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CONTENTS
Volume 12, Number 3, March 2017
 

Abstract
The problem of cylindrical cavity expansion incorporating deformation dependent of intermediate principal stress in rock or soil mass is investigated in the paper. Assumptions that the initial axial total strain is a nonzero constant and the axial plastic strain is not zero are defined to obtain the numerical solution of strain which incorporates deformation-dependent intermediate principal stress. The numerical solution of plastic strains are achieved by the 3-D plastic potential functions based on the M-C and generalized H-B failure criteria, respectively. The intermediate principal stress is derived with the Hook\'s law and plastic strains. Solution of limited expansion pressure, stress and strain during cylindrical cavity expanding are given and the corresponding calculation approaches are also presented, which the axial stress and strain are incorporated. Validation of the proposed approach is conducted by the published results.

Key Words
quasi-plane strain-softening problem; intermediated principal stress; 3-D plastic potential function; deformation dependent; cylindrical cavity expansion

Address
School of Civil Engineering, Central South University, No.22, Shaoshan South Road, Central South University Railway Campus, Changsha, Hunan Province, People's Republic of China.

Abstract
The unloading effect from excavations can cause the deformation of adjacent tunnels, which may seriously influence the operation and safety of those tunnels. However, systematic studies of the deformation characteristics of tunnels located along side excavations are limited, and simplified methods to predict the influence of excavations on tunnels are also rare. In this study, the simulation capability of a finite element method (FEM) considering the small-strain characteristics of soil was verified using a case study. Then, a large number of FEM simulations examining the influence of excavations on adjacent tunnels were conducted. Based on the simulation results, the deformation characteristics of tunnels at different positions and under four deformation modes of the retaining structure were analyzed. The results indicate that the deformation mode of the retaining structure has a significant influence on the deformation of certain tunnels. When the deformation magnitudes of the retaining structures are the same, the influence degree of the excavation on the tunnel increased in this order: from cantilever type to convex type to composite type to kick-in type. In practical projects, the deformation mode of the retaining structure should be optimized according to the tunnel position, and kick-in deformation should be avoided. Furthermore, two methods to predict the influence of excavations on adjacent tunnels are proposed. Design charts, in terms of normalized tunnel deformation contours, can be used to quantitatively estimate the tunnel deformation. The design table of the excavation influence zones can be applied to determine which influence zone the tunnel is located in.

Key Words
deep excavation; tunnel; influence zone; deformation mode; prediction method

Address
(1) MOE Key Laboratory of Coast Civil Structure Safety, Tianjin University, 92 Weijin Rd., Nankai District, Tianjin 300072, China;
(2) Department of Civil Engineering, Tianjin University, 92 Weijin Rd., Nankai District, Tianjin 300072, China.

Abstract
A series of direct shear tests were conducted to investigate the frictional properties of the interface between structures and the filling soil of Chongqing airport fourth stage expansion project. Two types of structures are investigated, one is low carbon steel and the other is the bedrock sampled from the site. The influence of soil water content, surface roughness and material types of structure were analyzed. The tests show that the interface friction and shear displacement curve has no softening stage and the curve shape is close to the Clough-Duncan hyperbola, while the soil is mainly shear contraction during testing. The interface frictional resistance and normal stress curve meets the Mohr-Coulomb criterion and the derived friction angle and frictional resistance of interface increase as surface roughness increases but is always lower than the internal friction angle and shear strength of soil respectively. When surface roughness is much larger than soil grain size, soil-structure interface is nearly shear surface in soil. In addition to the geometry of structural surface, the material types of structure also affects the performance of soil-structure interface. The wet interface frictional resistance will become lower than the natural one under specific conditions.

Key Words
direct shear test; gravel sand; steel; sand rock; surface roughness; water content; friction angle; frictional resistance

Address
Department of Civil Engineering, Tsinghua University, Beijing 100084, China.

Abstract
The stone columns are increasingly being used as a soil improvement method for supporting a wide variety of structures (such as road embankment, buildings, storage tanks etc.) especially built on soft soil. Soil improvement by the stone column method overcomes the settlement problem and low stability. Nevertheless, stone column in very soft soils may not be functional due to insufficient lateral confinement. The required lateral confinement can be overcome by encasing the stone column with a suitable geosynthetic. Encasement of stone columns with geogrid is one of the ideal forms of improving the performance of stone columns. This paper presents the results of a series of experimental tests and numerical analysis to investigate the behavior of stone columns with and without geogrid encasement in soft clay deposits. A total of six small scale laboratory tests were carried out using circular footing with diameters of 0.05 m and 0.1 m. In addition, a well-known available software program called PLAXIS was used to numerical analysis, which was validated by the experimental tests. After good validation, detailed of parametric studies were performed. Different parameters such as bearing capacity of stone columns with and without geogrid encasement, stiffness of geogrid encasement, depth of encasement from ground level, diameter of stone columns, internal friction angle of crushed stone and lateral bulging of stone columns were analyzed. As a result of this study, stone column method can be used in the improvement of soft ground and clear development in the bearing capacity of the stone column occurs due to geogrid encasement. Moreover, the bearing capacity is effected from the diameter of the stone column, the angle of internal friction, rigidity of the encasement, and depth of encasement. Lateral bulging is minimized by geogrid encasement and effected from geogrid rigidity, depth of encasement and diameter of the stone column.

Key Words
stone column; geogrid encasement; soft clay; bearing capacity; finite element analysis; lateral bulging

Address
(1) Ahmet Demir:
Department of Civil Engineering, Osmaniye Korkut Ata University, Karacaoğlan Campus 80000 Osmaniye Turkey;
(2) Talha Sarici:
Department of Civil Engineering, Inonu University, 44280 Malatya, Turkey.

Abstract
The determination of the mixture parameters of stabilization has become a great concern in geotechnical applications. This paper presents an effort about the application of artificial intelligence (AI) techniques including radial basis neural network (RBNN), multi-layer perceptrons (MLP), generalized regression neural network (GRNN) and adaptive neuro-fuzzy inference system (ANFIS) in order to predict the unconfined compressive strength (UCS) of silty soil stabilized with bottom ash (BA), jute fiber (JF) and steel fiber (SF) under different freeze-thaw cycles (FTC). The dosages of the stabilizers and number of freeze-thaw cycles were employed as input (predictor) variables and the UCS values as output variable. For understanding the dominant parameter of the predictor variables on the UCS of stabilized soil, a sensitivity analysis has also been performed. The performance measures of root mean square error (RMSE), mean absolute error (MAE) and determination coefficient (R2) were used for the evaluations of the prediction accuracy and applicability of the employed models. The results indicate that the predictions due to all AI techniques employed are significantly correlated with the measured UCS (p

Key Words
freeze-thaw cycle; unconfined compressive strength; silty soil; artificial intelligence; sensitivity analysis; bottom ash; jute fiber; steel fiber

Address
Department of Civil Engineering, University of Gaziantep, 27310, Gaziantep, Turkey.

Abstract
Thermal effect has great influence on wellbore stability in Dongfang 1-1 (DF 1-1) gas field, a reservoir with high-temperature and high-pressure. In order to analyze the wellbore stability in DF1-1 gas field, the variation of temperature field after drilling was analyzed. In addition, the effect of temperature changing on formation strength and the thermal expansion coefficients of formation were tested. On this basis, a wellbore stability model considering thermal effect was developed and the thermal effect on fracture pressure and collapse pressure was analyzed. One of the main challenges in this gas field is the decreasing temperature of the wellbore will reduce fracture pressure substantially, resulting in the drilling fluid leakage. If the drilling fluid density was reduced, kick or blowout may happen. Therefore, the key of safe drilling in DF1-1 gas field is to predict the fracture pressure accurately.

Key Words
computing model of temperature field; rock mechanical characteristic; thermal effect; mud circulation; wellbore stability; Dongfang 1-1 gas field; high temperature high pressure

Address
(1) Chuanliang Yan, Yuanfang Cheng:
School of Petroleum Engineering, China University of Petroleum (Huadong), Qingdao, 266580, China;
(2) Chuanliang Yan, Jingen Deng:
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, 102249, China;
(3) Xinjiang Yan, Junliang Yuan:
CNOOC Research Institute, Beijing, 100027, China;
(4) Fucheng Deng:
Yangtze University, Jingzhou, 434023, China.

Abstract
Uncertainty is a fact belonging to engineering practice. An important uncertainty that sets geotechnical engineering is the variability associated with the properties of soils or, more precisely, the characterization of soil profiles. The reason is due largely to the complex and varied natural processes associated with the formation of soil. Spatial variability analysis for the study of the stability of natural slopes, complementing conventional analyses, is able to incorporate these uncertainties. In this paper the characterization is performed in back-analysis for a case of landslide occurred to verify afterwards the presence of the conditions of shear strength at failure. This approach may support designers to make more accurate estimates regarding slope failure responding, more consciously, to the legislation dispositions about slope stability evaluation and future design. By applying different kriging techniques used for spatial analysis it has been possible to perform a 3D-slope reconstruction. The predictive analysis and the areal mapping of the soil mechanical characteristics would support the definition of priority interventions in the zones characterized by more critical values as well as slope potential instability. This tool of analysis aims to support decision-making by directing project planning through the efficient allocation of available resources.

Key Words
soil uncertainty; spatial variability; shear strength; kriging; slope stability

Address
(1) Mara Lombardi:
Department of Chemical Materials Environment Engineering, Sapienza University of Rome, Safety Engineering, via Eudossiana 18 - Rome, Italy;
(2) Monica Cardarilli, Giuseppe Raspa:
Department of Chemical Materials Environment Engineering, Sapienza University of Rome, via Eudossiana 18 - Rome, Italy.

Abstract
A fundamental study of drilled shafts-soil systems subjected to lateral cyclic loading in weathered soil was conducted using numerical analyses. The emphasis was on quantifying the soil resistance of laterally cyclic loaded pile using 3D finite element analysis. The appropriate parametric studies needed for verifying the cyclic p-y characteristic are presented in this paper. A framework for determining the cyclic lateral load transfer curve (p-y curves) on the basis of numerical analyses is proposed. Through comparisons with results of field load tests, the three-dimensional numerical methodology in the present study is in good agreement with the general trend observed by in situ measurements and thus, represents a realistic soil-pile interaction for laterally loaded piles in soil than that of existing p-y method. It can be said that a rigorous present analysis can overcome the limitations of existing cyclic p-y methods to some extent by considering the effect of realistic three-dimensional combination of pile-soil forces. The proposed cyclic p-y curve is shown to be capable of predicting the behavior of the drilled shafts in weathered soil.

Key Words
drilled shafts; lateral cyclic load; cyclic p-y curves; 3D finite element method; weathered soil

Address
(1) Sangseom Jeong, Jeongsik Park:
Department of Civil and Environmental Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea;
(2) Junyoung Ko:
Department of Civil, Environmental, and Construction Engineering, Texas Tech University, 911 Boston Ave., Lubbock, TX 79409, USA;
(3) Byungchul Kim:
Overseas Civil Project Management Team, Daelim Industrial Co., 36, Jong-ro 1-gil, Jongno-gu, Seoul 03152, Republic of Korea.

Abstract
Clay soils are typical for their swelling properties upon absorption of water during rains and development of cracks during summer time owing to the profile desorption of water through the inter-connected soil pores by water vapour diffusion leading to evaporation. This type of unstable soil phenomenon by and large poses a serious threat to the strength and stability of structures when rest on such type of soils. Even as lime and cement are extensively used for stabilization of clay soils it has become imperative to find relatively cheaper alternative materials to bring out the desired properties within the clay soil domain. In the present era of catastrophic environmental degradation as a side effect to modernized manufacturing processes, industrialization and urbanization the creative idea would be treating the waste products in a beneficial way for reuse and recycling. Bottom ash and ecosand are construed as a waste product from cement industry. An optimal combination of bottom ash-eco sand can be thought of as a viable alternative to stabilize the clay soils by means of an effective dispersion dynamics associated with the inter connected network of pore spaces. A CATIA model was created and imported to ANSYS Fluent to study the dispersion dynamics. Ion migration from the bottom ash-ecosand pile was facilitated through natural formation of cracks in clay soil subjected to atmospheric conditions. Treated samples collected at different curing days from inner and outer zones at different depths were tested for, plasticity index, Unconfined Compressive Strength (UCS), free swell index, water content, Cation Exchange Capacity (CEC), pH and ion concentration to show the effectiveness of the method in improving the clay soil.

Key Words
stabilization; bottom ash-ecosand; ANSYS fluent; plasticity index; UCS

Address
(1) Sathyapriya Subramanian, P.D. Arumairaj:
Department of Civil Engineering, Government College of Technology, Coimbatore, India;
(2) T. Subramani:
Department of Mining Engineering, Anna University, Chennai, India.

Abstract
In this research, experimental and numerical simulations were adopted to investigate the effects of ligament angle on compressive strength and failure mode of rock-like material specimens containing two noncoplanar filled fissures under uniaxial compression. The experimental results show that with the increase of ligament angle, the compressive strength decreases to a nadir at the ligament angle of 60°, before increasing to the maximum at the ligament angle of 120°, while the elastic modulus is not obviously related to the ligament angle. The shear coalescence type easily occurred when α < β, although having the same degree difference between the angle of ligament and fissure. Numerical simulations using PFC2D were performed for flawed specimens under uniaxial compression, and the results are in good consistency with the experimental results. By analyzing the crack evolution process and parallel bond force field of rock-like material specimen containing two non-coplanar filled fissures, we can conclude that the coalescence and propagation of crack are mainly derived from parallel bond force, and the crack initiation and propagation also affect the distribution of parallel bond force. Finally, the displacement vectors in ligament region were used to identify the type of coalescence, and the results coincided with that obtained by analyzing parallel bond force field. These experimental and numerical results are expected to improve the understanding of the mechanism of flawed rock engineering structures.

Key Words
rock-like materials; filled fissures; PFC; parallel bond force; crack coalescence

Address
State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, PR China.


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