In order to improve the surface hardness and wear resistance of magnesium, Al-13%Si (mass fraction) alloy coating was deposited on pure magnesium by droplet spraying process. The microstructure was studied by electron probe microanalysis and X-ray diffraction. The micro-hardness and wear resistance of coating were investigated in comparison with those of the substrate. It is found that the coating layer is composed of α-Al cellular due to rapid solidification. Formation mechanism of the coating is due to the obstruction of diffusion by in-situ formed Mg2Si in interfacial layer. The coating exhibits higher hardness compared to that of the Mg substrate. As result of its high hardness, the wear resistance of the coating layer is about ten times that of the substrate. The droplet spraying process demonstrates that the magnesium surface can be strengthened by using the existing Al-Si alloys.
Indirect extrusion of Mg-10%Sn (mass fraction) alloys was performed at three different working temperatures. The effect of working temperature on the microstructure, texture and tensile properties of the extruded alloys was investigated by optical microscope (OM), scanning electronic microscope (SEM), X-ray diffraction (XRD) and a standard universal testing machine. Grain size, area fraction of second phase particles and texture of the alloys are found to be significantly influenced by working temperature. The grain size refinement is greatly dependent on processing conditions with the low working temperature being the most effective. While the high working temperature results in a coarser grain size and a stronger fiber texture and the reason for this phenomenon was examined in terms of second phase particle, grain type and dynamic recrystallization mechanism. Tested in the different conditions, the tensile strengths of the Mg-10Sn alloys extruded at the high working temperature are remarkably better than those of the other studied alloys. This significant improvement in tensile properties is mainly due to the particle strengthening and texture strengthening resulted from the more and finer primary dispersed particles and stronger texture, respectively.
In order to simulate the stress of turbine rotor in aeroengine, based on the ANSYS, the simplification model of the turbine rotor was built up. By applying the simplification model, the contact stress of turbine rotor was computed. The maximum contact stress appears at the chamfer below the flank, which agrees with experiment result. At the same time, the contact stress changing with the flank angle and friction coefficient was calculated, The results show that the contact stress in the flank increases slowly with the increase of flank angle; with the friction coefficient increasing, the contact stress in flank length decreases; the contact stress will not change when the friction coefficient is over 0.25.
The controlling step and the extraction reaction rate equation of zinc extraction from Zn(II)-NH3 solution by using a newly synthesized organic compound, 2-acetyl-3-oxo-dithiobutyric acid-myristyl ester as the zinc extractant, were clarified. The effects of agitation speed, specific interfacial area, temperature, extractant concentration and Zn ion concentration on the extraction rate are studied in constant interfacial area cell. The results show that the extraction rate depends on interfacial chemical reaction and diffusion by using this new extractant to extract zinc, and the apparent activation energy of this extraction reaction is measured as 28.2 kJ/mol, which demonstrates that the extraction reaction is controlled by the mixed-controlled reaction rate. The apparent reaction orders a and b are measured as 1 and 0.38, and the constant k0 is 138.70. So, when extraction conditions are controlled as [HR]=20%–50%, T=0–30 °C, N=120–177 r/min and S=72.6–127.5 m−1, the solvent extraction reaction rate can be depicted as
Hot rolled strip requires diverse and flexible control of cooling path in order to take full advantages of strengthening mechanisms such as fine grain strengthening, precipitation strengthening, and transformation strengthening, adapting to the development of advanced steel materials and the requirement of reduction-manufacturing. Ultra fast cooling can achieve a great range of cooling rate, which provides the means that the hardened austenite obtained in high temperature region can keep at different dynamic transformation temperatures. Meanwhile, through the rational allocation of the UFC (ultra fast cooling) and LFC (laminar flow cooling), more flexible cooling path control and cooling strategy of hot rolled strip are obtained. Temperature distribution and control strategies under different cooling paths based on UFC are investigated. The process control temperature can be limited within 18 °C, and the mechanical properties of the steels get a great leap forward due to the cooling paths and strategies, which can decrease costs and create great economic benefits for the iron and steel enterprises.
The production of environmental friendly emulsion paint is of great significance. Vacuum steam stripping of methyl isobutyl ketone (MIBK) and methyl ethyl ketone (MEK) from cathodic electrophoretic emulsion was studied. The effects of mass ratio of vapor to feed (V/F), vacuum degree and feed temperature on removal rate of MIBK and MEK, emulsion size and solid volume fraction of the emulsion were investigated, and the removal of MIBK and MEK from cathodic electrophoretic emulsion by vacuum desorption was also studied. The results show that removal rates of both MIBK and MEK increase with the increase of V/F, vacuum degree and feed temperature. Removal rates of MIBK and MEK are 98.3% and 93.6%, respectively, at the operating condition V/F of 0.7, feed temperature of 27 °C and vacuum degree of 90 kPa. The emulsion size of cathodic electrophoretic emulsion increases slightly with feed temperature when temperature is below 42 °C, and increases rapidly with feed temperature when temperature is above 42 °C. Solid volume fraction increases by 10% as vacuum degree increases from 0 to 90 kPa at V/F of 0.7 and feed temperature of 27 °C. Compared with vacuum desorption, vacuum steam stripping can get a higher removal rate of MIBK and MEK under the same feed flow, vacuum degree and feed temperature.
To avoid the machine problems of excessive axial force, complex process flow and frequent tool changing during robotic drilling holes, a new hole-making technology (i.e., helical milling hole) was introduced for designing a new robotic helical milling hole system, which could further improve robotic hole-making ability in airplane digital assembly. After analysis on the characteristics of helical milling hole, advantages and limitations of two typical robotic helical milling hole systems were summarized. Then, vector model of helical milling hole movement was built on vector analysis method. Finally, surface roughness calculation formula was deduced according to the movement principle of helical milling hole, then the influence of main technological parameters on surface roughness was analyzed. Analysis shows that theoretical surface roughness of hole becomes poor with the increase of tool speed ratio and revolution radius. Meanwhile, the roughness decreases according to the increase of tool teeth number. The research contributes greatly to the construction of roughness prediction model in helical milling hole.
The accurate measurement of kinematic parameters in satellite separation tests has great significance in evaluating separation performance. A novel study is made on the measuring accuracy of monocular and binocular, which are the two main vision measurement methods used for kinematic parameters. As satellite separation process is transient and high-dynamic, it will bring more extraction errors to the binocular. Based on the design approach of intersection measure and variance ratio, the monocular method reflects higher precision, simpler structure and easier calibration for level satellite separation. In ground separation tests, a high-speed monocular system is developed to gain and analyze twelve kinematic parameters of a small satellite. Research shows that this monocular method can be widely applied for its high precision, with position accuracy of 0.5 mm, speed accuracy of 5 mm/s, and angular velocity accuracy of 1 (°)/s.
After reviewing three different definitions of mode field diameter of single-mode fibers, coupled efficiency calculation methods associated with lateral offset, longitude separation and wavelength, the effects produced by them, and the influences of splicing defects were discussed in detail. The regularities of the effects were studied according to the first order derivation of couple efficiency formula, and a simplified formula for couple efficiency calculation was presented under the circumstance of slight misalignment, with respect to wavelength, λ, and in a good agreement with the theoretical model. The simplified formula provides a new but simple approach to evaluate wavelength dependent couple efficiency of single-mode fibers. Theoretical analyses and numerical calculations show that, when those defects exist, the wavelength produces additional effects on the couple loss that growth of wavelength causes an increase on the couple efficiency for the lateral offset or longitude separation whereas lessens the couple efficiency due to angular misalignment or mode fields mismatching, and that the wavelength degrades the couple efficiency distinctly when λ ≥ 2.5 μm whereas it distorts the couple slightly in range of λc≤λ≤2 μm.
The design and optimization of a self-complementary two-arm Archimedean spiral antenna backed by an absorptive cavity were presented. Parametric studies on the proposed antenna structure were carried out by using CST MWS. Simulation results show that the proper choice of spiral turns and cavity depth can miniaturize the dimensions of the cavity-backed spiral antenna presented here. According to simulation results, prototype antennas operating in the 6–12 GHz band are fabricated and the dimension of the proposed cavity-backed spiral antenna is 22 mm (diameter)×15 mm (height). The performance of the proposed antenna was measured and compared with the simulation results. It is shown that the experimental results are consistent with the theoretical predictions and the suggested antenna is good enough to adapt for various wideband applications.
An adaptive method of residual life estimation for deteriorated products with two performance characteristics (PCs) was proposed, which was sharply different from existing work that only utilized one-dimensional degradation data. Once new degradation information was available, the residual life of the product being monitored could be estimated in an adaptive manner. Here, it was assumed that the degradation of each PC over time was governed by a Wiener degradation process and the dependency between them was characterized by the Frank copula function. A bivariate Wiener process model with measurement errors was used to model the degradation measurements. A two-stage method and the Markov chain Monte Carlo (MCMC) method were combined to estimate the unknown parameters in sequence. Results from a numerical example about fatigue cracks show that the proposed method is valid as the relative error is small.
Most of the developed immune based classifiers generate antibodies randomly, which has negative effect on the classification performance. In order to guide the antibody generation effectively, a decision hyper plane heuristic based artificial immune network classification algorithm (DHPAINC) is proposed. DHPAINC taboos the inner regions of the class domain, thus, the antibody generation is limited near the class domain boundary. Then, the antibodies are evaluated by their recognition abilities, and the antibodies of low recognition abilities are removed to avoid over-fitting. Finally, the high quality antibodies tend to be stable in the immune network. The algorithm was applied to two simulated datasets classification, and the results show that the decision hyper planes determined by the antibodies fit the class domain boundaries well. Moreover, the algorithm was applied to UCI datasets classification and emotional speech recognition, and the results show that the algorithm has good performance, which means that DHPAINC is a promising classifier.
To get better tracking performance of attitude command over the reentry phase of vehicles, the use of state-dependent Riccati equation (SDRE) method for attitude controller design of reentry vehicles was investigated. Guidance commands are generated based on optimal guidance law. SDRE control method employs factorization of the nonlinear dynamics into a state vector and state dependent matrix valued function. State-dependent coefficients are derived based on reentry motion equations in pitch and yaw channels. Unlike constant weighting matrix Q, elements of Q are set as the functions of state error so as to get satisfactory feedback and eliminate state error rapidly, then formulation of SDRE is realized. Riccati equation is solved real-timely with Schur algorithm. State feedback control law u(x) is derived with linear quadratic regulator (LQR) method. Simulation results show that SDRE controller steadily tracks attitude command, and impact point error of reentry vehicle is acceptable. Compared with PID controller, tracking performance of attitude command using SDRE controller is better with smaller control surface deflection. The attitude tracking error with SDRE controller is within 5°, and the control deflection is within 30°.
The optimal transmission lines assignment with maximal reliabilities (OTLAMR) in the multi-source multi-sink multi-state computer network (MMMCN) was investigated. The OTLAMR problem contains two sub-problems: the MMMCN reliabilities evaluation and multi-objective transmission lines assignment optimization. First, a reliability evaluation with a transmission line assignment (RETLA) algorithm is proposed to calculate the MMMCN reliabilities under the cost constraint for a certain transmission lines configuration. Second, the non-dominated sorting genetic algorithm II (NSGA-II) is adopted to find the non-dominated set of the transmission lines assignments based on the reliabilities obtained from the RETLA algorithm. By combining the RETLA and the NSGA-II algorithms together, the RETLA-NSGA II algorithm is proposed to solve the OTLAMR problem. The experiments result show that the RETLA-NSGA II algorithm can provide efficient solutions in a reasonable time, from which the decision makers can choose the best solution based on their preferences and experiences.
In order to solve discrete multi-objective optimization problems, a non-dominated sorting quantum particle swarm optimization (NSQPSO) based on non-dominated sorting and quantum particle swarm optimization is proposed, and the performance of the NSQPSO is evaluated through five classical benchmark functions. The quantum particle swarm optimization (QPSO) applies the quantum computing theory to particle swarm optimization, and thus has the advantages of both quantum computing theory and particle swarm optimization, so it has a faster convergence rate and a more accurate convergence value. Therefore, QPSO is used as the evolutionary method of the proposed NSQPSO. Also NSQPSO is used to solve cognitive radio spectrum allocation problem. The methods to complete spectrum allocation in previous literature only consider one objective, i.e. network utilization or fairness, but the proposed NSQPSO method, can consider both network utilization and fairness simultaneously through obtaining Pareto front solutions. Cognitive radio systems can select one solution from the Pareto front solutions according to the weight of network reward and fairness. If one weight is unit and the other is zero, then it becomes single objective optimization, so the proposed NSQPSO method has a much wider application range. The experimental research results show that the NSQPS can obtain the same non-dominated solutions as exhaustive search but takes much less time in small dimensions; while in large dimensions, where the problem cannot be solved by exhaustive search, the NSQPSO can still solve the problem, which proves the effectiveness of NSQPSO.
Security vulnerability of denial of service (DoS) in time out-medium access control (T-MAC) protocol was discussed and analysis of power consumption at each stage of T-MAC protocol was carried out. For power efficient authentication scheme which can provide reliability, efficiency, and security for a general T-MAC communication, a novel synchronization and authentication scheme using authentication masking code was proposed. Authentication data were repeated and masked by PN sequence. The simulation results show that the proposed approach can provide synchronization and authentication simultaneously for nodes in wireless sensor network (WSN). 63 bits AMC code gives above 99.97% synchronization detection and 93.98% authentication data detection probability in BER 0.031 7.
Although the modified Goldstein filter based on the local signal-to-noise (SNR) has been proved to be superior to the classical Goldstein and Baran filters with more comprehensive filter parameter, its adaptation is not always sufficient in the reduction of phase noise. In this work, the local SNR-based Goldstein filter is further developed with the improvements in the definition of the local SNR and the adaption of the filtering patch size. What’s more, for preventing the loss of the phase signal caused by the excessive filtering, an iteration filtering operation is also introduced in this new algorithm. To evaluate the performance of the proposed algorithm, both a simulated digital elevation model (DEM) interferogram and real SAR deformation interferogram spanning the L’ Aquila earthquake are carried out. The quantitative results from the simulated and real data reveal that up to 79.5% noises can be reduced by the new filter, indicating 9%–32% improvements over the previous local SNR-based Goldstein filter. This demonstrates that the new filter is not only equipped with sufficient adaption, but also can suppress the phase noise without the sacrifice of the phase signal.
As known to all that Hénon chaotic system is not appropriate for generating the key-streams because it has non-uniformly distributed output signal, a new key-stream generation scheme based on Hénon chaotic system is presented. In order to get the key-streams with good statistics and long enough cycle length, a specific method for dividing the Hénon attractor into numerous non-overlapping sub-regions, and a new one-to-one mapping strategy between the divided sub-regions and elements of dynamically generated matrix consisting of 0’s and 1’s are proposed. Experimental results demonstrate that the generated key-streams are with long enough cycle length and very sensitive to the initial values and secret keys. For example, key-streams with the cycle length of 1032 can easily be obtained. Moreover, even if the fluctuation to the initial values or secret keys is as small as 10−14, uncorrelated key-streams will be generated. Experimental results also demonstrate that the generated key-streams have good randomness and they can pass all the standard criteria specified in FIPS PUB 140-2 with no less than 98%.
Globally exponential stability (which implies convergence and uniqueness) of their classical iterative algorithm is established using methods of heat equations and energy integral after embedding the discrete iteration into a continuous flow. The stability condition depends explicitly on smoothness of the image sequence, size of image domain, value of the regularization parameter, and finally discretization step. Specifically, as the discretization step approaches to zero, stability holds unconditionally. The analysis also clarifies relations among the iterative algorithm, the original variation formulation and the PDE system. The proper regularity of solution and natural images is briefly surveyed and discussed. Experimental results validate the theoretical claims both on convergence and exponential stability.
The parametric temporal data model captures a real world entity in a single tuple, which reduces query language complexity. Such a data model, however, is difficult to be implemented on top of conventional databases because of its unfixed attribute sizes. XML is a matured technology and can be an elegant solution for such challenge. Representing data in XML trigger a question about storage efficiency. The goal of this work is to provide a straightforward answer to such a question. To this end, we compare three different storage models for the parametric temporal data model and show that XML is not worse than any other approaches. Furthermore, XML outperforms the other storages under certain conditions. Therefore, our simulation results provide a positive indication that the myth about XML is not true in the parametric temporal data model.
To improve the understanding of the transport mechanism in shale gas reservoirs and build a theoretical basic for further researches on productivity evaluation and efficient exploitation, various gas transport mechanisms within a shale gas reservoir exploited by a horizontal well were thoroughly investigated, which took diffusion, adsorption/desorption and Darcy flow into account. The characteristics of diffusion in nano-scale pores in matrix and desorption on the matrix surface were both considered in the improved differential equations for seepage flow. By integrating the Langmuir isotherm desorption items into the new total dimensionless compression coefficient in matrix, the transport function and seepage flow could be formalized, simplified and consistent with the conventional form of diffusion equation. Furthermore, by utilizing the Laplace change and Sethfest inversion changes, the calculated results were obtained and further discussions indicated that transfer mechanisms were influenced by diffusion, adsorption/desorption. The research shows that when the matrix permeability is closed to magnitude of 10−9 D, the matrix flow only occurs near the surfacial matrix; as to the actual production, the central matrix blocks are barely involved in the production; the closer to the surface of matrix, the lower the pressure is and the more obvious the diffusion effect is; the behavior of adsorption/desorption can increase the matrix flow rate significantly and slow down the pressure of horizontal well obviously.
To improve the energy utilization efficiency of internal combustion (IC) engine, exergy analysis was conducted on a passenger car gasoline engine. According to the thermodynamic theory of IC engine, in-cylinder exergy balance model was built. The working processes of gasoline engine were simulated by using the GT-power. In this way, the required parameters were calculated and then gasoline engine exergy balance was obtained by programming on computer. On this basis, the influences of various parameters on exergy balance were analyzed. Results show that, the proportions of various forms of exergy in gasoline engine from high to low are irreversible loss, effective work, exhaust gas exergy and heat transfer exergy. Effective exergy proportion fluctuates with cylinder volumetric efficiency at full load, while it always increases with break mean effective pressure (BMEP) at part load. Exhaust gas exergy proportion is more sensitive to speed, and it increases with speed increasing except at the highest speed. The lower proportion of heat transfer exergy appears at high speed and high load. Irreversible loss is mainly influenced by load. At part load, higher BMEP results in lower proportion of irreversible loss; at full load, the proportion of irreversible loss changes little except at the highest speed.
Solidification/stabilization (S/S) is one of the most effective methods of dealing with heavy metal contaminated soils. The effects of cyclic wetting and drying on solidified/stabilized contaminated soils were investigated. A series of test program, unconfined compressive strength (UCS) test, TCLP leaching test and scanning electron microscopy (SEM) test, were performed on lead and zinc contaminated soils solidified/stabilized by fly ash. Test results show that UCS and the leaching characteristics of heavy metal ions of S/S contaminated soils are significantly improved with the increase of fly ash content. UCS of S/S soils firstly increases with the increase of the times of drying and wetting cycles, after reaching the peak, it decreases with it. When the pollutant content is lower (1 000 mg/kg), the TCLP concentration first slightly decreases under cyclic drying and wetting, then increases, but the change is minor. The TCLP concentration is higher under a high pollutant content of 5 000 mg/kg, and increases with the increase of the times of drying and wetting cycles. The results of scanning electron microscopy (SEM) test are consistent with UCS tests and TCLP leaching tests, which reveals the micro-mechanism of the variations of engineering properties of stabilized contaminated soils after drying and wetting cycles.
Municipal solid waste (MSW) and its disposal are gaining significant importance in geotechnical and geoenvironmental engineering. However, conventional research is primarily focused on fresh MSW or MSW that is compacted under its own weight in the landfill. In this work, a series of tests to study the properties of a densified MSW after ground treatment were presented. The tests involved oedometer test, simple shear test, triaxial shear test, and permeability test, which were conducted to investigate the compressibility, shear strength, creep behavior and permeability of the MSW. The results show that the compressibility modulus of the MSW increases as the dry density increases. However, the influence of density on modulus decreases once the density reaches a certain value. Like most soils, the stress-strain curve of the densified MSW can be approximated by a hyperbola in the triaxial shear test. Fibrous components provide additional cohesion for MSW, but have a relatively smaller effect on friction angle. Permeability is also found to be closely related to the dry density of the MSW, i.e., MSW with a higher dry density has a smaller permeability. The permeability coefficient may be less than 10-7 cm/s if the density is high enough.
As a major component of lignin and abundantly existing in softwood and hardwood, ferulic acid has been used as a lignin-related compound for lignin biodegradation study. Biodegradation of ferulic acid by Cupriavidus sp. B-8, a newly isolated strain, was studied. This strain is able to utilize a wide range of lignin-related aromatic compounds as the sole carbon and energy source, including guaiacol, veratric acid, vanillic acid, cinnamic acid, p-coumaric acid, ferulic acid, and sinapic acid. In addition, the effects of different concentrations of ferulic acid on growth of Cupriavidus sp. B-8 were studied. The growth of Cupriavidus sp. B-8 is better under the condition of lower concentration. High-performance liquid chromatography (HPLC) analysis reveals that above 95% of ferulic acid is degraded within 12 h by Cupriavidus sp. B-8. Based on identification of biodegradation intermediates and further metabolites, the biodegradation pathway of ferulic acid by Cupriavidus sp. B-8 was proposed. Ferulic acid is initially converted to 4-vinylguaiacol, and further oxidized to vanillic acid and protocatechuic acid.
To study the mechanism of unsteady heat-moisture transfer of wet surrounding rock in deep mining, a series of experiments with different initial and boundary conditions were carried out. Test results show that rock temperature decreases quickly at the initial stage, and reduces slowly to be a constant value finally for transient heat-moisture transfer. The quasi-steady surface temperature of wet airway is lower than that of dry airway due to the moisture transfer. The diffusion radius is less than the cooling radius owing to the large diffusion resistance. The outlet airflow enthalpy of wet airway is much larger than that of dry airway. Latent heat caused by the moisture transfer plays a significant role in a deep thermal environment. For periodic heat-moisture transfer, temperature, humidity and enthalpy of outlet airflow and rock temperature also change periodically. The wave amplitude of rock temperature decreases gradually with increasing distance away from the airway surface, and the wave phase of rock temperature is also behind that of airflow. Moreover, direction of the heat-moisture transfer between airway and airflow is bidirectional, which is different from results of transient transfer.
Solvent extraction experiments were conducted from acidic solutions containing germanium(IV) and other metal ions, such as Ga3+, Fe3+, Zn2+ and Fe2+ in hydrometallurgical process of zinc. The purpose of this work was to enhance the efficiency of the extraction and stripping processes and the selectivity of germanium and other metals, while making the method as simple as possible. Germanium was recovered from sulfuric acid, using di-(2-ethylhexyl) phosphoric acid (P204) as an extractant, tributyl phosphate (TBP) as modifier diluted in sulfonate kerosene and stripped by NaOH aqueous solution. Extraction studies were carried out under different acid concentrations and solvent concentrations, and optimized conditions were determined. The numbers of stages required for extraction and stripping of metal ions were determined from the McCabe-Thiele plot. The results show that the extracting and stripping efficiencies are 94.3% and 100%, respectively, through two-stage extraction and two-stage strip. Moreover, the synergistic effect of TBP on the system P204/kerosense/Ge4+ is revealed with respect to the extraction of germanium.
A parameter, known as the parameter of humidification vibration deformation, was proposed, describing quantitatively the impact of water content on vibration settlement deformation, and its relationship with humidification water content, dynamic shear stress peak value, initial consolidation stress and vibration frequency was built. The result shows that 1) the parameter of humidification vibration deformation increases with the vibration shear stress peak value increasing. 2) The humidification water content has significant influence on the curve of the parameter of humidification vibration deformation and the peak vibration shear stress. When the humidification water content is low, the curve increases slowly. However, when the humidification water content is high, the curve increases rapidly. 3) Initial consolidation stress has significant influence on the humidification vibration deformation coefficient. When initial consolidation stress is not large enough to destroy the loess structure, with initial consolidation stress increasing, the humidification vibration deformation coefficient decreases. On the contrary, the humidification vibration deformation coefficient increases with initial consolidation stress increasing. 4) With the increase of vibration time, the parameter of humidification vibration settlement shows an increasing trend overall. The initial dynamic shear stress peak value and humidification water content all have significant effects on the curve of the parameter of humidification vibration settlement and vibration time. However, the humidification water content is even more significant.
Numerous experimental studies reveal that the mechanical and deformational behaviors of sands are dependent on the combined effect of void ratio and stress. To predict this complex behavior of sands, a hypo-elastic model is developed based on the cross-anisotropic elasticity model, which involves four parameters: bulk module, tangent Young’s module, volume deformation coefficient and Poisson ratio. A parameter defined as virtual peak deviatoric stress dependent on state parameter is introduced into hyperbolic stress-strain relationship to determine tangent Young’s module. In addition, an existing fitting equation for isotropic compression curves and an existing dilatancy equation, which can consider the effect of state of sands, are employed to determine bulk module and volume deformation coefficient. Thirteen model constants are involved in the proposed model, the values of which are fixed for a sand over a wide range of initial void ratios and initial confining pressures. Well known experimental data for drained and undrained triaxial compression tests of Toyoura sand are successfully modeled.
Laboratory tests were performed on Toyoura sand specimens to investigate the relationship between degree of saturation Sr, B-value and P-wave velocity Vp. Different types of pore water (de-aired water or tap water) and pore gas (air or CO2) as well as different magnitudes of back pressure were used to achieve different Sr (or B-value). The measured relationship between B-value and Vp was not consistent with the theoretical prediction. The measurement shows that the Vp value in the specimen flushed with de-aired water is independent of B-value (or Sr) and is always around the one in fully saturated condition. However, the Vp value in the specimen flushed with tap water increases with B-value, but the shape of the relationship between Vp and B-value is quite different from the theoretical prediction. The possible explanation for the discrepancy between laboratory measurement and theoretical prediction lies in that the air exists in the water as air bubbles and therefore the pore fluid (air-water mixture) is heterogeneous instead of homogenous assumed in the theoretical prediction.
In order to find out the bearing behavior of super-long piles located in deep soft clay over stiff layers around Dongting Lake, China, a test pile was first designed with the field loading test finished afterward. Based on the measured test results, load transfer mechanism and bearing behavior of the pile shaft were discussed in detail. Then, by introducing a bi-linear model for shaft friction and the tri-linear model for pile tip resistance, respectively, the governing differential equation of pile-soil system was set up by the load transfer method with the analytical solutions derived as well, taking into account the effect by stratified feature and various bearing conditions of subsoil, material nonlinearity, and the sediment under pile tip. Furthermore, formulas to determine the axial capacity of super-long piles by the pile top settlement were advised and applied to analyze the test pile. Good agreement between the predicted load-settlement variations and the measured data is obtained to verify the validity of the present method. The results also show that, the axial bearing capacity of super-long piles should be controlled by the allowable pile top settlement, and buckling stability of the pile shaft should be paid attention as well.
A complete case of a deep excavation was explored. According to the practical working conditions, a 3D non-linear finite element procedure is used to simulate a deep excavation supported by the composite soil nailed wall with bored piles in soft soil. The modified cam clay model is employed as the constitutive relationship of the soil in the numerical simulation. Results from the numerical analysis are fitted well with the field data, which indicate that the research approach used is reliable. Based on the field data and numerical results of the deep excavation supported by four different patterns of the composite soil nailed wall, the significant corner effect is founded in the 3D deep excavation. If bored piles or soil anchors are considered in the composite soil nailed wall, they are beneficial to decreasing deformations and internal forces of bored piles, cement mixing piles, soil anchors, soil nailings and soil around the deep excavation. Besides, the effects due to bored piles are more significant than those deduced from soil anchors. All mentioned above prove that the composite soil nailed wall with bored piles is feasible in the deep excavation.
In order to identify the critical properties and failure criteria of in-situ silt under vehicle or wave loading, anisotropically consolidated silt under undrained cyclic principal stress rotation was studied with hollow cylinder dynamic tests. The results show that for the slightly anisotropically consolidated samples with consolidation ratios no larger than 1.5, the structure collapses and the deviator strain and pore pressure increase sharply to fail after collapse. For the highly anisotropically consolidated samples with consolidation ratios larger than 1.5, the strain increases steadily to high values, which shows characteristics of ductile failure. 4% is suggested to be the threshold value of deviator stain to determine the occurrence of collapse. The normalized relationship between pore pressure and deviator strain can be correlated by a power function for all the anisotropically consolidated samples. Based on it, for the highly anisotropically consolidated samples, the appearance of inflection point on the power function curve is suggested to sign the failure. It can be predicted through the convex pore pressure at this point, whose ratio to the ultimate pore pressure is around linear with the consolidation ratio in spite of the dynamic shear stress level. And the corresponding deviator strain is between 3% and 6%. The strain failure criterion can also be adopted, but the limited value of stain should be determined according to engineering practice. As for the slightly anisotropically consolidated samples, the turning points appear after collapse. So, the failure is suggested to be defined with the occurrence of collapse and the collapse pore pressure can be predicted with the ultimate pore pressure and consolidation ratio.
Linear failure criterion is widely used in calculation of earth pressure acting on shallow tunnels. However, experimental evidence shows that nonlinear failure criterion is able to represent fairly well the failure of almost all types of rocks. A nonlinear Hoek-Brown failure criterion is employed to estimate the supporting pressures of shallow tunnels in limit analysis framework. Two failure mechanisms are proposed for calculating the work rate of external force and the internal energy dissipation. A tangential line to the nonlinear failure criterion is used to formulate the supporting pressure problem as a nonlinear programming problem. The objective function formulated in this way is minimized with respect to the failure mechanism and the location of tangency point. In order to assess the validity, the supporting pressures for the proposed failure mechanisms are calculated and compared with each other, and the present results are compared with previously published solutions when the nonlinear criterion is reduced to linear criterion. The agreement supports the validity of the proposed failure mechanisms. An experiment is conducted to investigate the influences of the nonlinear criterion on collapse shape and supporting pressures of shallow tunnels.
An optimal drainage tunnel location determination method for landslide prevention was proposed to solve the existing problems in drainage tunnel construction. Current applications of drainage tunnel systems in China were reviewed and the functions of drainage tunnel were categorized as catchment and interception. Numerical simulations were conducted. The results show that both catchment and interception tunnels have variation of the function in the simulation of monolayer model, which shows the reduction of permeability condition in lower layer. The function of catchment can be observed in the deep slope, while the function of interception is observed near groundwater source. By using the slope safety factor and discharge water amount as the objectives of optimal drainage tunnel location, and pore-water pressure in fixed node and section flux as the judgment for construction quality of adjacent drainage tunnel, the design principle of drainage tunnel was introduced. The K103 Landslide was illustrated as an example to determine the optimal drainage tunnel location. The measured drainage tunnel efficiency was evaluated and compared with that from the numerical analyses based on groundwater data. The results validate the present numerical study.
Buckling of submarine pipelines under thermal stress is one of the most important problems to be considered in pipeline design. And pipeline with initial imperfections will easily undergo failure due to global buckling under thermal stress and internal pressure. Therefore, it is vitally important to study the global buckling of the submarine pipeline with initial imperfections. On the basis of the characteristics of the initial imperfections, the global lateral buckling of submarine pipelines was analyzed. Based on the deduced analytical solutions for the global lateral buckling, effects of temperature difference and properties of foundation soil on pipeline buckling were analyzed. The results show that the snap buckling is predominantly governed by the amplitude value of initial imperfection; the triggering temperature difference of Mode I for pipelines with initial imperfections is higher than that of Mode II; a pipeline with a larger friction coefficient is safer than that with a smaller one; pipelines with larger initial imperfections are safer than those with smaller ones.
The rapid development of high-speed transportation infrastructure such as highway and high-speed railway has resulted in the advancement of soft soil improvement techniques. Vacuum preloading combined with vertical drains has been proved to be an effective method in the treatment of soft foundation. A three-dimensional numerical analysis of the coupled methods was presented, in which the smear zone and the well resistance were taken into account. The variations of the basic soil parameters including the permeability coefficient and the coefficient of volume compressibility were considered in the numerical model. The result of the numerical model was then compared to the measured value. The results indicate that the decrease of coefficient of volume compressibility accelerates the consolidation of the soil while the influence of hydraulic conductivity is insignificant. A cube drain presents the closest result to the real situation compared to the other equivalent methods of prefabricated vertical drain (PVD). The case study indicates that the numerical model with variation of soil parameters is closer to the measured value than the numerical model without variation of soil parameters.
Pile-slab structure roadbed is a new form of ballastless track for high speed railway. Due to lack of corresponding design code, based on the analysis of its structure characteristics and application requirements, it is proposed to carry out load effect combination according to ultimate limit state and serviceability limit state, and the most unfavorable combination of each state is chosen to carry through design calculation for pile-slab structure. Space model of pile-slab structure can be simplified as a plane frame model, by using the orthogonal test method, and the design parameter of pile-slab structure is optimized. Moreover, based on the engineering background of Suining-Chongqing high-speed railway, the dynamic deformation characteristics of pile-slab structure roadbed are further researched by carrying on the indoor dynamic model test. The test results show that the settlement after construction of subgrade satisfies the requirement of settlement control to build ballastless track on soil subgrade for high-speed railway. Slab structure plays the role of arch shell as load is transmitted from slab to pile, and the vertical dynamic stress of subgrade soil is approximately of “K” form distribution with the depth. The distribution of pile stress is closely related to soil characteristics, which has an upset triangle shape where the large dynamic stress is at the top. Pile compared with soil shares most dynamic stress. Pile structure expands the depth of the dynamic response of subgrade and improves the stress of subgrade soil, and the speed of train has limited effect on dynamic response. These results can provide scientific basis for pile-slab structure roadbed used on soil subgrade.