Rock characterization while drilling and application of roof bolter drilling data for evaluation of ground conditions

Despite recent advances in mine health and safety, roof collapse and instabilities are still the leading causes of injury and fatality in underground mining operations. Improving safety and optimum design of ground support requires good and reliable ground characterization. While many geophysical methods have been developed for ground characterizations, their accuracy is insufficient for customized ground support design of underground workings. The actual measurements on the samples of the roof and wall strata from the exploration boring are reliable but the related holes are far apart, thus unsuitable for design purposes. The best source of information could be the geological back mapping of the roof and walls, but this is disruptive to mining operations, and provided information is only from rock surface.Interpretation of the data obtained from roof bolt drilling can offer a good and reliable source of information that can be used for ground characterization and ground support design and evaluations. This paper offers a brief review of the mine roof characterization methods, followed by introduction and discussion of the roof characterization methods by instrumented roof bolters. A brief overview of the results of the preliminary study and initial testing on an instrumented drill and summary of the suggested improvements are also discussed.

Correlations between various rock mass classification/characterization systems for the Zagros tunnel-W Iran

This study deals with the comparative investigation on various classification/characterization systems for sedimentary rocks in two parts,40 kmlong of the Zagros tunnel,west of Iran.The results of extensive geotechnical explorations and field measurements were applied to obtain the rock mass classification/characterization systems such as Rock Mass Rating(RMR),Rock Condition Rating(RCR),Q-system(Q),Rock Mass Number(QN),Rock Mass index(RMi),Rock Structure Rating(RSR),and Geological Strength Index(GSI)for a wide range of sedimentary rocks.A set of systems inter-relationship is proposed.Some of these correlation relations such as RMR-Q,RMR-RMi,RMi-Q,RCR,GSI-GSI(Cai)are similar to the one or more relations proposed in the previous studies,however,some of them such as RSR-RMR,RSR-Q,RCR-QN and GSI-RMR are not similar to the previous works.Joint set orientation and joint set number are more important parameters that cause weak correlation coefficients where both side classifications are not similar in considering them in calculating values.So it is proposed to find relations between any pairs of systems that both of them consider or not consider these parameters.The relations are proposed for a wide range of sedimentary rocks and can be applied for similar geological environments.

Geochemical Characterization of Intermediate to Silicic Rocks in the Global Ophiolite Record

Ophiolites consist predominantly of mafic-ultramafic rocks but also contain in subordinate amounts intermediate to silicic intrusive–extrusive rocks in them.These rocks,although not in large volumes in comparison to mafic–ultramafic units,reveal significant clues about melt evolution,magmatic accretion processes,and partial melting of pre-existing oceanic crust during ophiolite evolution.They also yield ample accessory minerals,such as zircon and monazite,which are widely used to date the timing of oceanic crust generation.We present a global synthesis of the occurrence of such leucocratic,intrusive and volcanic rocks from 150 Phanerozoic to Archean ophiolites,and evaluate models for their genesis during the development of oceanic crust in different tectonic environments.In the ophiolite complexes we have investigated,intrusive and extrusive rocks show a wide range in composition.Intermediate rocks（with Si O2 between 52and 63 wt.%）include andesite and diorite,whereas the silicic rocks（with Si O2 more than 63 wt.%）include dacite,trondhjemite,tonalite and granite.For subduction-relatedandsubduction-unrelated MORB-type ophiolites in the Phanerozoic orogenic belts,the most commonly reported intermediate to silicic intrusive rocks,independent of their original tectonic setting,are trondhjemite,plagiogranite and tonalite,and less commonly quartz-diorite and diorite.These rock types have been documented from 80 percent of the 104ophiolites included in this study.Intermediate to silicic lavas and/or pyroclastic rocks（basaltic andesite,andesite,dacite and rhyolite）are less abundant,and have been reported from only 35 percent of the 104 ophiolites.Trachyte occurs in some of the Rift/Continental Margintype,subduction-unrelated ophiolitesEvolvedrocksinsubduction-unrelated,Rift/Continental Margin ophiolites are predominantly basaltic andesite and andesite,whereas MOR type（mid-ocean ridge）ophiolites exhibit nearly equal proportions of basaltic andesite/andesite and rhyodacite and Plume/MOR type ophiolites are characterized by rhyolites.Intermediate to silicic volcanic uints in the Backarc sub-group of subduction-related ophiolites are characterized by similar amounts of basaltic andesite/andesite and rhyodacite,whereas in the Backarc to Forearc,Forearc,and Volcanic Arc sub-groups they are mainly basaltic andesite/andesite.Intermediate to silicic rocks in Rift/Continental Margin and Plume/MOR type ophiolites are generally LREE-enriched,whereas those in the MOR type vary from LREE-depleted to LREE-enriched.The Backarc and Backarc to Forearc types are similar to the MOR type;silicic rocks of the Forearc and Volcanic Arc types are generally LREE-enriched.The main process in the formation of the majority of the intermediate to silicic rocks in both subduction-unrelated and subduction-related ophiolites is partial melting of basaltic and/or gabbroic rocks beneath the spreading centers,whereas a minor volume in subduction-related ophiolites are adakites that were produced from partial melting of a subducting slab.Silcic to intermediate rocks in Plume/MOR type ophiolites are generated by fractional crystallization of basaltic melt.The incompatible,non-conservative elements,such as Ba and Th,are weakly to strongly enriched in subduction-related ophiolites as a result of shallow to deep enrichment associated with subduction zone processes.The field occurrence and the geochemical character of leucocratic rocks in ophiolites show considerable variations,providing additional constraints on the petrogenesis of ophiolites in different tectonic settings.Fractional crystallization appears to have been an important process in the formation of the intermediate to silicic rocks in Rift/CM and P/MOR ophiolites in the subduction-unrelated class,as well as VA ophiolites in the subduction-related class.In these types of ophiolites magma chambers might have operated as closed-systems for a sufficient amount of time for fractionation and compositional zoning of the magma to take place（Fig.1C1）.Fractional crystallization was of subordinate importance during the igneous construction of the MOR,BA,FA,and BA-FA ophiolites.Instead,partial melting of hydrothermally altered crust was the most common process resulting in the majority of the intermediate to felsic rocks of the Rift/CM（estimated to 60%）,MOR（estimated to 95%）,and the BA,FA and BA-FA（estimated to 75%）ophiolites,as well as a high proportion of the VA ophiolites（;0%）(Fig.1C2).Slab-generated melts that result in the production of intermediate to silicic rocks of adakitic character represent a relatively small fraction（;5%in Phanerozoic ophiolites）of subduction-related ophiolites（Fig.1C3）.Some adakites are very low in incompatible elements（e.g.,La）,suggesting that these melts were generated from highly depleted MORB.Precambrian ophiolites contain a higher percentage of adakites（ca.35%）,indicating that physical conditions were more favorable for slab melting during the Precambrian than in the Phanerozoic.This phenomenon may have resulted from higher geothermal gradient along relatively shallow-dippingsubductionzonesduringthe Precambrian.

Rock mass structural recognition from drill monitoring technology in underground mining using discontinuity index and machine learning techniques

A procedure to recognize individual discontinuities in rock mass from measurement while drilling(MWD)technology is developed,using the binary pattern of structural rock characteristics obtained from in-hole images for calibration.Data from two underground operations with different drilling technology and different rock mass characteristics are considered,which generalizes the application of the methodology to different sites and ensures the full operational integration of MWD data analysis.Two approaches are followed for site-specific structural model building:a discontinuity index(DI)built from variations in MWD parameters,and a machine learning(ML)classifier as function of the drilling parameters and their variability.The prediction ability of the models is quantitatively assessed as the rate of recognition of discontinuities observed in borehole logs.Differences between the parameters involved in the models for each site,and differences in their weights,highlight the site-dependence of the resulting models.The ML approach offers better performance than the classical DI,with recognition rates in the range 89%to 96%.However,the simpler DI still yields fairly accurate results,with recognition rates 70%to 90%.These results validate the adaptive MWD-based methodology as an engineering solution to predict rock structural condition in underground mining operations.

Reservoir quality of the Late Cretaceous Volador Formation of the Latrobe group,Gippsland Basin,Australia:Implications from integrated analytical techniques

Increasing demand for energy due to the populous Eastern Australia has driven oil and gas industries to find new sources of hydrocarbons as they are the primary energy suppliers.Intensive study has been done on the Volador Formation in the Gippsland Basin by means of core-based petrophysical,sedimentological,and petrographic analyses as well as well log-based interpretation and capillary pressure test.Five wells from Kipper,Basker and Tuna fields with available dataset were investigated in this study:Kipper-1,Basker-1,Basker-2,Basker-5 and Tuna-4.Overall,the formation has good reservoir quality based on the high porosity and permeability values obtained through core and well log petrophysical analyses.The formation made up of mostly moderate to coarse quartz grains that has experienced strong anti-compaction and is poorly cemented.Montmorillonite and illite clays are seen dispersed in the rock formation,with the minority being mixed clays.These clays and diagenetic features including kaolinite cement and quartz overgrowth that can lead to porosity reduction only have insignificant impact on the overall reservoir quality.In addition,capillary pressure data shows that most samples are found in the transition to good reservoir zones(<50%saturation).The results obtained from this study have shown that the Volador Formation in the Gippsland Basin is worth for hydrocarbon exploration.

Revisiting support optimization at the Driskos tunnel usinga quantitative risk approach

With the scale and cost of geotechnical engineering projects increasing rapidly over the past few decades,there is a clear need for the careful consideration of calculated risks in design.While risk is typically dealt with subjectively through the use of conservative design parameters,with the advent of reliability-based methods,this no longer needs to be the case.Instead,a quantitative risk approach can be considered that incorporates uncertainty in ground conditions directly into the design process to determine the variable ground response and support loads.This allows for the optimization of support on the basis of both worker safety and economic risk.This paper presents the application of such an approach to review the design of the initial lining system along a section of the Driskos twin tunnels as part of the Egnatia Odos highway in northern Greece.Along this section of tunnel,weak rock masses were encountered as well as high in situ stress conditions,which led to excessive deformations and failure of the as built temporary support.Monitoring data were used to validate the rock mass parameters selected in this area and a risk approach was used to determine,in hindsight,the most appropriate support category with respect to the cost of installation and expected cost of failure.Different construction sequences were also considered in the context of both convenience and risk cost.

Characterization and analysis of coded excitation ultrasound parameters for rock properties

Coded excitation technology （CET） can effectively enhance the penetration and resolution of ultrasonic testing. To analyze the influence of rock properties on pulse compression performance （PCP） of coded excitation signals （CES）, a numerical simulation, and an ultrasonic experiment on different rock samples are performed; and the detection ability of several CESs are also investigated and compared. The results of experiments showed that the loss of the signal-to-noise ratio （SNR） of Barker coded signal with tapered linear frequency modulated carrier （BTLFM） is always less than Barker coded signal with sine carrier （BS）, while the resolution loss of BTLFM is lower than tapered linear frequency modulated signal （TLFM）. In sum, the results not only verifiy the effectiveness of CET, but also provide a basis for the parameter settings of coded signals used in rock ultrasonic testing.