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Volume 11, Number 5, November 2016

Rockburst is becoming more serious in Chinese coal mine. One of the effective methods to control rockburst is blasting. In the paper, we monitored and analyzed the blasting waves at different blast center distances by the Hilbert-Huang transform (HHT) in a coal mine. Results show that with the increase of blast center distance, the main frequency and amplitude of blasting waves show the decreasing trend. The attenuation of blasting waves is slower in the near blast field (10-75 m), compared with the far blast field (75-230 m). Besides, the frequency superposition phenomenon aggravates in the far field. A majority of the blasting waves energy at different blast center distances is concentrated around the IMF components 1-3. The instantaneous energy peak shows attenuation trend with the blast center distance increase, there are two obvious energy peaks in the near blast field (10-75 m), the energy spectrum appears "fat", and the total energy is greater. By contrast, there is only an energy peak in the far blast field, the energy spectrum is "thin", and the total energy is lesser. The HHT three dimensional spectrum shows that the wave energy accumulates in the time and frequency with the increasing of blast center distance.

Key Words
blasting wave; rockburst; HHT; instantaneous energy

(1) Xuelong Li, Enyuan Wang, Zhonghui Li, Liang Chen, Junjun Feng:
Key Laboratory of Gas and Fire Control for Coal Mines, School of Safety Engineering, China University of Mining and Technology, 221116, Xuzhou, Jiangsu, China;
(2) Xiaofei Bie:
Qianqiu Coal Mine, Yima Coal Mining Group Co. Ltd., 472300, Yima, Henan, China;
(3) Nan Li:
State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, 221116, Xuzhou, Jiangsu, China.

This paper presents field study and numerical modeling results for a single-cell low-fill concrete box culvert under a flexible pavement subjected to traffic loading. The culvert in the field test was instrumented with displacement transducers to capture the deformations resulting from different combinations of static and traffic loads. A low-boy truck with a known axle configuration and loads was used to apply seven static load combinations and traffic loads at different speeds. Deflections under the culvert roof were measured during loading. Soil and pavement samples were obtained by drilling operation on the test site. The properties of the soil and pavement layers were determined in the laboratory. A 3-D numerical model of the culvert was developed using a finite difference program FLAC3D. Linear elastic models were used for the pavement layers and soil. The numerical results with the material properties determined in the laboratory were compared with the field test results. The observed deflections in the field test were generally smaller under moving loads than static loads. The maximum deflections measured during the static and traffic loads were 0.6 mm and 0.41 mm respectively. The deflections computed by the numerical method were in good agreement with those observed in the field test. The deflection profiles obtained from the field test and the numerical simulation suggest that the traffic load acted more like a concentrated load distributed over a limited area on the culvert. Elastic models for culverts, pavement layers, and surrounding soil are appropriate for numerical modeling of box culverts under loading for load rating purposes.

Key Words
culvert; deflection; numerical method; pavement; stress

(1) Raju Acharya:
Engineering & Testing Services, Inc., 5226 Indian River Road, Virginia Beach, Virginia 23464, USA;
(2) Jie Han, Robert L. Parsons:
Department of Civil, Environmental, & Architectural Engineering, The University of Kansas, 1530 West 15th Street, Lawrence, Kansas 66045, USA;
(3) James J. Brennan:
Kansas Department of Transportation, 2300 Van Buren, Topeka, KS 66611, USA.

The effect of particle breakage and intermediate principal stress ratio on the behaviour of crushable granular assemblies under true triaxial stress conditions is studied using the discrete element method. Numerical results show that the increase of intermediate principal stress ratio b (b = (σ2σ3) / (σ1σ3)) results in the increase of dilatancy at low confining pressures but the decrease of dilatancy at high confining pressures, which stems from the distinct increasing compaction caused by breakage with b. The influence of b on the evolution of the peak apparent friction angle is also weakened by particle breakage. For low relative breakage, the relationship between the peak apparent friction angle and b is close to the Lade-Duncan failure model, whereas it conforms to the Matsuoka-Nakai failure model for high relative breakage. In addition, the increasing tendency of relative breakage, calculated based on a fractal particle size distribution with the fractal dimension being 2.5, declines with the increasing confining pressure and axial strain, which implies the existence of an ultimate graduation. Finally, the relationship between particle breakage and plastic work is found to conform to a unique hyperbolic correlation regardless of the test conditions.

Key Words
particle breakage; discrete element method; intermediate principle stress ratio; particle size distribution; plastic work

(1) Lunlun Zhou, Xihua Chu, Yuanjie Xu:
School of Civil Engineering, Wuhan University, Wuhan, 430072, China;
(2) Xue Zhang:
ARC Centre of Excellence for Geotechnical Science and Engineering, The University of Newcastle, NSW, 2308, Australia.

The energy dissipation of coal under dynamic loads is a major issue in geomechanics and arising extensive concerns recently. In this study, dynamic loading tests of coal were conducted using a split Hopkinson pressure bar (SHPB) system, the characteristics of dynamic behavior and energy dissipation of coal were analyzed, and the mechanism of energy dissipation was discussed based on the fracture processes of coal under dynamic loads. Experimental results indicate that the energy dissipation of coal under dynamic loads has a positive linear correlation with both incident energy and dynamic compressive strength, and the correlation coefficients between incident energy, dynamic compressive strength and the energy dissipation rate are 0.74 and 0.98, respectively. Theoretical analysis demonstrates that higher level of stress leads to greater energy released during unstable crack propagation, thus resulting in larger energy dissipation rate of coal under dynamic loads. At last, a semi-empirical energy dissipation model is proposed for describing the positive relationship between dissipated energy and stress.

Key Words
split Hopkinson pressure bar; energy dissipation; incident energy; dynamic compressive strength; fracture processes

(1) Key Laboratory of Gas and Fire Control for Coal Mines, China University of Mining and Technology, Xuzhou, 221116, China;
(2) Faculty of Safety Engineering, China University of Mining and Technology, Xuzhou, 221116, China.

This work presents a static flexure analysis of laminated composite plates by utilizing a higher order shear deformation theory in which the stretching effect is incorporated. The axial displacement field utilizes sinusoidal function in terms of thickness coordinate to consider the transverse shear deformation influence. The cosine function in thickness coordinate is employed in transverse displacement to introduce the influence of transverse normal strain. The highlight of the present method is that, in addition to incorporating the thickness stretching effect (εz ≠ 0), the displacement field is constructed with only 5 unknowns, as against 6 or more in other higher order shear and normal deformation theory. Governing equations of the present theory are determined by employing the principle of virtual work. The closed-form solutions of simply supported cross-ply and angle-ply laminated composite plates have been obtained using Navier solution. The numerical results of present method are compared with those of the classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) of Reddy, higher order shear and normal deformation theory (HSNDT) and exact three dimensional elasticity theory wherever applicable. The results predicted by present theory are in good agreement with those of higher order shear deformation theory and the elasticity theory. It can be concluded that the proposed method is accurate and simple in solving the static bending response of laminated composite plates.

Key Words
shear deformation; stretching effect; static flexure; laminated plate

(1) Kada Draiche:
Département de Génie Civil, Université Ibn Khaldoun Tiaret, BP 78Zaaroura, 1400 Tiaret, Algérie;
(2) Kada Draiche, Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(3) Abdelouahed Tounsi:
Laboratoire de Modélisation et Simulation Multi-echelle, Département de Physique, Faculte des Sciences Exactes, Département de Physique, Université de Sidi Bel Abbés, Algeria;
(4) S.R. Mahmoud:
Department of Mathematics, Faculty of Science, King Abdulaziz University, Saudi Arabia;
(5) S.R. Mahmoud:
Mathematics Department, Faculty of Science, University of Sohag, Egypt.

In this study, the uplift capacity of anchor plates embedded in sand was investigated by conducting model tests. Square shaped anchors were used in the tests and parameters such as relative density of sand, embedment ratio (H/B), spacing ratio between anchors (S/B) and anchor configuration affecting the uplift capacity were investigated. Breakout factor and group efficiency which are dimensionless parameters were used to show the results. A series of finite element analyses and analytical solutions were additionally performed to ascertain the validity of the findings from the laboratory model tests and to supplement the results of the model tests. It can be concluded that the embedment depth in dense sand soil condition is the most important parameter with respect to the other parameters as to influencing the uplift capacity of group anchors.

Key Words
anchor plates; laboratory tests; uplift capacity; breakout factor; group efficiency

Department of Civil Engineering, Cukurova University, Adana, 01330, Turkey.

Shear wave velocities of three selected sandy soils subject to drained triaxial compression test were continuously measured using the bender elements. The shear wave velocity during isotropic compression, as widely recognized, increased as confining pressure increased and they were correlated well. However, during drained shearing, the mean effective stress could no further provide a suitable correlation. The shear wave velocity during this stage was almost constant with respect to the mean effective stress. The vertical stress was found to be more favorable at this stage (since confining stress was kept constant). When sample was attained its peak stress, the shear wave velocity reduced and deviated from the previously existed trend line. This was probably caused by the non-uniformity induced by the formation of shear band. Subsequently, void ratios computed based on external measurements could not provide reasonable fitting to the initial stage of post-peak shear wave velocity. At very large strain levels after shear band formation, the digital images revealed that sample may internally re-arrange itself to be in a more uniform loose stage. This final stage void ratio estimated based on the proposed correlation derived during pre-peak state was close to the value of the maximum void ratio.

Key Words
shear wave velocity; shear band; triaxial compression test; sandy soil

(1) Supot Teachavorasinskun:
Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Phayathai Road, Pathumwan, Bangkok, Thailand;
(2) Pulpong Pongvithayapanu:
Department of Civil Engineering, Faculty of Engineering at Si Racha, Kasetsart University, Chonburi, Thailand.

A theoretical study of the behavior of structured soils is presented herein. By introducing the effect of soil structure and loading history into the Cam Clay model, a new model was formulated. The concept of differing void ratios was modified to combine structural parameters and the over consolidation ratio, and an evolution law was proposed. Upon introducing the concept of the subloading yield surface, a new two-yield surface model was obtained. The predicted results were compared to the experimental data, demonstrating that the new model provided satisfactory qualitative modeling of many important features of structured soils.

Key Words
structure; over consolidation; subloading yield surface; constitutive relationships

(1) Sheng Zhang, Haichao Li, Jidong Teng:
School of Civil Engineering, Central South University, Changsha, Hunan 410075, China;
(2) Sheng Zhang, Jidong Teng:
National Engineering Laboratory for High Speed Railway Construction,ChangshHunan 410075, China.

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