Investigation of block foundations resting on soil–rock and rock–rock media under coupled vibrations

In the present study,the dynamic response of block foundations of different equivalent radius to mass(R_o/m) ratios under coupled vibrations is investigated for various homogeneous and layered systems.The frequency-dependent stiffness and damping of foundation resting on homogeneous soils and rocks are determined using the half-space theory.The dynamic response characteristics of foundation resting on the layered system considering rock-rock combination are evaluated using finite element program with transmitting boundaries.Frequencies versus amplitude responses of block foundation are obtained for both translational and rotational motion.A new methodology is proposed for determination of dynamic response of block foundations resting on soil-rock and weathered rock-rock system in the form of equations and graphs.The variations of dimensionless natural frequency and dimensionless resonant amplitude with shear wave velocity ratio are investigated for different thicknesses of top soil/weathered rock layer.The dynamic behaviors of block foundations are also analyzed for different rock-rock systems by considering sandstone,shale and limestone underlain by basalt.The variations of stiffness,damping and amplitudes of block foundations with frequency are shown in this study for various rock—rock combinations.In the analysis,two resonant peaks are observed at two different frequencies for both translational and rotational motion.It is observed that the dimensionless resonant amplitudes decrease and natural frequencies increase with increase in shear wave velocity ratio.Finally,the parametric study is performed for block foundations with dimensions of 4 m × 3 m × 2 m and 8m×5m×2m by using generalized graphs.The variations of natural frequency and peak displacement amplitude are also studied for different top layer thicknesses and eccentric moments.     

Compression–shear strength criterion of coal–rock combination model considering interface effect

Surrounding rocks around coal tunnel in western mining area of China are typical composite structures composed of weakly cemented soft rock and hard coal, and the tunnel stability is closely related to the overall mechanical behavior of the combination body. The equivalent homogeneous model of coal–rock combination body and its stress state expressions were firstly established based on the strain energy equivalency principle. Then, the general compression–shear failure criterion of the equivalent model which takes into account the cohesive strength of the interface between coal and soft rock was derived by assuming that the yielded mediums all met Mohr–Coulomb criterion. Furthermore, accuracy of the proposed analytical model was verified by carrying out laboratory test for coal-mudstone specimen, and it found that the theoretical results were in good agreement with the test values. Strength of the combination body lies between the strong body and weak body. Finally, the effects of interface cohesion strength, rock thickness and stress level on the failure behavior of combination model were analyzed based on the analytical model. Results show that the proposed model not only contains the classical sliding failure theory for two-dimensional weak plane presented by Jaeger, but also reflect strength behavior of a more complex composite model composed of different rock mediums and structural plane. Thus, the analytical model provides theoretical basis for further studying the mechanical behavior of coal–rock combination model.     

Behaviour of beam–column joints made of recycled-aggregate concrete under cyclic loading

In this work, a recycled-aggregate concrete (RAC) was prepared by replacing 30% virgin with recycled concrete aggregate coming from an industrial crushing plant in which concrete from building demolition is suitably treated. A reference concrete was also prepared by using 100% virgin aggregate with the same workability and strength class. Concrete specimens were manufactured for evaluating compressive, tensile, flexural and bond strengths with reinforcing steel bars, as well as static elastic modulus to assess RAC suitability for structural use. The behaviour of beam–column joints (scale of 2–3) made of reinforced concrete and subjected to cyclic loading was also studied. The results obtained gave experimental evidence of the suitability of RAC for structural use.     

Structural damage and shear performance degradation of fiber–lime–soil under freeze–thaw cycling

The freeze–thaw cycling damages the soil structure, and the shear performance of soil are degraded. A series of tests on lime–soil(L–S) and fiber–lime–soil(F–L–S), including freeze–thaw test, the triaxial compression test, nuclear magnetic resonance (NMR) test and scanning electron microscope (SEM) test, were completed. The test results showed that fiber reinforcement changed the stress–strain behavior and failure pattern of soil. The cohesion and internal friction angle of soil gradually decreased with the increase of freeze–thaw cycles (F–T cycles). The pore radius and porosity of soil increased, while the micro pore volume decreased, and the small pore volume, medium pore volume and large pore volume increased, and the large pore volume had a little variation after 10 F–T cycles. The number of pores of F–L–S was less than L–S, demonstrating that the addition of fiber helped to reduce the pore volume. The interweaved fibers limited the development and the connection of cracks. By means of the spatial restraint effect of fiber on the soil and the friction action between fiber and soil, the shear performances and freeze–thaw durability of F–L–S better were than that of L–S.     

Numerical simulation of performance of near-surface mounted FRP-upgraded beam–column sub-assemblages under cyclic loading

This study deals with the performance of the upgrading schemes for the existing gravity load designed (GLD) reinforced concrete (RC) beam–column sub-assemblages using near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars. In this study, exterior beam–column sub-assemblage of a general RC-framed structure has been considered. Numerical investigations of the sub-assemblages have been carried out under cyclic loading using nonlinear finite element analysis. Experimentally validated numerical models have been used for evaluating the performance of various upgrading schemes using NSM bars. Cyclic behaviour of reinforcement, concrete modelling based on fracture energy, bond–slip relations between concrete and steel reinforcement have been incorporated. The study also includes numerical investigation of crack and failure patterns, ultimate load-carrying capacity, strain comparisons and formation of plastic hinges, load–displacement hysteresis, energy dissipation and ductility. Seismic performance in terms of energy dissipation and development of strain in beam bar shows that some of the upgraded schemes are found to be comparable to the seismically designed ductile specimens. The findings of this study would be helpful to the practising and design engineers for developing detailing criteria for newly designed – or strengthening of deficient – reinforced concrete structure.     

Shear properties and pore structure characteristics of soil–rock mixture under freeze–thaw cycles

Bulletin of Engineering Geology and the Environment - Soil–rock mixtures (S-RMs) are widely distributed in the shallow surfaces of cold regions that experience frequent freeze–thaw...     

Development of upgradation schemes for gravity load designed beam–column sub-assemblage under cyclic loading

In this paper, it is attempted to upgrade the poor gravity load designed (‘GLD’) exterior beam–column sub-assemblage for improving the seismic performance. Three different upgradation schemes have been proposed for ‘GLD’ sub-assemblage under seismic loading. In all three schemes, shear upgradation was carried out by using GFRP wrapping, and joint region was upgraded by using steel plate jacketing with through–through steel bolts. For flexural upgradation, CFRP fiber and laminates were respectively used in first two schemes. Third upgradation scheme was similar to that proposed in the first scheme but limited to the D-region (disturbed region) only. Before implementing the upgradation schemes, proper surface treatment on original specimens were carried out. First, the original ‘GLD’ and target ‘ductile’ sub-assemblages were experimentally investigated under reserve cyclic loading. Thereafter, the upgraded sub-assemblages were investigated under same cyclic load history as that was opted for ‘GLD’ one. Specimen details considered, materials used, execution procedure for upgradation adopted and experimental investigation carried out are discussed in step by step. It was observed from the investigation that the ‘GLD’ specimen seized to function under reserve loading and the lack in proper anchorage of beam bottom reinforcement formed a huge crack at the joint face. Under reverse cyclic loading, it was found that the upgraded specimens showed a considerable improvement in seismic performance. Further, the CFRP laminate based upgraded specimen showed better performance over the CFRP fiber based one and the plastic hinge could be successfully shifted from the joint zone to a predefined location.     

Multiaxial tensile–compressive strengths and failure criterion of plain high-performance concrete before and after high temperatures

Multiaxial tensile–compressive tests were performed on 100 mm × 100 mm × 100 mm cubic specimens of plain high-performance concrete (HPC) at all kinds of stress ratios after exposure to normal and high temperatures of 20, 200, 300, 400, 500, and 600 °C, using a large static–dynamic true triaxial machine. Friction-reducing pads were three layers of plastic membrane with glycerine in-between for the compressive loading plane; the tensile loading planes of concrete samples were processed by attrition machine, and then the samples were glued-up with the loading plate with structural glue. The failure mode characteristic of specimens and the direction of the crack were observed and described, respectively. The three principally static strengths in the corresponding stress state were measured. The influence of the temperatures, stress ratios, and stress states on the triaxial strengths of HPC after exposure to high temperatures were also analyzed respectively. The experimental results showed that the uniaxial compressive strength of plain HPC after exposure to high temperatures does not decrease completely with the increase in temperature, the ratios of the triaxial to its uniaxial compressive strength depend on brittleness–stiffness of HPC after different high temperatures besides the stress states and stress ratios. On this basis, the formula of a new failure criterion with the temperature parameters under multiaxial tensile–compressive stress states for plain HPC is proposed. This study is helpful to reveal the multiaxial mechanical properties of HPC structure enduring high temperatures, and provides the experimental and theory foundations (testing data and correlated formula) for fire-resistant structural design, and for structural safety assessment and maintenance after fire.     

Neural network using the Levenberg–Marquardt algorithm for optimal real-time operation of water distribution systems

ABSTRACT

This paper proposes an Adaptive Neural Network (NN) controller for the real-time pressure control in water distribution systems. Pressure control is one of the main technical options that can be implemented by a water utility to increase the hydraulic and energy efficiency of systems. The network adopted the Levenberg–Marquardt backpropagation algorithm, being responsible for maintaining the pump head at an optimal value, eliminating the excess pressure of the system. The advantage of the approach is that, once the network is trained, it allows instantaneous evaluation of solutions at any desired number of points; thus, spending little computing time. The controller was applied in the experimental setup, and the results showed excellent performance regarding pressure regulation. Finally, it is expected that the NN controller can be easily implemented in similar water distribution systems.     

Correction to: Shear properties and pore structure characteristics of soil–rock mixture under freeze–thaw cycles

Bulletin of Engineering Geology and the Environment - A Correction to this paper has been published: https://doi.org/10.1007/s10064-021-02169-7     

Mechanical behavior and decay model of the sandstone in Urumqi under coupling of freeze–thaw and dynamic loading

Bulletin of Engineering Geology and the Environment - In cold regions, recurrent freeze–thaw action and loading conditions are important factors affecting the long-term durability of natural...     

Limit analysis of collapse mechanisms in cavities and tunnels according to the Hoek–Brown failure criterion

The reliable prediction of the state of collapse in tunnels and natural cavities is still one of the most difficult tasks in rock engineering. By making reference to the Hoek–Brown failure criterion, an exact solution is presented in the realm of plasticity theory with the help of classical tools of the calculus of variations. The resulting formulae are extremely simple and can be very useful to make comparisons with empirical methods and numerical analyses. Examples by means of some widely used software packages are also provided and discussed.     

Dynamic analysis of liquid storage tank under blast using coupled Euler–Lagrange formulation

A growing number of terror attacks all over the world have become a threat to the human civilization. In the last two decades, bomb blasts in crowded business areas, underground railway stations and busy roads have taken numerous lives and destroyed properties in different parts of the world. However, blast response of many important civil infrastructures has still not been well understood due to the complexities in their material behavior, loading and higher nonlinearities. One such example of important civil infrastructure is liquid storage tanks which are undividable parts of any society for storage of water, milk, liquid petroleum, chemicals in industries etc. Blast loading on liquid storage structures may lead to disaster due to water and milk crisis, health hazard owing to the spread of chemicals and fire hazard due to the spread of liquid fuel. Hence, understanding the dynamic behavior of liquid storage structures under blast loading through numerical simulations is of utmost importance. In the present study, three dimensional (3D) finite element (FE) simulations of a steel water storage tank for different tank aspect ratios, percentages of water stored in the tank, tank wall thicknesses, boundary conditions at the bottom of the tank and magnitudes of blast loading have been performed using the FE software Abaqus. The coupled Euler–Lagrange (CEL) formulation in Abaqus has been adopted herein which has the advantage of considering the coupling of structural mechanics and fluid mechanics fundamental equations. The maximum hoop stress and shear stress in the tank wall, the water sloshing heights in tanks and the energy response of the tanks have been studied. It is observed that stresses and liquid sloshing heights in the tank increase with decreasing scaled distance of the explosive material and increasing aspect ratio, i.e. height to radius ratio.     

Correlation of the Hoek–Brown failure criterion for a sparsely jointed rock mass with an extended plane of weakness theory

An appropriate estimate of rock mass strength is necessary for the design of civil and mining structures built in or on rock. Rock mass is an inhomogeneous and anisotropic material with complex behaviour, which contains random planes of discontinuities that tend to reduce its strength. The direct estimation of this strength is practically unfeasible, due to difficulties in sampling and testing. This has led to the development of empirical failure criteria. These, express the strength of the rock mass in terms of properties of the intact rock and the discontinuities. The Hoek–Brown criterion is the most widely accepted one. However, albeit its use for many years, no experimental in situ validation with the actual rock mass strength has been demonstrated. Therefore, the Hoek–Brown criterion is investigated analytically through an extended plane of weakness theory, already validated with experimental evidence on physical specimens. Various intact rock qualities with blocky and very blocky structure are examined. The results indicate deviations in the rock mass strength predicted by the two approaches, especially when the intact rock strength is low.     

Investigation of geotextile–soil interaction under a cyclic vertical load using the discrete element method

Geotextiles are often used in roadway construction as separation, filtration, and reinforcement. Their performance as reinforcement in geotextile-reinforced bases depends on geotextile–soil interaction. This paper investigates the geotextile–soil interaction under a cyclic wheel load using the Discrete Element Method (DEM). In this study, soil was modeled as unbonded particles using the linear contact stiffness model, and the geotextile was modeled as bonded particles. The micro-parameters of the soil and the geotextile were determined using biaxial tests and a tensile test, respectively. The influence of the placement depth and the stiffness of the geotextile on the performance of the reinforced base was investigated. The DEM results show that the depth of the geotextile significantly affected the degree of interaction between the geotextile and the soil. Under the applied cyclic vertical load, the geotextile developed a low tensile strain. The effect of the stiffness of the geotextile on the deformation was more significant when the geotextile was placed at a shallower location than when placed at a deeper location.     

Investigation into the effects of grain size on strength and failure behaviors of granites using a breakable polygonal grain–based model

Bulletin of Engineering Geology and the Environment - The microstructure of rock is one of the most important factors that affect its mechanical behaviors. In order to study the effects of grain...     

Strength and behavior of steel plate–concrete wall structures using ordinary and eco-oriented cement concrete under axial compression

The main objectives of this study are to describe the compressive behavior and to determine the squash load of steel plate–concrete (SC) wall structures using ordinary and eco-oriented cement concrete. The major parameters in this research were the material of the concrete and width–thickness (B/t) ratio of surface steel plate. Six SC wall specimens were tested in compression in this test. In the three specimens, to reduce emissions of carbon dioxide (CO₂), some of the cement in weight was replaced by the Hwangtho (red clay) which is traditional and environmental material. The failure behavior, buckling behavior of the surface steel plate, the effective buckling length factors and plate buckling coefficient are discussed. Based on the test results, simplified rule was suggested to evaluate the buckling stress for surface steel plate. Several comparisons were made to evaluate the predicted strengths and test results.     

Investigation on combustion of fire retardant board under different N2–O2 mixture gas atmospheres by using thermogravimetric analysis

By thermogravimetric analysis (TGA) and kinetic study, the thermal decomposition and combustion processes of a fire retardant board were investigated under different N₂–O₂ mixture gas atmospheres, with 20%, 15%, 10% and 5% oxygen, respectively. The samples were heated from 373 K to 1223 K with a constant heating rate of 30 K/min. The trend of the thermogravimetry (TG) curves and derivative thermogravimetry (DTG) curves were interpreted regarding the conversion yields and the reactivity of samples. There are nine reaction stages which are discernible easily from DTG curves for samples under different gas atmospheres. Each sample’s top value among maximum mass loss rates of all reaction stages appears during reaction 4 stage. The reaction orders and apparent activation energies of all samples during all reaction stages vary between 1.4 and 4.0 and between 7.358 kJ/mol and 535.555 kJ/mol.     

Study on the seepage characteristics and degradation mechanism of a single-jointed sandstone under the cyclic dry–wet process in the Three Gorges reservoir

Bulletin of Engineering Geology and the Environment - The hydro-fluctuation belt is the most sensitive part of the reservoir bank slope. The rock mass in the hydro-fluctuation belt has been...