Hydraulic fracturing of rocks boosts the production rate by increasing the fracture-face surface area through the use of a pressurized liquid. Complex stress distribution and magnitude are the main factors that hinder the use of information gathered from in situ hydraulic fracturing in other locations. Laboratory tests are a good method for precisely determining the characteristics of these processes. One of the most important parameters is breakdown pressure, defined as the wellbore pressure necessary to induce a hydraulic fracture. Therefore, the main purpose of this investigation is to verify fracture resistance of rock samples fractured with the assistance of the most popular industry fluids. The experiments were carried out using a stand designed specifically for laboratory hydraulic fracturing. Repeatable results with a relative error within the range of 6-11% prove that the experimental methodology was correct. Moreover, the obtained results show that fracturing pressure depends significantly on fluid type. In the case of a water test, the fracturing pressure was 7.1±0.4 MPa. A similar result was achieved for slickwater, 7.5±0.7 MPa; however, a much lower value (4.7±0.5 MPa) was registered in the case of carbon dioxide.

 Widespread opinion holds that calcareous rocks have limited suitability for use in the production
 

 of aggregates and stone products having adequate frost resistance. However, some of the rocks, in
 

 particular those from earlier geological periods, provide a promising alternative to silicate rocks.
 

 The paper presents results of the analysis of Devonian carbonate rock originating from two selected
 

 mines in the Swietokrzyskie region. The examined mines extract limestone from two different
 

 deposits of the same age. The rock samples are collected from beds lying at different depths, distinct
 

 in texture and color in macroscopic examination. It was found that despite the changes in bulk density,
 

 porosity and absorption, all the examined samples were frost resistant.
 

 Using the Differential Analysis of Volumetric Strain method, the content of ice formed in the pore
 

 spaces was determined. In addition, the ratio of the content of water capable of freezing to the total
 

 pore volume, and the total amount of water absorbed due to capillary action in rock samples soaked
 

 in water, were analyzed. In all cases, it was revealed that the destructive action of freezing water was
 

 weakened due to a relatively low content of water capable of freezing and a substantial volume of
 

 pores that are not filled with water in capillary absorption.
 

 It is extremely important to be able to classify the available rock material. The generally adopted
 

 methods, including absorptivity tests, do not allow for precise categorization. In the investigations,

the authors focused on the analysis of the basic factors that are decisive for rock durability, including bulk density, pore filling level and volume absorption. The authors do not correspond compressive

strength and resistance to abrasion as this will be the subject of further research.

The authors studied the fracture mechanical properties under half-symmetric loading in this paper. The stress distribution around the crack tip and the stress intensity factor of three kinds of notched specimens under half symmetric loading were compared. The maximum tensile stress σ_max of double notch specimens was much greater than that of single notch specimens and the maximum shear stress τ_max was almost equal, which means that the single notch specimens were more prone to Mode II fractures. The intensity factors K_II of central notch specimens were very small compared with other specimens and they induced Mode I fractures. For both double notch and single notch specimens, K_II was kept at a constant level and did not change with the change of a/h, and K_II was much larger than K_I. K_II has the potential to reach its fracture toughness K_IIC before K_I and Mode II fractures occurred. Rock-like materials were introduced to produce single notch specimens. Test results show that the crack had been initiated at the crack tip and propagated along the original notch face, and a Mode II fracture occurred. There was no relationship between the peak load and the original notch length. The average value of K_IIC was about 0.602 MPa×m^1/2, and KIIC was about 3.8 times K_IC. The half symmetric loading test of single notch specimens was one of the most effective methods to obtain a true Mode II fracture and determine Mode fracture toughness.

What is patriotism as opposed to nationalism? And which of these is what sometimes surfaces in contemporary rock music?

Three types of rock glaciers (moraine, cirque and subslope ones) were distinguished in northwestern Wedel Jarlsberg Land. Subslope rock glaciers were found different from nival moraines. A development of subslope and fossil cirque rock glaciers was connected with the older Holocene whereas of active cirque and moraine rock glaciers with the Little Ice Age.

Recalling the body of experience gathered in the collieries of the Upper Silesian Coal Basin, the

increased risk of seismicity and rockburst occurrences in confined conditions including the exploitation of

remnants were identified. This study investigates geomechanical aspects of longwall mining in the areas

affected by old excavations aimed at relaxation of a multi-bed deposits within a thick coal seam or a group

of seams. It is assumed that high-energy seismicity is another factor determining the rockburst hazard

alongside the state of stress. A case study is recalled, describing a colliery where mining-induced seismic

activity of a de-stressed coal seam remained at the level comparable to or higher than it was experienced

in the de-stressed seam operations. An analytical model was used to study the stress state and potential

loss of structural continuity of an undisturbed rock body surrounding the longwall panel being mined

beneath or over the abandoned workings. Recalling the developed model of the system involving nonlinear

functions demonstrating the existence of abandoned mine workings within the rock strata, computer

simulations were performed to evaluate the rockburst hazards along the face area. Discussions of results

are based on observations of immediate roof convergence and the vertical stress concentration factor at

the longwall face zone. Computational data of the modelled mining situations demonstrates that despite

using the de-stressing method of mining, the occurrence of events impacting on mine working beneath

and over abandoned workings cannot be precluded. Here the scale of rockburst hazards is determined by

local mining and geological conditions, such as the type and extent of abandoned workings, their age and

vertical distance between them and the coal seam currently mined.

The assessment of a rock’s behaviour around excavations and the effectiveness of its reinforcement in underground ore mines is dependent on the performance of the rock-bolt and rock-mass interaction, which can be estimated on the basis of appropriately designed measurements. Based on the background of various measurements solutions described in the literature, concerning rock bolt monitoring methods, the authors proposed a new, original device for mass measurements in mine conditions. After examining the advantages and disadvantages of existing constructions, the article presents the essence, principle of operation and method of measuring anchor load in an underground excavation with the a instrument, indicator WK-2/8. The prototype has been carefully researched and successfully tested in a full-scale laboratory environment. This instrument, also referred to as a load indicator or force pad, does not require electrical power and allows for relatively accurate (with a resolution of 10-14kN, up to about 90kN loading capacity) and a remote reading of the axle loading of the anchor (AGH patent) by any person present in the specified area. The device can be installed in mining excavations under loading conditions. The relatively low cost of a measuring instrument, practically used as an additional washer, as well as an easy assembly method, makes it universally applicable in mines where anchoring is used as a means of strengthening the rock.

This article presents a concept method which aids the forecasting of the reclamation cost in post- rock mining areas. The method may also prove useful in estimating the investment profitability of a mining operation at its planning stage as well as managing a potential Reserve Fund to cover future activities, such as land reclamation. The development of the method consisted in defining a set of basic/typical land reclamation directions and the typical structure of reclamation operations/works, which are based on “statistically stable” values. The estimations included the distribution of the probable cost of these works with respect to the reclamation direction and were calculated on the basis of the analyzed current price lists and historical land reclamation projects. The article proposes a method for estimating the cost structure of multi-directional projects by combining the basic directions. The changeability and predictability of various land reclamation solutions was analyzed in terms of fuzzy logic. A price list was developed, which included unit costs for separate types of reclamation works, independent of their type and scale. The assumed optimal measure involved comparing the cost of individual types of operations to the surface of the reclamation area. As an example, the method was also applied to hypothetical data from a clastic rock mine with a surface of 20 ha, and for the forest, agricultural and forest-agricultural reclamation directions. The forest-agricultural reclamation directions was presented in the proportions of 0.3:0.7.

Geodesic measurements of mining area deformations indicate that their description fails to be regular,

as opposed to what the predictions based on the relationships of the geometric-integral theory suggest.

The Knothe theory, most commonly applied in that case, considers such parameters as the exploitation

coefficient a and the angle of the main influences range tgβ, describing the geomechanical properties of the

medium, as well as the mining conditions. The study shows that the values of the parameters a = 0.8 and

tgβ = 2.0, most commonly adopted for the prediction of surface deformation, are not entirely adequate in

describing each and every mining situation in the analysed rock mass. Therefore, the paper aims to propose

methodology for determining the value of exploitation coefficient a, which allows to predict the values

of surface subsidence caused by underground coal mining with roof caving, depending on geological and

mining conditions. The characteristics of the analysed areas show that the following factors affect surface

subsidence: thickness of overburden, type of overburden strata, type of Carboniferous strata, rock mass

disturbance and depth of exploitation. These factors may allow to determine the exploitation coefficient a,

used in the Knothe theory for surface deformation prediction.

The currently applicable legal provisions and also the economic concepts emphasize the importance of circular economy. In this aspect, it is very important to reduce the waste production respectively planning and running a business. Technical research is the key to finding a new applications for waste, in particular disposed on landfilling. Mining and energy industries belong to the biggest producers of waste in Poland. The total share of these two branches in waste production is up to 70% (mining and quarrying 53%; electricity, gas, steam and air conditioning supplay 17%). In environment, economy and social aspect, it is very important to develop this waste. The paper presents research on the physico-mechanical properties of the aggregates based on colliery shale supplemented by fly ash (20% - 40% supplement of fly ash). The following tests should be mentioned among performed: particle size distribution, the sand equivalent test, freeze resistance and direct shear tests. Also the chemical properties found in the literature was invoked. The research shows good physico-mechanical properties of the mixes, such as cohesion (44.62 kPa - 68.57 kPa) or internal firiction angle (34.74° - 40.52°). Though low resistance to weathering and a large susceptibility to frost heave (the mass loss after the freezing cycles is 76%) may limit its applicatin in road engineering. The sand equivalent tests were made only for aggregates. Tested materials shows usefulness for earthen structures. However, the research should be supplemented by chemical tests and also observations of the material properties changes as the effect of time. The research on the leachability of chemical pollutants, which will determine the acceptable share of ash in the mix, could be especially significant. The fact that fly ash contains a lot of sulphates and chlorides, which leach into the environment may pose a threat to living organisms.

In this paper, the different mechanical behaviors of layered rocks with different bedding angles during uniaxial compression tests are studied. Numerical simulation models of layered rock are validated based on laboratory tests, and uniaxial compression tests are conducted by using Particle Flow Code (PFC). Using these simulations, the uniaxial compressive strength, failure patterns, development of micro-cracks, and displacement of meso particles are analyzed. When the bedding angle is similar to the failure angle, the macro failure planes develop directly along the beddings, the bedding behavior dictates the behavior of the layered rock, reducing the compressive strength.