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CONTENTS
Volume 1, Number 3, September 2009
 

Abstract
For a two-way drainage deposit under a surcharge load, it is possible to leave a layer adjacent to the bottom drainage boundary without prefabricated vertical drain (PVD) improvement and achieve approximately the same degree of consolidation as a fully penetrated case. This depth is designated as an optimum PVD installation depth. Further, for a two-way drainage deposit under vacuum pressure, if the PVDs are fully penetrated through the deposit, the vacuum pressure will leak through the bottom drainage boundary. In this case, the PVDs have to be partially penetrated, and there is an optimum installation depth. The equations for calculating these optimum installation depths are presented, and the usefulness of the equations is studied by using finite element analysis as well as laboratory model test results.

Key Words
prefabricated vertical drain (PVD); ground improvement; vacuum consolidation; laboratory test; pre-loading; soft clayey deposit.

Address
J.-C. Chai: Department of Civil Engineering, Saga University, 1 Honjo, Saga 840-8502, Japan
N. Miura: Institute of Soft Ground Engineering, Co., Ltd., 4-1-52 Ohtakara, Saga 840-0811, Japan
T. Kirekawa: Institute of Soft Ground Engineering, Co., Ltd., 4-1-52 Ohtakara, Saga 840-0811, Japan
T. Hino: Institute of Lowland Technology, Saga University, 1 Honjo, Saga 840-8502, Japan

Abstract
A 10.4-m high highway embankment retained behind mechanically stabilized earth (MSE) walls is under construction in the northeastern part of the Indian state of Bihar. The structure is constructed with compacted, micaceous, grey, silty sand, reinforced with polyester (PET) geogrids, and faced with reinforced cement concrete fascia panels. The connections between the fascia panels and the geogrids failed on several occasions during the monsoon seasons of 2007 and 2008 following episodes of heavy rainfall, when the embankment was still under construction. However, during these incidents the MSE embankment itself remained by and large stable and the collateral damages were minimal. The observational data during these incidents presented an opportunity to develop and calibrate a simple procedure for estimating rainfall induced pore water pressure development within MSE embankments constructed with backfill materials that do not allow unimpeded seepage. A simple analytical finite element model was developed for the purpose. The modeling results were found to agree with the observational and meteorological records from the site. These results also indicated that the threshold rainwater infiltration flux needed for the development of pore water pressure within an MSE embankment is a monotonically increasing function of the hydraulic conductivity of backfill. Specifically for the MSE embankment upon which this study is based, the analytical results indicated that the instabilities could have been avoided by having in place a chimney drain immediately behind the fascia panels.

Key Words
mechanically stabilized earth (MSE) wall; embankment; rainfall; unsaturated; seepage; stability; drainage.

Address
Debasis Roy: Department of Civil Engineering, IIT Kharagpur, WB 721302, India
Chiranjeevi K: Department of Civil Engineering, IIT Kharagpur, WB 721302, India
Raghvendra Singh: Department of Civil Engineering, IIT Kharagpur, WB 721302, India
Dilip K Baidya: Department of Civil Engineering, IIT Kharagpur, WB 721302, India

Abstract
The bearing capacity factor Ny is computed for a rough conical footing placed over horizontal ground surface. The axisymmetric lower bound limit analysis formulation, in combination with finite elements and linear programming, proposed recently by the authors is used in this study. The variation of Ny with cone apex angle (B), in a range of 30o-180o, is obtained for different values of ?; where ? is soil friction angle. For ? < 30o, the magnitude of Ny is found to decrease continuously with an increase in B from 30o to 180o. On the other hand, for ? > 30o, the minimum magnitude of Ny is found to occur generally between B = 120o and B = 150o. In all the cases, it is noticed that the magnitude of Ny becomes maximum for B = 30o. For a given diameter of the cone, the area of the plastic zone reduces generally with an increase in B. The obtained values of Ny are found to compare quite well with those available in literature.

Key Words
axi-symmetry; bearing capacity; failure; limit analysis; optimization; plasticity.

Address
Vishwas N Khatri: Civil Engineering Department, Indian Institute of Science, Bangalore-560012, India
Jyant Kumar: Civil Engineering Department, Indian Institute of Science, Bangalore-560012, India

Abstract
Vertical vibration tests were conducted using model footings of different size and mass resting on the surface of finite sand layer with different height to width ratios and underlain by either rigid concrete base or natural red-earth base. A comparative study of the ratio of predicted and observed natural frequency ratio of the finite sand stratum was made using the calculated values of equivalent stiffness suggested by Gazetas (1983) and Baidya and Muralikrishna (2001). Comparison of results between model footings resting on finite sand stratum underlain by the rigid concrete base and the natural red-earth base showed that, the presence of a finite base of higher rigidity increases the resonant frequency significantly. With increase in H/B ratio beyond 2.0, the influence of both the rigid concrete and natural red-earth base decreases. Increase in the contact area of the footing increases the resonant frequency of the model footings resting on finite sand stratum underlain by both the types of finite bases. Both the predicted and the observed resonant frequency ratio decreases with increase in force rating and height to width ratio for a given series of model footing.

Key Words
dynamic response; resonant frequency; displacement amplitude; frequency ratio; equivalent stiffness.

Address
M.T. Prathap Kumar: G.C.E., Ramanagara, India and UVCE, Bangalore, India
H.N. Ramesh: Faculty of Engineering (Civil), UVCE, Bangalore University, Bangalore, India
M.V. Raghavendra Rao: Faculty of Engineering (Civil), UVCE, Bangalore University, Bangalore, India
M.E. Raghunandan: UVCE, Bangalore, India

Abstract
The one-dimensional compressibility of sand is an important property for the estimation of settlement or deformation of sand deposits. The K0 value of sand is also an important design parameter. Experimental results are presented in this paper to study the compressibility of sand in K0 consolidation tests. The K0 consolidation tests were carried out using a triaxial cell and a plane-strain apparatus. Specimens prepared using both the moist tamping and the water sedimentation methods were tested. The testing data demonstrate that the type of testing apparatus does not affect the K0 measurement if proper boundary conditions are imposed in the tests. The data also show that the compressibility and the K0 value of loose sand specimens prepared using the moist tamping method are very sensitive to the variation of void ratio. The K0 values measured from these tests do not agree with the K0 values calculated from Jaky

Key Words
earth pressure; compressibility; consolidation; laboratory tests; sand fabric; triaxial; planestrain.

Address
D. Wanatowski: Nottingham Centre for Geomechanics, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
J. Chu: School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798
C. L. Gan: SPS Overlay Asia Pte Ltd., 1 Maritime Square, Harbour Front Centre, Singapore 099253

Abstract
This paper examines the potential of relevance vector machine (RVM) in prediction of pullout capacity of small ground anchors. RVM is based on a Bayesian formulation of a linear model with an appropriate prior that results in a sparse representation. The results are compared with a widely used artificial neural network (ANN) model. Overall, the RVM showed good performance and is proven to be better than ANN model. It also estimates the prediction variance. The plausibility of RVM technique is shown by its superior performance in forecasting pullout capacity of small ground anchors providing exogenous knowledge.

Key Words
relevance vector machine; small ground anchor; pullout capacity; artificial neural network.

Address
Pijush Samui: Department of Civil Engineering, Tampere University of Technology, Tampere, Finland
T.G. Sitharam: Department of Civil Engineering, Indian Institute of Science, Bangalore-560012, India


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