Requirements for backfill soil

As the original poster said, quality control for backfill soil is indeed a concern. For backfill soil, the type of soil used for backfilling varies depending on the design. In terms of quality control, the construction unit and the supervisor must work together to ensure proper quality supervision! Moreover, the supervision responsibilities are significant. Backfilling work falls under concealed works, and therefore the process control and inspection of concealed works are also part of quality control. Video recording~What construction companies fear the most are pieces of evidence; just have a camera and they’ll be worried.

II. Preparations before soil backfilling 1. Selection of backfill material: The backfill material for this project will primarily be the soil excavated during the construction; any backfill material deemed unsuitable by the engineers shall not be used. 2. Standard compaction test: After the backfill material is determined, the quality control officer and sampler from the project team, together with the supervision engineer, will take samples at the backfill site. The soil samples taken must be representative, including those from all different soil layers and types. After sampling, the soil samples are sent to the site laboratory for standard compaction tests in order to determine the maximum dry density at the optimal moisture content. Through experiments, it was determined that the optimal moisture content for the backfill material is 16.8%, and the maximum dry density is 1.71 g/cm3. In accordance with the requirement in the contractual technical specifications that the compaction degree of the backfill soil should be D≥90%, the minimum dry density to be controlled during construction was determined to be 1.71 g/cm3 × 90% = 1.54 g/cm3. By referring to the \"water content versus dry density curve\", the water content range corresponding to this acceptable dry density was identified as 11%–24%. 3. On-site rolling test: After the standard compaction test is completed, a rolling test is carried out at the construction site. The purpose of this rolling test is: (1) to verify whether the soil can reach the designed dry density value after compaction ； (2) Check whether the performance of the compaction equipment meets the construction requirements ； (3) Selecting appropriate construction compaction parameters: soil layer thickness, maximum particle size allowed for soil aggregates, suitable range of moisture content, compaction method, and number of compaction passes ； (4) Determine the technical requirements and testing methods for quality control. Compaction tests were conducted in the four designated filling areas; different compaction equipment was used for each area. The number of ramming passes with the frog rammer started at 4, after which samples were taken using a ring cutter to determine the dry density. If the required density was not achieved, an additional 6 or 8 ramming passes were carried out until the desired density was obtained ； The crawler bulldozer was used for measurements starting from the 6th pass; then measurements were taken at 8 passes and 10 passes, and finally the appropriate number of compaction passes, soil layer thickness, maximum particle size of the soil clumps, and other parameters were determined through these measurements. 4. Technical instructions prior to construction: Before soil backfilling, the technical department provides detailed technical instructions to the quality inspectors of the work teams, clarifying issues such as the division of the backfill area, the compaction parameters determined through compaction tests, and the construction methods. III. Construction Plan: The backfilling for this project will be carried out in accordance with the construction sequence of the box culvert. To accommodate the construction of the main building and to meet the requirements regarding backfilling for that building, the backfilling will be carried out in sections of approximately 210 meters each; the speed of backfilling will match the speed of building construction, with backfilling operations proceeding continuously. During soil backfilling, two methods are employed: on one side of the soil stacking area, large bulldozers are used to deliver soil to the foundation pit, while on the other side, excavators are used to load the soil; dump trucks then transport the soil from one end to the other, ensuring that backfilling occurs evenly on both sides as the level rises. After the soil is backfilled to 1 m above the top of the box culvert (i.e., ▽1.70), large bulldozers are used to push it into place. IV. Construction Methods and Procedures 1. Construction procedures: 2. Construction methods 2.1 Division of the earthwork filling area 2.2 Filling methods 2.2.1 Filling of Area 1: The filling surface in this area is narrow and deep, with an inverted triangular cross-section; it is not possible to use a bulldozer to push the fill material into place directly. Instead, an excavator is used on the secondary platform to deposit the soil in place, after which it is leveled by hand and compacted using rammers. 2.2.23 Earthback filling in Area 2.2.23: When the width of the filling work area in Area 1 exceeds 5m, filling is carried out in Area 3; the soil on the right side is pushed into place using large bulldozers, while small bulldozers are used for leveling and compaction ； The soil on the left side is transported to the site using dump trucks, and a small bulldozer is used for spreading and compacting it. On the right side, 4 D60 large bulldozers are used for pushing the soil, while 2 74KW bulldozers are used for spreading and compacting it. On the left side, 5 dump trucks are used to transport the soil, 1 D60 bulldozer is used for spreading the soil, and 2 74KW bulldozers are used for spreading and compacting it. Within a range of 0.5m on both sides of the building, soil is manually laid and compacted using rammer tools. 2.2.32 Earthback filling in Area 2.2.32: For earthback filling in this area, bulldozers are used to push the soil, and dump trucks transport the soil to the edge of the building; thereafter, excavators pour the soil onto the top of the box culvert, after which it is leveled by hand and compacted manually. Once the soil filling on top of the box culvert exceeds 1 meter, earthfilling in Zone 3 begins. At this stage, 6 large D60 bulldozers are used to push the soil into place in Zone 3, while 5 74KW bulldozers are used to spread and compact the soil. 2.34 Earthback filling in the area: The topsoil with a thickness of 0.3~0.5m is transported to the site using dump trucks, and then spread out using bulldozers. After the surface soil has been filled in, the surface facilities are restored in accordance with the engineer’s instructions and the requirements specified in the construction drawings. 2.4 Control of earth filling: During the earth filling process, strict control is exercised over the filling operations by adhering to the optimal moisture content of the soil determined through tests, as well as the thickness of the layers applied, along with the number of passes required for rolling and compacting. When the bulldozer spreads soil, it is necessary to create steps at the slope edges; the width of these steps is determined based on the slope excavation coefficient and the thickness of the soil to be spread. The thickness of the fill material shall not exceed the thickness determined through testing. For bulldozer rolling, the alternate advancing and retreating method is used, and the overlap width of the rolling tracks should be greater than 10 cm. Manual ramming is carried out in stages of 20m per layer to meet the requirements, with the progress direction being parallel to the axis during backfilling, spreading of soil, rolling, and ramming. The overlap at the junction of manual tamping and rolling shall not be less than 0.5 m. Areas with pressure loss or insufficient pressure that occur during rolling, as well as dead corners that cannot be reached by rolling, are all remedied using manual ramming. When rolling in sections, the joints should be made at a slope of more than 1:3; the tracks left by rolling should overlap by 0.5 m, and the offset between adjacent layers should not be less than 1 m. Before rainfall, the loose soil on the surface of the work area should be compacted in a timely manner, and the area should be shaped into an arch or slope to facilitate drainage. After the rain, the area should be dried out or the silt on the filled surface removed; only after it meets the required standards can filling continue. Throughout the backfilling process, a dedicated person is assigned to ensure the proper operation of the observation instruments and measurement equipment, as well as to protect the installed instruments and measurement markers from damage. V. Quality Inspection 1. Before filling, the terrain and cross-section of the backfill area are first measured and verified, and the measurement data are submitted to the engineer for reinspection. Next, the measured foundation trench is cleaned to prepare its surface, after which it is submitted to the engineer for inspection prior to backfilling; backfilling can only take place once the inspection is successful. 2. During soil filling, experienced engineering and technical personnel are assigned to the filling area to supervise the process on-site and work closely with the engineers and supervisors. 3. During the earth filling process, each layer of soil is inspected in accordance with the earth filling inspection plan approved by the engineer. Once the inspection is successful, the relevant inspection data are submitted to the engineer, who then conducts random inspections. Only after the re-inspection is successful and approved can the next layer of soil be filled. 4. At the soil stacking site, the moisture content of the soil is checked from time to time; soil with a high moisture content must be exposed to the sun until its moisture content meets the required level before it can be used for backfilling. 5. After inspection by the engineer, the substandard backfill soil shall be thoroughly reworked, repaired, and reinforced in accordance with the engineer’s instructions. 6. After the earthwork filling is completed, first conduct a self-inspection of all filled areas of the project in accordance with the relevant provisions specified in the applicable standards and regulations; once the self-inspection is successful, submit it to the engineer for acceptance. Last edited by Lailai on 2009-3-28 12:13]

The construction guide for soil backfill compaction is sourced from the internet for educational purposes. 1. Referenced standards: SDJ213-83 \"Technical Specifications for the Construction of Roller-Compacted Earth and Rock Dams\", SL260-98 \"Construction Specifications for Dike Projects\", SL38-92 \"Quality Rating Standards for Units of Water Resources and Hydropower Infrastructure Projects (VII)\", SL239-1999 \"Procedures for Quality Assessment and Acceptance of Dike Project Construction\". 2. Construction preparation: 2.1 Thoroughly study the contract and design documents, taking into account all relevant conditions, in order to prepare a proper construction organization plan. 2.2 Make all necessary technical preparations, complete the temporary construction work involving “four connections and one leveling,” and prepare all kinds of equipment and materials. The diversion and drainage works have been completed. 2.3 The surveying and setting-out work has been approved as satisfactory; sturdy markers have been installed at the key survey points, and the setting-out for the dam body takes into account the settlement allowance specified in the design. 2.4 Conduct an on-site inspection of the soil stockpile; the available quantity should be 1.5–2.5 times greater than the amount required. The soil quality and natural moisture content meet the design requirements. 2.5 The construction machinery and testing equipment have been installed; tests on the soil used for the impermeable layer have been conducted, and the foundation cleaning has been completed and approved. 3. Construction operation requirements 3.1 Earthwork excavation 3.1.1 Before excavating the material site, the area to be excavated should be defined; tree roots, rocks, and all obstacles that could hinder construction must be removed, and any standing water on the site should be drained, with drainage ditches dug as necessary. 3.1.2 When the natural moisture content of the soil is close to the value specified for construction control, vertical excavation is used; when the moisture content is higher, horizontal excavation is employed. 3.1.3 When there are defective layers in the stratified soil that need to be removed, horizontal excavation is used; when mixing is permitted for the stratified soil, vertical excavation is employed. 3.1.4 Vertical excavation is preferred for winter construction. 3.1.5 The walls of the soil excavation pit must be stable; bottom excavation is strictly prohibited during vertical cutting. 3.2 Laying of material 3.2.1 The laying of the soil material for the impermeable layer shall be carried out parallel to the axis of the dike in a sequential manner; each section should be at least 100 meters long, and when done manually, the length should be at least 50 meters. 3.2.2 The working area should be divided into three stages: soil laying, rolling, and inspection, to facilitate sequential operations. The soil should be laid in layers in a uniform manner, rolled uniformly as well, and samples should be taken for inspection by designated personnel; the presence of boundary ditches is strictly prohibited. 3.2.3 The working surfaces of adjacent construction sections should rise evenly; if a height difference inevitably occurs, it should be connected by a slope of 1:3 to 1:5. 3.2.4 The soil material should be unloaded using the dumping method, and then spread to the designated location with a bulldozer or by hand; it is strictly prohibited to mix gravel or other permeable materials with cohesive soil materials. 3.2.5 The limits for the thickness of the soil layer and the diameter of the soil clumps are shown in the table below: Table of Limits for Soil Layer Thickness and Soil Clump Diameter. 3.2.6 When laying the material at the edge of the embankment, a certain excess should be provided on each side of the designed boundary line; this excess is 10 cm for manual laying and 30 cm for mechanical laying. 3.2.7 Control the thickness of the filled soil by keeping the fill surface level, measuring and feeding materials in appropriate amounts, and monitoring the thickness regularly. The allowable error for soil thickness is +0-5 cm. 3.3 Rolling 3.3.1 The moving direction of the rolling machinery should be parallel to the lifting axis. For segmented and slotted rolling, the overlapping width between adjacent rolling surfaces should be no less than 0.5 m in the direction parallel to the axis of elevation, and no less than 3 cm in the direction perpendicular to the embankment line. 3.3.2 When using rolling machinery for rolling, the method of alternating forward and backward movements is employed. The rolling overlap width is greater than 10 cm. When the dozer is used as a compaction machine, the wheel trace compaction method is employed, with the wheel traces overlapping by 1/3 of the wheel width. 3.3.3 In areas that cannot be compacted by mechanical rolling, use a frog rammer or a wooden rammer for compaction. The compaction should be carried out using the ring connection method, with the compression marks overlapping in both directions; 1/3 of the ramming depth should be applied per pass, and 1/3 per row. When compacting in segments, the overlap width of the compression marks should be no less than 1/3 of the rammer’s diameter. 3.3.4 Carry out soil spreading, rolling, and inspection in a continuous manner; do not leave the loosened soil unattended overnight. After rolling with a flat roller, before laying the upper layer of soil, it is necessary to roughen the surface or roll it again with a bulldozer to facilitate the bonding between the upper and lower layers of soil. 3.3.5 The designed dry density is achieved by controlling the moisture content of the soil, the thickness of the soil layer applied, and the number of rolling passes. For soil with a low moisture content, appropriate watering and mixing are necessary; for soil with too high a moisture content, drainage ditches should be dug at the storage site, the soil should be exposed to the sun on-site, and then compacted to prevent the formation of springy soil. 3.3.6 Prevent shear failure of the fill by methods such as using the filling method for unloading and reducing the distance that loaded vehicles travel on the dam surface; any such failure detected must be corrected thoroughly through rework. 3.4 Dry density test 3.4.1 After each layer of soil is compacted, its dry unit weight must be measured to ensure it meets the design requirements before the next layer of soil can be applied. 3.4.2 The dry unit weight is determined using the ring cutter method; the inner diameter of the ring cutter should be not less than 70 mm for embankment projects, and not less than 100 mm for reservoir projects. 3.4.3 The number of samples taken per layer should be 1 sample per 100–150 cubic meters; for particularly narrow and long embankments, 1 sample should be taken every 20–30 meters. The samples should be distributed evenly, with a total of 3 samples taken. The sampling locations should be at the lower 1/3 of the layer thickness. 3.4.4 The areas that fail the ring knife sampling test must be re-rolled or treated locally until they pass the re-inspection before proceeding to the next stage of work. 3.5 Filling during the rainy season: 3.5.1 The filling surfaces of the core wall and slope walls should slope slightly upstream; in the case of homogeneous dams, a bulge in the middle can be created to slope upward and downward to facilitate the drainage of rainwater. 3.5.2 Conduct proper rain forecasts; before it rains, use trucks and rollers to quickly compact the loose soil in the layer, and ensure that the filling surface is level to prevent water accumulation. 3.5.3 Ensure proper protection of the dam surface; do not trample on it during or after rain, prohibit vehicle traffic there, and work can resume only after the surface has been dried or treated appropriately following rainfall. 3.5.4 Plastic sheeting for rain protection in narrow spaces. Large machinery moved out to the embankment surface before the rain to carry out filling work. 3.5.5 Ensure proper protection of slopes to prevent them from being damaged by rainwater. 3.6 Filling at Negative Temperatures in Winter: 3.6.1 When working at negative temperatures, soil materials with positive temperatures should be used; processes such as loading the soil, spreading it, compacting it, and taking samples must all be carried out quickly and continuously. The temperature during soil compaction must be above -1°C. Construction should be halted when the lowest temperature on that day is below -10°C or 0°C, and the wind speed is greater than 10 m/s. 3.6.2 When constructing at low temperatures, the moisture content of cohesive soils shall not exceed 90% of their limit, while the moisture content of gravel materials should be less than 4%. 3.6.3 During winter filling, the thickness of the soil layer applied should be reduced or the compaction efficiency increased, using heavy-duty rolling machinery. 3.6.4 Before construction, the ice and snow on the filling surface must be removed completely; it is strictly prohibited to include ice and snow in the fill material. 3.6.5 Ensure proper insulation of the core wall and inclined wall impermeabilization structures to prevent the compacted soil layers from freezing. 4 Quality Standards 4.1 For the dry unit weight of the reservoir impermeable layer after rolling, the pass rate must be no less than 90%; defects shall not be concentrated, and the dry unit weight of defective areas must not be lower than 98% of the overall dry unit weight. 4.2 Inspection items and standards for the quality of earth dam construction units using compaction 　4.2.1 Acceptance criteria for the compaction quality of earth dam construction units using compaction 　Note: 1. The dry density of unsatisfactory samples shall not be lower than 96% of the designed dry density value. 2. Unqualified samples must not be concentrated in a localized area. 4.2.2 Qualification standards for the appearance quality of rammed earth embankments 5 Precautions: 5.1 The foundation clearing must be carried out in accordance with the design specifications; only after the clearing is completed and approved by the supervisor and the designer can filling begin. Any special conditions identified during the foundation clearing must be addressed in line with the design requirements, and relevant records must be kept. 5.2 The sequence of filling in different sections must be determined in accordance with the construction plan; when filling soft soil foundations, the principles of applying layers thinly in sequence, filling in a cross-pattern, and advancing evenly should be followed. 5.3 Establish proper observation points for surface settlement and horizontal displacement, and strictly control the loading rate to prevent instability. 5.4 Maintain construction machinery on schedule, carry out repairs as required, work only with valid licenses; driving without a license is strictly prohibited to ensure construction safety. 5.5 When there is a change in the material yard, promptly work together with the design and supervision parties to carry out rolling tests in order to control the quality of rolling. 5.6 Construction work must comply with flood control measures; emergency response teams should be organized to ensure moisture prevention and safety. This post was last edited by zhangya*ong on 2009-3-28 08:34]