wet subgrade design elevation (m) 3.20 3.25 2.90 3.05

Height of wet packing (m) 0.95 1.35 1.55 0.5

2, subgrade treatment

Special partial (1) bridge

Fill the embankment section of the approach road in wet state, clear the platform and level it, backfill subgrade soil, and then make the subgrade bed at the place 20 cm away from the top surface under the pavement below 40cm, and then treat the lime soil (5% lime) solidified by the soil curing agent and the cement ash (2%+3% cement lime) solidified by the soil curing agent at the present layer to ensure that there is no soft shell foundation in the soil.

(2) Pond subgrade treatment

○ In a big pond and ditch 1, the route department will build a big dam. After pumping, dredging and slag filling, it will be leveled, compacted and layered (20 cm and 30 cm respectively) away from the highway to the place below the top surface of the bed 100 cm, and 20 cm of gravel will be filled on the scattered and layered gravel dust through the bidirectional plastic geogrid. Large open-pit slopes such as ponds and ditches should be kicked in two steps: 0.4m high, 0.6m wide and ≥ 1.6m wide. ..

2 when routing a large pond, the pond should be leveled with dams, with slag cushion and geogrids. , to ensure the integrity of subgrade.

(3) Bridge subgrade

○ 1 On both sides of the bridge foundation treated according to geological conditions, the treatment method of reinforced soil piles (cement mixing piles)+lime soil (8%) is adopted during the filling height and construction period, and the reinforced soil piles are arranged in a plum blossom shape. When the road exceeds the toe of the slope, the grading range of the laterally arranged reinforced soil piles should be at least the same as that of adults.

2 should be carved into the first 50 cm, the first 30 cm piles of iron, and then spread on the geogrid, and finally the hole 30 cm of iron.

○ Under the control of the treatment range of 50 cubic meters at the bridge head, according to the uneven settlement before and after treatment, under the condition that 8% lime soil is filled in the bridge subgrade within 50 meters nearby (except the abutment back backfill), the filler should be rolled by layers to meet the requirement of 90% compactness. The abutment backfill is compacted by 14% lime soil layer.

(6) Lime filling should follow "four sections" and "eight processes"

Architecture. The "four stages" point out: "soil spreading area, mixing and drying area, flat grinding to post-slaughter health care area", and the "eight processes" point out: "soil spreading, paving, spreading, grey cloth, mixing, leveling, rolling and health care" are as follows:

1, detection and calibration

Soil moisture and liquid natural plastic field soil samples should be taken and measured by standard limit soil hardening test to determine the best water content and maximum dry density.

2, measuring lofting

The fine survey group released the road center line.

3. The borrow pits, excavators and loaders will be transported to the embankment, where the dump trucks will be loaded. According to the width of subgrade, the volume of side dump truck and the thickness of loose paving, lime steel wire mesh shall be spread to determine the position of spoil for each truck and ensure the filling thickness.

4. Considering that the virtual paving coefficient is less than the design value, the height of the virtual paving first rail is determined on the basis of the coarse soil layer. In this case, remedial measures should be taken in time, and the rotary cultivator that meets the requirements should be used and rolled over. Before dust removal, soil moisture should be checked, and it should be done in time when the ash is close to the optimal water content.

5. Laying lime: The whole soil element is under stable pressure. According to the route of the eyes, lay a grid facing 5 x 10 meters, and lay an artificial uniform quantity ratio for each grid according to the needs of lime. Ensure that the gray dust contains no impurities and is digested by the gray blocks.

6. Road mixer mixing: After the lime paving is completed, it needs to be mixed with a road mixer, and the mixing time is more than twice that of others behind. Check the mixing depth from time to time, and it is advisable to mix the mixture into the top surface of the road bed with a depth below 5 10 mm to ensure that there is no plain soil interlayer to ensure uniform color mixing. The mixed dose of water and ash should be detected in the ash-free area of flowers and flowers, and the water content should be controlled at 65438+.

7. Leveling and compaction: marking and tracking control of water level rise. When the requirements of elevation and cross slope are met, the pressure shall be stabilized once with vibratory roller, then vibrated twice with vibratory roller, and then rolled three times with 182 1 ton, and rolled from the middle to the shoulder. When the raceway overlaps 1/2, the pressure on the wide shoulder is 23 times higher. It is forbidden to roll on the road sections that have finished or are eager to twist or roll the brakes, so as to ensure that the surface of lime soil will not be damaged. If the phenomenon of "spring" appears in the rolling process, measures should be taken to dig, fill or reconvert lime or cement mixture. Before compacting the end of the flat-end roller, the grader should compact it again to make the longitudinal direction smooth and the road arch meet the design requirements. The final leveling should be carried out seriously, and some parts must be scraped off, and the road surface should be cleaned, and the local low-lying areas should not be repaired, and the treatment may spread the lower layer.

8. Judgment: After the subgrade is complete for a period of time, analyze the degree of pavement shape, compactness and ash dosage in time. Check the personnel, and reduce the post-construction acceptance after the self-inspection report of the supervision engineer is qualified.

Management of measurement frequency and quality standard outline

Specify the project inspection method and frequency value.

Elevation of vertical section (mm) +5-20 1 every 20 linear meters.

& gt thickness (mm)- 10-25 yuan 15002000 M26.

Width does not exceed 40%

Straightness 1 (mm) linear meter design value 153m ruler, every 200 linear meters 10 feet.

Transverse slope (%)+0.5, -0.5 per 100 linear meter 3.