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CONTENTS
Volume 6, Number 5, May 2014
 

Abstract
Soil improvement by preloading with PVD in combination with vacuum is helpful when a considerable load is required to meet the desired rate of settlement in a relative short time. To facilitate the vacuum propagation, vertical drains are usually employed in conjunction. This ground improvement method is more and more applied in the Mekong delta of Vietnam to meet the needs of fast infrastructuredevelopment. This paper reports on a pilot test that was carried out to investigate the effect of ground improvement by vacuum and PVD on the rate of consolidation at the site of Saigon International Terminals Vietnam (SITV) in Ba Ria-Vung Tau Province, Viet Nam. Three main aspects of the test will be presented, and namely, instrumentation and field monitoring program, calculation of consolidation settlement and back-analysis of soil properties to see the difference before and after ground improvement.

Key Words
Mekong Delta; soft clay; soil improvement; preloading; PVD; vacuum; back-analysis

Address
N.D. Quang and P.H. Giao:
Geotechnical & Earth Resources Engineering, Asian Institute of Technology, Pathumthani 12120, Thailand.

Abstract
This paper studies the swelling and strength characteristics of unimproved and improved expansive soils in terms of the swell potential, swelling pressure, rate of secondary swelling, unconfined compressive strength and California bearing ratio (CBR). The admixtures used in this study are locally available cement and fly ash. The soils used in this study were taken from the Mae Moh power plant, Lampang Province, in northern Thailand. A conventional consolidation test apparatus was used to determine the swelling of the soil specimen. The optimum admixture contents are determined to efficiently reduce the swelling of unimproved soil. The rate of secondary swelling for unimproved soil is within the range of highly plastic montmorillonite clay, whereas the specimens improved with optimum admixture contents can be classified as non-swelling kaolinite. A soil type affects the swelling pressure. Expansive soil improvement with fly ash alone can reduce swelling percentage but cannot enhance the unconfined compressive strength and CBR. The strength and swelling characteristics can be predicted well by the swelling percentage in this study.

Key Words
expansive soil, consolidation, degree of expansion, soil improvement

Address
(1) Panich Voottipruex:
Department of Technical Training in Civil Engineering, King Mongkut's University of Technology North Bangkok, Thailand;
(2) Pitthaya Jamsawang:
Department of Civil Engineering, King Mongkut's University of Technology North Bangkok, Thailand.

Abstract
As the traffic increased, the original capacity of the tunnel has been unable to meet the needs, so it must be expanded. Based on the features of tunnel, the intermittent trough method must be supposed for tunnel enlarging. Under the situation on the buried deep of the tunnel, it could be used the reasonable arch axis model to descript the past covered rock pressure for mechanism calculating of self-bearing arch. Then establish the three-arch combination effectible model for the analysis which is relied on the tunneling enlarging to Chongqing Yu-Zhou tunnel. It has determined the proper width for the intermittent trough in shallow buried tunnel enlarging.

Key Words
tunnel enlarging; intermittent trough; arch effect; the reasonable arch axis; combination arches

Address
(1) Yi-Zhong Tan, Yuan-Xue Liu and Zhong-You Li:
Department of Civil Engineering, Logistical Engineering University, Chongqing, China;
(2) Yi-Zhong Tan, Yuan-Xue Liu and Zhong-You Li:
Chongqing Key Laboratory of Geomechanics & Geoenvironmental Protection, Chongqing, China.

Abstract
A series of bearing capacity tests was conducted with eccentrically loaded model surface and shallow strip footings resting close to a slope to investigate behavior of such footings (ultimate loads, failure surfaces, load-displacement curves, rotation of footing, etc.). Ultimate loads of footing close to slope decreased with increasing eccentricity for both surface and shallow footings. Failure surfaces were not symmetrical, primary failure surfaces occurred on the eccentricity side (the slope side) and secondary failure surfaces occurred on the other side. Lengths of failure surfaces decreased with increasing eccentricity. Footings always rotated towards eccentricity side a few degrees. For eccentrically loaded footing, decrease in ultimate load with increasing eccentricity is roughly in agreement with Customary Analysis.

Key Words
bearing capacity; eccentrically loaded footings; footings resting close to slope; strip footings; plane-strain conditions

Address
Evrim Cure, Erol Sadoglu, Emel Turker and Bayram Ali Uzuner:
Department of Civil Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey.

Abstract
A three dimensional finite element model was used to simulate rapid impact compaction (RIC) in loose granular soils using ABAQUS software for one impact point. The behavior of soil under impact loading was expressed using a cap-plasticity model. Numerical modeling was done for a site in Assalouyeh petrochemical complex in southern Iran to verify the results. In-situ settlements per blow were compared to those in the numerical model. Measurements of improvement by depth were obtained from the in-situ standard penetration, plate loading, and large density tests and were compared with the numerical model results. Contours of the equal relative density clearly showed the efficiency of RIC laterally and at depth. Plastic volumetric strains below the anvil and the effect of RIC set indicated that a set of 10 mm can be considered to be a threshold value for soil improvement using this method. The results showed that RIC strongly improved the soil up to 2 m in depth and commonly influenced the soil up to depths of 4 m.

Key Words
rapid impact compaction; numerical modeling; cap plasticity; set; relative density

Address
Elham Ghanbari and Amir Hamidi:
Department of Engineering, Kharazmi University, Tehran, Iran.

Abstract
On the basis of Hoek.Brown failure criterion, a numerical solution for the shape of collapsing block in the rectangular cavity subjected to seepage forces is obtained by upper bound theorem of limit analysis. The seepage forces obtained from the gradient of excess pore pressure distribution are taken as external loadings in the limit analysis, and the pore pressure is easily calculated with pore pressure coefficient. Thus the seepage force is incorporated into the upper bound analysis as a work rate of external force. The upper solution of the shape of collapsing block is derived by virtue of variational calculation. In order to verify the validity of the method proposed in the paper, the result when the pore pressure coefficient equals zero, and only hydrostatic pressure is taken into consideration, is compared with that of previous work. The results show good effectiveness in calculating the collapsing block shape subjected to seepage forces. The influence of parameters on the failure mechanisms is investigated.

Key Words
limit analysis; cavity; Hoek-Brown criterion; seepage force; collapse

Address
X.L. Yang and C.B. Qin:
School of Civil Engineering, Central South University, Hunan 410075, China.


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