-- Construction of urban road subgrade
1. The machine management between the exposed property management room is handed over to the security guard
characteristics of subgrade construction;
(1) The construction of urban road subgrade engineering is in the open air, which is greatly affected by natural conditions, there are many professional types, many structures, and criss-cross pipelines in the construction area of the project, and there are many cooperative work and interference between professions and society, resulting in many construction changes. In particular, the old road reconstruction project has extremely high traffic pressure, complex underground pipelines, and high requirements for driving safety, pedestrian safety, and protection of trees and structures.
(2) The subgrade construction is mainly based on mechanical operation, supplemented by manual cooperation; when manual cooperation with earthwork operation, a special person must be set up to command; and the mode of parallel operation of flowing water or segmentation is adopted.
2. Soil (stone) square hole wall shoulder slope pipe
Urban road subgrade engineering includes the subgrade (roadbed) itself and related earthwork (stone), culverts, retaining walls, shoulders, slopes, various pipelines and other projects along the line.
3. Prepare attachments
The basic process of subgrade construction: preparatory work→ ancillary structures→ subgrade (earth, stone) construction
4. Fence who handed over, test the network line pile
Preparation for subgrade construction
(1) Set up a fence in accordance with the traffic guidance plan approved by the traffic management department to guide temporary traffic
(2) Before the start of construction, the technical person in charge of the construction project shall make a technical safety disclosure to the construction personnel according to the approved construction plan, emphasizing the engineering difficulties, technical points and safety measures. Operators can grasp the key points and clarify responsibilities.
(3) Closed and encrypted the known measurement control points, establish a measurement control network, and then carry out the construction control pile pay-off measurement, restore the center line, repair the corner pile, the outer pile on both sides of the road, etc.
(4) Before construction, according to the engineering geological survey report, the subgrade soil should be tested for natural water content, liquid limit, plastic limit, standard compaction, CBR, and if necessary, particle analysis, organic matter content, soluble salt content, frost heave and expansion should be tested.
5. Water limit test
Before the construction of the subgrade, the natural water content, liquid limit, plastic limit, standard compaction, CBR test should be carried out on the subgrade soil according to the engineering geological survey report, and if necessary, particle analysis, organic matter content, soluble salt content, frost heave and expansion should be tested.
6. Comply with the drainage dismantling, modification and consolidation
(1) Underground pipelines, culverts (pipes) and other structures can be carried out at the same time as the roadbed (earthwork), but the construction of new underground pipelines must follow the principles of "underground first, then aboveground" and "deep first and then shallow".
(2) Demolition, reconstruction, reinforcement and protection of existing underground pipelines and other structures.
(3) Build drainage facilities for surface water and groundwater to create conditions for subsequent earthwork and stone engineering construction.
7. Digging, filling, flattening, repairing, and building
Subgrade (earth, stone) construction process: excavation of trenches, filling of embankments, leveling of subgrades, compaction of subgrades, trimming of roadbeds, construction of protective works, etc.
8. In addition to the flat fill, high partial pressure
When the original ground elevation is lower than the design subgrade elevation, earthwork (i.e., fill subgrade) is required.
(1) Remove the water from the original area, remove tree roots, weeds, silt, etc. The pits of grave pits, wells, and tree root pits should be properly disposed of, and filled in layers to the height of the original ground.
(2) The filling section should be leveled in advance, when the ground lateral slope is steeper than 1:5, it needs to be repaired into the form of steps, the height of each layer of steps should not be greater than 300mm, and the width should not be less than 1.0m.
(3) According to the measurement centerline pile and downhill foot pile, fill and compact in layers.
(6) The height of the subgrade fill should be increased according to the design elevation. When filling to the last layer, the thickness of the fill should be controlled according to the design section and elevation and rolled and trimmed in time.
(7) The fillers with different properties should be classified, layered filling, and compacted, and special construction plans should be formulated for the construction of high slopes of the roadbed.
(1) The filling should be carried out in layers. After the lower layer of filling is qualified, the upper layer can be filled. The width of the roadbed fill should be 500mm wider on each side than the design width.
9. In addition to the dry evidence to avoid the ban, divide the digging and leave the pressure fill,
When the design elevation of the roadbed is lower than the elevation of the original ground, it is necessary to excavate and form the subgrade - excavate the roadbed.
(1) Before the construction of the roadbed, the water on the ground should be eliminated and drained, and the root pits, grave pits, wells and other parts should be technically treated.
(2) Excavation according to the measurement center line and side piles.
(3) When excavating, it should be excavated in layers from top to bottom, and it is strictly forbidden to dig holes. During mechanical excavation, structures and pipelines must be avoided, and manual excavation should be used within 1m from the pipeline edge, and manual excavation must be used within 2m from the directly buried cable. The excavation section shall not be over-excavated, and the amount of compaction that should be rolled to the design elevation shall be left.
(6) The trench of the rainwater branch pipe and the inspection well should be filled with lime soil or lime fly ash gravel.
10. Clear the edge and fill the pressure
(1) The surface should be cleaned up when building a rock-filled embankment, the edge of the building should be stacked first, and then the stone should be filled horizontally layer by layer to ensure the stability of the slope.
(4) The trenches around the pipelines and structures within the subgrade should be backfilled.
11. The machine is thick and heavy
(1) Before the formal compaction of the subgrade, the test section should be done when conditions permit, so as to obtain the technical parameters related to the construction of the subgrade.
(2) The main purposes of the test are:
1) Determine the value of subgrade pre-settlement.
2) Reasonable selection of compaction equipment, the selection of machinery and tools to consider the factors of different grades of the road, the size of the engineering quantity, geological conditions, operating environment and construction period requirements.
3) According to the requirements of compaction, determine the number of compaction times.
4) determine the thickness of each layer of virtual paving within the width of the roadbed.
5) According to the type of soil, humidity, equipment and site conditions, choose the compaction method.
12. 5080 light solid protection
(1) When the pipeline is located within the subgrade, the compaction degree of the backfill of the trench shall comply with the provisions of the "Code for the Construction and Acceptance of Water Supply and Drainage Pipeline Engineering" GB50268-2008, and light compaction tools should be used within 50cm above the top of the pipe.
(2) When the covering thickness from the top surface of the pipeline structure to the roadbed is not more than 50cm, the pipeline structure should be reinforced.
(3) When the covering thickness from the top surface of the pipeline structure to the roadbed is 50~80cm, protection or reinforcement measures should be taken for the pipeline structure when the roadbed is compacted.
13. The original velocity is in the direction of the distance, and the machine inspection water is high
The key points of urban road subgrade compaction should be mastered: according to the actual situation of the project, the relationship between the compaction machine, compaction method and compaction thickness should be reasonably adjusted to achieve the required compaction density.
(1) Compaction method (formula): gravity compaction (static pressure) and vibration compaction.
(2) The principle of soil subgrade compaction should be followed: "first light and then heavy, first static and then vibrating, first low and then high, first slow and then fast, and the wheel tracks are overlapped." "The maximum speed of the roller should not exceed 4 km/h.
(3) Rolling should be carried out from the edge of the roadbed to the center, and the outer edge of the roller wheel should be kept at a safe distance from the edge of the roadbed.
(4) The parts that cannot be rolled should be compacted with a small tamping press to prevent leakage, and the tamping area is required to overlap 1/4~1/3.
(4) The roller is not less than 12t grade, and the rolling should be carried out from both sides of the road to the center of the road until there is no obvious wheel track on the surface.
(3) The rock-filled embankment should be compacted with a vibrating roller of more than 12t, a tire roller of more than 25t or a rammer of 2.5t.
(5) When rolling, measures such as sprinkling or changing soil and drying should be taken according to the dryness and wetness of the soil.
(2) Loosen and dry the over-wet soil, or add water evenly to the over-dry soil to make its water content close to the optimal water content range.
(5) The top surface of the pipe culvert within the fill height can be filled with more than 500mm before it can be rolled by a road roller.
(4) Check the width, thickness and moisture content of the paved soil layer before rolling, and roll it after it is qualified.
14. The layer bed is bent and curved
(1) Mainly check the compaction degree of each layer, and take measures to improve when it does not meet the quality standards.
(2) The road bed should be smooth and solid, without significant wheel tracks, slurry, waves, peeling and other phenomena.
(3) The embankment slope should be compact, stable and smooth.
(4) The top surface of the roadbed (roadbed) should be tested for compaction and deflection value, and meet the requirements of the design or related standards.
15、压弯高平线宽坡 9530
Inspection and acceptance items: the main control items are compaction degree and deflection value (0.01mm), and the general items have requirements such as longitudinal elevation of the roadbed, centerline deviation, flatness, width, cross slope and embankment slope.
| Subgrade compaction standard | |||||
| Cut-and-fill type | The depth below the top surface of the bed, cm | The type of road | Compaction % | Frequency of inspection | Test Method |
| Every 1000㎡ | A set of 3 points per layer | ||||
| Excavation | 0~30 | Expressways, trunk roads | ≥95 | The ring knife method is used for fine-grained soil, and the sand filling method is used for coarse-grained soil | |
| Secondary trunk roads | ≥93 | ||||
| Branch | ≥90 | ||||
| fill | 0~80 | Expressways, trunk roads | ≥95 | ||
| Secondary trunk roads | ≥93 | ||||
| Branch | ≥90 |
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