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Specification for construction and acceptance of urban roads subgrade engineering
1 General
1.0.1 This specification is developed in order to unify the national technical standards for urban road subgrade engineering construction, ensure the quality of road subgrade engineering and improve the economic benefits of projects.
1.0.2 This specification is applicable to the construction and acceptance of subgrade engineering of urban roads (including suburban roads), squares, and parking lots. It may be used for reference for accommodation roads in factories, mines, airports, docks and other places.
1.0.3 In the case of joint or cross construction of urban road subgrade engineering and railways, highways, subways, pipelines, civil air defense and other projects, the relevant engineering technical standards shall be referred to in addition to the provisions of this specification. The safety measures of subgrade construction shall be carried out according to the relevant provisions.
1.0.4 On the premise of ensuring the design requirements, subgrade construction may be localised to make reasonable use of local materials and industrial wastes. At the same time, the pollution of hazardous substances shall be prevented.
For all kinds of pipeline projects and auxiliary structures within the scope of subgrade land, the principles of “underground first, ground second” and “deep first, shallow second” shall be followed to avoid repeated road excavation. Attention must be paid to the quality of pipeline and groove backfill, so as to achieve the same design strength as subgrade.
2 Construction preparation and construction survey
2.1 Construction preparation
2.1.1 Construction personnel must be familiar with design documents and drawings. The unclear problems and suggestions on revision in the design may be submitted to the design department for solution during the design disclosure.
2.1.2 The construction personnel must survey the construction site to determine the construction deployment and carry out the restoration alignment measurement.
2.1.3 The relevant construction personnel shall hear the design disclosure of designers.
2.1.4 The construction unit shall meet the following requirements when preparing for construction:
(1) Recheck the location and elevation of underground concealed facilities and indicate them on the drawings for construction disclosure.
(2) The exposed inspection wells, fire hydrants, civil air defense vents, etc. shall be marked on the drawings for verification, to avoid burial or blockage.
(3) Cultural relics and historic sites, survey markers must be protected; landscaping and public facilities, etc. shall avoid pollution damage.
(4) Traffic management shall be strengthened. If it is necessary to close traffic, the time for stopping traffic should be shortened and traffic should be restored as soon as possible.
(5) Pay attention to environmental protection during construction.
2.1.5 Technical disclosure shall be carried out step by step before construction. The construction technology requirements of the master operation and key parts, the location and elevation of underground concealed works shall be handed over to the direct operators. All kinds of construction disclosures shall be recorded for future reference.
2.2 Construction survey
2.2.1 The person in charge of construction shall work with the design or survey department to hand over the centerline control piles and design benchmarks on site, and set the fender piles.
The temporary benchmarks shall be re-measured and closed with the design benchmarks, and the allowable closing errors: mm for expressways, main and secondary trunk roads; mm for access roads (L is the length of the leveling line in kilometers).
2.2.2 Restore the center pile of the road, and the pile distance should be 15 ~ 20 m in the straight line section; 10 m in the curve section. Piles must be added to the starting and ending points of horizontal and vertical curves and topographic change points. Allowable error of span: for less than 200 m; for 200 ~ 500 m; for more than 500 m.
The auxiliary base shall be pilot tested at the position unaffected by the construction, and plane control piles were set up for timely replenishment of piles during construction.
Determine the curb line and the upper and lower side slope piles, and check whether the land occupation and demolition meet the construction needs. The existing obstacles within the construction range shall be clearly marked.
2.2.3 The distance of temporary benchmarks shall be based on the principle of height measurement without turning points. The distance of benchmarks shall not exceed 200 m in plains and should be 100 m in mountainous areas or hills.
The temporary benchmarks must be firm and stable. For cross-year projects or benchmarks suspected to be moved, they shall be used only after retesting and re-checking.
Set the piles on both sides of the center pile which are not affected by the construction, and determine the elevation of the center of the road (or the edge of shoulder).
2.2.4 Site surveyors shall retest the original cross section according to the center pile position, and complementally survey the cross section at the added pile position, and calculate the amount of earthwork and stonework.
2.2.5 Site surveyors shall review the location and elevation of the original bridges and culverts, underground pipelines and other required related measurements.
2.2.6 During the construction, the site surveyors shall accurately and timely measure the plane and leveling, and provide construction personnel with measured data and pile delivery in a timely manner on site. The measuring marks shall be firm and stable, and receive careful protection from the construction personnel.
2.2.7 After the basic completion of subgrade engineering, site surveyors must carry out the as-built survey of the whole line. The as-built survey includes: the position of the center line, elevation, the cross-sectional diagram, the actual position and elevation of the accessory structures and underground pipelines. The survey results shall be marked in the as-built drawing.
3 Subgrade construction drainage
3.1 General requirements
3.1.1 The subgrade construction drainage shall meet the following requirements:
(1) Effectively eliminate the surface water and construction water flowing into the subgrade due to precipitation or from nearby areas during construction.
(2) Dredge, block and isolate the groundwater which is harmful to the subgrade.
3.1.2 Drainage routes for subgrade construction must be arranged reasonably, and permanent drainage facilities built and newly built along the route shall be fully utilized. The water flow of all construction temporary drainage pipes, drainage ditches and blind drains shall be directed to pipelines or ditches.
Suburban roads shall be combined with local topography, and drainage, interception, blocking and other measures shall be taken to discharge water to ditches or low-lying areas.
All construction drainage outlets shall be settled through negotiation with the relevant departments.
3.2 Elimination of surface water
3.2.1 When excavating and filling the subgrade in layers, the surface shall be built with 2 ~ 4% of transverse slope according to the permeability of soil, and pay attention to longitudinal drainage. The site shall be leveled frequently to clean up the scattered soil, so as to facilitate surface drainage.
3.2.2 Drainage structures within the subgrade shall be constructed first, and if not, they may be constructed simultaneously with the subgrade to be used for drainage, and gradually shaped with the construction process.
3.2.3 In subgrade construction, temporary drainage facilities shall be set up when surface water elimination is difficult and no permanent pipe channels are available. Temporary drainage facilities may adopt movable or stationary pipelines, side ditches, intercepting ditches, drainage ditches, water drops, chutes, etc. When the drainage discharge is relatively large, hydraulic calculations shall be carried out to select the appropriate drainage section and longitudinal slope. The excavation of side ditches, intercepting ditches and drainage ditches shall be dug from downstream to upstream; the bottom of the ditch shall be smooth, the side slopes shall be repaired neatly, and the ramming shall be solid.
3.2.4 When self-flow drainage cannot be used for retaining wall foundation pits, road pits, borrow areas and transportation corridors, water shall be diverted to the water collecting wells and pumped out.
3.2.5 When laying all kinds of underground pipelines, it is strictly prohibited to pump out the accumulated water in the service trench to the subgrade area.
3.2.6 In subgrade engineering with long construction period or crossing rainy season, sections such as permeable soil layer or cracked rock layer with drainage facilities locations, and areas with large flow velocity and concentrated water yield, reinforcement measures to prevent leakage and erosion shall be taken.
3.3 Elimination of groundwater
3.3.1 In subgrade construction, if groundwater seriously affects subgrade stability, the design department shall be required immediately to provide underground drainage design. If the influence of groundwater is small, the construction unit may take appropriate measures to deal with it according to the situation.
3.3.2 The blind ditch groove should adopt the vertical ditch with supporting bearing instead of great ascent. The support form may be determined according to soil quality, groundwater condition, groove depth, excavation method, ground load and other factors.
I. Horizontal support (transverse support) is suitable for grooves with good soil quality and small amount of groundwater.
II. Vertical support (vertical plate support) is suitable for deep ditches with poor soil quality and large amount of underground water.
III. Sheet-pile support is suitable for deep grooves with high groundwater level and drift sand.
The demolition of support may start from the bottom along with the installation of blind ditch. The support may also be pulled out after the installation and backfill. The gaps left in the trench wall shall be filled with gravel and tamped.
3.3.3 The drainage of blind ditch groove may be divided into open ditch collecting well drainage and deep-well pump drainage. The excavation of blind ditch shall be carried out from downstream to upstream, and shall be supported and pumped along with excavation. The blind ditch foundation shall be flat and excavated, installed and backfilled in sections.
3.3.4 If the newly-built road is in a section with high underground water level, and the water surface is less than 0.6 m away from the rolling surface of the soil base, side ditches may be excavated along both sides of the subgrade before construction to lower the groundwater level. The excavation of the side ditch shall be deep to 0.3 m below the aquifer.
4 Protection and reinforcement of subgrade
4.1 General requirements
4.1.1 Subgrade protection and reinforcement engineering may be divided into three types: side slope protection, embankment protection and reinforcement along rivers and coasts, and subgrade retaining engineering.
4.1.2 Subgrade protection is based on the stability of the original side slope and related protective structures, and must be checked and accepted before construction. It is strictly forbidden to protect unstable soil.
Subgrade reinforcement or retaining engineering requires not only its own firmness and stability, but also the conditions and quality of preliminary engineering that must be inspected and verified before construction.
4.1.3 Subgrade protection and reinforcement engineering construction shall meet the following requirements:
(1) Strictly implement the relevant provisions and quality standards of the masonry and brickwork; the materials must meet the strength, specifications and other quality requirements specified in the design.
(2) For backfill soil, sandy soil should be chosen with strictly-controlled water content, and should be filled in layers with adequate compaction (punning).
(3) The location of the drain hole and expansion joint shall be accurate with correct holes and straight seams, and the sizes shall comply with the design requirements.
4.2 Slope protection
4.2.1 Slope protection shall be selected according to subgrade soil quality, which may be divided into plant protection and slope treatment, or a mixed use of both.
4.2.2 Plant protection is a simple protection measure. For the side slopes where plants may easily grow, grass, turfing and shrub protection may be used.
4.2.3 Grass planting protection is applicable to the soil slope with low side slope and slight slope erosion, which is beneficial to the growth of grass. For the frequently or long-term submerged embankment slopes, it should not be adopted.
4.2.4 Turfing may be used for soil slopes with steeper slopes, serious scouring, and only seasonal submergence. Paving methods include tiling, superimposed tiling, checkering, etc. The turf shall be paved with staggered joints from bottom to top and fixed with bamboo and wooden pickets.
4.2.5 When planting trees for side slope protection, the layout form of trees shall be determined according to the protection purpose and the tree species adopted. The tree shall be prevented from flowing water submergence damage with a velocity greater than 3 m/s before the tree becomes viable, and if necessary, additional protective barriers may be installed for protection.
4.2.6 Slope treatment may be used for steep side slopes and severely weathered rock side slopes. The treatment methods include plastering, guniting, pointing, grouting, stone side slope or facing wall, etc. Slope treatment requires the original side slope to be stable without groundwater exposure. Before treatment, the collapse rocks shall be cleaned, the weathered surface layer stripped, the pits and grooves embedded, and the dirt and impurities cleaned.
4.2.7 Plastering materials such as cement mortar, cement-lime mortar or lime cinder mixed mortar may be used with the requirement of evenly attachment to the slope; expansion joints shall be reserved when plastering area is large.
4.2.8 Guniting may be used for easily weathered and relatively complete rocks with a thickness of 1 to 2 cm. Rocky side slopes with narrow and shallow rock joints and fissures may be pointed, and those with wide and deep joints and fissures may be grouted. Available perfusion materials include cement mortar or cement-lime mortar, and concrete with fines for wide and deep cracks.
4.2.9 The slope protection and facing wall may be paved with materials such as rubbles (block stones) and concrete. When paving locally, the masonry shall go deep into the incompetent bed or depressions, and the masonry surface shall be smoothly connected with the slope surface. Masonry and brickwork materials selection and construction requirements shall be implemented according to the provisions of Subclause 4 of this Clause.
4.3 Embankment protection and reinforcement
4.3.1 The protection and reinforcement of embankments along rivers and coasts may be carried out by riprap, dry or mortar rubbles (block stones), gabion and diversion structures.
4.3.2 Ripraps may be used to protect the side slope and slope toe of the underwater part of subgrade or river bank. The riprap is roughly in trapezoidal stone packs, and the stone size should be 30 ~ 50 cm. The total thickness is about 3 ~ 4 times and not less than 2 times of the stone size. The enrockment should be carried out at low water level.
4.3.3 Slope protection of dry-laid rubbles (block stones) may be used for smooth riverbanks or general embankment slopes at the flow direction. Slope protection may be paved in single or double layer with the thickness not less than 20 cm, and side slope not steeper than 1:2. The selected building stones shall meet the quality standards. Masonry shall be flat in cushion course, tightly embedded, extensively smooth-going and staggered up and down.
4.3.4 The slope protection with mortar rubbles (block stones) may be used for embankment slopes washed by the mainstream. The thickness of masonry should be 30 ~ 60 cm. The building stones shall meet the quality standards. Masonry shall have smooth cushion, full mortar, and no invalid supports, voids and zigzag seams.
4.3.5 When the water flow is fast and there is a lack of large stones in the local area, the frame cage may be made, and the internal filling stone rolls into the water to reinforce the embankment gabion. The manufacturing method and specifications of the gabion may be determined according to the local conditions.
1 General
2 Construction preparation and construction survey
2.1 Construction preparation
2.2 Construction survey
3 Subgrade construction drainage
3.1 General requirements
3.2 Elimination of surface water
3.3 Elimination of groundwater
4 Protection and reinforcement of subgrade
4.1 General requirements
4.2 Slope protection
4.3 Embankment protection and reinforcement
4.4 Retaining engineering
5 Construction of soil subgrade
5.1 General requirements
5.2 Earth cutting of subgrade
5.3 Subgrade filling
5.4 Compaction of soil subgrade
5.5 Subgrade renovation
6 Construction of stone subgrade
6.1 General requirements
6.2 Excavation of stone subgrade
6.3 Filling of stone subgrade
6.4 Blasting of stone subgrade
7 Construction of special soil subgrade
7.1 General requirements
7.2 Miscellaneous fill
7.3 Saline soil
7.4 Expansive soil
7.5 Collapsible loess
8 Treatment of wet-soft soil base and construction in rainy season and winter
8.1 Treatment of wet-soft soil base
8.2 Rainy season construction
8.3 Winter construction
9 Engineering quality acceptance standards of subgrade
9.1 General requirements
9.2 Soil subgrade
9.3 Stone subgrade
9.4 Roadbed
9.5 Side slope and side ditch
9.6 Accessory structure
Annex I Corresponding relationship between unified classification of soil and original subgrade soil classification
Annex II Subgrade soil classification according to excavation difficulty
Annex III Determination of water content and loss on ignition of soil
Annex IV Compaction test of soil
Annex V Test for soil compactness of subgrade
Annex VI Rock classification according to excavation difficulty
Annex VII Classification of saline soil
Annex VIII Saline soil subgrade is higher than the minimum height of underground water level in long-term
Annex VIIII Explanation of wording in this specification
