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Volume 2, Number 3, September 2010

Discrete Element Method (DEM) simulations were developed to investigate the effectiveness of geosynthetic reinforcement and the effectiveness of maintenance techniques performed on a simulated ballast bed subjected to dynamic loading. The results from four samples subjected each one to a total of 425 load cycles are presented: one unreinforced and unmaintained sample, one unmaintained but reinforced sample, one unreinforced sample subjected to maintenance in the form of stoneblowing after 200 load cycles, and one unreinforced sample subjected to maintenance in the form of tamping after 200 load cycles. The obtained values of permanent deformation as a function of the applied number of load cycles for the four cases are presented together allowing a comparison of the effectiveness of each technique. Moreover, snapshots of the simulated track sections are presented at different moments of the simulations. The simulations indicated that the geosynthetic reinforcement may not be beneficial for the analyzed case while stoneblowing was the most effective maintenance technique.

Key Words
railtracks; ballast; particle crushing; tamping; stoneblowing; geosynthetics; discrete element method; numerical analysis.

Sebastian Lobo-Guerrero: American Geotechnical & Environmental Services, Inc., Canonsburg, PA, U.S.A.
Luis E. Vallejo: Department of Civil and Environmental Engineering, University of Pittsburgh, 949 Benedum Hall, Pittsburgh, PA 15261, U.S.A.

This paper presents the details of indigenous development of the piezovibrocone and calibration chamber. The developed cone has a cylindrical friction sleeve of 150 cm2 surface area, capped with a 600 apex angle conical tip of 15 cm2 cross sectional area. It has a hydraulic shaker, coupled to the cone penetrometer with a linear displacement unit. The hydraulic shaker can produce cyclic load in different types of wave forms (sine, Hover sine, triangular, rectangular and external wave) at a range of frequency 1-10 Hz with maximum amplitude of 10 cm. The piezovibrocone can be driven at the standard rate of 2 cm/sec using a loading unit of 10 ton capacity. The calibration chamber is of size 2m

Key Words
calibration chamber; cone penetration test; piezovibrocone; site characterization; sand.

Pijush Samui: Centres for Disaster Mitigation and Management, VIT University, Vellore-632014, Tamilnadu, India
T.G. Sitharam: Department of Civil Engineering, Indian Institute of Science, Bangalore - 560 012, India

The porosity (including the specific surface area and pore volume-diameter distribution) of montmorillonitic soft rock (MSR) was studied experimentally with an electrochemical treatment, based on which the change in porosity was further analyzed from the perspective of its electrokinetic potential (

Key Words
montmorillonitic soft rock; electrochemical modification; specific surface area; pore volume-diameter,

Dong Wang: Institute of Mining Technology, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China
Shanxi Coal Transportation and Sales Group Co.Ltd, Taiyuan, Shanxi 030002, China
Tianhe Kang: Institute of Mining Technology, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China
Wenmei Han: Institute of Mining Technology, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China
School of Science, North University of China, Taiyuan, Shanxi 030052, China
Zhiping Liu: College of Chemical Engineering and Technology, Taiyuan University of Technology,
Taiyuan, Shanxi 030024, China
Zhaoyun Chai: Institute of Mining Technology, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China

An experimental program of isotropic loading tests on a compacted kaolin using a conventional triaxial equipment modified for testing unsaturated soils was perform to investigate a loading collapse curve of unsaturated soils along wetting and drying paths. The test data are presented in terms of effective stress on a range of constant suction. The suction hardening behavior was observed for both wetted and dried samples. With the use of an appropriate effective stress parameter, the unique relationship for loading collapse curve for wetting and drying processes was obtained.

Key Words
wetting-drying processes; unsaturated soils; loading collapse curve; triaxial tests.

Anuchit Uchaipichat: Department of Civil Engineering, Vongchavalitkul University, Nakhon Ratchasima, 30000, Thailand

Compacted layers of sand-bentonite mixtures have been proposed and used in a variety of geotechnical projects as engineered barriers for the enhancement of impervious landfill liners, cores of zoned earth dams and radioactive waste repository systems. This paper presents a study on the valorization of local materiel such as dune sand from Laghouat region and mine bentonite intended for the realization of liner base layers in the conception of insulation barriers for hazardous waste centers. In the practice we try to get an economical mixture that satisfies the hydraulic and mechanical properties specified by regulation rules. The effect of the bentonite additions on the mixture is reflected by its capability of clogging the matrix pores upon swelling. In order to get an adequate dune sand-bentonite mixture, an investigation on hydraulic and mechanical behaviours is carried out in this study for different mixtures. Using oedometer test, the adequate bentonite addition to the mixture, which satisfies the conditions on permeability, is found to be around 12% to 15%. These results are also confirmed by direct measurement using triaxial cell.

Key Words
dune sand; bentonite; saturated permeability; insulation barriers; south of Algeria.

M.K. Gueddouda and M. Lamara: Laboratoire de recherche de Genie Civil, Universite Amar Teledji, BP.37, G. Laghouat, Algeria
N. Abou-bekr: Laboratoire Eau et Ouvrages dans Leur Environnement, Universite A. Belkaid, BP 230 - 13000 Tlemcen, Algeria
S. Taibi: Laboratoire Ondes et Milieux Complexes, FRE CNRS 1302, Universite du Havre, 53 rue de Prony, 76600 Le Havre, France

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