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CONTENTS
Volume 18, Number 5, August10 2019
 

Abstract
It is important to estimate the shear strength of shallow compacted soils as a construction material. A series of constant water content triaxial compression (CWCC) tests under low confining state in this study were performed on compacted geomaterials. For establishing a relationship of the shear strengths between saturated and unsaturated states on compacted geomaterials, the suction stresses were derived by two methods: the conventional suction-measured method and the Suction stress-SWRC Method (SSM). Considering the suction stress as an equivalent confining stress component in the (sigma_net, tau) plane, it was found that the peak deviator stress states agree well with the failure line of the saturated state from the triaxial compression test when the SSM is applied to obtain the suction stress. On the other hand, the cavitation phenomenon on the measurement of suction affected the results of the conventional suction-measured method. These results mean that the SSM is distinctly favorable for obtaining the suction value in the CWCC test because the SSM is not restricted by the cavitation phenomenon. It is expected that the application of the SSM would reduce the time required, and the projected cost with the additional equipment such as a pore water measuring device in the CWCC test.

Key Words
compacted geomaterials; suction stress-SWRC Method (SSM); suction stress; soil-water retention curve; shear strength

Address
Byeong-Su Kim:Graduate School of Environmental and Life Science, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama City, Okayama 700-8530, Japan

Shoji Kato: Graduate School of Engineering, Kobe University,
1-1 Rokkodai-cho, Nada-ku, Kobe City, Hyogo 657-8501, Japan

Seong-Wan Park:Department of Civil & Environmental Engineering, Dankook University,Jukjeon-ro 152, Suji-gu, Yongin City, Gyeonggi-do 16890, Korea

Abstract
The constructions of engineering structures such as airports, highways and railway on clayey soils may create many problems. The economic losses and damages caused by these soils have led researchers to do many studies using different chemical additives for the stabilization of them. Lime is a popular additive used to stabilize the clayey soils. When the base course is stabilized by mixing with an additive, inevitable delays may occur during compaction due to reasons like insufficient workers, breakdown of compaction equipment, etc. The main purpose of this study is to research the effect of compaction delay time (7 days) on the strength, compaction, and dynamic properties of a clay soil stabilized with lime content of 0, 3, 6, 9, 12 and 15% by dry weight of soil. Compaction characteristics of these mixes were determined immediately after mixing, and after 7 days from the end of mixing process. Within this context, unconfined compressive strength (UCS) under the various curing periods (uncured, 7 and 28 days) and dynamic triaxial tests were performed on the compacted specimens. The results of UCS and dynamic triaxial tests showed that delayed compaction on the strength of the lime-stabilized clay soil were significantly effective. Especially with the lime content of 9%, the increase in the shear modulus (G) and UCS of 28 days curing were more prominent after 7 days mellowing period. Because of the complex forms of hysteresis loops caused by the lime additive, the damping ratio (D) values differed from the trends presented in the literature and showed a scattered relationship.

Key Words
lime; stabilization; delayed compaction; strength; dynamic properties

Address
Murat Türköz: Eskisehir Osmangazi University, Civil Engineering Department, 26480, Turkey

Abstract
Due to the underground openings, the tangentially concentrated stress of the tunnel remains larger at excavation boundary and decreases toward the interior of the surrounding rock with a certain gradient. In order to study the effect of different gradient stress on rockburst, the true-triaxial gradient and hydraulic-pneumatic combined test apparatus were carried out to simulate the rockburst processes. Under the different gradient stress conditions, the rock-like specimen (gypsum) was tested independently through three principal stress directions loading--fast unloading of single surface--top gradient and hydraulic-pneumatic combined loading, which systematically analyzed the macro-mesoscopic damage phenomena, force characteristics and acoustic emission (AE) signals of the specimen during rockburst. The experimental results indicated that the rockburst test under the gradient and hydraulic-pneumatic combined loading conditions could perfectly reflect the rockburst processes and their stress characteristics; Relatively high stress loading could cause specimen failure, but could not determine its mode. The rockburst under the action of gradient stress suggested that the failure mode of specimen mainly depended on the stress gradient. When the stress gradient was lower, progressive and static spalling failure occured and the rockburst grades were relatively slight. On the other hand, shear fractures occurred in rockbursts accounted for increasingly large proportion as the stress gradient increased and the rockburst occurred more intensely and suddenly, the progressive failure process became unconspicuous, and the rockburst grades were moderate or even stronger.

Key Words
rockburst; failure modes; true-triaxial; stress gradient; hydraulic-pneumatic combined loading

Address
Xiqi Liu and Yuanyou Xia: School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070, China

Manqing Lin: School of Xingfa Mining Engineering, Wuhan Institute of Technology, Wuhan 430062, China

Mahfoud Benzerzour: Institute Mines-Telecom Lille Douai, Douai 59500, France

Abstract
Internal stability is an important safety issue for levees, embankments, and other earthen structures. Since a large part of the world\'s population lives near oceans, lakes and rivers, floods resulting from breaching of dams can lead to devastating disasters with tremendous loss of life and property, especially in densely populated areas. There are some main factors that affect the internal stability of dams, levees and other earthen structures, such as the erodibility of the soil, the water velocity inside the soil mass and the geometry of the earthen structure, etc. Thus, the mechanism of internal erosion and stability of soils is very complicated and it is vital to investigate the assessment methods of internal stability of soils in embankment dams and their foundations. This paper presents an improved support vector machine (SVM) model to predict the internal stability of soils. The grid search algorithm (GSA) is employed to find the optimal parameters of SVM firstly, and then the cross – validation (CV) method is employed to estimate the classification accuracy of the GSA-SVM model. Two examples of internal stability of soils are presented to validate the predictive capability of the proposed GSA-SVM model. In addition to verify the effectiveness of the proposed GSA-SVM model, the predictions from the proposed GSA-SVM model were compared with those from the traditional back propagation neural network (BPNN) model. The results showed that the proposed GSA-SVM model is a feasible and efficient tool for assessing the internal stability of soils with high accuracy.

Key Words
internal stability; piping; support vector machine; grid search algorithm; cross-validation

Address
Xinhua Xue: State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource and Hydropower, Sichuan University, No.24 South Section 1, Yihuan Road, Chengdu, 610065, P.R. China


Abstract
In the present, the liquefaction potential of fiber-reinforced sandy soils was investigated through the energy-based approach by conducting a series of strain-controlled cyclic simple shear tests. In the tests, the effects of the fiber properties, such as the fiber content, fiber length, relative density and effective stress, and the test parameters on sandy soil improvement were investigated. The results indicated that the fiber inclusion yields to higher cumulative liquefaction energy values compared to the unreinforced (plain) ground by increasing the number of cycles and shear strength needed for the liquefaction of the soil. This result reveals that the fiber inclusion increases the resistance of the soil to liquefaction. However, the increase in the fiber content was determined to be more effective on the test results compared to the fiber length. Furthermore, the increase in the relative density of the soil increases the efficiency of the fibers on soil strengthening.

Key Words
earthquake, fiber, liquefaction, reinforced soil, sand, cyclic simple shear test, energy-based model

Address
Yetis Bulent Sonmezer: Department of Civil Engineering, Faculty of Engineering, Kirikkale University, 71450 Kirikkale, Turkey

Abstract
A karst collapse, as a natural hazard, is totally different to a normal collapse. In recent years, karst collapses have caused substantial economic losses and even threatened human safety. A risk assessment model for karst collapse was developed based on the fuzzy analytic hierarchy process (FAHP) and grey relational analysis (GRA), which is a simple and effective mathematical algorithm. An evaluation index played an important role in the process of completing the risk assessment model. In this study, the proposed model was applied to Jiaobai village in southwest China. First, the main controlling factors were summarized as an evaluation index of the model based on an investigation and statistical analysis of the natural formation law of karst collapse. Second, the FAHP was used to determine the relative weights and GRA was used to calculate the grey relational coefficient among the indices. Finally, the relational sequence of evaluation objects was established by calculating the grey weighted relational degree. According to the maximum relational rule, the greater the relational degree the better the relational degree with the hierarchy set. The results showed that the model accurately simulated the field condition. It is also demonstrated the contribution of various control factors to the process of karst collapse and the degree of collapse in the study area.

Key Words
karst collapse; risk assessment; evaluation index; fuzzy analytic hierarchy process (FAHP); grey relational analysis (GRA)

Address
Hanghang Ding, Qiang Wu, Dekang Zhao and Shuai Yu: 1.)College of Geoscience and Surveying Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China
2.) National Engineering Research Center of Coal Mine Water Hazard Controlling, Beijing 100083, China

Wenping Mu: School of Water Resources and Environment, China University of Geosciences, Beijing 100083, China

Abstract
Although ground investigation had carried out prior to the construction, many problems have arisen during the civil-engineering works because of the presence of the unexpected underground utility lines or anomalies. In this study, a new geophysical exploration method was developed to solve those problems by improving and supplementing the existing methods. This new method was based on the difference of electrical resistance values between anomalies and surrounding ground medium. A theoretical expression was suggested to define the characteristics of the anomalies such as location, size and direction, by applying the electric field analysis. An inverse analysis algorithm was also developed to solve the theoretical expression using the measured electrical resistance values which were generated by the voltage flowing the subsurface medium. To verify the developed method, field applications were conducted at the sites under construction or planned. From the results of the field tests, it was found that not only the new method was more predictive than the existing methods, but its results were good agreed with the measured ones. Therefore, it is expected that application of the new exploration method reduces the unexpected accidents caused by the underground uncertainties during the underground construction works.

Key Words
electrical resistivity; electric field analysis; inverse analysis; underground structure

Address
Seon-Ah Jo, Kyoung-Yul Kim and Hee-Hwan Ryu: Structural & Seismic Tech. Group, Power Transmission Laboratory, Korea Electric Power Corporation Research Institute, 105 Mungi-ro, Yuseong-gu, Daejeon 34056, Republic of Korea

Abstract
Building on/with expansive soils with no treatment brings complications. Compacted expansive soils specifically fall short in satisfying the minimum requirements for transport embankment infrastructures, requiring the adoption of hauled virgin mineral aggregates or a sustainable alternative. Use of hauled aggregates comes at a high carbon and economical cost. On average, every 9m high embankment built with quarried/hauled soils cost 12600 MJ.m-2 Embodied Energy (EE). A prospect of using mixed cutting-arising expansive soils with industrial/domestic wastes can reduce the carbon cost and ease the pressure on landfills. The widespread use of recycled materials has been extensively limited due to concerns over their long-term performance, generally low shear strength and stiffness. In this contribution, hydromechanical properties of a waste tyre sand-sized rubber (a mixture of polybutadiene, polyisoprene, elastomers, and styrene-butadiene) and expansive silt is studied, allowing the short- and long-term behaviour of optimum compacted composites to be better established. The inclusion of tyre shred substantially decreased the swelling potential/pressure and modestly lowered the compression index. Silt-Tyre powder replacement lowered the bulk density, allowing construction of lighter reinforced earth structures. The shear strength and stiffness decreased on addition of tyre powder, yet the contribution of matric suction to the shear strength remained constant for tyre shred contents up to 20%. Reinforced soils adopted a ductile post-peak plastic behaviour with enhanced failure strain, offering the opportunity to build more flexible subgrades as recommended for expansive soils. Residual water content and tyre shred content are directly correlated; tyre-reinforced silt showed a greater capacity of water storage (than natural silts) and hence a sustainable solution to waterlogging and surficial flooding particularly in urban settings. Crushed fine tyre shred mixed with expansive silts/sands at 15 to 20 wt% appear to offer the maximum reduction in swelling-shrinking properties at minimum cracking, strength loss and enhanced compressibility expenses.

Key Words
embankment; compaction; expansive; hydromechanical; tyre

Address
Soheil Ghadr: Department of Civil Engineering, Urmia university, 15km Sero Way, Iran

Sajjad Mirsalehi:Department of Civil Engineering, University of Politecnica de Catalunya, Barcelona, Spain

Arya Assadi-Langroudi: School of the Architecture, Computing & Engineering, University of East London, London, U.K.

Abstract
The customary approach used in the blast vibration analysis is to derive empirical relations between the peak particle velocities of blast-induced waves and the scaled distance, and to develop patterns limiting the amounts of explosives. During the periods when excavations involving blasting were performed at sites far from residential areas and infrastructure works, this method based on empirical correlations could be effective in reducing vibrations. However, blasting procedures applied by the fast-moving mining and construction industries today can be very close to, in particular cities, residential areas, pipelines, geothermal sites, etc., and this reveals the need to minimize blast vibrations not only by limiting the use of explosives, but also employing new scientific and technological methods. The conventional methodology in minimizing blast vibrations involves the steps of i) measuring by seismograph peak particle velocity induced by blasting, ii) defining ground transmission constants between the blasting area and the target station, iii) finding out the empirical relation involving the propagation of seismic waves, and iv) employing this relation to identify highest amount of explosive that may safely be fired at a time for blasting. This paper addresses practical difficulties during the implementation of this conventional method, particularly the defects and errors in data evaluation and analysis; illustrates the disadvantages of the method; emphasizes essential considerations in case the method is implemented; and finally discusses methods that would fit better to the conditions and demands of the present time compared to the conventional method that intrinsically hosts the abovementioned disadvantages.

Key Words
blasting; vibration; peak particle velocity; signature blast; scaled distance; non-linear behavior

Address
G. Gulsev Uyar: Hacettepe University Faculty of Engineering, Department of Mining Engineering, Ankara, Turkey

C.O. Aksoy: Dokuzeylül University Faculty of Engineering, Department of Mining Engineering, İzmir, Turkey

Abstract
The purpose of this paper is to investigate the thermal effects on the behaviour reinforced-concrete beams strengthened by bonded angle-ply laminated composites laminates plate [+/- theta_n/90m]s. . Effects of number of 90o layers and number of +/- theta layers on the distributions of interfacial stress in concrete beams reinforced with composite plates have also been studied. The present results represent a simple theoretical model to estimate shear and normal stresses. The effects the temperature, mechanical properties of the fibre orientation angle of the outer layers, the number of cross-ply layers, plate length of the strengthened beam region and adhesive layer thickness on the interfacial shear and normal stresses are investigated and discussed.

Key Words
interfacial stresses; concrete beam; angle-ply laminates; fibre angle

Address
Mokhtar Bouazza: 1.) Department of Civil Engineering, University of Tahri Mohamed of Bechar, 08000, Algeria
2.) Laboratory of Materials and Hydrology, University of Sidi Bel Abbes, 22000, Algeria

Kamel Antar: Laboratory of Materials and Hydrology, University of Sidi Bel Abbes, 22000, Algeria

Khaled Amara: 1.) Laboratory of Materials and Hydrology, University of Sidi Bel Abbes, 22000, Algeria
2.) Department of Civil Engineering, University Centre of Ain Temouchent, 46000, Algeria

Samir Benyoucef: 1.) Laboratory of Materials and Hydrology, University of Sidi Bel Abbes, 22000, Algeria
2.) Department of Civil Engineering, University of Sidi Bel Abbes, 22000, Algeria

El Abbes Adda Bedia: Centre of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, 21589, Saudi Arabia


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