JTG/T 3610-2019Technical Specifications for Construction of Highway Subgrades (English PDF)

1 General provisions

This specification is made in order to raise the technical level of highway subgrade construction and to ensure the quality and the safety of the works.

It applies to the subgrade construction of new, rebuilt and widened highways of every grade.

The highway subgrade shall meet the strength, the stability and the durability required by the design.

Subgrade construction shall comply with the national laws and regulations on construction works; a sound quality assurance system shall be set up, the responsibility for quality shall be defined and quality management shall be strengthened.

Subgrade construction shall comply with the national laws and regulations on work safety; a sound work safety management system shall be set up, safety responsibilities shall be defined, safety technical measures shall be drawn up, the safe operating procedures shall be strictly observed and the occupational health of the construction personnel shall be safeguarded.

Subgrade construction shall comply with the national laws and regulations on environmental protection: land shall be used sparingly, farmland shall be occupied as little as possible, pollution shall be reduced and the environment shall be protected. On completion, borrow pits and spoil sites shall be reinstated as required.

Reliable new techniques, new processes, new materials and new equipment shall be actively promoted and applied, and subgrade construction shall be standardised so as to raise the level of regularity and refinement.

In addition to this specification, subgrade construction shall also comply with the relevant current national and industry standards.

2 Terms and symbols

subgrade: strip-shaped structure built according to the position of the route and to defined technical requirements, which forms the foundation of the pavement and carries the traffic load transmitted by it.

roadbed: part of the subgrade within 0.8 m or 1.20 m below the pavement structural layers, divided into an upper and a lower roadbed. The upper roadbed is 0.3 m thick; the lower roadbed is 0.5 m thick on highways carrying light, medium and heavy traffic and 0.9 m thick on those carrying very heavy and extremely heavy traffic.

embankment: fill subgrade above the original ground. Structurally it is divided into an upper and a lower embankment: the upper embankment is the fill within 0.7 m below the roadbed, the lower embankment the fill below that.

cutting: subgrade excavated below the original ground.

high embankment: embankment whose maximum side slope height of fill exceeds 20 m.

steep slope embankment: embankment on ground sloping more steeply than 1:2.5.

rock fill embankment: embankment filled with stone of which more than 70 % by mass has a particle size greater than 40 mm.

earth-rock embankment: embankment filled with an earth and rock mixture whose stone content is 30 % to 70 % by mass.

deep cutting: earth cutting with a slope height over 20 m, or rock cutting with a slope height over 30 m.

special subgrade: subgrade located in a special soil section or in an area of poor geology, strongly affected by water, climate and other natural factors.

collapsibility loess: loess whose structure is rapidly destroyed and which settles markedly when wetted under its own weight or under a given pressure.

laterite: reddish-brown silty or clayey soil formed by the weathering of carbonate rocks in a warm and humid climate.

high liquid limit soil: fine-grained soil with a liquid limit greater than 50 %.

expansive soil: highly plastic clay containing hydrophilic minerals and showing a marked swelling on wetting and shrinkage on drying.

saline soil: soil whose content of readily soluble salts exceeds the specified value.

permafrost: soil that has remained frozen below 0 degrees Celsius for two or more consecutive years and contains ice.

foamed mixture lightweight soil: lightweight solid material containing many uniform closed micro-cells, formed by preparing a foam from a foaming agent by physical means, mixing that foam in a specified proportion into a uniformly stirred slurry of cement paste with admixtures or fine aggregate, casting it and curing it to a solid.

expanded polystyrene, EPS: expanded polystyrene foam plastic.

California bearing ratio, CBR: index characterising the strength of subgrade soil, granular material and stabilised soil, being the ratio of the test load applied to a standard specimen at a specified penetration to the load applied to a standard crushed stone material at the same penetration, expressed as a percentage.

Clause 2.2 gives the symbols used throughout the specification.

3 Preparation for construction

Before the subgrade works begin, the design documents shall be studied and the intent of the design understood. A construction survey and a check on site shall be made, and the construction organisation design shall be drawn up from the requirements of the design, the conditions of the contract and the situation on site.

Before the subgrade works start, sound quality, environmental and occupational health and safety management systems shall be set up, and all classes of construction personnel shall be given post training and a technical and safety briefing.

Temporary works shall meet the needs of normal construction, shall preserve the function of the existing roads and structures within the area affected by the subgrade works and shall protect farmland irrigation and drainage facilities; they should be combined with the permanent works.

Where new techniques, processes, materials or equipment are to be used, the research and the justification shall be completed in advance.

The survey method shall be chosen from the grade of the highway and the accuracy required. Control stakes shall be handed over on site; on the basis of a re-survey of the original control network they shall be suitably densified and optimised as construction requires, a construction survey control network shall be established and it shall be properly protected. Horizontal control shall be by satellite positioning, traverse, triangulation or trilateration, to the grade and the technical requirements of Table 3.2.2-1.

The clause also covers the tests to be made, the treatment of the ground surface and the trial section.

4 Ordinary subgrade

Fill material: well-graded coarse-grained soils such as gravelly and sandy soils should be chosen. Soil containing turf, domestic refuse, tree roots or humus shall not be used as fill. Peat, silt, frozen soil, strongly expansive soil, organic soil and soil whose readily soluble salt content exceeds the permitted value shall not be used directly to fill the subgrade; where their use is unavoidable they shall be treated by technical measures and may be used only after inspection has shown the requirements to be met. Silty soil should not be used directly to fill the roadbed of highways of grade two and above, and shall not be used directly to fill the roadbed in frost-affected areas or the submerged part of an embankment.

Minimum bearing ratio and maximum particle size of the fill (Table 4.1.2): for the upper roadbed, from 0 to 0.30 m below the pavement, the minimum CBR is 8 % on expressways and grade one highways, 6 % on grade two highways and 5 % on grade three and four highways, with a maximum particle size of 100 mm; for the lower roadbed, 0.30 m to 0.80 m under light, medium and heavy traffic and 0.30 m to 1.20 m under very heavy and extremely heavy traffic, the values are 5 %, 4 % and 3 % with the same maximum particle size; for the upper embankment, 0.8 m to 1.5 m and 1.2 m to 1.9 m respectively, they are 4 %, 3 % and 3 % with a maximum particle size of 150 mm; and for the lower embankment, below 1.5 m and below 1.9 m respectively, they are 3 %, 2 % and 2 %, again with a maximum particle size of 150 mm.

The clause goes on to specify the roadbed, subgrade in cutting, earth embankment, rock fill embankment, earth-rock embankment, high and steep slope embankments, filling behind abutments and walls, fly ash embankment, EPS embankment, foamed mixture lightweight soil embankment, coal gangue embankment, industrial residue embankment, sand fill embankment, borrow and spoil, and the widening and reconstruction of the subgrade.

5 Subgrade drainage works

Before construction the drainage design shall be checked on site and any problem shall be reported and dealt with promptly; the ditches, channels, bridges and culverts of the whole line shall form a complete drainage system.

Temporary drainage facilities should be combined with the permanent ones and shall be maintained regularly during construction. Where an embankment section has a culvert in the design, the culvert should be built first, and the temporary and permanent facilities for surface water and groundwater shall be completed in good time.

While the embankment is being filled, the working surface shall be given a drainage cross fall of 2 % to 4 % and no water shall be allowed to stand on it; temporary drainage measures shall be taken on the slopes. In cuttings the surface water shall be drained away promptly.

The upstream side of side ditches, drainage ditches, intercepting ditches and other surface drainage facilities shall not stand above the ground surface, and local hollows shall be filled level.

The concrete and the mortar masonry of the drainage facilities shall comply with the current Technical Specifications for Construction of Highway Bridges and Culverts, JTG/T F50.

The clause also covers surface drainage, subsurface drainage and the quality standards for subgrade drainage works.

6 Subgrade protection and retaining works

Before the protection works begin, the slope shall be trimmed and loose rock and soil shall be removed from it; the trimmed slope surface shall be level over its whole area, shall drain freely and shall be in keeping with the surrounding natural landform.

The protection works shall follow the cut and fill works closely and sensibly: one stage shall be excavated and that stage protected. The design of the protection shall be checked section by section against the geological and hydrological conditions of the excavated face, and any large departure from the design shall be reported and dealt with promptly.

Safety protection shall be strengthened during construction, and large-scale blasting and large-scale excavation are forbidden.

Every class of protection work shall rest on a stable foundation or slope body, and the slope protection layer shall be in close contact with the slope face, with no gap left.

Effective measures shall be taken during construction to intercept and drain surface water and to lead away groundwater. The quality of the stone, reinforcement, steel strand, cement concrete and other materials shall meet the requirements, and every slope protection shall be provided with an inspection access and the necessary handrails.

The clause then covers vegetation protection, slope surface engineering protection, protection of subgrade along rivers, slope anchoring, gravity, gabion, cantilever, counterfort, anchor rod, anchored plate and reinforced earth retaining walls, anti-slide piles, soil nailing support and the flexible protection net system.

7 Special subgrade

Before construction of a special subgrade, the necessary foundation tests shall be made, the geological data, the extent of the treatment in the design and the design parameters shall be checked, and a special construction scheme shall be drawn up.

Where the actual geology differs from the design, or the treatment in the design cannot be carried out for any reason, the matter shall be reported and dealt with promptly. Construction of a special subgrade should be monitored dynamically, and in addition to this clause it shall also comply with Clause 4.

Landslide sections: before construction the topography, the geology, the nature, the causal type and the scale of the landslide section shall be verified, and a special construction scheme and an emergency plan shall be drawn up for the section. Before the remedial measures are carried out, unloading of the resisting part and loading of the sliding part of the landslide body are forbidden. Remedial works should not be carried out in the rainy season. During the works, stability monitoring and geological logging shall be carried out and the actual geology verified; where the geology differs from the design, where signs of sliding appear or where anything else is abnormal, the matter shall be reported and dealt with promptly, and emergency measures shall be taken at once if a landslide occurs. Other works and facilities within the area affected by the landslide shall be protected, and inspection of the section shall be intensified during and after rainfall.

The clause covers in turn landslide sections, rockfall and talus sections, debris flow areas, karst areas, soft soil areas, laterite and high liquid limit soil areas, expansive soil areas, loess areas, saline soil areas, permafrost areas, wind-blown sand areas, snow-damage sections, icing sections, mined-out areas, coastal areas, reservoir areas, seasonally frozen soil areas and sections along rivers.

8 Subgrade construction in winter and in the rainy season

A sensible construction scheme shall be drawn up for winter and rainy-season working from the characteristics of the season and from the geological and topographical conditions of the section. Temporary drainage shall be provided and connected smoothly to the permanent drainage, weather information shall be collected in good time so as to avoid disasters and accidents, and all preparations shall be completed beforehand.

In seasonally frozen soil areas, work is treated as winter working whenever the mean day and night temperature stays below -3 degrees Celsius for ten days or more, or whenever the mean day and night temperature is above -3 degrees Celsius but the frozen soil has not thawed completely.

Earth embankments on expressways and grade one highways, and embankments in areas of poor geology, should not be built in winter. No winter working is allowed within 1 m below the roadbed of an earth embankment, nor in half-fill half-cut sections or at the junction between cut and fill.

During winter subgrade construction, measures shall be taken to drain rain and snow water and the groundwater met in excavating cuttings without delay.

9 Safety of subgrade construction

The contractor shall set up a sound work safety management system, establish a safety management body, employ full-time safety management staff, draw up work safety rules and put the work safety responsibility system into effect, so that safety management, safety technique and safe working are managed and controlled throughout and in every respect.

Personnel shall be familiar with the relevant work safety laws, regulations and technical standards and may take up their post only after passing the training. Those engaged in special operations shall be specially trained, shall hold the corresponding qualification and shall carry the certificate at work; construction personnel shall observe the safe operating procedures of their trade.

Subgrade construction shall strictly apply the Technical Specifications for Construction Safety of Highway Engineering, JTG F90, together with GB 50720, GB/T 29639, JGJ 46, JGJ 80, GB 3608, GB 5725, GB 6095, GB 6722 and GA 838.

Before the works start, the contractor shall survey the site and, from the topography, geology, hydrology, meteorology and environmental conditions of the section, together with the design documents and the construction scheme, shall draw up safety measures.

The clause also covers fire protection, electricity, lighting and ventilation; construction drainage; construction access roads; the use of machinery and equipment; the demolition of existing structures; the excavation of cuttings, foundation pits and trenches; the filling of embankments and roadbeds; the construction of supporting structures and drainage facilities; and borrow and spoil.

10 Environmental protection in subgrade construction

Subgrade construction shall comply with the national laws and regulations on land administration, soil and water conservation, environmental protection, ecological protection, the use of resources, the use of energy and the circular economy; resources and energy shall be used sensibly, pollution shall be controlled and the environment protected.

Before the works start, the topography, geology, hydrology, meteorology and ecological conditions of the site and the state of the existing structures shall be surveyed, and environmental protection measures and an energy-saving and emission-reduction scheme shall be drawn up and carried out, in accordance with the national rules on the environmental management of construction projects and with the relevant regulations and technical standards on saving resources and energy and reducing emissions.

Noise and vibration: the vehicles and machinery used shall be maintained and serviced so that their technical performance stays stable and environmental noise pollution is prevented. The construction organisation design shall lay down the working hours and the working methods of machinery producing strong noise near sensitive receptors, and the sound level at the site boundary shall comply with the current Limits of Environmental Noise Emitted by Construction Sites, GB 12523. Where continuous working is unavoidable in a residential or noise-sensitive area and the boundary noise may exceed the emission standard, measures against noise pollution shall be drawn up. Strongly vibrating machinery should be fitted with silencing, sound insulation and anti-vibration pads; where dynamic compaction or impact rolling is carried out near dwellings or other vibration-sensitive buildings, the buildings at risk shall be monitored and vibration isolation measures taken; and where blasting takes place near a sensitive building, the charge and the advance per round shall be limited so as to lessen the vibration.

The clause also covers the use of land resources and soil and water conservation, ecological protection and restoration, the protection of water resources and the control of waste pollution, the control of air pollution and the protection of cultural relics.

11 Finishing and acceptance of the subgrade

Before the handover acceptance of the subgrade works, the appearance shall be made good and local defects shall be repaired. Finishing covers both the making good after the contractor's own inspection and that after the handover acceptance, its purpose being to bring the subgrade works up to the technical and quality standards of the design documents and of this specification.

In making good the surface layer of the subgrade, a sensible scheme and process shall be chosen for the particular defect. The compacted thickness of any soil layer added shall be not less than 100 mm; after compaction the surface shall be even, and shall not be loose or peeling. The finished slope face shall be smooth, of good appearance and firm, and shall meet the slope required by the design.

The protection and retaining works shall be checked for missing or blocked weep holes and for deformation or displacement of the structures, and any defect shall be made good. The surfaces of the ditches and channels of the drainage system shall be neat, their invert level, and the drainage free-flowing and watertight; any defect shall be made good. Temporary works and facilities shall be dealt with sensibly so that they fit the natural surroundings.

On completion of a work item, a work part or a unit work, the intermediate handover inspection and acceptance shall be carried out as required. Before the handover acceptance, the traverse points and bench marks within the section shall be reinstated, together with any other marker stakes required or likely to be needed in the acceptance, and a self-inspection shall be made as required by this specification and by the current Quality Inspection and Evaluation Standards for Highway Engineering, Section 1: Civil Engineering, JTG F80/1; once that self-inspection has been passed, the handover documents shall be prepared and the handover acceptance applied for.

The completion (handover) acceptance of the subgrade shall follow the relevant rules of the Ministry of Transport and of JTG F80/1, and the items that the design documents and this specification require to be monitored shall be monitored thereafter as required.