-
About Us
-
-
-
Contact Us
Classification of Filling Methods (by Filling Material Conveyance Method) — Structured Flow Filling
Classification of Filling Methods (by Filling Material Conveyance Method) — Structured Flow Filling
In mining backfilling operations, classified according to the method of slurry delivery, structured-flow backfilling is one of the most widely used and efficient backfilling methods. The core criterion for its classification is the particle-size distribution of the backfill slurry and Rheological parameters In actual construction, precise parameter control is required to ensure conveyance stability and filling effectiveness; the following provides a detailed explanation based on practical engineering operations.
I. Definition and Formation Conditions of Structural Flow Filling
The formation of structural-flow filling requires the simultaneous fulfillment of two critical parameter requirements, neither of which can be omitted, as follows:
- 1. Particle size distribution requirements: in the filling material -20 μm The fine particle content must reach 15%~20% (mass fraction).
Calculation example: Take a sample of a certain filling material, with a total mass of 1000g , after screening and inspection, -20 μm The particle mass is 180g then the fine particle content of this sample is: ( 180/1000 ) ×100% = 18% , meeting the particle-size distribution requirements for structural-flow filling; if the mass of fine particles is 140g , calculated as 14% , it has not met the minimum standard and therefore cannot form a structural flow.
- 2. Rheological parameter requirements: the slump of the filling slurry shall be controlled within 25–30 cm (Determined by the standard slump test method).
Additional clarification: When the slump is within this range, the filling slurry exhibits no significant concentration gradient in the vertical direction across the pipe’s cross-section; the fluid within the pipe does not generate any relative motion, and there is no exchange of material particles between flow layers at different radii, thereby forming plug flow (also known as structured flow). This configuration helps to prevent particle settling and pipeline blockage during transportation.
II. Characteristics of Structural Flow Filling
The characteristics of structural-flow filling are all directly related to the aforementioned parameters, as follows:
- 1. High concentration: The mass concentration of the filling slurry typically can reach 70%~85% (adjusted specifically based on the fine-particle content), calculation example: if the total mass of the filling slurry is 1000kg , where the mass of the solid material is 780kg then the mass concentration is ( 780/1000 ) ×100% = 78% , which falls within the conventional concentration range for structural-flow filling. Higher concentrations can reduce the water content of the slurry and decrease subsequent settling.
- 2. Settling and shrinkage: Measured data show that the settlement rate of structural flow fill is typically ≤3% , significantly lower than that of ordinary mortar filling (the typical settlement rate is 5%~8% ). Calculation example: For a certain mining area, the filling height is 10m , after structural flow filling, the settlement is 0.25m then the settlement rate is ( 0.25/10 ) ×100% = 2.5% , which meets the requirements, can effectively prevent post-filling deformation and ensure stope stability.
- 3. High early strength: Due to the high concentration and low water content, the hydration reaction of the filling material is more complete, resulting in a rapid increase in early strength. Under normal circumstances, 3d Early strength can reach 1.53.0MPa，7d Strength can reach 3.05.0MPa , meeting the time requirements for roof support in the mining area (calculation example: a certain structural flow fill material, 3d The compressive strength test value is 2.2MPa，7d for 4.1MPa , meeting the strength requirements for the backfill under the stope’s mining interval).
- 4. High roof-contact rate: The structured slurry exhibits moderate flowability with no significant segregation, enabling thorough filling of stopes and typically resulting in a high roof-contact rate. ≥95% , thereby reducing the risk of roof collapse. Calculation example: The volume of the goaf in a certain mining area is 1000 cubic meters , the measured void volume after filling is 42 cubic meters then the roof-contact rate is ( 1000-42 ) /1000×100% = 95.8% , meeting the design standards.
III. Common Types
Structural flow filling is not a single form; depending on the mix ratio and state of the filling material, the common types include the following: 3 All classes satisfy the aforementioned conditions for structural flow formation:
- 1. Paste filling: the most typical form of structural-flow filling, in which the fine-particle content of the filling material is usually close to 20% , the slump is controlled at 2528cm The slurry is paste-like, with no significant flowability, and exhibits plug-flow behavior during transportation. Its mass concentration is generally 75%85% It exhibits high early strength, making it suitable for the mining of medium-to-thick ore bodies that demand high fill strength.
- 2. Paste-like filling: fine particle content is 15% 18% , the slump is 2730cm , the slurry exhibits slightly higher flowability than a paste and still falls under the category of structured flow. The mass concentration is 70%~78% , balancing fluidity and strength, making it suitable for mining areas with complex orebody geometries and long conveying distances.
- 3. Homogeneous mortar filling: the core characteristic is the absence of a concentration gradient in the vertical direction across the pipe cross-section, with a fine-particle content 15%20% , slump 2530cm It exhibits excellent slurry homogeneity, with no particle segregation, and demonstrates strong transport stability, making it suitable for large-scale, low-cost stope filling.
IV. Case Studies
Taking the full-tailings structured-flow filling project at the Longqiao Iron Mine as an example, this mine extracts medium-to-thick ore bodies and previously employed conventional mortar filling, which suffered from significant settlement, low roof-contact rates, and inadequate stope stability. Subsequently, the operation was upgraded to a full-tailings structured-flow filling process, yielding excellent field performance. The specific operational details and process parameters are presented below, closely aligned with actual site conditions and avoiding purely theoretical descriptions.
- 1. Mining operating conditions: The production capacity of the mine’s filling system is 100–120 m³/h , average height of the goaf 8m , the single-fill volume is approximately 1600 cubic meters , must meet the filling body 28d Intensity ≥2MPa , Roof Contact Rate ≥95% The design requirements call for the use of full-tailings as the filling material, combined with a cementing agent to form a thixotropic slurry that can flow by gravity and be conveyed directly to the underground mined-out areas.
- 2. Structural flow parameter control and calculation:
（ 1 ) Particle-size distribution control: Collect a full-tailings sample. 1000g , after screening and inspection, -20 μm The mass of fine particles is 170g , the fine particle content is calculated as ( 170/1000 ) ×100% = 17% ,处于 15%~20% within the standard range, meeting the particle-size distribution requirements for structured flow formation, and employing a high-efficiency deep-cone thickener to concentrate and dewater the tailings, thereby ensuring uniform distribution of fine particles.
（ 2 ) Slump control: The on-site measured slump is 27cm , compliant with 25–30 cm The requirement is that the slurry exhibits no significant concentration gradient along the conveying pipeline, thereby forming a stable piston flow and preventing particle settling during transport. Continuous stirring is achieved using a two-stage horizontal mixer to ensure slurry homogeneity.
（ 3 ) Concentration and mix ratio calculation: The grouting slurry shall be prepared with a cement-to-sand ratio of 1:12 (Cement-to-total-tailings mass ratio), the measured total slurry mass is 1000kg , among which the solid material (whole tailings) + (Cementing agent) quality is 630kg , calculate the slurry mass concentration as ( 630/1000 ) ×100% = 63% , after adjustment based on mine operating conditions, the concentration is controlled at 62% 64% Within the range, though slightly lower than usual. 70%85% within the concentration range, yet, when tailored to the characteristics of the mine’s total tailings, it can still form a stable structured flow.
- 3. Practical application results and calculations:
（ 1 ) Settlement rate: Filling completed 7d Subsequently, the measured settlement of the stope filling height was 0.18m , the settlement rate is calculated as ( 0.18/8 ) ×100% = 2.25% ，≤3% The standard requirements are far lower than those for ordinary mortar filling prior to renovation. 5.5% The settlement rate is effectively controlled, thereby preventing post-filling deformation and ensuring stope stability.
（ 2 ) Roof-Contact Rate: After filling is completed, the measured void volume in the stope is 64 cubic meters , calculate the roof-contact rate as ( 1600-64 ) /1600×100% = 96% , reach ≥95% The design standards have reduced the risk of head exposure.
（ 3 ) Strength testing: Actual measurement of the filling body 3d Early strength is 1.8MPa，7d The intensity is 3.2MPa，28d The intensity is 2.3MPa , all of which meet the design requirements and are suitable for the mine’s stope retreat interval and roof support needs.
- 4. Case Summary: By precisely controlling the fine-particle content, slump, and slurry concentration, this mine successfully implemented full-tailings structured-flow filling, thereby overcoming the shortcomings of the original filling process. Moreover, by fully utilizing tailings resources, the mine reduced filling costs. The parameter-control approach and practical operational experience gained can serve as a valuable reference for similar structured-flow filling projects in medium-to-thick ore bodies.
V. Precautions
- 1. The fine-particle content must be monitored in real time; samples of each batch of filling material must be taken and sieved to determine the fine-particle content, ensuring that it remains within 15%~20% Within the specified range, ensure that insufficient fine particles do not prevent the formation of structural flow.
- 2. The slump must be measured on site; if the slump is less than 25cm , the water volume may be increased appropriately (while simultaneously recalculating the concentration to ensure it does not fall below 70% ); if higher than 30cm , fine aggregate needs to be added to adjust the mix to the specified range.
- 3. Conveyance pipelines require regular cleaning. Due to the high slurry concentration in the system, long-term operation can lead to scaling on the inner pipe walls. The cleaning interval should be determined based on the throughput; typically, every 3 to 5 Clean the system once a day to prevent pipe blockages.
Summary: The core of structured-flow filling lies in controlling the fine-particle content and slump to establish a stable plunger flow. Its characteristics—high concentration, minimal settlement, high early strength, and high roof-contact rate—make it widely used in mining fill applications.
