Mechanical Properties Of Cemented Backfill Research Articles

Mechanical properties of cemented backfill under different unloading rates after cured at different temperatures

In the process of deep filling mining in coal mine, due to the influence of mining and other factors, the confining pressure on both sides of cemented backfill decreases. It is necessary to master the mechanical characteristics of cemented backfill under unloading conditions in different temperature environments to ensure the stability of cemented backfill. To simulate the unloading process of cemented backfill in the deep highland environment of coal mine, triaxial unloading confining pressure tests of cemented coal gangue- fly ash backfill at different unloading rates after curing at different temperatures (20 ℃, 35 ℃ and 50 ℃) were carried out by the Rock Triaxial Testing System, and the mechanical characteristics of cemented backfill unloading were systematically studied. The findings of the study show that, for the same unloading rate, the peak strength of cemented backfill specimen reduces initially before increasing with curing temperature rises. After curing at the same temperature, the peak strength of cemented backfill specimen varies exponentially with an increase in unloading rate. The deformation modulus and volume strain at different unloading rates satisfy an exponential function relationship, while the generalized Poisson's ratio and volume strain satisfy a quadratic function relationship. Under unloading conditions, there was no large fracture or fragmentation of cemented backfill, only cracks appeared on surface. At the same unloading rate, cemented backfill specimen cured at 35 ℃ and 50 ℃ exhibits significantly more shear cracks after failure compared to the material cured at 20 ℃. As the unloading rate increases, the proportion of shear cracks generated during unloading failure of cemented backfill specimen cured at 35 ℃ and 50 ℃ gradually increases. In addition, the theoretical curve of the four-stage cemented backfill unloading constitutive model established in sections is essentially compatible with experimental curve, confirming the theoretical model's reasonableness. The study's findings provide a theoretical basis for evaluating stability of cemented backfill after unloading in deep high temperature (35–50 ℃) environments.

Mechanical properties under triaxial compression of coal gangue-fly ash cemented backfill after cured at different temperatures

The triaxial mechanical properties of cemented backfill are the key indicators that affect the stability of cemented backfill in underground mining areas, and the high temperature environment in mines has become one of the main factors affecting the mechanical properties of cemented backfill. Understanding the triaxial mechanical properties of cemented backfill in high temperature environments is crucial for the stability of cemented backfill in mining areas. To investigate the effect of temperature on the mechanical characteristics of cemented backfill under triaxial compression, triaxial compression experiments were done on coal gangue-fly ash cemented backfill that had been cured at three temperatures (20 °C, 35 °C, and 50 °C). The deviatoric stress-strain curve of cemented backfill under triaxial compression was produced, its deformation parameters, dilatancy, and failure characteristics were investigated, and a more appropriate strength criteria was proposed. The research results indicate that, peak strength and dilatancy stress of cemented backfill under the same confining pressure decrease first and then increase as the curing temperature increases. The failure patterns of cemented backfill under triaxial compression will exhibit layered splitting failure except tension and shear failure since the curing temperature has increased. By comparing it with several other criteria, the Mogi-Coulomb strength criteria was found to be a good reflection of the failure strength properties of cemented backfill cured at different temperatures under triaxial compression. With curing temperature rises, internal friction angle of cemented backfill steadily lowers, while the cohesion first decreases and subsequently increases. The alteration in cohesion is consistent with the peak strength change rule, illustrating that the primary factor influencing peak strength of cemented backfill is cohesion. This study provides a good theoretical reference value for guiding the design of deep mine filling and optimizing the mixture ratio of cemented backfill.

Experimental Study on the Mechanical and Acoustic Characteristics of Cemented Backfill with Unclassified Tailings at Different Curing Ages under Uniaxial Compression

In order to study the influence of the cement–tailing ratio and curing age on the mechanical properties of cemented backfill with unclassified tailings and improve the accuracy of the backfill monitoring method, the mechanical characteristics of the failure process of cemented backfill with unclassified tailings at different curing ages were studied using the acoustic emission and infrasound method. The results show that the peak strength and modulus of elasticity of backfill are positively correlated with the curing age. During the failure process of cemented backfill with unclassified tailings, the acoustic emission ringing count shows a “stabilizing–rising–falling–rising” trend, and the infrasonic ringing count will have a “multiple peak” phenomenon. The ib value of the acoustic emission signal generally increases with the extension of the curing age. The ib value of the infrasonic signal generally has a negative correlation with the increase of the curing age. When the ib value of the acoustic emission and infrasonic wave all start to decline in a jumping manner, this indicates that the backfill is about to be damaged. The dominant frequency ratio of acoustic emission signals (FAE) is distributed between 0–4 during the failure process, and the total number of FAE shows the phenomenon of “first decreasing and then increasing” with the curing age. The dominant frequency ratio of infrasonic signals (Fs) is distributed between 0–6. During the failure process of cemented backfill with unclassified tailings, the quantity ratio of class A and B of acoustic emission signals shows a gradually increasing trend, and the quantity ratio of class A and B of infrasonic signals shows a “decreasing–increasing–decreasing” trend, and the quantity ratio of class A and B of acoustic signals shows a sharp increase at the stage of entering the crack’s unstable growth stage.

Study on mechanical properties of cemented backfill with different mineral admixtures

In order to establish storages in mining goaf, calcium bentonite (Ca-B), slag powder (SP) and silica fume (SF) were added into the backfill to obtain a cemented backfill with high stability and certain anti-seepage function. Uniaxial compressive strength (UCS), porosity, permeability and scanning electron microscopy (SEM) tests were carried out. Results show that SP and SF can significantly improve the strength at the same level of incorporation, the highest increases are 216.37% and 125.51% compared with the control group, while Ca-B has strong swelling and low pozzolanic activity, the strength can only be increased by 32.83%, and the strength can be significantly reduced by 28.34% if the Ca-B content is too high. The incorporation of mineral admixtures can increase the number of closed pores in the compaction stage, and the damage mode of backfill can be changed with the increase of the incorporation amount. There is a power function relationship between permeability and porosity, permeability increases with the increase of porosity. The strong pozzolanic reaction of SP and SF can produce more gel compounds to block pore channels, refine pore size and reduce permeability. Compared with the control group, the permeability can be reduced by 46.05% and 36.84% at the highest, while Ca-B due to strong swelling, low activity, and insufficient reaction cause the backfill porous, and the permeability is greater than the control group under different incorporation amounts.

Modeling the heat development in hydrating CPB structures

Cemented paste backfill (CPB) is a mixture of dewatered tailings, hydraulic binders and water. In addition to contributing to the stability of mine workplaces, CPB greatly benefits the environment by minimizing surface tailings disposal. Hence, it has become one of the most commonly used ways in mine backfilling around the world. Temperature can significantly affect the mechanical properties of cemented backfill. A source of heat in CPB is produced by binder hydration. Hence, a FLAC based numerical model is developed to predict and analyse the heat developed by hydrating CPB structures. To validate the model, results of the developed model are compared with three case studies (mathematical, laboratory, and field investigations). The validation results show a good agreement between the developed model and these cases. The effects of stope geometry, thermal properties of both rock and CPB, filling rate, binder content and initial boundary conditions are also investigated.