Foundation pit backfilling method for fluid solid waste cementing material

Abstract

The invention discloses a foundation pit backfilling method for a fluid solid waste cementing material. The method comprises the following steps: mixing alkaline residues, cement, slag powder and water according to a water-solid ratio of 1.30-1.50 to form fluid alkaline residue slurry; the slurry is conveyed to a foundation pit through pumping equipment; pouring is conducted in the foundation pit in a layered mode, and the filling thickness of each layer is 2.5-3.0 m; moisturizing and maintaining for 3-5 days after each layer is poured; and repeatedly pouring to the designed elevation. By optimizing the water-solid ratio and the glue waste ratio, the single-layer filling thickness is increased, the maintenance period is shortened, and the layering frequency and the construction waiting time are reduced; the slurry storage tank monitors the volume weight of the slurry in real time to ensure uniformity and avoid the risk of segregation; and industrial solid wastes such as alkaline residues are used as raw materials, so that resource consumption and environmental pollution are reduced, and efficient, economical and environment-friendly foundation pit backfilling is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of foundation pit backfilling, and in particular to a method for backfilling a foundation pit with a fluidized solid waste binder. Background Art

[0002] Traditional foundation pit backfill projects often use materials such as sand, gravel, concrete, or conventional stabilized soil. However, these materials present challenges such as low construction efficiency, high material costs, high resource consumption, and insufficient environmental friendliness. In recent years, with the advancement of solid waste resource utilization technologies, fluidized solid waste binders, prepared from industrial solid wastes such as alkali slag and desulfurization ash, have gradually been adopted in engineering applications. These binders, created by mixing solid waste with cementitious materials and water in a specific ratio to form a fluid slurry, offer advantages such as high fluidity, easy pumping, and controllable strength, making them suitable for filling complex foundation pit structures.

[0003] However, the existing fluidized solid waste binder still has significant deficiencies in foundation pit backfill construction. For example, in the layered pouring process, the existing technology usually requires strict limits on the thickness of each layer of filling to ensure the initial setting strength of the material, and the upper layer construction can only be carried out after the lower layer is completely initially set. This process not only prolongs the construction period, but also increases equipment idle time and labor costs. In addition, due to the limitations of material ratios and process control accuracy, the existing methods are difficult to optimize the layered filling thickness while ensuring the strength and construction efficiency of the fluidized alkali slag. Especially in deep foundation pit projects, the interval time and thickness restrictions of layer-by-layer pouring have become the key bottlenecks restricting construction efficiency. How to improve the single-layer filling thickness and shorten the maintenance period while ensuring the stability of the backfill body by improving material properties and construction technology is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for backfilling a foundation pit with a fluid solid waste binder, so as to solve the problem that the existing technology cannot increase the single-layer filling thickness and shorten the curing period while ensuring the stability of the backfill body.

[0005] The present invention provides a method for backfilling a foundation pit with a fluidized solid waste binder, comprising the following steps:

[0006] S1: mixing alkali slag, cement, slag powder and water at a water-to-solid ratio of 1.30-1.50 to form a fluidized alkali slag slurry, wherein the water-to-solid ratio is the ratio of the mass of water to the total mass of the alkali slag, cement and slag powder;

[0007] S2: transporting the fluidized alkali slag slurry to the foundation pit through a pumping device;

[0008] S3: Layered pouring is carried out in the foundation pit, with each layer filling thickness of 2.5-3.0 meters;

[0009] S4: After each layer is poured, the current layer is subjected to moisturizing curing for 3-5 days;

[0010] S5: Repeat steps S3 to S4 until the casting reaches the designed elevation.

[0011] Furthermore, in step S1, the water-solid ratio is 1.40.

[0012] Furthermore, in step S1, the flow value of the fluidized alkali residue slurry is 200-400 mm, and the flow value is measured by a cylinder test method with an inner diameter of 80 mm and a net height of 80 mm.

[0013] Furthermore, step S3 includes:

[0014] S31: Clean up debris in the foundation pit before layered pouring;

[0015] S32: temporarily storing the fluidized alkali residue slurry in a slurry storage tank, and monitoring the slurry bulk density in real time during pumping;

[0016] S33: Adjust pumping parameters based on monitoring results to ensure slurry uniformity.

[0017] Furthermore, step S32 includes:

[0018] S321: Take slurry samples every 10-15 minutes;

[0019] S322: Determine bulk density and record deviation value;

[0020] S323: If the deviation exceeds 5%, an alarm is triggered and pumping is suspended.

[0021] Furthermore, in step S4, the moisturizing maintenance includes covering with a plastic film and spraying water mist to maintain the surface humidity not less than 90%.

[0022] Furthermore, in step S1, the cement is P.O42.5 specification cement, and the slag powder is S95 grade slag powder.

[0023] Furthermore, in step S1, the moisture content of the alkali residue is 20%-30%.

[0024] Furthermore, in step S1, the cement-waste ratio is 0.20-0.30, and the cement-waste ratio is the ratio of the total mass of cement and slag powder to the mass of alkali slag.

[0025] Furthermore, in step S3, the filling thickness of each layer is 3.0 meters, and the interval between pouring two adjacent layers does not exceed 2 hours.

[0026] Beneficial effects of the present invention: The present invention significantly improves construction efficiency while ensuring the fluidity and compressive strength of the slurry by optimizing the ratio of fluidized alkali slag and the layered pouring process. By shortening the curing time to 3-5 days and allowing the interval between adjacent layers to be no more than 2 hours, the idle equipment and manual waiting period are reduced, which is particularly suitable for deep foundation pit projects. At the same time, the real-time monitoring and dynamic adjustment mechanism of the bulk density of the slurry storage tank effectively controls the uniformity of the slurry and avoids the risk of backfill settlement due to material segregation. In addition, the use of industrial solid waste as raw material reduces resource consumption and environmental pollution, taking into account both economic benefits and environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0028] Figure 1 This is a flow chart of the method for backfilling a foundation pit with a fluid solid waste binder provided by the present invention. DETAILED DESCRIPTION

[0029] It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present application may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs.

[0030] See also Figure 1 The method for backfilling a foundation pit with a fluidized solid waste binder provided by an embodiment of the present invention is implemented by the following steps:

[0031] S1: Alkali slag, cement, slag powder and water are mixed at a water-solid ratio of 1.30-1.50 to form a fluidized alkali slag slurry, wherein the water-solid ratio is the ratio of the mass of water to the total mass of the alkali slag, cement and slag powder.

[0032] In this step, the raw materials need to be strictly screened and controlled. Alkali slag is the main solid waste raw material, and its source includes alkaline solid waste generated by the chlor-alkali industry, petroleum refining or metallurgical industry. It is necessary to ensure that its moisture content is controlled within the range of 20%-30% to avoid affecting the stability of the mix ratio due to excessive moisture. Cement uses ordinary Portland cement with a specification of P.O42.5. It has high early strength and good activity matching with S95 grade slag powder, which can accelerate the solidification process of fluidized alkali slag. The fineness of the slag powder must meet the S95 grade standard to improve the hydration reaction efficiency of the cementitious material. The cement-waste ratio is the ratio of the total mass of cement and slag powder to the mass of alkali slag, which is controlled between 0.20-0.30. By adjusting the proportion of cementitious materials, the fluidity of the slurry and the final compressive strength are balanced. The mixing process must be completed by special mixing equipment, and the mixing time must be no less than 5 minutes to ensure that the components are evenly distributed. The flowability of the mixed slurry must be measured using a cylinder test method with an inner diameter of 80 mm and a net height of 80 mm. The flowability range should be controlled within 200-400 mm to meet pumping and pouring requirements. If the flowability is outside this range, the water-to-solid ratio or the rubber-to-waste ratio must be readjusted.

[0033] S2: transporting the fluidized alkali slag slurry to the foundation pit through a pumping device.

[0034] Before pumping, the slurry needs to be temporarily stored in a slurry storage tank. The capacity of the slurry storage tank must be designed according to the total amount of foundation pit backfill and equipped with a stirring device to prevent the slurry from settling. During the pumping process, the slurry bulk density must be monitored in real time. Samples are taken from the slurry storage tank outlet every 10-15 minutes, and the bulk density deviation is measured using a densitometer. If the bulk density deviation exceeds 5%, the alarm system is triggered and pumping is suspended. Operations can be resumed after adjusting the mixing parameters or recalibrating the ratio. The diameter of the pumping pipe must be selected according to the slurry flow value, usually 100-150 mm, to reduce conveying resistance. The pumping pressure is controlled at 0.5-1.0 MPa to avoid slurry segregation due to excessive pressure. Through the pumping process, the fluidized alkali slag can be directly transported to the bottom of the foundation pit or narrow areas without relying on manual paving. It is particularly suitable for deep foundation pits with a depth of more than 5 meters or backfilling in complex terrain.

[0035] S3: Layered pouring is carried out in the foundation pit, with each layer filling thickness of 2.5-3.0 meters.

[0036] Before pouring in layers, the base of the foundation pit needs to be cleaned to ensure that there is no water accumulation, debris or loose soil. The flatness deviation of the base must be less than 50 mm, and manual finishing or mechanical compaction should be used when necessary. The thickness of each layer is controlled by a laser rangefinder or elevation marker, with an allowable error range of ±50 mm. Compared with the traditional process where each layer is limited to no more than 2 meters, this method optimizes the glue-waste ratio and the water-solid ratio so that the fluid alkali slag can still quickly form initial setting strength under thicker filling. During filling, the slurry needs to be poured continuously from one side of the foundation pit to the other to avoid local accumulation and uneven thickness. For foundation pits with larger areas, multi-point simultaneous pouring can be used, but the progress difference between adjacent pouring points must be controlled to no more than 1 meter to prevent the formation of cold joints. After each layer of filling is completed, the pouring time needs to be recorded and the construction interval of the next layer needs to be determined according to the ambient temperature. In an environment of 20-30℃, the interval between pouring two adjacent layers can be shortened to less than 2 hours, significantly improving construction continuity.

[0037] S4: After each layer is poured, the current layer is subjected to moisturizing maintenance for 3-5 days.

[0038] Moisturizing maintenance adopts a combination of covering with plastic film and spraying water mist. The thickness of the plastic film shall not be less than 0.1 mm, the overlap width shall be greater than 200 mm, and the edges shall be compacted with sandbags to prevent water evaporation. During the maintenance period, the integrity of the film shall be inspected daily and any damage shall be repaired immediately. The surface humidity is monitored by a humidity sensor and maintained at not less than 90%. If the ambient temperature is higher than 35°C, the frequency of water mist spraying shall be increased to at least 3 times a day; if it is lower than 10°C, the outer layer of the film shall be covered with thermal insulation cotton. The curing time is adjusted according to the performance of the cementitious material and the environmental conditions. The shortest time can be compressed to 3 days, but the current layer must be confirmed to have reached an initial strength of more than 0.2 MPa through on-site test block strength testing before the next layer can be constructed.

[0039] S5: Repeat steps S3 to S4 until the casting reaches the designed elevation.

[0040] After the final layer is filled to the design elevation, the top surface must be meticulously leveled to a flatness deviation of less than 20 mm. The top surface curing period is extended to seven days to ensure consistent surface strength with the interior. After all backfill is complete, the backfill undergoes an overall quality inspection. This includes density testing using sand filling or a nuclear density meter, and compressive strength testing using on-site core sampling or standard test block data. If the test results do not meet design requirements, additional filling or local reinforcement is required in the defective areas.

[0041] The present invention overcomes the technical bottleneck of the traditional layered backfill process, which limits the thickness of a single layer to less than 2 meters, by designing a precise water-to-solid ratio of 1.30-1.50 and a glue-waste ratio of 0.20-0.30, combined with the synergistic solidification mechanism of alkali slag, cement, and slag powder. This increases the thickness of each layer to 2.5-3.0 meters, while shortening the maintenance period to 3-5 days. This innovation significantly reduces the number of layers and the total construction period for deep foundation pit backfill, making it particularly suitable for the rapid construction of large-scale infrastructure projects. Through real-time monitoring of the bulk density of the slurry storage tank and dynamic adjustment of pumping parameters, the problem of controlling the uniformity of the slurry under thick layer filling is solved, and the problem of internal voids or uneven strength of the backfill body caused by material segregation is avoided. In addition, by using industrial solid waste such as alkali slag as the main raw material, large-scale resource utilization of waste is achieved, the amount of natural sand and gravel mining is reduced, the project cost is reduced by 10%-15%, and the land occupation and environmental pollution caused by solid waste storage are reduced. Through the deep integration of process parameters and material properties, the present invention achieves the simultaneous improvement of construction efficiency, economic benefits and environmental benefits while ensuring project safety, and provides a reliable technical path for the promotion and application of fluid solid waste binders in the field of foundation pit backfill.

[0042] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for backfilling a foundation pit with a fluidized solid waste binder, characterized in that: The following steps are involved: S1: mixing alkali slag, cement, slag powder and water at a water-to-solid ratio of 1.30-1.50 to form a fluidized alkali slag slurry, wherein the water-to-solid ratio is the ratio of the mass of water to the total mass of the alkali slag, cement and slag powder; S2: transporting the fluidized alkali slag slurry to the foundation pit through a pumping device; S3: Layered pouring is carried out in the foundation pit, with each layer filling thickness of 2.5-3.0 meters; S4: After each layer is poured, the current layer is subjected to moisturizing curing for 3-5 days; S5: Repeat steps S3 to S4 until the casting reaches the designed elevation.

2. The method for backfilling foundation pit with fluidized solid waste binder according to claim 1, characterized in that: In step S1, the water-solid ratio is 1.

40.

3. The method for backfilling foundation pit with fluidized solid waste binder according to claim 1, characterized in that: In step S1, the flow value of the fluidized alkali residue slurry is 200-400 mm, and the flow value is measured by a cylinder test method with an inner diameter of 80 mm and a net height of 80 mm.

4. The method for backfilling foundation pit with fluidized solid waste binder according to claim 1, characterized in that: Step S3 includes: S31: Clean up debris in the foundation pit before layered pouring; S32: temporarily storing the fluidized alkali residue slurry in a slurry storage tank, and monitoring the slurry bulk density in real time during pumping; S33: Adjust pumping parameters based on monitoring results to ensure slurry uniformity.

5. The method for backfilling foundation pit with fluidized solid waste binder according to claim 4, characterized in that: Step S32 includes: S321: Take slurry samples every 10-15 minutes; S322: Determine bulk density and record deviation value; S323: If the deviation exceeds 5%, an alarm is triggered and pumping is suspended.

6. The method for backfilling a foundation pit with a fluidized solid waste binder according to claim 1, characterized in that: In step S4, the moisturizing maintenance includes covering with a plastic film and spraying water mist to maintain the surface humidity not less than 90%.

7. The method for backfilling foundation pit with fluidized solid waste binder according to claim 1, characterized in that: In step S1, the cement is P.O42.5 specification cement, and the slag powder is S95 grade slag powder.

8. The method for backfilling foundation pit with fluidized solid waste binder according to claim 1, characterized in that: In step S1, the moisture content of the alkali residue is 20%-30%.

9. The method for backfilling a foundation pit with a fluidized solid waste binder according to claim 1, characterized in that: In step S1, the cement-waste ratio is 0.20-0.30, and the cement-waste ratio is the ratio of the total mass of cement and slag powder to the mass of alkali slag.

10. The method for backfilling foundation pit with fluidized solid waste binder according to claim 1, characterized in that: In step S3, the filling thickness of each layer is 3.0 meters, and the interval between pouring two adjacent layers does not exceed 2 hours.

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