Rock Mass Classification Based Approach for the Intelligent Sensing of Roof Quality at Coal Entry Excavation

Author:Yang Sen

Supervisor:zhang nong liu shi min


Degree Year:2019





The intelligent sensing of the natural bearing capacity of coal entry roof plays an essential role in the intelligentization of roadway construction.Machines understand the real world through a digitization of objects,which means the intelligent sensing of the natural bearing capacity of coal entry roof replies on a quantitative evaluation of the roof quality.As a summary of vast engineering experience,rock mass classification is currently the only method that can provide ground support design with systematic,quantified,and verifiable information of rock mass engineering properties.Therefore this work chose rock mass classification as a basis for the roof quality evaluation,through digitalizing and automatizing its data acquisition and analysis methods in order to achieve the intelligent sensing of roof quality.This work is a comprehensive study on the intelligent sensing of coal entry roof quality,involved methods include theoretical analysis,in-situ test,laboratorial test,numerical computation,algorithm development,and equipment development.Through research,the different influences of varying properties of immediate roof and overlying strata on the stability of unsupported roof were investigated;a quantified GSI system faced to digital image analysis was established to provide a criterion for the high-efficient evaluation of immediate roof quality;a full-automatic statistical analysis system of discontinuity parameters was developed,the system can fulfill its mission autonomously;the feasibility of acoustic wave based approach for rock strength parameter extraction was discussed.The main conclusions are listed as follow:(1)A three-dimensional mechanical model of the unsupported roof of coal entry head was established by using elastic thin plate theory.The proposed model was utilized to investigate the different influences of varying properties of immediate roof and overlying strata on the stability of unsupported roof.Results show:the increase of the effective thickness of immediate roof can reduce peak values of deflection,tensile stress,and shear stress of the immediate roof,this reducing effect for deflection is the most significant,for tensile stress is the second,for shear stress is the weakest,but can still be observed clearly.The peak values of deflection,maximum value of tensile stress perpendicular to heading direction((σx)Tmax),and maximum value of tensile stress parallel to heading direction((σy)Tmax)all increase with the increasing Poisson’s ratio of immediate roof.The enhancing effect of Poisson’s ratio to the peak value of(σx)Tmax is strong in a short unsupported span,but relatively weak in a large unsupported span.This effect for the peak value of(σy)Tmax is just the opposite.The variation of the Poisson’s ratio of immediate roof show no obvious influence on the peak values of maximum value of shear stress perpendicular to heading direction((τxz)Tmax),and maximum value of shear stress parallel to heading direction((τyz)Tmax).The peak values of deflection,(σx)Tmax,(σy)Tmax,(τxz)Tmax,and(τyz)Tmax all increase with the increasing thickness of overlying weak strata,their increasing patterns receive different perturbations from the varying unsupported span.(2)Among widely accepted rock mass classification systems,GSI is the only one which is completely based on a visual assessment of the overall rock mass structure,this unique feature paves a way forward to achieve an digital-image-analysis-based automatic and rapid evaluation of immediate roof quality.In this work,the quantification of GSI interlocking factor was converted into a quantification of rock mass fracture development.The fits of two quantification methods—Structure Rating and RQD to the GSI interlocking groups was analyzed by using descriptive terms for block size intervals suggested by ISRM,results show that the Structure Rating is more suitable.Joint Condition Digital Imaging Rating was proposed in order to quantify the GSI surface condition.(3)A full-automatic statistics system for discontinuity parameter analysis was developed,named Digital Image Analysis Based Approach for Immediate Roof Rating at Coal Entry Excavation Face。Its signature feature is the full automation,which means the system can fulfill its mission autonomously.The technique flow is presented as follow:firstly,the rock face are photographed by using a digital camera,the obtained image is then preprocessed by using regional histogram equalization,adaptive gamma correction,and median filtering.Subsequently,the extraction of discontinuity profiles is accomplished through region growing segmentation and Hough transform.The profiles are thinned and linked,then converted into main axes.Finally,the discontinuity parameters and GSI ratings are calculated.The recognition and analysis algorithms developed in this work exhibited good performance in industrial tests.(4)The developed system exhibited high and stable performance at hard light environment,and can maintain moderate performance at weak light environment below 300 Lux.The decrease of beam angle posed a weakening effect upon system performance,but it showed good adaptability to relatively small angle changes.The system performance decreased with the increasing humidity,however,while humidity was less than 70%,recognition rate can be kept higher than 50.7%.The humidity of coal entry head is commonly lower than 70%,therefore the system can overcome the disturbance from working environment humidity.The increase of dust concentration shows no obvious influence to system performance,in other words,the system can maintain high performance at dust environment.(5)The P-and S-wave velocities of coal-measure sandstone showed different responses to the increasing number of test cycles.When cyclic loading was lower than elastic limit,the P-wave velocity gradually decreased with the increasing cyclic number but the S-wave velocity remained relatively constant.The decrease in P-wave velocities indicates that low-level cyclic stress induces the initiation and development of cracks oriented horizontally or subhorizontally,and the more stable S-wave velocity means that few irreversible microstructural changes are oriented in a vertical direction.Both P-and S-wave showed obvious velocity declines at high stress values.The decline indicates that,at these stress levels,damage develops rapidly in the rock’s microstructure and this clearly indicates brittle behavior.Long-term creep involves multiple structural deformations that alter the internal structure of sample,thus resulting in fluctuation of the ultrasonic velocities and the dynamic moduli.The mechanical response of samples under creep compression is a result of competition between compaction and cracking,in which the cracking deteriorates the structure and increases the ultrasonic attenuation,whilst the compaction causes the densification along axial axis and reduces attenuation.There are 106 figures,46 tables and 252 references in this dissertation.