Rocker Bearings Research Articles

Advanced modeling of seepage dynamics and control strategies in thick coal seams under high-confined aquifer conditions: A case study

The hydraulic behavior of the connection between the floor failure area and the aquifer water-conductive zone is considered to be the root cause of mine water inrush disasters. Therefore, unraveling the floor failure mechanism is particularly important for safe coal mining above the high-confined aquifer. This paper estimates the depth of the baseplate failure to be 18.4–27.3 m by combining network parallel electrical methods with drilling visualization technology. The FLAC3D-based numerical model considering the strain hardening of caved rock was established with rigorous calibration and verification. The results showed that the depth of damage to the floor is 23.1 m, and the dominating floor failure mechanism is shear failure caused by the vertical stress exceeding the rock bearing capacity. Moreover, the stress recovery process of the baseplate does not alter the failure morphology of the baseplate. Based on the above research findings, the in-situ floor control technique of the working face No. 4305 is proposed and practiced in the field. Field measurements show that floor control performance is satisfactory with water inflow in the goaf being roughly stable at 50 m3/h. Our results can provide useful reference for safe mining above confined aquifer and prevention and mitigation of water-related hazards.

Dynamic responses and failure behaviors of submerged reefs containing pre-drilled hole subjected to repetitive impacting

The drilling-hammer method is adopted for the breaking over submerged reefs in waterway regulation engineering. However, rocks with pre-drilled holes are highly susceptible to the repetitive impacts from drop hammers or drilling equipment. Exploring the dynamic responses and failure behaviors of drilled-hole rocks under repetitive impacting is important for promoting implementation of this technique. In this study, the repetitive impacting tests were conducted on the drilled rocks by the split Hopkinson pressure bar to investigate the rock bearing capacity, deformation property, failure behavior, and energy evolution. The results indicate that the presence of pre-drilled holes and the decreasing loading rates attenuate the bearing capacity of rocks subjected to repetitive impacting. In contrast, the rock deformation capacity is impacted subtly by the impact loading rate and increases with the number of impacts and borehole size. The drilled rock failure occurred with the prevalence of intergranular fractures; subsequently, the proportion of transgranular fractures increased, contributing to the loading rate-dependent bearing capacity. The inverted S-shaped damage evolution curve was assessed using the inverted logistic growth model. The specimen absorbed few incident energies for fracture generation and propagation, and the rock with a larger drill size displays higher energy utilization and larger fragments.

The mechanism and performance of rock breakage by undercutting disc cutter with advanced slotting

To study the mechanism and performance of rock breakage by an undercutting disc cutter with advanced slotting, a three-dimensional numerical model of rock cutting by a disc cutter with advanced slotting assistance was established based on the discrete element method. The parallel bond constitutive model was selected to describe the micromechanical properties of rock. The correctness of the established numerical model is verified through rock breakage experiments, and the rock cutting process by the disc cutter was analyzed by a combination of the force chain and crack distribution. The influencing factors, such as advanced slotting depth, cutting thickness, rock strength, and cutter rotation speed, on rock cutting performance were investigated. The results show that a compact zone is gradually formed between the rock and disc cutter at the beginning, then a large number of microscopic tensile and shear cracks in the compact zone due to micro failure of rock are formed; the subsequent main rock fragment is mainly caused by tensile failure; advanced slotting can reduce the rock bearing capacity and bending resistance, the rock above the advanced slotting fractured easily due to its lower bending resistance, and the volume compact zone is relatively small. When the advanced slotting depth is equal to 12.5 mm, the propulsive force and specific energy consumption of rock cutting by the disc cutter are reduced by 61.6% and 16.5%, respectively. The propulsive force and specific energy consumption increase as the rock strength increases, but they tend to close when the rock strength is greater than 80 MPa, which indicates that advanced slotting assistance is more suitable for hard rock. The results obtained in this paper can provide the operating parameters determination under different factors to some extent of the undercutting disc cutter in a pre-cut condition, which further improve the rock breaking performance of mechanized cutter.

Experiment on deformation and failure characteristics of sandstone at different unloading rates

The unloading effect is an important factor for the failure of surrounding rock in deep underground engineering projects, especially under high-stress conditions. To investigate the deformation and failure characteristics of sandstone at different unloading rates, the evolution law of the surrounding rock stress caused by excavation was clarified. Then, the single-side unloading test of surrounding rock at different unloading rates was conducted using a true triaxial rock mechanics test system. During the test, the acoustic emission (AE) signals were monitored using an AE monitoring system. The test results show that excavation disturbance leads to complete single-side unloading at the boundary of the surrounding rock, and partial single-side unloading occurs as the depth of the surrounding rock increases. The ultimate strength of the sandstone specimen decreases as a power function with the increasing unloading rate. The unloading rock mass is mainly subject to shear failure. However, the increasing unloading rate raises the proportion of tension cracks. The sudden high strain rate on the unloading side can be used as precursor information of rock fracture, which can effectively prevent accidents caused by loss of rock bearing capacity. The AE signal is active and releases less energy in the unloading stage. At this time, the internal fractures are in the development stage, and the energy is still mainly accumulated. The unloading and failure are not synchronized but suffer from the hysteresis effect. Additionally, the AE and the strain rate change on the unloading side are consistent. Due to the hysteresis effect of damage on unloading, anchor bolts (cables) should be installed to support the surrounding rock immediately to compensate for the stress loss caused by excavation in engineering practice.

Study on the Creep Characteristics and Fractional Order Model of Granite Tunnel Excavation Unloading in a High Seepage Pressure Environment

The creep associated with unloading surrounding rock during the excavation of deep tunnels seriously affects the stability of the tunnel, and a high seepage pressure will aggravate the strength attenuation and structural deterioration of the surrounding rock. Based on the background of the excavation-induced unloading of the surrounding rock of a deeply buried granite tunnel with high seepage pressure, in this paper we carry out a triaxial unloading seepage creep test that considers the effects of both excavation disturbance and seepage pressure. We also analyze the mechanism of unloading and seepage pressure leading to sample failure and construct a fractional creep damage constitutive model that considers the unloading effect. The results include the following findings, firstly, seepage pressure will affect the creep deformation of rock for a long time, and the circumferential expansion of the granite creep process is more obvious than the axial expansion. Secondly, a high seepage pressure will reduce the rock bearing capacity. Under 0, 2 and 4 MPa seepage pressures, the long-term strength of the samples are 193.7 MPa, 177.5 MPa and 162.1 MPa, respectively. Thirdly, the rock damage factor increases with increasing seepage pressure, time and deviatoric stress. Finally, the rationality of a fractional-order model that considers the effect of unloading and seepage is verified by the test data. These research results may provide some reference for the stability analysis of surrounding rock during excavation in environments under high-stress and high-seepage-pressure.

Experimental study on failure characteristics of single-sided unloading rock under different intermediate principal stress conditions

Investigation of unloading rock failure under different σ2 facilitates the control mechanism of excavation surrounding rock. This study focused on single-sided unloading tests of granite specimens under true triaxial conditions. The strength and failure characteristics were studied with micro-camera and acoustic emission (AE) monitoring. Furthermore, the choice of test path and the effect of σ2 on fracture of unloading rock were discussed. Results show that the increased σ2 can strengthen the stability of single-sided unloading rock. After unloading, the rock's free surface underwent five phases, namely, inoculation, particle ejection, buckling rupture, stable failure, and unstable rockburst phases. Moreover, at σ2≤30 MPa, the b value shows the following variation tendency: rising, dropping, significant fluctuation, and dropping, with dispersed damages signal. At σ2≥40 MPa, the tendency shows: a rise, a decrease, a slight fluctuation, and final drop, with concentrated damages signal. After unloading, AE energy is mainly concentrated in the micro-energy range. With the increased σ2, the micro-energy ratio rises. In contrast, low, medium and large energy ratios drop gradually. The increased tensile fractures and decreased shear fractures indicate that the failure mode of the unloading rock gradually changes from tensile-shear mode to tensile-split one. The fractional dimension of the rock fragments first increases and then decreases with an inflection point at 20 MPa. The distribution of SIF on the planes changes as σ2 increases, resulting in strengthening and then weakening of the rock bearing capacity.

PFC Simulation Study on Time-dependent Deformation Failure Properties and Energy Conversion Law of Sandstone under Different Axial Stress

Rock burst mostly happens in deep rock engineering, which obviously performs obvious time-dependent destruction and releases huge energy. Thus, the uniaxial compressive time-dependent deformation failure tests of sandstone under different axial stress are conducted and the optimized Parallel-bonded stress corrosion (PSC) model is established based on PFC method. The results show that tension micro-cracks are the direct reason of rock bearing capacity reduction during the whole failure process. The time-dependent deformation stage is composed of the initial strain stage, the steady-state strain stage and the accelerated strain stage. As the axial stress increases, rock mass enters into the accelerated strain stage more quickly and the strain amount of time-dependent deformation stage decreases. From the comparison of energy conversion between PFC simulation and experiments, the higher elastic strain energy will be accumulated and the less dissipation energy will be produced while the axial stress increases when reaching the failure point. After the failure point, the elastic strain energy has a small increase because the strain rate changes faster than the failure relaxation rate. Based on the calculation results of residual elastic energy index (AEF), the rock burst shows a tendency that from weakness to moderation as the axial stress increases. The research results will provide a certain reference in predicting the rock burst.

The theory of sedimentation cyclicity of N.B. Vassoevich in the educational and scientific activities of the Petroleum Geology Department of Lomonosov Moscow State University in the XXI century

The article is devoted to the 120th anniversary of Nikolay Bronislavovich Vassoevich (1902–1981) – a famous petroleum geologist, professor, corresponding member of the USSR Academy of Sciences. The article recalls his significant achievements in the field of fundamental geology. The first and main work in this field was his monograph on the methodology for studying the sedimentation cyclicity of flysch strata (1948), with the continuation of the topic in the next book, published in 1951. The scientific heritage of N.B. Vassoevich, who headed the Petroleum Geology Department of Lomonosov Moscow State University in 1963–1981, is preserved and developed in the modern educational and scientific activities of this Department. Teachers, staff and students with deep gratitude and respect honor the memory of N.B. Vassoevich, using his methodological recommendations on sedimentation cyclicity both in the training course of lithofacial analysis and applied in practical work in the study of oil and gas bearing strata of sedimentary rock basins. A huge role in the development of the terminology of this theory is associated with the development of the conceptual base of this geological direction. Professor N.B. Vassoevich had invested continuous work on the creation of systematic and logical classifications according to the composition, structure, genesis and hierarchy of geological sedimentary bodies that make up oil and gas bearing rock complexes.

Bubbled roller-compacted concrete dam: an idea of a hollow dam

Roller-compacted concrete (RCC) is widely known for its relatively low cost and short construction time. RCC gravity dams require high foundation (rock) bearing capacity. Research studies have been carried out which propose to rationalise the amount of material in the dam by creating inner voids, in the shape of bubbles. As a key requirement, the introduced bubbles should not affect the dam stability and safety. The bubbles will reduce the self-weight of the dam and minimise the required rock-bearing capacity. A system of pipes connecting the bubbles ensures drainage of the bubbles. The proposed dam would save about 12% of the required concrete volume. Different construction methods were studied and the best alternative is the use of precast hollow boxes. This decreases RCC placement in the dam by 32.5%. The objective is to speed the construction process and minimise the risk of the heat of hydration.

KARAKTERISTIK GEOLOGI TEKNIK DESA KATEKAN, KECAMATAN GANTIWARNO, KABUPATEN KLATEN, PROVINSI JAWA TENGAH

Supporting data for sustainable development is increasingly being considered to fulfill good primary development data. One of the data that is often ignored is the engineering geology of the land. These data are needed to describe the response of the land to various aspects imposed on the land from a geological and engineering point of view. Thus, it is necessary to investigate the characteristics of engineering geology before the land is used or as part of the evaluation. Katekan village, with its rapid population growth, requires the construction of various life support facilities. This is evidenced by the construction of many new houses in various village areas and access roads with cast and asphalt materials. The development that occurs, not a few uses agricultural land which has clay-rich soil material. Many problems occur in the construction, including house cracks, cracks in the road, and puddles. It becomes interesting to investigate related to geological engineering conditions. Investigation of the technical geological characteristics of Katekan Village, which was carried out by qualitative and quantitative field mapping, resulted in the distribution of rock units in the form of alluvial deposits of clay, sand, and silt. Slope variation between 3°-8°. The level of ease of excavation of rock mass ranges from easy to excavate to challenging to excavate. Rock bearing capacity is 72.42-154.63 t/m2, and the soil bearing capacity is 13.63-41.51 t/m2.

New insights into the formation and emplacement of impact melt rocks within the Chicxulub impact structure, following the 2016 IODP-ICDP Expedition 364

Abstract This study presents petrographic and geochemical characterization of 46 pre-impact rocks and 32 impactites containing and/or representing impact melt rock from the peak ring of the Chicxulub impact structure (Yucatán, Mexico). The aims were both to investigate the components that potentially contributed to the impact melt (i.e., the pre-impact lithologies) and to better elucidate impact melt rock emplacement at Chicxulub. The impactites presented here are subdivided into two sample groups: the lower impact melt rock–bearing unit, which intrudes the peak ring at different intervals, and the upper impact melt rock unit, which overlies the peak ring. The geochemical characterization of five identified pre-impact lithologies (i.e., granitoid, dolerite, dacite, felsite, and limestone) was able to constrain the bulk geochemical composition of both impactite units. These pre-impact lithologies thus likely represent the main constituent lithologies that were involved in the formation of impact melt rock. In general, the composition of both impactite units can be explained by mixing of the primarily felsic and mafic lithologies, but with varying degrees of carbonate dilution. It is assumed that the two units were initially part of the same impact-produced melt, but discrete processes separated them during crater formation. The lower impact melt rock–bearing unit is interpreted to represent impact melt rock injected into the crystalline basement during the compression/excavation stage of cratering. These impact melt rock layers acted as delamination surfaces within the crystalline basement, accommodating its displacement during peak ring formation. This movement strongly comminuted the impact melt rock layers present in the peak ring structure. The composition of the upper impact melt rock unit was contingent on the entrainment of carbonate components and is interpreted to have stayed at the surface during crater development. Its formation was not finalized until the modification stage, when carbonate material would have reentered the crater.

Groundwater Inrush Control and Parameters Optimization of Curtain Grouting Reinforcement for the Jingzhai Tunnel

Based on the systematic study on the characteristics of water and mud inrush during the excavation of Jingzhai tunnel, the mechanism of water inrush seepage transformation caused by excavation disturbance is analyzed. By means of electromagnetic geophysical prospecting, the potential water bearing area of the tunnel was analyzed. The constitutive model of rock mass and grouting parameters are considered in the numerical simulation. The law of tunnel crack initiation and expansion under different curtain grouting parameters is proposed. The characteristics of seepage water inrush caused by excavation are described. It is considered that there are three stages in the seepage characteristics of tunnel: incubation, sudden, and stable. Numerical simulation was used to analyze the crack propagation track and water inflow characteristics under the grouting thickness of 3 m, 5 m, and 7 m. When the curtain grouting thickness was 3 m, the fracture field penetrated the curtain grouting area. The dominant seepage channel is formed, which greatly increases the probability of water inrush. When the curtain thickness is 5~7 m, the expansion of the crack zone can be controlled basically, so that the fracture and water bearing rock layer cannot form a seepage channel. At last, the grouting scheme of 6 m thick grouting and 20 m advanced grouting was selected, and the water seepage was reduced by 83%.

Evaluation of Bored Piles Load Capacity in Rock Bearing. (Dept. C)

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Seismic Isolation Retrofitting of Typical Multi-Span Steel Girder Bridges in New York State

Many of the existing multi-span simply supported bridges in New York State, U.S., are susceptible to earthquake damage and need to be retrofitted to reduce their seismic risk. In this study, seismic retrofit of a five-span simply supported bridge with typical high-type fixed and expansion steel rocker bearings is conducted. A refined three-dimensional (3D) finite element model of the bridge is developed in ANSYS by considering foundation impedances. Multi-support time history analyses have been implemented in the seismic retrofit design for two levels of ground motions: 1,000- and 2,500-year return period earthquakes. The site-specific ground motions with consideration of the spatial variation are generated based on the geotechnical information. Seismic retrofit by replacing existing steel bearings with lead-rubber bearing (LRB) isolators has been adopted. The parameters of the isolators are determined by considering factors such as the seismic performance and translational resistance during normal service. The vulnerability of structural members and seismic retrofit effectiveness are quantified by the demand-to-capacity (D/C) ratio for the combined demands at the extreme limit state. The analyses show that after seismic isolation retrofit the pervasive vulnerabilities in pier columns and cap beams are eliminated. Comparing with strengthening the vunerable structural members, seismic isolation is proved a cost-effective retrofit solution. The overall seismic isolation design and analysis procedures presented in this study can help guide future seismic retrofit of similar types of bridges.

Rock Mass Characterization for Assessment of Safe Cut Slope and Rock Bearing Capacity at Gondang Dam Site, Karanganyar, Indonesia

This paper presents results of surface rock mass characterization for assessment of safe cut slopes and allowable bearing capacity of foundation rocks at the construction area of Gondang Dam. The rock mass characterization involved determination of intact rock engineering properties and rock mass quality based on the Geological Strength Index. The rock mass characterization results showed that the research area consisted of moderately to highly weathered and very weak to weak andesite breccia and andesite tuff breccia. The andesite breccia had very poor to fair rock mass quality, while the andesite tuff breccia had poor to fair rock mass quality. The research area was divided into three zones of safe cut slope and allowable bearing capacity. Landslides occurred at natural slopes having poor to very poor rock mass quality and inclinations greater than the determined safe cut slopes.The foundation rock of the embankment dam had fair rock massquality and 135–280 T/m2 allowable bearing capacity

A Predictive Model of Mining Collapse Extent and Its Application

To reveal the mechanical behavior mechanism of collapse and to control risks effectively, the instability extent of the collapse area was established through theoretical mechanics and numerical methods, taking one metal mine as a case study; on this basis, a routine reinforcement program was determined, and the effect of the program was evaluated. The results show the following. (1) Analytical formulas of the critical slip angle and the collapse height of the ore body were derived by the mechanics method, and the rock mechanics parameters were obtained by field coring and physical and mechanical experiments. The slipping line angle increases along with uniform force Q and is inversely proportional to the bending stiffness. Meanwhile, the calculation formula for the maximum subsidence of ore body was deduced. (2) Numerical results can be used to determine the basic form of the collapse area, and a “U‐shaped” collapse area formed when a plastic area passed completely through, resulting in the overall destruction. (3) The grouting reinforcement program includes “determining the instability region ⟶ roadway temporary support ⟶ improve the water environment and surrounding rock bearing capacity ⟶ mining planning” which were determined on the basis of prediction. (4) The hierarchical structure of the rock body and filling were improved combined with the Delphi method, and the grouting effect evaluation model was constructed and verified using the improved FD‐AHP method; the evaluation value indicating that the grouting reinforcement improved the bearing capacity of ore body and filling body in collapse area. The research results provide systematic reference and technical support for the analysis of stope collapse mechanism, prediction of hidden trouble, and the subsequent mining.

Evaluation of Dynamic Characteristics of the Footbridge with Integral Abutments

Abstract The paper presents the results of dynamic field tests and numerical analysis of the footbridge designed as a three-span composite structure with integral abutments. The adopted design solution which has allowed to achieve a high resistance of the structure to dynamic loads and to meet the requirements of the criteria of comfort of use with a large reserve has been characterized. For comparative purposes, numerical analyzes of three construction variants of the footbridge were presented: F-1 - construction with integral abutments (realized variant), F-2 - construction with girders anchored in the abutments by means of tension rocker bearings, F-3 - construction with concrete side spans.

Failures of US bridge rocker bearings

Bridge bearings made of iron or steel, first used in early railroad bridges about 150 years ago, are relatively small structural components that support the loads of bridge superstructures. Fixed bearings directly transfer forces from a bridges superstructure to its substructure. Movable bearings, such as sliding bearing plates, rollers and rockers, accommodate the thermal expansion of the superstructure without transferring it to the substructure. Rocker bearings tilt to accommodate thermal movement, theoretically without imposing stresses on the substructure. This paper concerns rocker bearings which are non-redundant components and have two states: stable and toppled over. When these bearings topple over, no alternate load paths exist, which results in a failed superstructure. As such, rocker bearings are critical bridge components. An overview is given of the history of use and failures of rocker bearings from nineteenth-century railroad bridges to US highway bridges with tall and slender rocker bearings that date from the late 1950s.

English

This is part two of the paper on conceptual design of an engine valve. The previous paper describes the background and the need of an engine valve for an internal combustion engine. The present state of the engine valve technology and the innovations incorporated in its design has been described. This paper presents the conceptualization of an innovative valve train aiming at lesser number of components, reduction in friction and wear, proper sealing, and trimming down pumping losses. Various geometric designs of valve trains have been detailed and compared. Finally a convolution based poppet valve mechanism, which is free from numerous mechanical elements like camshaft, cam, push rod, rocker arm and rocker bearing has been recommended. Finite element analysis of convoluted spring has been carried out to ascertain safe limits in terms of stresses and achieving desirable valve lift. Magnetorheological fluid and electromagnet are used to vary the valve-lift.

Impact of bearing plates dimensions on interaction of mine workings support and rock mass

Abstract The aim of the research presented in this article is to assess the impact of bearing plates dimensions on the interaction of steel arch support and rock mass. The analysis of the bearing plates was based on laboratory tests and numerical calculations using the FLAC3D program (a finite difference method) and the strain-hardening/softening model based on prescribed variations of Mohr–Coulomb properties. The article presents the results of laboratory tests on selected bearing plates and the results of numerical analysis of the interaction between the bearing plates and rock mass with coal, clay stone and sandstone properties.