The objective of this paper is to propose a new quality evaluation method for asphalt concrete mixture using X-ray CT scanner. To achieve this aim, asphalt mixtures should be subjected to the X-ray CT scanning and its characteristics should be clarified. The approach employed in this study was as follows: 1) Coarse aggregate, fine aggregate, filler and bitumen were prepared; 2) dense-graded, coarse-graded and porous asphalt mixtures were made; 3) materials and mixtures were subjected to the X-ray CT scanning; 4) frequency of CT-value, threshold value, average slice CT-value, average segment CT-value were computed. In the material examination, CT-value of aggregate becomes smaller in the order of coarse aggregate, fine aggregate and filler and CT image of bitumen was nearly homogeneous. In the mixture examination, histograms of CT-value and four segmentation images made from CT images expressed the material and mixture characterization such as particle size and the difference in bitumen content and mixture type visibly and the bitumen content varies with the threshold values. In addition, the average segment CT-value without threshold value by dividing the fine aggregate from the coarse aggregate and average CT-value of the coarse aggregate, especially is highly correlated with average CT-value of the bitumen.
Effective evaluation of rock permeability is required in different energy, engineering and environmental projects. Although much research has been conducted on rock permeability, it is still one of the most difficult tasks for practicing rock engineers to accurately determine rock permeability. Based on a comprehensive literature review, this paper outlines the key aspects of rock permeability by presenting the representative values of the permeability of different rocks, describing the empirical and semi-empirical correlations for estimating the permeability of rocks, and discussing the main factors affecting the permeability of rocks. The factors discussed include stress, depth, temperature, and discontinuity intensity and aperture. This paper also highlights the scale effect on rock permeability, interconnectivity of discontinuities, and anisotropy of rock permeability. This paper provides the fundamental and essential information required for effective evaluation of rock permeability.
A major goal of coastal engineering is to develop models for the reliable prediction of short- and long-term near shore evolution. The most successful coastal models are numerical models, which allow flexibility in the choice of initial and boundary conditions. In the present study, evolutionary algorithms (EAs) are employed for multi-objective Pareto optimum design of group method data handling (GMDH)-type neural networks that have been used for bed evolution modeling in the surf zone for reflective beaches, based on the irregular wave experiments performed at the Hydraulic Laboratory of Imperial College (London, UK). The input parameters used for such modeling are significant wave height, wave period, wave action duration, reflection coefficient, distance from shoreline and sand size. In this way, EAs with an encoding scheme are presented for evolutionary design of the generalized GMDH-type neural networks, in which the connectivity configurations in such networks are not limited to adjacent layers. Also, multi-objective EAs with a diversity preserving mechanism are used for Pareto optimization of such GMDH-type neural networks. The most important objectives of GMDH-type neural networks that are considered in this study are training error (TE), prediction error (PE), and number of neurons (
Prefabricated ultra-thin radiant heating panel, as a new heating terminal type, is becoming a highlight in Yangtze River Valley area, China recently. However, there is a lack of operating characteristic research in this region, especially the energy consumption and operating mode are even less. To obtain these data, a heating system was set up in a duplex house in Chongqing. The test results show that the floor heating system could almost satisfy thermal comfort requirement at supply water temperature 45°C. But the preheating time was up to 4.5 h which was 1 h longer than that at supply water temperature 50°C. Meanwhile, the energy consumption at supply water temperature 50°C increased 0.10 Nm3/h, and the operating efficiency decrease about 2.6% compared to those at water temperature 45°C. Considering both the thermal lag and operating efficiency, a reasonable suggestion was proposed in this paper. That was, the standard families which just stay home at night should adopt the interim mode of partial room with part time. And the supply water temperature should be properly raised during the preheating period and lowered down in the steady heating stage.
This article examines the capability of Gaussian process regression (GPR) for prediction of effective stress parameter (
Experimental results show the significant influence of cement content on the mechanical properties of cement-treated clays. Cementation is produced by mixing a certain amount of cement with the saturated clay. The purpose of this paper is to model the cementation effect on the mechanical behavior of cement-treated clay. A micromechanical stress-strain model is developed considering explicitly the cementation at inter-cluster contacts. The inter-cluster bonding and debonding during mechanical loading are introduced in two ways: an additional cohesion in the shear sliding and a higher yield stress in normal compression. The model is used to simulate isotropic compression and undrained triaxial tests under various confining stresses on cement-treated Ariake clay and Singapore clay with various cement contents. The applicability of the present model is evaluated through comparisons between numerical and experimental results. The evolution of local stresses and local strains in inter-cluster planes are discussed in order to explain the induced anisotropy due to debonding at contact level under the applied loads. The numerical simulations demonstrate that the proposed micromechanical approach is well adapted for taking into account the main physical properties of cement-treated clay, including damage and induced anisotropy under mechanical loading.
Sandwich masonry wall, namely, multi-leaf masonry wall, is widely applied as energy-saving wall since the interlayer between the two outer leaves can act as insulation layer. New types of sandwich walls keep appearing in research and application, and due to their unique connection patterns, experimental studies should be performed to investigate the mechanical behavior, especially the compressive performance. 3 new types of sandwich masonry wall were investigated in this paper, and 3 different technical measures were considered to guarantee the cooperation between the two leaves of the walls. Based on the compression tests of 13 specimens, except for some damage patterns similar with the conventional masonry walls, several new failure patterns are found due to unique connection construction details. Comparisons were made between the tested compression capacity and the theoretical one which was calculated according to the Chinese Code for Design of Masonry Structures. The results indicate that the contributions of the 3 technical measures are different. The modification coefficient (
The objectives of this study are to explain the repairing and strengthening methods which are used to improve the structural performance of the bridge structure, to analyze the static and dynamic responses after strengthening, and to evaluate the performance of the bridge structure after repairing and strengthening. The methods of repairing and strengthening include reconstruction the deck of the bridge by casting 10 cm layer of concrete, strengthening the web and bottom floor of box girders of middle spans and side spans by sticking the steel plates, strengthening the whole bridge structure by using external pre-stressing tendons, and treatment the cracks. The results of theoretical analysis show that the values of tensile stress and vertical deflection are decreased and the compressive stress is increased after strengthening. There are not tensile stresses are appeared in the sections of the bridge structure. The modal analysis results show that the value of natural frequency is equal to 2.09 Hz which is more than the values before strengthening which is equal to 1.64 Hz, indicating that the stiffness of the bridge structure is improved and the strengthening process is effective to improve the cracks resistance and bearing capacity of the bridge structure.
The strength-dilatancy characteristics of frictional materials embraced in the hypoplastic model proposed by Gudehus and Bauer are investigated and compared with the revised model suggested by Huang. In the latter the deviatoric stress in the model by Gudehus and Bauer is replaced by a transformed stress according to the stress transformation technique proposed by Matsuoka. The flow rule, the failure state surface equation and the strength-dilatancy relationship embraced in both models are derived analytically. The performance of the two hypoplastic models in reproducing the relationship between the peak strength and the corresponding dilation rate under triaxial compression, plane compression and plane shearing are then extensively investigated and compared with experimental results and with the predictions made by particular classical stress-dilatancy theories. Numerical investigations show that the performance in reproducing the strength-dilatancy relationship is quite satisfactory under triaxial compression stress state in both models and the predictions made by the transformed stress based model are closer to the results obtained from classical stress-dilatancy theories for plane compression and plane shearing problems.
Large dams are complex structures with nonlinear dynamic behavior. Engineers often are forced to assess dam safety based on the available incomplete data, which is extremely difficult. This important problem can be solved with the modern theory of complex systems. It is possible to derive characteristics of the whole unknown dynamics of a structure using few data sets of certain carefully selected representative parameter(s). By means of high quality continuous records of some geotechnical characteristic(s) of a dam and modern methods of time series linear/nonlinear analysis the main dynamical features of the entire, unknown process (here—dam deformation) can be analyzed. ?We created the cost-effective Monitoring Telemetric System for Dam Diagnostics (DAMWATCH), which consists of sensors (tiltmeters), terminal and central controllers connected by the GSM/GPRS Modem to the diagnostic center. The tilt data recorded for varying reservoir level are compared with static design model of dam deformations computed by a finite element method (FEM) for the dam-reservoir-foundation system. Besides, recently developed linear/nonlinear data analysis and prediction schemes may help to quantify fine dynamical features of the dam behavior. The software package DAMTOOL has been developed for this purpose. ?The differences between measured and theoretically predicted response parameters of the dam may signal abnormal behavior of the object. The data obtained already by testing of the DAMWATCH/DAMTOOL system during operation of the high Enguri arc dam and reservoir (Georgia) show interesting long-term and short-term patterns of tilts in the dam body, which can be used for dam diagnostics. The proposed real-time telemetric monitoring (DAMWATCH) complex and linear/nonlinear dynamical analysis system (DAMTOOL) are unique.
Debris flow is a rapid flow which could lead to severe flooding with catastrophic consequences such as damage to properties and loss of human lives. It is important to study the movement of debris flow. Since during a debris flow process, the erosion and deposition processes are important, the no entrainment assumption is not acceptable. In this study, first we considered the debris flow as equivalent fluid and adopted the depth-averaged govern equations to simulate the movements and evolution of river bed. Secondly, the set of partial differential equations was solved numerically by means of explicit staggered leap-frog scheme that is accurate in space and time. The grid of difference scheme was derived from GIS raster data. Then the simulation results can be displayed by GIS and easily used to form the hazard maps. Finally, the numerical model coupled with GIS is applied to simulate the debris flow occurred on Oct. 20th, 2010, in Amamioshima City, Japan. The simulation reproduces the movement, erosion and deposition. The results are shown to be consistent with the field investigation.