What are the requirements for constructing filled embankments?

Construction Plan for Filled Subgrade I. Pre-construction Preparation Work 1.1 Verify the type and distribution of the fill material; conduct re-inspections and tests on it. Fill materials that do not meet the design requirements must not be used for filling. 1.2 Cut down the trees within the filling area, remove their roots and grass roots, or transplant them to a location designated by the owner for disposal ； The ground structures are to be demolished. 1.3 Investigate the conditions of fish ponds, spring sources, wells, canals, pipelines, cultural relics, roads, groundwater levels, and the softness of the original ground surface within the filling area. When these conditions differ from those specified in the design and special treatment is required due to unfavorable filling conditions, it is necessary to report promptly to the owner, the design unit, and the supervision engineer so that a suitable treatment plan can be devised without delay. II. Construction methods for filling soil and rock materials in the subgrade 2.1 Before filling begins, the supervision engineer will select an excavation site or the construction area from which the filling materials will be obtained; samples will be taken for inspection, and only those materials that meet the required standards can be used after obtaining the supervisor’s approval. Before commencing work, select an appropriate test section approved by the supervising engineer to conduct compaction tests, in order to determine the correct compaction method, the type of compaction equipment and its sequence required to achieve the specified degree of compaction, the number of passes each type of compaction equipment needs to perform under the optimal combination, as well as the thickness of the soil layer that can be effectively compacted. The subgrade filling should be spread and compacted in layers, with a smooth surface and an appropriate road crown. Temporary drainage measures should be implemented and integrated with the designed drainage system to prevent water accumulation from damaging the slopes. When using materials with poor water permeability or materials that are impermeable, in addition to controlling the compaction degree during layered paving, it is also necessary to regulate their moisture content; if the moisture content is too high, the materials should be exposed to sunlight until they reach their optimal moisture content before being compacted. When a embankment is constructed on a slope, if the original slope gradient measured perpendicular to the centerline of the road is steeper than 1:5, the original ground surface should be excavated into steps. The steps should have sufficient width and slope inward by 2%. At the junction of filled and excavated subgrades, the excavated subgrade should be treated with over-excavation and backfilling; the over-excavation depth at the junction should be no less than 30 cm, with a 1:5 slope used for the transition. The width of each layer of filler laid should extend 50 cm beyond the designed width of the embankment on each side; rolling should be carried out over this extended area to ensure that the edges of the embankment, after the slope has been trimmed, have sufficient compaction. For every 1m of embankment filled, a centerline inspection should be carried out, and the edge lines should be marked so that any excessive or insufficient width at the edges of the fill can be corrected promptly. Within a range of 1.5m from the top surface of the roadbed, filling should be carried out in eight layers. Strict control is required over the compaction degree of each layer of fill, as well as the alignment and elevation. Once the roadbed elevation is reached, the positions of the centerline and side lines must be determined with precision; meanwhile, strings should be used according to the slope ratio to eliminate any areas of excessive filling. 2.2 To improve the density of the filler, reduce porosity, enhance the contact surfaces between filler particles, increase cohesion or interlocking strength, and minimize deformation so that the subgrade can function properly, as required by the tender documents, the filling material shall be obtained from the earthwork and rockwork excavated in this contract section. Before filling, the fill material is subjected to particle analysis, determination of moisture content and density, liquid limit and plastic limit, as well as organic matter content, in accordance with the methods specified in the \"Highway Geotechnical Test Procedures\" (JTJ051‑93). Bearing capacity tests and compaction tests are also carried out. The moisture content of the fill is controlled based on the maximum dry density and optimal moisture content for different types of fill; appropriate machinery is selected, and heavy compaction testing is used to verify the standards for subgrade compaction. Implement in accordance with the following standards, Tables 2-1 and 2-2. Compaction standards for soil embankments Table 2-1 Filling and cutting types; depth range below the road surface (cm); compaction percentage. Expressways, first-class roads; other roads. Embankment: Upper subgrade – 0–30 cm, ≥95%; ≥93%. Lower subgrade – 30–80 cm, ≥95%; ≥93%. Upper subgrade – 80–150 cm, ≥93%; ≥90%. Lower subgrade – greater than 150 cm, ≥90%; ≥90%. No filling and cut subgrades – 0–30 cm, ≥95%; ≥90%. Minimum strength and maximum particle size requirements for subgrade fill Table 2-2 Category of items; depth below the road surface (cm); CBR value (%); maximum particle size of fill material. Stone-filled subgrades: Upper subgrade – 0–30 cm, 8.0%, 10 cm. Lower subgrade – 30–80 cm, 5.0%, 10 cm. Upper embankment – 80–150 cm, 4.0%, 15 cm. Lower embankment – below 150 cm, 3.0%, 15 cm. No filling and cut subgrades – 0–30 cm, 8.0%, 10 cm. Note: If the CBR value of the subgrade fill does not meet the requirements specified in the table, lime or other stabilizing materials can be used to treat it. 2.3 For the filling of the subgrade, from excavation, loading, transportation, filling, leveling to rolling, we will organize large-scale mechanized integrated operations; for earthwork and stonework within a distance of 100 meters, bulldozers will be used for the work ； For distances exceeding 100 meters, excavators, loaders, and dump trucks are used for transportation. The filling work is carried out strictly in accordance with the four phases (filling, leveling, rolling, inspection) and eight procedures (construction preparation, surveying and setting out, layered filling, spreading and leveling, rolling and compacting, inspection and certification, subgrade surface finishing, slope trimming). A. Subgrade preparation: For the cleaned site, if the slope of the ground is not steeper than 1:10, the embankment can be constructed directly on it; when the slope is between 1:10 and 1:5, the topsoil on the original ground surface should be loosened before embankment construction; if the slope is steeper than 1:1.5, steps with a width of at least 1 meter should be created in the original ground, with the top surfaces of these steps having an inward slope of 2%–4%, after which the embankment can be built. In areas where there is no filling or excavation, the compaction degree within 30 cm below the level of no filling/excavation should be determined using the heavy compaction standards specified in JTJ051–93, and it should be no less than 95%. If the compaction degree does not meet the requirements, the area 80 CM below the surface of the subgrade should be replaced so that the compaction degree meets the specified standards. In areas with standing water, drain the water as much as possible and remove silt and other unsuitable fill materials ； For the improvement of other poor soil sections, replacement filling or lime treatment is carried out in accordance with the design drawings or the instructions of the supervising engineer. B. Test section: Select a roadbed of 100 meters in length or the length indicated by the supervising engineer as the site compaction test section. Using all our equipment, determine the loose-laid thickness of each layer of material, the moisture content of the material, the number of rolling passes, the rolling speed, and other parameters required to achieve the specified degree of compaction. The results of these tests shall be submitted to the supervising engineer for approval, to serve as a basis for using this type of filler in construction. The embankment filling is carried out according to the determined construction parameters. C. Filled embankment: (1) The fill height for the filled subgrade must be controlled in layers, with each layer being parallel to the road surface ； The filling work should be spread in layers in a parallel manner ； Ensure the compaction degree of the subgrade. The width of each layer of filler laid should extend 300 mm beyond the designed width of the embankment on each side, to ensure sufficient compaction at the edges of the embankment after the slope is trimmed. Fillers of different soil types should be filled in layers, with the number of layers being minimized; the total thickness of each filler layer should be no less than 500 mm. The thickness of the compacted layer in the final layer filled on the subgrade surface for earth embankments should not be less than 100 mm. (2) When the embankment filling height is less than 800 mm (excluding the road surface thickness), for the soil base obtained after clearing and removing the original surface, the surface should be loosened to a depth of 300 mm, and then leveled and compacted. Its compaction degree shall meet the requirements of the “Specifications”. (3) When the fill height of the embankment is greater than 800 mm, the base of the embankment should be leveled and compacted prior to filling, with a compaction degree of not less than 85%. (4) When the natural horizontal or vertical slope of the ground is steeper than 1:5, the original ground should be excavated into steps; the width of these steps must meet the requirements for the operation of paving and compaction equipment, and shall not be less than 1 m. The top of the steps is made with an inward slope of 2%–4%. On sandy soils, no steps need to be dug, but the topsoil within 200–300 mm below the original ground level should be loosened. (5) For embankment works that connect structural elements, the construction methods used shall not compromise the safety and stability of those elements. (6) If a access road or bypass is constructed within the embankment area, such road or bypass shall not be considered part of the embankment filling; it must be refilled to form a new embankment that meets the specified requirements. (7) Any large pieces of hard material that cannot be crushed by compaction equipment should be removed or broken in advance; the maximum size of the broken hard material shall not exceed 2/3 of the thickness of the compacted layer, and it should be distributed evenly to achieve the required degree of compaction. (8) When a fill embankment is constructed in several sections, and the filling at the junction of two adjacent sections is not carried out at the same time, the section filled first should have steps created in layers at a slope of 1:1 ； If construction is carried out on both sections simultaneously, they should be constructed in layers with overlapping connections, and the overlap length must not be less than 2m. (9) When filling embankments with soil of low water permeability, the moisture content should be kept within the range of the optimal moisture content ±2% ； When filling the lower layer of the embankment, its top should have a 4% two-way cross slope ； When filling the upper layer, it should not be placed on the embankment slopes filled with soil with better water permeability. D. Backfilling at structures (1) The backfilling of structures (including the areas behind bridge and culvert abutments and the cone slopes) refers to the process of filling, in layers using the required materials, the area remaining between the structure and the subgrade after the structure has been completed. (2) The backfilling at the structure shall be carried out in accordance with the drawings and the requirements of the supervision engineer. The specific requirements regarding the strength of the masonry during backfilling, as well as the timing for backfilling, shall be in accordance with the relevant provisions of the \"Technical Specifications for the Construction of Highway Bridges and Culverts\" (JTJ041－89). (3) Unless otherwise specified in the drawings, permeable materials such as gravel or other materials approved by the supervising engineer shall be used for backfilling ； The maximum particle size of the filler shall not exceed 50 mm. (4) Length of the fill behind the abutment in the direction of the route: at the top, it should be at a distance from the end of the wing wall that is not less than the height of the abutment plus 2 meters ； The bottom should be at a distance of not less than 2m from the inner edge of the foundation. (5) The fill soil at the structure should be placed in layers, with each layer having a loose thickness not exceeding 150 mm. The compaction degree required at the structure, from the base of the fill material or the top of the culvert to the top surface of the roadbed, is 95%. (6) During backfill compaction work, backfilling should be carried out symmetrically to ensure the structure remains intact. In areas that cannot be reached by rollers, small motorized ramming tools or other methods approved by the supervising engineer should be used for compaction. E. Drainage: (1) In areas where the surface is excessively wet or in paddy fields, longitudinal drainage ditches should be dug outside the slope protection paths on both sides of the embankment, and vertical and horizontal drainage ditches should be dug within the subgrade area to remove accumulated water and reduce or cut off groundwater. The work shall be carried out in accordance with the drainage design or the instructions of the supervision engineer. (2) In the drainage ditch on the outside of the slope protection path, an earth embankment should be built on the outside of the ditch to prevent water from flowing in. (3) For the lateral drainage ditches excavated within the subgrade area, when their purpose is to cut off or lower the groundwater level, they should be backfilled with sand and gravel materials with good water permeability. (4) When there are large areas of low-lying and waterlogged zones within the subgrade area, earth embankments can be constructed first to drain the water, and weeds, silt, as well as any unsuitable materials should be removed from outside the embankment. The ground should then be loosened to the depth required by the supervising engineer (loosening may not be necessary if the density of the ground already meets the requirements); after this treatment, the area can be compacted. Compaction of the original ground surface should also be carried out in dry areas or when the surface soil is loose. The requirements for compaction degree shall all meet the requirements of the \"Specifications\". 2.4 At the junctions where filling and excavation occur in the subgrade (in both longitudinal and transverse directions), the embankment filling in A) areas with partial filling and partial excavation in the transverse direction should be carried out in layers as specified in the drawings, to prevent longitudinal cracks in the subgrade due to improper filling. B) The original ground surface of the partially filled section must be thoroughly cleaned; in accordance with the requirements of the drawings and the provisions of the technical specifications, the original ground surface should be loosened or turned into steps, before filling it in layers. C) During filling, it is necessary to spread and compact the material in layers from low to high; special attention must be paid to the joint at the boundary between filled and excavated areas, ensuring that the compaction is thorough with no visible seams. D) For the excavation of sections that are partially filled and partially excavated, it is necessary to first complete the treatment of the original ground surface in the lower filled section; only after it has been inspected and approved by the supervising engineer can the excavation of the upper excavated section begin. Materials that are not suitable for use in excavations must be discarded; it is strictly prohibited to use them in partially filled sections. E) The embankment filling at the junction of vertical filling and excavation should be carried out in layers as specified in the drawings, to prevent horizontal cracks in the embankment due to improper filling. F) At the junction of filling and excavation works, it is necessary to first thoroughly clean the original ground surface in the filled area; the length of cleaning required depends on the height of the fill material and the slope of the original ground surface. The cleaning of the original ground surface must comply with the requirements specified in the drawings as well as the technical specifications for this section of the project. G) Excavation at the junction of fill and cut work must be carried out only after the original ground surface in the fill area has been properly prepared and approved by the supervising engineer; materials that are not suitable for use in filling are strictly prohibited from being used in the excavation. H) When filling at the junction of fill and cut areas, it is necessary to spread and compact the material in layers from lower to higher levels; special attention should be paid to the joining of these areas, ensuring that the compaction is thorough with no gaps or seams. I) At the junction of vertical filling and excavation, a semi-filled and semi-excavated cross-section is often present; during construction, it should be arranged properly in accordance with the drawing requirements, ensuring balanced filling at the junction of vertical filling and excavation, as well as compacting that is thorough without any gaps. J) If the drawings specify the use of geosynthetic materials for reinforcement at the junctions between fill and excavation areas in a vertical direction, such geosynthetic materials shall be installed in accordance with the requirements of the drawings and the relevant provisions of the technical specifications for this contract section. 2.5 Subgrade shaping A) Restore all survey stakes in accordance with the design drawings, and check the subgrade’s centerline position, width, longitudinal slope, lateral slope, and corresponding elevations. A renovation plan shall be prepared based on the inspection results, and work may commence only after it is approved by the supervision engineer. B) For soil subgrades, manual or mechanical scraping or filling is used, combined with mechanical rolling to shape them. When the fill material is insufficient or the slope is eroded by rainwater, the original slope is excavated into steps and filled layer by layer. C) The surface of the soil subgrade is leveled using a bulldozer; when the soil removed is not sufficient to fill the depressions, soil identical to that of the subgrade is used for filling and compacting. Within 15 cm of the surface of the repaired subgrade, loose material and large stones shall be removed, and the area shall be filled and compacted with the same filler as that used for the subgrade. D) The renovation of side ditches should be carried out with the use of string lines, and the longitudinal slope of various ditches should be measured using instruments until they meet the requirements of the design specifications. E) The excess fill on both sides of the filled subgrade should be removed in advance; if there is a lack of soil at the slope edges, steps must be created and the fill should be applied in layers while being compacted. 2.6 Subgrade inspection A) Compaction degree inspection: After each layer of subgrade fill has been compacted, a test for the degree of compaction can be conducted; construction of the next layer can proceed only once the test shows satisfactory results. The density of earthwork subgrades is checked in accordance with Appendix B of JTJ071－98P and the density inspection method specified in JTJ059－95. B) Deflection: Earth fill roadbeds require deflection testing, to be carried out in accordance with Appendix I of JTJ071－98 and JTJ059－95. C) Cross-sectional elevation, centerline deviation, width, smoothness, cross-slope, and slope: The earthwork subgrade is inspected in accordance with the specifications. III. Main characteristics of earthwork and stonework construction 3.1 The allocation of earthwork and stonework is carried out strictly in accordance with the \"nearest\" principle, that is, excavation and filling are done at the nearest location, materials are sourced from the nearest source, and transportation is also conducted to the nearest location. 3.2 Concentrate efforts on carrying out phased assaults, focusing on the earthwork construction for subgrades in key and difficult areas such as highly filled sections. 3.3 When filling the subgrade during the rainy season, to prevent soil erosion and ensure construction quality, it is necessary to arrange proper surface drainage in advance and keep the drainage channels unobstructed. During construction, digging, transporting, filling, and compacting should be carried out continuously; each layer of fill should have a cross-slope of 2%–3%. The loose soil laid down should be compacted thoroughly before the rainy season starts and before work is completed. In addition, water barriers should be constructed, side ditches should be cleared, and measures should be taken to protect the subgrade. Once the subgrade is formed, the road shoulders should be promptly tidied up and slope protection measures should be implemented to maintain the overall stability of the subgrade. 3.4 During excavation of the subgrade in the rainy season, it is necessary to construct catchwater ditches and temporary drainage ditches to ensure unobstructed water flow and prevent soil erosion. 3.5 For the filling and compaction work of the backfill behind bridge and culvert abutments, attention should be paid to the coordination between subgrade construction and bridge construction, and the conflicts arising from farmland irrigation and drainage in the bridge and culvert areas and subgrade construction must be properly resolved.

Let me summarize it roughly: 1) The surface clearing must be thorough; the topsoil and humus soil need to be cleaned completely, with no weeds, tree roots, or other debris present. The width of the area cleared should exceed the width of the roadbed by at least 50 cm on each side. 2) It is necessary to check the width of the subgrade alignment to ensure that it meets the requirements for subgrade filling width. 3) Dig longitudinal drainage ditches and install appropriate on-site drainage facilities; construct a temporary access road on one side of the subgrade to meet the construction requirements ； 4) Filling shall not commence until the embankment foundation has been inspected and approved by the supervising engineer; similarly, filling of the next layer shall not take place until the previous layer has been inspected and approved by the engineer ； 5) Fillers of different soil types should be filled in layers; the loose thickness of each layer of non-stone fillers should not exceed 30 cm, and the total thickness of each filler layer must be at least 50 cm. When filling an earth embankment to the top surface of the subgrade, the compaction thickness of the final layer should not be less than 10 cm ； 6) When the fill height is less than 0.8 meters, for the soil foundation resulting from the clearing and removal of the original surface, it must be leveled to the elevation of the roadbed bottom, with the compaction degree of the foundation being no less than 94% ； 7) When the natural slope ratio is steeper than 1:5, the original ground surface should be excavated to form steps. The width of these steps must be sufficient to accommodate the operation of paving and compaction equipment, and it should not be less than 2.0 meters. The top surface of the steps should have an inward slope of 4%. On sandy soils, no steps need to be created; however, the topsoil within 20–30 cm below the original ground surface should be loosened ； 8) If a access road is constructed within the embankment area, such road or approach road shall not be considered part of the embankment fill; it must be refilled to form a new embankment that meets the specification requirements ； 9) When filling embankments with soil of poor water permeability or impermeable soil, the moisture content during compaction should be controlled within +2% of the optimum moisture content ； When using soil with lower water permeability to fill the lower layer of the embankment, its top should be given a 4% dual-slope gradient; if it is used to fill the upper layer, it should not cover the slope of the lower layer filled with soil with higher water permeability ； 10) Any hard materials that cannot be crushed by compaction equipment should be removed or broken down so that their maximum particle size does not exceed 2/3 of the compaction thickness; moreover, the particle sizes should be evenly distributed to achieve the required degree of compaction ； 11) When constructing fill embankments in sections and the filling at the joints is not carried out at the same time, the section filled first should have steps created in layers at a slope of 1:1 ； If construction is carried out on both sections simultaneously, they should be constructed in layers in an alternating manner, with the overlap length being no less than 2 meters. 12) The filling materials for the fine-grading layer below the surface of the subgrade should be crushed stone soil, gravel, waste materials, and mountain debris. In addition to meeting the requirements specified in Table 5.1.5 of the \"Technical Specifications for Highway Subgrade Construction\" (JTJ033-95), these filling materials must have a bearing ratio (CBR value) of more than 8%; they must also satisfy the detailed requirements outlined in the drawings.

The fill subgrade must have the fill elevation controlled in layers parallel to the road surface； The filling work should be spread in layers in a parallel manner ； Ensure the compaction degree of the subgrade.