International Journal of Civil Engineering
Volume:12 Issue: 4, Dec 2014

Physical modeling for study of deep foundations can be performed in simple chambers (1g), calibration chambers (CC), and centrifuge apparatus (ng). These common apparatus face certain limitations and difficulties. Recently, Frustum Confining Vessels (FCV) have been evolved for physical modeling of deep foundations and penetrometers. Shaped as the frustum of a cone, this device applies steady pressure on its bottom and creates a linear stress distribution along its vertical central core. This paper presents the key findings in FCV, as developed in AUT. The FCV has a height of 1200 mm, with top and bottom diameters of 300 and 1300 mm, respectively. By applying bottom pressure up to 600 kPa, the in-situ overburden stress conditions, equivalent up to 40 m soil deposits, become consistent with the embedment depth of commonly used piles. Observations indicated that a linear trend of stress distribution exists, and this device can create overburden stress in the desired control volume along the central core. Moreover, a couple of compressive and tensile load tests were performed on steel model piles driven in sand with a length of 750 mm, and different length to diameter (L/D) ratios between 8-15. Comparison between measured and predicted ultimate capacity of model piles performed in FCV demonstrate a suitable conformity for similar confinement conditions in the field. Therefore, the FCV can be considered as an appropriate approach for the investigation of piling geotechnical behavior, and the examination of construction effects.

Presented is a method of two-dimensional analysis of the active earth pressure due to simultaneous effect of both soil weight and surcharge of strip foundation. The study’s aim is to provide a rigorous solution to the problem in the framework of upper-bound theorem of limit analysis method in order to produce some design charts for calculating the lateral active earth pressure of backfill when loaded by a strip foundation. A kinematically admissible collapse mechanism consisting of several rigid blocks with translational movement is considered in which energy dissipation takes place along planar velocity discontinuities. Comparing the lateral earth forces given by the present analysis with those of other researchers, it is shown that the results of present analysis are higher (better) than other researchers’ results. It was found that with the increase in
⁄, the proportion of the strip load (q) which is transmitted to the wall decreases. Moreover, Increasing the friction between soil and wall () will result in the increase of effective distance (). Finally, these results are presented in the form of dimensionless design charts relating the mechanical characteristics of the soil, strip load conditions and active earth pressure.

Due to the existence of fibrous materials such as plastic fragments, the strength anisotropy of Municipal Solid Waste (MSW) materials is the main source of differences between their mechanical response in direct shear and triaxial apparatus. As an extension of earlier research on the mechanical behavior of MSW using a large traixail apparatus, results presented in Shariatmadari et al. [1] and Karimpour-Fard et al. [2], the current study was programmed and executed. MSW samples were tested using a computer controlled large shear box apparatus with normal stress levels ranging between 20 to 200 kPa. The effect of fiber content, fiber orientation, aging and shearing rate on the response of MSW were addressed. The results showed that shear strength of MSW increases with normal stress, although, in spite of the presence of reinforcement elements in MSW and unlike the results from triaxial tests, no strain hardening could be observed in their mechanical response. An increase in the shear strength of MSW was observed with increasing the shearing rate. Increasing the shearing rate from 0.8 to 19 mm/min, enhanced the shear strength of samples from 16 to 27% depending on the shear displacement level. Although, the same trend was investigated in traixial tests, but lower rate-sensitivity in the mechanical response of MSW in direct shear tests were observed. Unlike the results of triaxial tests with aging process, mobilized shear strength level of MSW samples tested under direct shearing decreased comparing fresh samples. It was also observed that altering the fiber content and their orientation could affect the mechanical response and shear strength of the MSW. Additionally, there is an optimum fiber angle in MSW which yields the highest level of shearing strength.

This research examines the behavior of soil-reinforced piles and applied loads based on the analytical method and by using the numerical results of FLAC3D software for comparison with the analytical results. The analysis was based on a method called virtual retaining wall, the following into consideration: an imaginary retaining wall that passes the footing edge; the bearing capacity of footing on reinforced soil with piles, which was determined by applying equilibrium between active and passive forces on virtual wall; and a pile row that exists beneath the shallow foundation. To calculate the lateral pile resistance here, an analytical equation was then required. The main objective of this paper is to determine the percentage of applied load on pile. Similarly, the effect of adding pile in various positions relative to the present footing (underpinning) was studied in this research. The various parameters of this study included pile length, vertical distance of pile head to shallow footing, pile distance to center of footing and location of the pile. Finally, the findings were compared with the numerical results of FLAC3D and the formerly presented experimental results. Results show that the analytical method, while being close to other methods is more conservative.

In this study, a researching program is conducted by cyclic triaxial test to determine the post-cyclic behavior of Bushehr carbonate sand retrieved from the north of the Persian Gulf, under anisotropic consolidation at 200 kPa confining pressure. The article compares the post-cyclic monotonic strength and excess pore water pressures generated after the test with the precyclic monotonic results. The results attest to the existence of a relationship between CSR (Cyclic Stress Ratio) and the frequency of failure cycles. The article also investigates the relationship between the amount of excess pore pressures generated during both the cyclic and post-cyclic loading, revealing an increase in the post-cyclic strength and stiffness of sand retrieved from Bushehr. Also the effect of multi stages cyclic loading, density, pore pressure and stain history in post cyclic strength and stiffness is evaluated. The increasing in post cyclic strength and stiffness depends on excess pore pressure generated during cyclic loading and stain history. This article also reveals that a distinct trend in the relation between post cyclic behavior and crushing value does not exist at lower confining pressure.

In this study, the mechanical behavior of Vanyar dam was evaluated at the end of construction. A two-dimensional numerical analysis was conducted based on a finite element method on the largest cross-section of the dam. The data recorded by the instruments located in the largest cross-section were compared with the results of the numerical analysis at the place of instruments. The settlement, pore water pressure, and total vertical stress were the parameters used for evaluating the dam behavior at the end of construction. The results showed that the settlements obtained from the numerical analysis were in reasonable agreement with the data recorded by the instruments, which proved that the numerical analysis was implemented based on realistic material properties. In addition, the difference between the instruments and the numerical analysis in terms of total vertical stresses was discussed by focusing on the local arching around the pressure cells. Furthermore, the arching ratios were calculated based on the results of the numerical analysis and the data recorded by the instruments. Moreover, the pore water pressures and total vertical stresses, recorded by piezometers and pressure cells, respectively, were the two parameters utilized for evaluating the hydraulic fracturing phenomena in the core. The results demonstrated that the maximum settlement obtained from the numerical analysis was 1 m, which corresponded to 46 m above the bedrock on the core axis. The recorded data in the core axis indicated that maximum settlement of 0.83 m happened 40 m above the bedrock. In addition, maximum pore water pressure ratio recorded by the instruments (Ru =0.43) was more than that obtained from the numerical analysis (Ru =0.26); this difference was due to the local arching around the pressure cells. Furthermore, the arching ratios in Vanyar dam were found to be 0.83 to 0.90. In general, the results revealed that the dam was located on a safe side in terms of critical parameters, including settlement and hydraulic fracturing. In addition, results of the numerical analysis were consistent with those provided by the monitoring system.

Compared to quartz sand, the shear behavior of carbonate sand differs in appearance, origin, and kind. Carbonate sand is found mainly in the northern coast of the Persian Gulf and the Oman Sea. In this research, a comparison is made between the shear behavior of carbonate sand retrieved from the eastern region of the Chabahar Port, located north of the Oman Sea, and quartz sand obtained from Firoozkooh, north of Iran. Both carbonate and quartz sands have identical and uniform particle size distributions. A total of 4 one-dimensional consolidation tests, and 16 triaxial consolidated-undrained (CU) tests under confining pressures of 100, 200, 400, and 600 kPa were performed with initial relative densities of 20%-80%. The results indicated that despite their uniform properties, including size and grading, the two types of sand can differ in other properties as inherent interlocking, compressibility, stress-strain behavior, internal friction angle, changes in pore water pressure and stress path. For instance, Chabahar carbonate sand has more compressive potential than Firoozkooh sand because of the fragility of its grains. Moreover, the internal friction angle of carbonate sand is more than that of quartz sand. Quartz sand is more affected by initial relative density, whereas, carbonate sand is influenced by inherent packing.