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CONTENTS
Volume 25, Number 3, May10 2021
 


Abstract
Wave interaction in marine structures is an important issue where requires to be considered in view of number of bases, piles and arrangement method. In this research, effect of waves and their forces on piles with different arrangements was investigated using numerical modeling. Simulations were performed in presence of bracing elements between piles against the force of waves and also were compared with simple arrangement without bracing elements in different arrangements. Results showed that in models that were fitted with bracing elements, the displacement rate reduced about 96%, and tension tolerances increased more than 53% and abutment responses also decreased about 70%.

Key Words
ocean waves; structural reaction; pile bracing; numerical modeling; pile arrangement

Address
Mohammad Rezazadeh Ghorbanipour: Department of Civil Engineering, Alaodoleh Semnani University of Higher Education, Garmsar, Iran

Hamed Sarkardeh: Department of Civil Engineering, Faculty of Engineering, Hakim Sabzevari University, Sabzevar, Iran

Abstract
In this paper, to study the stability of surrounding rock during roadway excavation in different rock mass structures, the physical model test for roadway excavation process in three types of intact rock mass, layered rock mass and massive rock mass were carried out by using the self-developed two-dimensional simulation testing system of complex underground engineering. Firstly, based on the engineering background of a deep mine in eastern China, the similar materials of the most appropriate ratio in line with the similarity theory were tested, compared and determined. Then, the physical models of four different schemes with 1000 mm (height) x1000 mm (length)x 250 mm (width) were constructed. Finally, the roadway excavation was carried out after applying boundary conditions to the physical model by the simulation testing system. The results indicate that the supporting effect of rockbolts has a great influence on the shallow surrounding rock, and the rock mass structure can affect the overall stability of the surrounding rock. Furthermore, the failure mechanism and bearing capacity of surrounding rock were further discussed from the comparison of stress evolution characteristics, distribution of stress arch, and failure modes in different schemes.

Key Words
physical model; rock mass structure; stress evolution; mechanical bearing characteristic; failure mechanism

Address
Zhenlong Zhao, Hongwen Jing, Lijun Yang and Qian Yin: State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, P.R. China

Xinshuai Shi: 1.) State Key Laboratory for Geomechanics and Deep Underground Engineering,
China University of Mining and Technology, Xuzhou 221116, P.R. China
2.) Graduate School of Engineering, Nagasaki University, 1-14 Bunkyo, Nagasaki 852-8521, Japan

Yuan Gao: 1.) State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, P.R. China
2.) Department of Civil Engineering, Monash University, Clayton, Victoria 3800, Australia

Abstract
Time effect on the deformation and strength characteristics of geogrid reinforced sand retaining wall has become an important issue in geotechnical and transportation engineering. Three physical model tests on geogrid reinforced sand retaining walls performed under various loading conditions were simulated to study their rate-dependent behaviors, using the presented nonlinear finite element method (FEM) analysis procedure. This FEM was based on the dynamic relaxation method and return mapping scheme, in which the combined effects of the rate-dependent behaviors of both the backfill soil and the geosynthetic reinforcement have been included. The rate-dependent behaviors of sands and geogrids should be attributed to the viscous property of materials, which can be described by the unified three-component elasto-viscoplastic constitutive model. By comparing the FEM simulations and the test results, it can be found that the present FEM was able to be successfully extended to the boundary value problems of geosynthetic reinforced soil retaining walls. The deformation and strength characteristics of the geogrid reinforced sand retaining walls can be well reproduced. Loading rate effect, the trends of jump in footing pressure upon the step-changes in the loading rate, occurred not only on sands and geogrids but also on geogrid reinforced sands retaining walls. The lateral earth pressure distributions against the back of retaining wall, the local tensile force in the geogrid arranged in the retaining wall and the local stresses beneath the footing under various loading conditions can also be predicted well in the FEM simulations.

Key Words
geogrid reinforced soil; retaining wall; numerical model; rate-dependent property; tensile force

Address
Fulin Li: 1.) State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116, P.R. China
2.) School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116, P.R. China

Tianran Ma: School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116, P.R. China

Yugui Yang: State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116, P.R. China

Abstract
Several additives are used to enhance the geotechnical properties (e.g., shear wave velocity, shear modulus) of soils to provide sustainable, economical and eco-friendly solutions in geotechnical and geo-environmental engineering. In this study, piezoelectric ring actuators are used to measure the shear wave velocity of unreinforced, fiber, cemented, and fiber reinforced cemented Toyoura sand. One dimensional oedometer tests are performed on medium dense specimens of Toyoura sand-cement-fiber-silica flour mixtures with different percentages of silica flour (0-42%), fiber and cement (e.g., 0-3%) additives. The experimental results indicate that behavior of the mixtures is significantly affected by the concentration of silica flour, fiber and cement additives. Results show that with the addition of 1-3% of PVA fibers, the shear wave velocity increases by only 1-3%. However, the addition of 1-4% of cement increases the shear wave velocity by 8-35%. 10.5-21% increase of silica flour reduces the shear wave velocity by 2-5% but adding 28-42% silica flour significantly reduces the shear wave velocity by 12-31%. In addition, the combined effect of cement and fibers was also found and with only 2% cement and 1% fiber, the shear wave velocity increase was found to be approximately 24% and with only 3% cement and 3% fibers this increased to 35%. The results from this study for the normalized shear modulus and normalized mean effective stress agree well with previous findings on pure Toyoura sand, Toyoura silty sand, fiber reinforced, fiber reinforced cemented Toyoura sand. Any variations are likely due to the difference in stress history (i.e., isotropic versus anisotropic consolidation) and the measurement method. In addition, these small discrepancies could be attributed to several other factors. The potential factors include the difference in specimen sizes, test devices, methods of analysis for the measurement of arrival time, the use of an appropriate Ko to convert the vertical stresses into mean effective stress, and sample preparation techniques. Lastly, it was investigated that there is a robust inverse relationship between α factor and β_0 exponent. It was found that less compressible soils exhibit higher α factors and lower β_0 exponents.

Key Words
shear wave velocity; piezoelectric ring actuators; ground improvement; ground remediation; sustainability; oedometer tests

Address
Muhammad Safdar and Faheem Shah: Earthquake Engineering Center, Department of Civil Engineering, University of Engineering and Technology, Peshawar, Pakistan

Tim Newson: Department of Civil and Environmental Engineering, Western University, London, Ontario, Canada

Colin Schmidt: Thurber Engineering Ltd. Calgary, Alberta, Canada

Kenichi Sato and Takuro Fujikawa: Department of Civil Engineering, Fukuoka University, Nanakuma, Jonan, Fukuoka, Japan

Abstract
A two dimensional model of linearly elastic soil spring used for the settlement analysis of the flexible mat foundation is suggested in this study. The spring constants of the soils underneath the foundation were modeled assuming uniformly vertical load applied onto the foundation. The soil spring constants were back calculated using the three-dimensional finite element analysis with Midas GTS NX program. Variation of the soil spring constants was modeled as a two-dimensional polynomial function in terms of the normalized spatial distances between the center of foundation and the analytical points. The Lysmer's analog spring for soils underneath the rigid foundation was adopted and calibrated for the flexible foundation. For validations, the newly proposed soil spring model was incorporated into a two dimensional finite difference analysis for a square mat foundation at the surface of an elastic half-space consisting of soft clays. Comparative study was made for elastic soils where the shear wave velocity is 120~180 m/s and the Poisson's ratio varies at 0.3~0.5. The resulting foundation settlements from the two dimensional finite difference analysis with the proposed soil springs were found in good agreement with those obtained directly from three dimensional finite element analyses. Details of the applications and limitations of the modified Lysmer's analog springs were discussed in this study.

Key Words
soil stiffness, mat foundation, flexural displacement, modified Lysmer's analog model

Address
Der-Wen Chang and Ming-He Hung: Department of Civil Engineering, Tamkang University, #151 Ying-Chuan Road, Tamsui District, New Taipei City 25137, Taiwan

Sang-Seom Jeong: School of Civil and Environmental Engineering, Yonsei University, 50 Yonsei Ro, Seodaemun Gu,
Seoul 03722, Republic of Korea


Abstract
Rib spalling is a major issue affecting the safety of steeply inclined coal seam. And the failure coal face and support system can be affected with each other to generate a vicious cycle along with inducing large-scale collapse of surrounding rock in steeply inclined coal seam. In order to analyze failure mechanism and propose the corresponding prominent control measures of steeply inclined coal working face, mechanical model based on coal face-support-roof system and mechanical model of coal face failure was established to reveal the disaster mechanism of rib spalling and the sensitive analysis of related factors was performed. Furthermore, taking 3402 working face of Chen-man-zhuang coal mine as engineering background, numerical model by using FLAC3D was built to illustrate the propagation of displacement and stress fields in steeply inclined coal seam and verify the theory analysis as mentioned in this study. The results show that the coal face slide body in steeply inclined working face can be observed as the failure height of upper layer smaller than that of lower layer exhibiting with an irregular quadrilateral pyramid shape. Moreover, the cracks were originated from the upper layer of sliding body and gradually developed to the lower layer causing the final rib spalling. The influence factors on the stability of coal face can be ranked as overlying strata pressure (P) > mechanical parameters of coal body (e.g., cohesion (c), internal fraction angle (𝛟)) > support strength (F) > the support force of protecting piece (F

Key Words
steeply inclined coal seam; coal face-roof-support system; rib spalling; sensitively analysis; numerical simulation

Address
Dezhong Kong: 1.) College of Mining, Guizhou University, Guiyang 550025, Guizhou, China
2.) Guizhou Coal Mine Design and Research Institute, Guiyang 550025, Guizhou, China

Yu Xiong, Guiyi Wu and Yong Liu: College of Mining, Guizhou University, Guiyang 550025, Guizhou, China

Zhanbo Cheng: School of Engineering, University of Warwick, Coventry CV47AL, U.K.

Nan Wang: School of Resource and Safety Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China

Abstract
The present study investigated the ageing effect on compressibility, permeability and shear strength behavior of kaolin and bentonite samples in the presence of NaCl and CaCl2 solutions. The compressibility, permeability and shear strength parameters were determined on the 60, 190, and 250 days cured samples. The results have shown that, the kaolin sample becomes more compressible in the presence Ca2+ ions with ageing. Generally, the normalized compression index values of bentonite samples increased at the end of 60 days and 250 days curing time periods. The normalized permeability value of kaolin decreased by ageing in the presence of Na+ ions almost twofold. The permeability values of bentonite increased both in NaCl and CaCl2 solutions during ageing. In the presence of Na+ ions kaolin had higher max. shear stress value than Ca2+ ions. When the max. shear stress values of 0, 60 and 190 days samples were compared, it was seen that NaCl solution had no significant effect on the shear strength of kaolin sample. However, the shear strength of kaolin increased in the CaCl2 solution during ageing. In the presence of Ca2+ ions the max. shear stress value of bentonite was higher. The results of this study have shown that ageing has significant effects on the compressibility, permeability and shear strength of kaolinitic and bentonitic clayey soils.

Key Words
ageing effect; salt solutions; kaolin; bentonite; compressibility; shear strength

Address
Emel Çakar: Department of Civil Engineering, Celal Bayar University, Manisa, Turkey

Yeliz Yukselen-Aksoy: Department of Civil Engineering, Dokuz Eylul University, Izmir, Turkey

Abstract
In this paper, we discuss a mathematical method for determining the return energy of the wave from the sample and comparing it with the mechanical energy consumed to change the dimension of the sample in the triaxial test of the rock. We represent a method to determine the mechanical energy and then we provide how to calculate the return energy of the wave. However, the static energy and pulse return energy will show higher amounts with axial pressure increase. Three types of clastic sedimentary rocks including sandstone, pyroclastic rock, and argillitic tuff were selected. The sandstone showed the highest strength, young's modulus and ultrasonic P and S waves' velocities versus others in the triaxial test. Also, from the received P wavelet, the calculated pulse wave returning energy indicated the best correlation between axial stress compared to wave velocities in all specimens. The fact that the return energy decreases or increases is related to increasing lateral stress and depends on the geological characteristics of the rock. This method can be used to determine the stresses on the rock as well as its in-situ modulus in projects that are located at high depths of the earth.

Key Words
return energy of the wave; triaxial test; sedimentary rocks; pyroclastic rock; ultrasonic wave velocities

Address
Mojtaba Heidari, Rassoul Ajalloeian and Akbar Ghazi Fard:Department of Geology, University of Isfahan, Isfahan, Hezar-Jarib Avenue, Islamic Republic of Iran

Mahmoud Hashemi Isfahanian: Department of Civil Engineering and transportation, University of Isfahan, Isfahan, Hezar Jirib Avenue, Islamic Republic of Iran


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