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Volume 6, Number 1, January 2014

In this study, artificial neural network (ANN) and multiple regression (MR) models were developed to predict the critical factor of safety (Fs) of the homogeneous finite slopes subjected to earthquake forces. To achieve this, the values of Fs in 5184 nos. of homogeneous finite slopes having different slope, soil and earthquake parameters were calculated by using the Simplified Bishop method and the minimum (critical) Fs for each of the case was determined and used in the development of the ANN and MR models. The results obtained from both the models were compared with those obtained from the calculations. It is found that the ANN model exhibits more reliable predictions than the MR model. Moreover, several performance indices such as the determination coefficient, variance account for, mean absolute error, root mean square error, and the scaled percent error were computed. Also, the receiver operating curves were drawn, and the areas under the curves (AUC) were calculated to assess the prediction capacity of the ANN and MR models developed. The performance level attained in the ANN model shows that the ANN model developed can be used for predicting the critical Fs of the homogeneous finite slopes subjected to earthquake forces.

Key Words
artificial neural networks; critical factor of safety; homogeneous finite slope; pseudostatistic approach; simplified Bishop method

Yusuf Erzın and T. Cetin:
Celal Bayar University, Faculty of Engineering, Department of Civil Engineering, 45140 Manisa, Turkey.

This paper investigates the development of failure surfaces induced by an embankment on soft marine clay deposits and the characteristics of such surfaces through numerical simulations and its comparative study with monitoring results. It is well known that the factor of safety of embankment slopes is closely related to the vertical loading, including the height of the embankment. That is, an increase in the embankment height reduces the factor of safety. However, few studies have examined the relationship between the lateral movement of soft soil beneath the embankment and the factor of safety. In addition, no study has investigated the distribution of the pore pressure coefficient B value along the failure surface. This paper conducts a continuum analysis using finite difference methods to characterize the development of failure surfaces during embankment construction on soft marine clay deposits. The results of the continuum analysis for failure surfaces, stress, displacement, and the factor of safety can be used for the management of embankment construction. In failure mechanism, it has been validated that a large shear displacement causes change of stress and pore pressure along the failure surface. In addition, the pore pressure coefficient B value decreases along the failure surface as the embankment height increases. This means that the rate of change in stress is higher than that in pore pressure.

Key Words
trial embankment; pore pressure coefficient B; lateral movement; failure surface; continuum analysis

(1) Eun-Soo Hong:
BON E&C Co., Ltd. B-610, Seongnam Woorim Lions Vally 2, 146-8, Jungwon-gu, Seongnam-si, Gyeonggi-do, 462-120, Republic of Korea;
(2) Ki-Il Song and Yeo-Won Yoo:
Department of Civil Engineering, Inha University, 100 Inha-ro, Nam-gu, Incheon, 402-751, Republic of Korea;
(3) Jong-Wan Hu:
3Department of Civil and Environmental Engineering, College of Urban Science, University of Incheon, Incheon, 406-840, Republic of Korea; and Head of Center, Incheon Disaster Prevention Research Center, University of Incheon, 406-840, Republic of Korea.

Use of geotextile as reinforcement material to improve the weak soil is a popular method these days. Tensile strength of geotextile and the soil-geotextile interaction are the major factors which influence the improvement of the soil. Change in fine content within the sand can change the interface behavior between soil and geotextile. In the present paper, the bearing capacity of unreinforced and geotextile-reinforced sand with different percentages of fines has been studied. A series of model tests have been carried out and the load settlement curves are obtained. The ultimate load carrying capacity of unreinforced and reinforced sand with different percentages of fines is compared. The interface behavior of sand and geotextile with various percentages of fines is also studied. It is observed that sand having around 5% of fine is suitable or permissible for bearing capacity improvement due to the application of geosynthetic reinforcement. The effectiveness of the reinforcement in load carrying capacity improvement decreases due to the addition of excessive amount of fines.

Key Words
bearing capacity; compaction; fine; geotextile-reinforced sand; soil-geotextile interface friction and adhesion

Kousik Deb and Sanku Konai:
Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur - 721302, India.

In this paper, asymmetric drainage boundaries modeled by exponential functions which can simulate intermediate drainage from pervious to impervious boundary is proposed for the one-dimensional consolidation problem, and the solution for the new boundary conditions was derived. The new boundary conditions satisfy the initial and the steady state conditions, and the solution for the new boundary conditions can be degraded to the conventional solution by Terzaghi. Convergence study on the infinite series solution showed that only one term in the series is needed to meet the precision requirement for larger degree of consolidation, and that more terms in the series for smaller degree of consolidation. Comparisons between the present solution with those by Terzaghi and Gray are also provided.

Key Words
Terzaghi's one-dimensional consolidation equation; exponential drainage boundary

(1) Guo-Xiong Mei and Jun Xia:
College of Transportation Engineering, Nanjing University of Technology, Nanjing 210009, China;
(2) Thomas M.H. Lok and Sheng Shen Wu:
Faculty of Science and Technology, University of Macau, Macau SAR, China.

Organic soils exhibit problematic properties such as high compressibility and low shear strength; these properties may cause differential settlement or failure in structures built on such soils. Organic soil removal or stabilization are the most important methods to overcome geotechnical problems related to peat soils\' engineering characteristics. This paper presents soil mechanical intervention for stabilization of peat with sand columns and focuses on a comparison between the mechanical characteristics of undisturbed peat and peat stabilized with 20%, 30% and 40% of sand on the laboratory scale. Cylindrical columns were extruded in different diameters through a nearly undisturbed peat sample in the laboratory and filled with sand. By adding sand columns to peat, higher permeability, higher shear strength and a faster consolidation was achieved. The sample with 70% peat and 30% sand displayed the most reliable compressibility properties. This can be attributed to proper drainage provided by sand columns for peat in this specific percentage. It was observed that the granular texture of sand also increased the friction angle of peat. The addition of 30% sand led to the highest shear strength among all mixtures considered. The peat samples with 40% sand were sampled with two and three sand columns and tested in direct shear and consolidation tests to evaluate the influence of the number and geometry of sand columns. Samples with three sand columns showed higher compressibility and shear strength. Following the results of this laboratory study it appears that the introduction of sand columns could be suitable for geotechnical peat stabilization in the field scale.

Key Words
peat; sand; geotechnical stabilization; mechanical characteristics

(1) M. Ehsan Jorat, Stefan Kreiter and Tobias Mörz:
MARUM - Center for Marine and Environmental Sciences, University of Bremen, Klagenfurter Strasse, DE-28359 Bremen, Germany;
(2) Vicki Moon, and Willem de Lange:
Department of Earth and Ocean Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand.

This paper presents an experimental and numerical study on the evaluation of a thermal response test using a precast high-strength concrete (PHC) energy pile and a closed vertical system with W-type ground heat exchangers (GHEs). Field thermal response tests (TRTs) were conducted on a PHC energy pile and on a general vertical GHE installed in a multiple layered soil ground. The equivalent ground thermal conductivity was determined by using the results from TRTs. A simple analytical solution is suggested in this research to derive an equivalent ground thermal conductivity of the multilayered soils for vertically buried GHEs. The PHC energy pile and general vertical system were numerically modeled using a three dimensional finite element method to compare the results with TRTs'. Borehole thermal resistance values were also obtained from the numerical results, and they were compared with various analytical solutions. Additionally, the effect of ground thermal conductivity on the borehole thermal resistance was analyzed.

Key Words
ground thermal conductivity; borehole thermal resistance; ground heat exchanger; thermal response test; numerical analysis

(1) Seok Yoon, Seung-Rae Lee, Gyu-Hyun Go and Dowon Park:
Department of Civil and Environmental Engineering, Korean Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea;
(2) Jianfeng Xue:
School of Applied Science and Engineering, Monash University, Churchill, Vic, 3842, Australia;
(3) Hyunku Park:
Division of Civil Engineering, Samsung C&T, Seoul 137-858, Republic of Korea.

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