This paper points out that the ARMA models followed by GARCH squares are volatile and gives explicit and general forms of their dependent and volatile innovations. The volatility function of the ARMA innovations is shown to be the square of the corresponding GARCH volatility function. The prediction of GARCH squares is facilitated by the ARMA structure and predictive intervals are considered. Further, the developments suggest families of volatile ARMA processes.

Steel arch-rectangular support has a wide range of applications in Polish coal mines due to its asymmetrical shape. The frame has an arched outline on one side of the side wall, while on the opposite side it is rectangular. As a result, the support is ideal for securing set up room and recovery room. It can also be successfully used to secure three-way intersections of underground workings. To a large extent, however, the importance of these advantages is diminished by relatively low load-bearing parameters, resulting from a partially straight canopy, as well as the asymmetrical distribution of the load acting on the support in underground conditions. In order to ensure the proper and optimal operation of such frames, in addition to the standard requirements for roof supports, additional conditions must be met. The basic requirement is to support the end of the canopy on the corner of the excavation. This article presents examples of arch-rectangular supports, their applications as well as laboratory tests and strength analysis of the frames and its elements. These tests allowed the requirements regarding the construction of the frame, the selection of the support and the conditions of building in the excavation to be specified.

Steel yielding arch support constructed of V profiles is commonly used to protect galleries and, in some cases, to reinforce or secure a shaft support. For this purpose, a closed, circular-shaped arch support is used, with arches overlapped by clamps that are typical for this type of construction. The support has high resistance to the impact of even (distributed over the entire surface of the support) load, however, as a result of significant deformation associated with a change in the radius of the curvatures, the support shows limited yielding capacity. This is due to the increase in resistance to slide on the locks, resulting from changes in the geometry of the ring caused by the rock mass. This article presents the results of research and analysis concerning the elements of the arch support with notches in arches. The research team tested the effect of the depth and location of the notches of the section’s flanges on the load impacting on the clamp’s bolts and the strength of the roof support. Moreover, the tests covered the influence of the number and location of clamps in a frictional joint on the change in the nature of work and yielding capacity. Finally, the research included both strength tests of the support’s elements, as well as strength analyses based on the finite element method.

The object of the investigation was metal contamination of bottom sediments of the Skroda and

Chwaliszówka rivers, which are the right contributaries of the Lusatian Neisse river, draining the territory of

the so called “anthropogenic lake district”. The district came into existence as a result of mining activities in the

border of Silesia and Lusatia, which date from the half of 19th century to 1974. The district includes about 100

reservoirs, of the total area of over 150 ha, which are from about 30 to 100 years old.

The rocks accompanying the Miocene coal-bearing formations were deposited on waste dumps. The dumps

form embankments of the aquifers arising as a result of post-exploitation mining subsidence. The streams dewatering waste dumps inflow directly or indirectly to the Chwaliszówka and Skroda rivers. The pyrite is the

mineral present in mine waste material. The pyrite weathering products inflow into surface waters and affect

adversely the water quality. In the last stage of migration the pollutants are accumulated in the bottom sediments

of rivers and lakes. The samples of bottom sediments of the two rivers were analysed by means of a five-step

sequential extraction procedure performed for the partitioning of selected trace metals (Fe, Mn, As, Cr and Al).

It was determined that the bottom sediments of the two analysed rivers contain significant concentrations of

aluminium and iron. The concentrations of other metals (Mn, Cr and As) are in the range of geochemical background of water sediments in Poland. Concentrations of arsenium, chromium and manganese, which are bound

to easy-available fractions (I – exchangeable and II – bound to carbonates) are not significant, so it could be

assumed that they are not expected to be released and they do not threaten the river ecological system. There is,

however, the possibility of the aluminium and iron re-mobilisation, taking into account the high concentrations

of easy-available fractions of these metals in the sediment. Fe and Al are potential source of water contamination, and re-mobilisation of these metals will produce the aggravation of quality parameters of river waters.

The Dez dam was commissioned in 1963 and since sediments accumulated in the reservoir up to an elevation of approximately 15m below the intake of the power tunnel. One of the possible measures to improve operation of the reservoir is by heightening of the existing dam. This paper describes the conducted procedure for static and thermal calibration of this 203m dam in Iran based on micro geodesies measurements. Also the nonlinear response of existing dam is investigated under maximum credible earthquake ground motions considering joint behavior and mass concrete cracking and safety of dam is evaluated for possible heightening. For thermal calibration of provided numerical model, transient thermal analysis was conducted and results were compared with thermometers records installed in central block. In addition, for static calibration; thermal distribution within dam body, dam self weight, hydrostatic pressure and silt load applied on the 3D fi nite element model of dam-reservoir-foundation were considered. Results show that the distribution of stresses will be critical within dam for heightening case under seismic loads in MCL.

Arch bridges are built since two thousand years at least. Structural materials changed during this time. The design methods were changed also. The biggest impact was noted with development of Finite Element Method and graphical methods of preparation of technical drawings which is strictly combined with development of computers. These processes appeared also in Polish construction industry, especially from the beginning of 90-ties XX century.

But in this paper we do not consider mentioned above problems. We would like to present development of arch bridges from construction technology point of view. This aspect of creation of bridge structures is not very often the subject-matter of analysis. For many investors, design engineers and contractors optimization of structures is most important issue. For most of them the reduction of volume (weight) of structural material is only solution. But sometimes it is not true – the construction technology gives much more efficient results.

We present below examples of realization in Poland medium and large span arch bridges – steel, concrete and hybrid structures.

In recent years, the Vietnamese coal mining industry has observed a dynamic increase in both its production and efficiency. In Vietnam, the most precious type of coal is anthracite, which is found in the Quang Ninh province. Industrial anthracite deposits are estimated to be over 2 billion Mg. At present, coal deposits are extracted mostly by the underground method. Coal production is gradually increasing in the underground mines in the Quang Ninh area and it is expected to constitute about 75% of the country’s total coal production in 2030. This involves an increase in the number and length of underground workings.

Cam Pha is the largest coal basin of Vietnam, located in the Quang Ninh province. So far, the yearly length of underground workings driven in underground mines in the Cam Pha basin is roughly 90÷150 km. About 84 % of these underground workings are supported by the steel arch support made of SWP profile. A similar situation can be observed in Russia, Ukraine, China, India and Turkey. In addition, the average length of repaired underground workings in the Cam Pha basin constitutes approximately 30% of the total length driven . The main cause was reported is loss of underground workings stability. This requires significant material and labour costs as well as the cost of replacing damaged elements. Additionally, it disturbs the continuity of the mining operations.

This article presents the results of the numerical modelling of the rock mass around underground workings driven in typical geo-mining conditions for underground coal mines in the Cam Pha basin, supported by the steel arch support made of SWP and V profiles. As a result of the conducted analyses, the range of failure zone of the rock mass around underground workings and the distribution of reduced stress in the steel arch support elements were determined. The effort states of the steel arch support made of SWP22 profile and V21 profile were compared. The simulations considered different inclinations angle of coal seam, following the structure of the rock mass in the Cam Pha basin. The analysis was carried out using the based-finite difference method code, FLAC2D. Based on the obtained results, actions for improving the stability of underground workings driven in the underground mines of the Cam Pha basin were proposed.

In this work, the support of two general galleries located in poor quality rock mass and subjected to the influence of high thickness coal layer exploitations is designed and optimized. The process is carried out in four phases:

A first preliminary support is defined employing different geomechanical classifications and applying the New Austrian Tunnelling Method (NATM) using bolts and shotcrete.

An instrumentation campaign is carried out with the goal of analysing the behaviour of the support. The study noticed the failure of the support due to the time of placement of the different elements.

A back-analysis using the Flac and Phases software has allowed the evaluation of the properties of the rock mass and the support, the study of the influence of the time of placement on the component elements (bolts and shotcrete), and the redefinition of that support.

Subsequently, a new support is designed and optimized through numerical modeling after the start of mining without experience in these sizes of sublevel caving that caused the failure of the previously designed support. The new support is formed by yieldable steel arches that are more suitable to withstand the stresses generated by nearby mining work.

Exploitation of lignite within the area of Muskau Arch, carried out from the mid-nineteenth century, contributed to the transformation of the natural environment and changes in water regime. In the post-mining subsidences pit lakes were formed. The chemical composition of waters is a consequence of the intensive weathering of pyrite (FeS2), which is present in Miocene lignite-bearing rock forming the embankments of the lakes. This process leads to the formation of Acid Mine Drainage (AMD) and finally acidification of lake waters.

This paper presents results of the identification of hydrogeochemical processes affecting the chemistry of waters from these reservoirs carried out using the speciation and statistical (cluster and factor) analyses. Cluster analysis allowed to separate from the analyzed group of anthropogenic reservoirs 7 subgroups characterized by a similar chemical composition of waters. The major processes affecting the chemistry of waters were identified and interpreted with help of factor and speciation analysis of two major parameters (iron and sulfur).

Difficult geological and mining conditions as well as great stresses in the rock mass result in significant deformations of the rocks that surround the workings and also lead to the occurrence of tremors and rock bursts. Yielding steel arch support has been utilised in the face of hard coal extraction under difficult conditions for many years, both in Poland and abroad. A significant improvement in maintaining gallery working stability is achieved by increasing the yielding support load capacity and work through bolting; however, the use of rock bolts is often limited due to factors such as weak roof rock, significant rock mass fracturing, water accumulation, etc. This is why research and design efforts continue in order to increase yielding steel arch support resistance to both static and dynamic loads. Currently, the most commonly employed type of yielding steel arch support is a support system with frames constructed from overlapping steel arches coupled by shackles. The yield of the steel frame is accomplished by means of sliding joints constructed from sections of various profiles (e.g. V, TH or U-type), which slip after the friction force is exceeded; this force is primarily dependent on the type of shackles and the torque of the shackle screw nuts.

This article presents the static bench testing results of ŁP10/V36/4/A, ŁP10/V32/4/A and ŁP10/V29/4/A yielding steel arch support systems formed from S480W and S560W steel with increased mechanical properties. The tests were conducted using 2 and 3 shackles in the joint, which made it possible to compare the load capacities, work values and characteristics of various types of support. The following shackle screw torques were used for the tests:

• Md = 500 Nm – for shackles utilised in the support constructed from V32 and V36 sections.

• Md = 400 Nm – for shackles utilised in the support constructed from V29 sections.

The shackle screw torques used during the tests were greater compared to the currently utilised standard shackle screw torques within the range of Md = 350-450 Nm.

Dynamic testing of the sliding joints constructed from V32 section with 2 and 3 shackles was also performed. The SD32/36W shackles utilised during the tests were produced in the reinforced versions and manufactured using S480W steel.

Since comparative testing of a rock bolt-reinforced steel arch support system revealed that the bolts would undergo failure at the point of the support yield, a decision was made to investigate the character of the dynamics of this phenomenon. Consequently, this article also presents unique measurement results for top section acceleration values registered in the joints during the conduction of support tests at full scale.

Filming the yield in the joint using high-speed video and thermal cameras made it possible to register the dynamic characteristics of the joint heating process at the arch contact point as well as the mechanical sparks that accompanied it. Considering that these phenomena have thus far been poorly understood, recognising their significance is of great importance from the perspective of occupational safety under the conditions of an explosive atmosphere, especially in the light of the requirements of the new standard EN ISO 80079-36:2016, harmonised with the ATEX directive.

Entries in steeply pitching seams have a more complex stress environment than those in flat seams. This study targets techniques for maintaining the surrounding rock mass stability of entries in steep seams through a case study of a steep-seam entry at a mine in southern China. An in-depth study of the deformation and instability mechanisms of the entry is conducted, employing field measurement, physical simulation experiment, numerical simulation, and theoretical analysis. The study results show that the surrounding rock mass of the entry is characterised by asymmetrical stress distribution, deformation, and failure. Specifically, 1) the entry deformation is characterised by a pattern of floor heaving and roof subsidence; 2) broken rock zones in the two entry walls are larger than those in the roof and floor, and the broken rock zone in the seam-floor side wall is larger than that in the seam-roof side wall; 3) rock bolts in the middle-bottom part of the seam-floor side wall of the entry are prone to failure due to tensile stress; and 4) rock bolts in the seam-roof side wall experience relatively even load and relatively small tensile stress. Through analysis, disturbances were found to occur in both temporal and spatial dimensions. Specifically, in the initial mining stage, the asymmetrical rock structure and stress distribution cause entry deformation and instability; during multiple-seam multiple-panel mining operations, a wedge-shaped rock mass and a quasi-arc cut rock stratum formed in the mining space may cause subsidence in the seam-floor side wall of the entry and inter-stratum transpression, deformation, and instability of the entry roof and floor. The principles for controlling the stability of the surrounding rock mass of the entry are proposed. In addition, an improved asymmetrical coupled support structure design for the entry is proposed to demonstrate the effective control of entry deformation.

The deformation modulus of the rock mass as a very important parameter in rock mechanic projects generally is determined by the plate load in-situ tests. While this test is very expensive and time-consuming, so in this study a new method is developed to combin artificial neural networks and numerical modeling for predicting deformation modulus of rock masses. For this aim, firstly, the plate load test was simulated using a Finite Difference numerical model that was verified with actual results of the plate load test in Pirtaghi dam galleries in Iran. Secondly, an artificial neural network is trained with a set of data resulted from numerical simulations to estimate the deformation modulus of the rock mass. The results showed that an ANN with five neurons in the input layer, three hidden layers with 4, 3 and 2 neurons, and one neuron in the output layer had the best accuracy for predicting the deformation modulus of the rock mass.

The mining of hard coal deposits at increasingly greater depth leads to an increase in hazards related to the loss of stability of steel arch supports as a result of excessive static and dynamic loads. Camber beam reinforcement via rockbolting is often utilised in order to improve the stability of the yielding steel arch support.

This article presents the results of comparative bench tests of the ŁP10/V36-type steel arch support, tested with and without reinforcement by means of self-drilling bolts with drunken R25 threads, using short joists formed from V32 and V25 sections. It also presents the results of comparative tests of the ŁPP10/4/V29/I-type steel arch support, tested with and without reinforcement by means of rock bolts with trapezoidal Tr22/13 threads, using short joists formed from V25 sections. The obtained test results, in the form of load courses and work values of the steel arch and mixed (arches and rock bolts) support systems, demonstrate that the utilisation of mixed support may significantly improve the stability of workings, particularly immediately after they are driven. A mixed support system quickly achieves its maximum load capacity together with a significant increase in its work value. It may thus prevent the stratification of the rocks surrounding the working, and therefore better utilise the self-supporting capacity of the rock mass. As evidenced by the test results, the mixed support work may be as much as 3.5 times as great compared to the steel arch support at the beginning of the height reduction process initiated by loading – i.e. until its reduction by a presupposed value of 100 mm.

The oral cavity due to its temperature fluctuations, changing pH, high humidity, action of mechanical forces and the presence of microorganisms is a favorable environment for degradation of dental materials. The paper presents comparative results on orthodontic arch-wires AISI304 steel before and after low temperature plasma nitriding carried out at cathodic potential (conventional) and at plasma potential, i.e. in a process incorporating an active screen. Corrosion resistance test on nitrided layers produced on stainless steel were carried out via electrochemical impedance spectroscopy (EIS) and the potentiodynamic method in non-deaerated artificial saliva solution at 37°C. The results were complemented with analysis of the structure, surface topography and microhardness. The results showed an increase in corrosion resistance of AISI304 steel after conventional glow-discharge nitriding.