Pressure transducers are increasingly used within soil mass or at soil-structure interface for appraisal of stresses acting at point of installation. Calibration of pressure transducers provides a unique relationship between applied pressure and voltage or strain sensed by transducer during various loading conditions and is crucial for proper interpretation of results obtained from pressure transducers. In the present study an in-house calibration device is used to calibrate pressure transducers and the study is divided into two parts: 1) demonstration of developed calibration device for fluid and in-soil calibration of pressure transducers; 2) effect of soil layer thickness on the earth pressure cell (EPC) output. Results obtained from the present study revealed successful performance of the developed calibration device, and significant effect of sand layer thickness on the calibration results. The optimum sand layer thickness is obtained as 1.5 times the diameter of EPC.
Settlement of the piled raft can be estimated even after years of completing the construction of any structure over the foundation. This study is devoted to carry out numerical analysis by the finite element method of the consolidation settlement of piled rafts over clayey soils and detecting the dissipation of excess pore water pressure and its effect on bearing capacity of piled raft foundations. The ABAQUS computer program is used as a finite element tool and the soil is represented by the modified Drucker-Prager/cap model. Five different configurations of pile groups are simulated in the finite element analysis. It was found that the settlement beneath the piled raft foundation resulted from the dissipation of excess pore water pressure considerably affects the final settlement of the foundation, and enough attention should
be paid to settlement variation with time. The settlement behavior of unpiled raft shows bowl shaped settlement profile with maximum at the center. The degree of curvature of the raft under vertical load increases with the decrease of the raft thickness. For the same vertical load, the differential settlement of raft of (10x10 m) size decreases by more than 90% when the raft thickness increased from 0.75 m to 1.5 m. The average load carried by piles depends on the number of piles in the group. The groups of (2x1, 3x1, 2x2, 3x2, and 3x3) piles were found to carry about 24%, 32%, 42%, 58%, and 79% of the total vertical load. The
distribution of load between piles becomes more uniform with the increase of raft thickness.
piled raft; foundation; finite elements; time; clay
Mohammed Y. Fattah : Building and Construction Engineering Department, University of Technology, Iraq
Mosa J. Al-Mosawi, Abbas A.O. Al-Zayadi : College of Engineering, Civil Engineering Department, University of Baghdad, Iraq
An important issue in the design of soil-nailing systems, as long-term retaining walls, is to assess their stability during seismic events. As such, this study is aimed at simulating the dynamic behavior and failure pattern of nailed structures using two series of numerical analyses, namely dynamic time history and pseudo-static. These numerical simulations are performed using the Finite Difference Method (FDM). In order to consider the actual response of a soil-nailed structure, nonlinear soil behaviour, soil-structure interaction effects, bending resistance of structural elements and construction sequences have been considered in the analyses. The obtained results revealed the efficiency of both analysis methods in simulating the seismic failure mechanism. The predicted failure pattern consists of two sliding blocks
enclosed by three slip surfaces, whereby the bottom nails act as anchors and the other nails hold a semi-rigid
soil mass. Moreover, it was realized that an increase in the length of the lowest nails is the most effective
method to improve seismic stability of soil-nailed structures. Therefore, it is recommended to first estimate
the nails pattern for static condition with the minimum required static safety factor. Then, the required seismic stability can be obtained through an increase in the length of the lowest nails. Moreover, placement of additional long nails among lowest nails in existing nailed structures can be considered as a simple retrofitting technique in seismic prone areas.
Constant rate of strain (CRS) consolidation tests were conducted for undisturbed Ariake clay samples from three boreholes in Saga Plain of Kyushu Island, Japan. The coefficients of consolidation (cv) were interpreted from the CRS test results by small- and large-strain theory. Large-strain theory was found to interpret smaller cv values and less strain rate effect on cv than that by small-strain theory. Comparing the theoretical strain distributions within a soil specimen to those obtained by numerical simulation shows that the small-strain theory can be used only for the dimensionless parameter (where is strain rate and H0 is the specimen height), and the large-strain theory can be used for a larger range of strain
rates. Applying the criterion to undisturbed Ariake clay with a cv value of about 1
constant rate of strain (CRS); coefficient of consolidation; strain rate effect; large-strain theory
Rui Jia, Takenori Hino : Institute of Lowland and Marine Research, Saga University, Saga, Japan
Jinchun Chai : Department of Civil Engineering and Architecture, Saga University, Saga, Japan
For rock materials, a transversely isotropic failure criterion established through the extended Lade-Duncan failure criterion incorporating an anisotropic state scalar parameter, which is a joint invariant of deviatoric microstructure fabric tensor and normalized deviatoric stress tensor, is verified with the results of triaxial compressive data on Tournemire shale. For torsional shear mode with 0
fabric tensor; transversely isotropy; anisotropic state scalar parameter; failure criterion
Civil and Traffic Engineering School, Guangdong University of Technology, Guangzhou, 510090, China