Study on Stability Control of Retained Gob‐Side Entry by Blasting Fracturing Roof Technology in Thick Immediate Roof

It is usually difficult to capture strata caving and gob evolution characteristic in longwall mining at engineering scales. This paper uses bonded block modelling (BBM) approach within a distinct element method (DEM) code to simulate strata behaviour in longwall mining, which captures the caving phenomena and bulking characteristics of roof strata successfully. Many features in longwall mining, including the caving and compaction of gob strata and the associated stress evolution, are reproduced in the model. Four zones in longwall gob are identified based on its stress characteristics: voussoir influencing zone, compacted zone, compacting zone, and pilling zone. The initial bulking factor of the caved strata ranges from 1.12 to 1.25 and decreases gradually to the residual bulk factor of approximately 1.05 as the longwall face advances. The caved strata in the longwall gob present strain hardening behaviour and the load carrying capacity increases exponentially as a function of strain. Moreover, the range of the interaction between the caving strata and the overburden in gob was discussed, which provides a reference when using a continuum method to simulate longwall mining.

Section: Determination Of the Range Of Compacted And Compacting Zonesmentioning

confidence: 99%

Strata Caving and Gob Evolution Characteristic in Longwall Mining

Pan

Zhao

2022

Study on Surrounding Rock Structure Evolution Characteristics and Roof Control Techniques of the Retained Roadway Formed by Roof Cutting in Inclined Coal Seams

Wang

Ren

et al. 2021

To control the roof during gob-side entry retaining by roof cutting in inclined coal seams, the retained gob-side roadway is zoned based on the mechanical principle and technological process of no-pillar mining with gob-entry retention. A simplified mechanical model for surrounding rocks in different subzones was established by using theoretical analysis and numerical simulation to attain the demand for the support resistance and deformation of the roof in different subzones. According to load and deformation characteristics of the roof and mechanical characteristics of NPR cables, single props, and a sliding-type gangue-retaining structure formed by U-shaped steel inserts, the supporting systems for roadways in different subzones and the constitutive model thereof were established. On this basis, the action of the supporting system was analysed and a field test was performed. The results show that the supporting system undergoes three stages of behaviour, i.e., pressure growth, yielding under constant pressure, and stabilisation during whole entry retention. It can guarantee the collaborative deformation of the supporting systems with the roof on the premise of constant support resistance, thus satisfying the requirement for roadway protection. The roadway 150 m back from the working face is stable, and the final convergence between the roof and floor of the retained entry is 257 mm, showing a favourable entry-retention effect.

Mechanism of Hard‐Roof Rock Burst Control by the Deep‐Hole Blasting: Numerical Study Based on Particle Flow

Bai

et al. 2021

In underground coal mines, the deep-hole blasting (DHB) technology is generally adopted for thick hard-roof control. This technology uses the energy released by explosives to weaken the energy storage capacity of hard roof so as to prevent hard-roof rock burst disasters. In this paper, a numerical simulation model of roof DHB was established based on particle flow and the damage range of single-hole blasting with concentrated cylindrical charge was studied. The temporal and spatial evolutions of overlying strata, the distribution of the force chain structure, and the working resistance of hydraulic pressure in the mining process before and after the application of DHB were contrastively analyzed. The following beneficial conclusions were drawn. The blasting-induced single-hole damage range is generally characterized by annular zoning. After the application of DHB, overall the collapse morphology of the key strata in the mining process changes from long-distance instantaneous slipping instability to stratified short-arm stepped synergistic subsidence. The density and strength of force chains in the overburden are notably reduced; the peak value of compressive force chain strength in the key strata in the mining process falls by 17.85% as a result of DHB. The monitoring results of the working resistance of hydraulic support reveal that the DHB technology can effectively shorten the step distance of periodic weighting and reduce the variation amplitude of overburden load during weighting. In summary, the mechanism of hard-roof rock burst control by DHB is reflected by both static load reduction and dynamic load reaction.