Abnormal stresses in underground pipeline due to static and dynamic reversal of several foundation blocks

The article discusses the issues of forecasting the strength of underground pipelines laid in seismically active areas through sections composed of relatively rigid moving blocks. In such dangerous areas, in addition to the normal pressure load of the transported product, the pipe is subjected to additional effects from the movements of the fragments of the block foundation. As the literature data show, the problems of the influence of the interaction of faults on the stress state of the pipeline have not yet been studied. The aim of the study is to develop a model for the analysis of abnormal stresses in the underground pipeline on a damaged foundation caused by static or time-harmonic reciprocal turns of the blocks around the axis of the pipe on both sides of several faults. Static equilibrium and harmonic oscillations of the pipeline are investigated in a linear setting, modelling it with a rod with an annular cross section. The inertia of the transported product is not taken into account. To consider the issues of the ultimate equilibrium of the pipe, the momentless theory of shells and the energy theory of strength are used. The soil backfill is considered as Winkler’s elastic layer. Multiple damages to the solid foundation are presented in the form of several faults on which there is a rupture of the angle of rotation around the axis of the pipe. We formulated boundary value problems for differential equations of static torsion and torsional harmonic oscillations with discontinuous right-hand sides. Based on the analytical solutions of these problems for the cases of antisymmetric and symmetrical reversal of the foundation blocks, the distributions of the torsion angle and equivalent stress in the pipe, depending on the distance between faults and the frequency of forced oscillations of the system, are investigated.

Low-index Catastrophe Model of Deep Gas-bearing Coal Seams

Coal and gas outburst always occur as some parameters reach its threshold in the mining process of gas-bearing coal seams. However, low-index catastrophes may happen in the deep mining although the parameters do not exceed its threshold values. This phenomenon has become a challenge for our traditional cognitions. In this paper, the mechanism of low-index catastrophes of high-stress area in the deep gas-bearing seams was investigated by the following methods including literature reviewing, on-site investigation, case analysis, physical experiments and theoretical analysis. The results indicate that there were not only primary state fissures but also many secondary fissures are formed after taking outburst eliminating measures, which is beneficial for improving the desorption performance of methane. A “three-zone” theory of gas migration in Coal Seams is given, coal seam in the front of coal mining face can be divided into three zones: the gas emission zone, the gas channel compaction zone, and disturbance gas desorption zone before reaching ultimate equilibrium, corresponding to coal and gas ejection zone, gas migration zone and gas launching zone after surpassing the limits. Importantly, the stress dike is redefined, and a new concept is proposed that the low-index catastrophe of gas bearing seams is caused by avalanche instability of the stress dikes, meanwhile its three modes are given by over static-load stress dike avalanche caused by hanging arch overlength, stress dike avalanche under roof breakage impact, and stress dike avalanche under floor breakage impact. In deep stress area, stress dike avalanche caused by dynamic-static loading could lead to low-index catastrophes of gas bearing seams. The insufficient residual gas energy could cause unusual gas emission. On the other hand, the sufficient gas energy may lead to coal and gas outbursts.

METHODOLOGICAL ASPECTS OF ASSESSING THE STEEL FRAMES RELIABILITY

The article highlights the proposed algorithm for evaluating the reliability of steel frames. In particular, it is possible to analyze the reliability of the most likely failure mechanism. Separate assumptions that determine the sequence of application ofthe limit equilibrium method are presented. A method for determining the reliability of statically indeterminate steel framesin the plastic stage is presented. This method provides an opportunity to determine the probable mechanism of destruction.The ultimate equilibrium method is used to calculate the forces at the final stage of destruction. In the work, the real mechanism of destruction is understood as a mechanism for which the work of external forces to create it is the least. It is revealedthat the real mechanism of destruction is approaching the beam or floor elementary mechanism.

RESULTS OF EXPERIMENTAL RESEARCH OF THE REINFORCED CONCRETE SHELL-SLAB

Introducton. The paper demonstrates the results of experimental research of the reinforced concrete shell-slab under the action of vertical uniformly distributed load. The authors also present the comparison of such research results with the results of stress-strain state evaluation performed in the “Lira” software package.Materials and methods. The authors tested the reinforced concrete model representing physically similar copy with the 1:5 scale coefficients by general size, and by separate details. The load was applied in 10–15% doze of the theoretical bearing capacity of the plate.Results. The authors calculated the experimental transverse stress σх,3,exp, which was in full-scale construction and in the 3 central sphere. The authors also made the comparison of such transverse stress with theoretical transverse stresses σх,3,teor and the comparison was performed in the “Lira” program complex. The diagrams of the above stresses were well matched by outlines and values.Discussion and conclusions. As a result, the experimental (σx, 3,exp.) and theoretical (σx,3,theor.) stresses are compressive near the shell-slab center. Its maximum stress values (σx, 3, exp) reach x/b=0,5 at a point with a relative coordinate, and the stress (σx,3,theor.) – x/b ≈ 0,45.The zero voltage values σx,3,exp. reach a quarter of the shelf width, theoretical stress –with x/b ≈ 0,3 mm ratio.Maximum values of experimental and theoretical tensile stresses σx, 3 reach x/b ≈ 0,15 ratio. Therefore, the values are close to each other, and do not exceed the standard concrete tensile resistance Rbt, ser.The practical significance of the study is to obtain experimental evidence of the abandoning possibility of the horizontal transverse reinforcement of the shelf, which would reduce the complexity and cost of the investigated structures production.The prospects conclude in:research of the shell-slab operation at the stage of ultimate equilibrium;research of the shell-slab crack resistance and stiffness at all stages of its operation;research of the shell-slab operation taking into account the fixation in the transverse direction of its longitudinal contour edges along entire length.

SET OF EQUATIONS OF AFEM AND PROPERTIES OF ADDITIONAL FINITE ELEMENTS

The paper considers the action of additional finite elements on the main set of linear equations when developed Additional Finite Element Method (AFEM) is used for analysis of structures with several nonlinear properties at limit states and failure models. AFEM is a variant of Finite Element Method (FEM) which adds to traditional sequence of solution of problem by FEM the units of two well-known methods of structural analysis: method of additional loads and method of ultimate equilibrium. AFEM suggests the additional finite elements and additional design diagrams for gradually transformation of the main set of equilibrium equations at the first step of loading to this set at the last one according to ideal failure model of structure.

Temporal Evolution of Seabed Scour Induced by Darrieus-Type Tidal Current Turbine

The temporal evolution of seabed scour was investigated to prevent damage around a monopile foundation for Darrieus-type tidal current turbine. Temporal scour depths and profiles at various turbine radius and tip clearances were studied by using the experimental measurements. Experiments were carried out in a purpose-built recirculating water flume associated with 3D printed turbines. The scour hole was developed rapidly in the initial process and grew gradually. The ultimate equilibrium of scour hole was reached after 180 min. The scour speed increased with the existence of a rotating turbine on top of the monopile. The findings suggested that monopile foundation and the rotating turbine are two significant considerations for the temporal evolution of scour. The scour depth is inversely correlated to the tip-bed clearance between the turbine and seabed. Empirical equations were proposed to predict the temporal scour depth around turbine. These equations were in good agreement with the experimental data.

Dichotomy Slope Optimization Design Methods Based on the Method of Bisection and CSF Technology

The Based on the analysis method of bisection, the critical slip field technology and the residual thrust method of slope ultimate equilibrium,the functional relationship between the slope angle θ and maximum residual thrust Pmax is established. As it can determine the θ value increment size and value range according to identify the positive and negative of equation P=f(θ); then by means of the searching for calculation and discrimination of system,it ultimately can solve the numerical solution of Pmax=0 in a limited height ,security status and engineering geological conditions and find the limit slope angle θ*. Thus it can deal with the open-air high and steep slope optimization design, and simultaneously resolve the design the technology of landslide treatment and the optimization program ,At the same time it has engineering application value.

Study on the Ultimate Pullout Force of Prestressed Cable Based on Triple Shear Unified Yield Criterion

Based on the triple shear unified yield criterion and the ultimate equilibrium principle, the ultimate pullout force of prestressed cable is studied. The ultimate pullout force of prestressed cable is related to the rock type, the shapes of rapture surface, grouting pressures and compressive strength of rock, etc. The results show that the intermediate principal stress effect parameter b have influences on the ultimate pullout force of prestressed cable. With the increase of the intermediate principal stress effect parameter b, the ultimate pullout force of prestressed cable increases too. When the grouting pressure increases, the ultimate pullout force of prestressed cable increases also.

Analysis of the Influences of Matric Suction of Unsaturated Soil on the Slope Stability

There is suction in unsaturated soil. This is the most obvious difference between unsaturated soil and saturated soil. It is very difficult to measure it, so research has always been done without account of the influences of matric suction of unsaturated soil. In this paper, based on the test result of engineering characteristics of unsaturated soil from Yellow River Embankments, the stability of slope of Yellow River Embankments is analyzed using ultimate equilibrium method and the influencing rule of matric suction on slope is advanced.