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CONTENTS
Volume 18, Number 4, July20 2019
 

Abstract
Rockmass parameters are used in the design of engineering structures built in rock and soil. One of the most important of these parameters is the rockmass Emass (Emass). Determination of the Emass of rockmass is a long, hard and expensive job. Therefore, empirical formulas developed by different researchers are used. These formulas use the elastic modulus of the material as a parameter. This value is a constant value in the design. However, engineering structures remain under different loads depending on many factors, such as topography, geometry of the structure, rock / soil properties. Time is other important parameter for rock/soil structure. With the start of the excavation, the loads that the structure is exposed to will change and remain constant at one level. In the new proposed method, the use of different Emass calculated from empirical formulas using the different material elastic modulus, which has different values under different loads as time dependent, was investigated in rock/soil structures during design. The performance of the stability analysis using different deformation modules was questioned by numerical modeling method. For this query, a sub-routine which can be integrated into the numerical modeling software has been developed. The integrated sub-routine contains the formula for the Emass, which is calculated from the material elasticity modules under time dependent and different constant loads in the laboratory. As a result of investigations conducted in 12 different field studies, the new proposed method is very sensitive.

Key Words
rock mechanics, numerical modeling, time-dependent deformation, stability analysis

Address
Okay C. Aksoy, Suleyman Safak and Vehbi Ozacar: Dokuz Eylul University, Engineering Faculty, Department of Mining Engineering, Izmir-Turkey

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

Semih Utku: Dokuz Eylul University, Engineering Faculty, Department of Computer Science, Izmir-Turkey


Abstract
Soil-rock mixture (S-RM) is an inhomogeneous geomaterial that is widely encountered in nature. The mechanical and physical properties of S-RM are important factors contributing towards different deformation characteristics and unstable modes of the talus slope. In this paper, the equivalent substitution method was employed for the preparation of S-RM test samples, and large-scale triaxial laboratory tests were conducted to investigate their mechanical parameters by varying the water content and confining pressure. Additionally, a simplified geological model based on the finite element method was established to compare the stability of talus slopes with different strength parameters and in different excavation and support processes. The results showed that the S-RM samples exhibit slight strain softening and strain hardening under low and high water content, respectively. The water content of S-RM also had an effect on decreasing strength parameters, with the decrease in magnitude of the cohesive force and internal friction angle being mainly influenced by the low and high water content, respectively. The stability of talus slope decreased with a decrease in the cohesion force and internal friction angle, thereby creating a new shallow slip surface. Since the excavation of toe of the slope for road construction can easily cause a landslide, anti-slide piles can be used to effectively improve the slope stability, especially for shallow excavations. But the efficacy of anti-slide piles gradually decreases with increasing water content. This paper can act as a reference for the selection of strength parameters of S-RM and provide an analysis of the instability of the talus slope.

Key Words
soil-rock mixture; triaxial test; water content; strength parameter; talus slope; slope stability

Address
Haofeng Xing and Liangliang Liu: Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China

Yong Luo: Department of Geology Survey and Design,Guizhou Transportation Planning Survey and Design Academe Co., Ltd., Guiyang, 550001, China


Abstract
In this study, the load carrying behavior of piled rafts installed in inclined bearing rock layer was investigated for rock-mounted and -socketed conditions. It was found that settlements induced for an inclined bearing rock layer are larger than for a horizontal layer condition. The load capacity of piled rafts for the rock-mounted condition decreased as rock-layer inclination angle (theta) increased, while vice versa for the rock-socketed condition. The load capacities of raft and piles both decreased with increasing theta for the rock-mounted condition. When bearing rock layer was inclined, loads carried by uphill-side piles were greater than those by downhill-side piles. The values of differential settlements of rock-mounted and -socketed conditions were not significantly different whereas slightly higher for the rock-socketed condition. The values of load sharing ratio (alpha_p) and its variation with settlement were not markedly changed by the inclination of bedrock. It was shown that alpha_p for piled rafts installed in rock layer was not affected by theta whereas actual loads carried by raft and piles may vary depending on the pile installation and rock-layer inclination conditions.

Key Words
piled rafts; rock socketed condition, inclined rock layer, load carrying capacity; settlement; load sharing ratio

Address
Yanghoon Roh: 1.) School of Civil and Environmental Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
2.) Geotechnical and Tunnel Division, Dohwa Engineering Co., LTD., 438 Samseong-ro, Gangnam-gu, Seoul 06178, Republic of Korea

Garam Kim, Incheol Kim and Junhwan Lee: School of Civil and Environmental Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea

Abstract
It is important to study the problem of durability for tunnel structures. As a main influence on the durability of tunnel structures, carbonation-induced corrosion is studied. For the complicated environment of tunnel structures, based on the data samples from real engineering examples, the intelligent method (genetic programming) is used to construct the service life prediction model of tunnel structures. Based on the model, the prediction of service life for tunnel structures in carbonation environments is studied. Using the data samples from some tunnel engineering examples in China under carbonation environment, the proposed method is verified. In addition, the performance of the proposed prediction model is compared with that of the artificial neural network method. Finally, the effect of two main controlling parameters, the population size and sample size, on the performance of the prediction model by genetic programming is analyzed in detail.

Key Words
prediction model; tunnel structure; genetic programming; service life; carbonation

Address
Wei Gao and Dongliang Chen: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering,
College of Civil and Transportation Engineering, Hohai University, Nanjing 210098, PR China


Abstract
The aim of this paper was to study the influence of the footing shape and the effect of the roughness of the foundation base on the bearing capacity of shallow foundations on rock masses. For this purpose the finite difference method was used to analyze the bearing capacity of various types and states of rock masses under the assumption of Hoek-Brown failure criterion, for both plane strain and axisymmetric model, and considering smooth and rough interface. The results were analyzed based on a sensitivity study of four varying parameters: foundation width, rock material constant (mo), uniaxial compressive strength and geological strength index. Knowing how each parameter influences the bearing capacity depending on the footing shape (circular vs strip footing) and the footing base interface roughness (smooth vs rough), two correlation factors were developed to estimate the percentage increase of the ultimate bearing capacity as a function of the footing shape and the roughness of the footing base interface.

Key Words
circular footing; strip footing; interface; roughness; rock mass; finite difference method

Address
Ana S. Alencar and Rubén A. Galindo: ETSI Caminos, C. y P., Technical University of Madrid (UPM), C/ Profesor Aranguren s/n, Madrid 28040, Spain

Svetlana Melentijevic: Faculty of Geology, Complutense University of Madrid (UCM), C/ José Antonio Nováis no. 2, Madrid 28040, Spain

Abstract
A controlled low strength material (CLSM) is a highly flowable cementitious material used for trench backfilling. However, when applying vertical loads to backfilled trenches, shear failure or differential settlement may occur at the interface between the CLSM and natural soil. Hence, this study aims to evaluate the characteristics of the interface friction between the CLSM and soils based on curing time, gradation, and normal stress. The CLSM is composed of fly ash, calcium sulfoaluminate cement, sand, silt, water, and an accelerator. To investigate the engineering properties of the CLSM, flow and unconfined compressive strength tests are carried out. Poorly graded and well-graded sands are selected as the in-situ soil adjacent to the CLSM. The direct shear tests of the CLSM and soils are carried out under three normal stresses for four different curing times. The test results show that the shear strengths obtained within 1 day are higher than those obtained after 1 day. As the curing time increases, the maximum dilation of the poorly graded sand–CLSM specimens under lower normal stresses also generally increases. The maximum contraction increases with increasing normal stress, but it decreases with increasing curing time. The shear strengths of the well-graded sand–CLSM interface are greater than those of the poorly graded sand–CLSM interface. Moreover, the friction angle for the CLSM–soil interface decreases with increasing curing time, and the friction angles of the well-graded sand–CLSM interface are greater than those of the poorly graded sand–CLSM interface. The results suggest that the CLSM may be effectively used for trench backfilling owing to a better understanding of the interface shear strength and behavior between the CLSM and soils.

Key Words
backfill; CLSM; curing time; direct shear test; interface friction

Address
WooJin Han, Sang Yeob Kim and Jong-Sub Lee: School of Civil, Environmental and Architectural Engineering, Korea University,145 Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea

Yong-Hoon Byun: 1.) School of Agricultural Civil & Bio-Industrial Engineering, Kyungpook National University,
80 Daehak-ro, Buk-gu, Daegu, 41566, Republic of Korea
2.) Institute of Agricultural Science & Technology, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu, 41566, Republic of Korea

Abstract
Gangue filling in the goaf is an effective measure to control the surface subsidence. However, due to the obvious deformation of gangue compression, the filling effect deserves to be further studied. To this end, the deformation of coal gangue filling in the goaf is analyzed by theoretical analysis, large-scale crushed rock compression test, and field investigation. Through the compression test of crushed rock, the deformation behaviour characteristics and energy dissipation characteristics is obtained and analysed. The influencing factors of gangue filling and predicted amount of main deformation are summarized. Besides, the predicted equation and filling subsidence coefficients of gangue are obtained. The gangue filling effect was monitored by the movement observation of surface rock. Gangue filling can support the roof of the goaf, effectively control the surface subsidence with little influence on the ground villages. The premeter and equations of the main deformation in the gangue filling are verified, and the subsidence coefficient is further reduced by adding cemented material or fine sand. This paper provides a practical and theoretical reference for further development of gangue filling.

Key Words
gangue filling; large-scale crushed rock compression test; deformation behaviour characteristics; energy dissipation characteristics; movement observation of surface

Address
Changxiang Wang, Yao Lu, Buchu Zhang and Yanbo Liang: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China
2.) State Key Laboratory of Mining Disaster Prevention and Control Co-Founded by Shandong Province and the Ministry of Science and Technology, Qingdao 266590, China

Yangyang Li: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China
2.) State Key Laboratory of Mining Disaster Prevention and Control Co-Founded by Shandong Province and the Ministry of Science and Technology, Qingdao 266590, China
3.) State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, China

Abstract
Waste materials are being produced in huge quantities globally, and the usual practice is to dump them into legal or illegal landfills. Recycled tiles (RT) are being used in soil stabilisation which is considered as sustainable solution to reduce the amount of waste and solve the geotechnical problems. Although the stabilisation of soil using RT improved the soil properties, it could not achieve the standard values required for construction. Thus, this study uses 20% RT together with low cement content (2%) to stabilise soft soil. Series of consolidated undrained triaxial compression tests were conducted on untreated and RT-cement treated samples. Each test was performed at 7, 14, and 28 days curing period and 50, 100, and 200 kPa confining pressures. The results revealed an improvement in the undrained shear strength parameters (cohesion and internal frication angle) of treated specimens compared to the untreated ones. The cohesion and friction angle of the treated samples were increased with the increase in curing time and confining pressure. The peak deviator stress of treated samples increases with the increment of either the effective confining pressures or the curing period. Microstructural and chemical tests were performed on both untreated and RT-cement treated samples, which included field emission scanning electron microscopic (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and energy dispersive X-ray spectrometer (EDX). The results indicated the formation of cementation compounds such as calcium aluminium hydrate (C-A-H) within the treated samples. Consequently, the newly formed compounds were responsible for the improvement observed in the results of the triaxial tests. This research promotes the utilisation of RT to reduce the amount of cement used in soil stabilisation for cleaner planet and sustainable environment.

Key Words
soft soil; consolidated undrained triaxial test; RT-cement; soil stabilisation; shear strength; curing time

Address
Mohammed A. M. Al-Bared, Indra S. H. Harahap and Montasir O. A. Ali: Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610, Malaysia

Aminaton Marto: Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia (UTM) Kuala Lumpur, 54100 Kulala Lumpur, Malaysia

Seyed Vahid Alavi Nezhad Khalil Abad: Department of Civil Engineering, Birjand University of Technology, Birjand, Iran

Abstract
The bearing capacity of roadside support is the key problem in gob-side entry retaining technology. To study the cooperative bearing characteristics of the roof-roadside support-floor along the gob-side entry retaining, a mechanical model of the composite structure of the roof-roadside support-floor was first established. A method for determining the structural parameters of gob-side entry retaining was then proposed. Based on this model, adaptability analysis of roadside support was carried out. The results showed that the reasonable width of the gob-side entry roadway was inversely proportional to the mining height, and directly proportional to the bearing strength of the roof and floor. And the reasonable width of the \"flexible-hard\" roadside support was directly proportional to its own strength, and inversely proportional to the width of the gob-side entry retaining. When determining the position and size of the roadside support along the gob-side entry retaining, the surrounding rock environment should be fully considered. Measured results from case study also show the rationality of the model and calculation method.

Key Words
\"flexible-hard\" roadside support; composite structures; cooperative bearing capacity; gob-side entry retaining

Address
Yunliang Tan, Zenghui Zhao and Dongmei Huang: 1.) State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology, Qingdao 266590, China
2.) College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China

Qing Ma,Qingheng Gu, Deyuan Fan and Shilin Song: College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China

Abstract
Physical model tests were first performed to investigate the failure pattern of multiple pillar-roof support system. It was observed in the physical model tests, pillars were design with the same mechanical parameters in model #1, cracking occurred simultaneously in panel pillars and the roof above barrier pillars. When pillars 2 to 5 lost bearing capacity, collapse of the roof supported by those pillars occurred. Physical model #2 was design with a relatively weaker pillar (pillar 3) among six pillars. It was found that the whole pillar-roof system was divided into two independent systems by a roof crack, and two pillars collapse and roof subsidence events occurred during the loading process, the first failure event was induced by the pillars failure, and the second was caused by the roof crack. Then, for a multiple pillar-roof support system, three types of failure patterns were analysed based on the condition of pillar and roof. It can be concluded that any failure of a bearing component would cause a subsidence event. However, the barrier pillar could bear the transferred load during the stress redistribution process, mitigating the propagation of collapse or cutting the roof to insulate the collapse area. Importantly, some effective methods were suggested to decrease the risk of catastrophic collapse, and the deep-hole-blasting was employed to improve the stability of the pillar and roof support system in a room and pillar mine.

Key Words
physical model test; pillar collapse mode; pillars-roof support system; deep hole blasting; Gypsum mining

Address
Lu Chen: 1.) School of Civil Engineering, Changsha University of Science and Technology, Changsha, Hunan, 410083, China
2.) School of Resources and Safety Engineering, Central South University, Changsha, Hunan, 410082, China

Zilong Zhou and Yuan Zhao: School of Resources and Safety Engineering, Central South University, Changsha, Hunan, 410082, China

Chuanwei Zang: 1.) School of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China
2.) Key Laboratory of Mining Disaster Prevention and Control, Qingdao 266590, China

Ling Zeng: School of Civil Engineering, Changsha University of Science and Technology, Changsha, Hunan, 410083, China


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