فهرست مطالب

International Journal of Civil Engineering
Volume:18 Issue: 7, Jul 2020

  • تاریخ انتشار: 1399/03/19
  • تعداد عناوین: 8
|
  • Evaluation the Shear Strength Behavior of aged MSW using Large Scale In Situ Direct Shear Test, a case of Tabriz Landfill
    Mohsen Keramati*, Masoud Shahedifar, MohammadHosein Aminfar, Hasan Alagipuor Pages 717-733

    The current study presents the physical and mechanical properties of municipal solid waste (MSW) with different ages of new and old Tabriz landfill. Although there are several theoretical and laboratory methods to investigate the shear strength parameters of MSW, field methods provide more accurate results due to the minimum MSW disturbance and changes, so in this study the shear strength parameters of MSW Tabriz landfill were evaluated using the “Large Scale in Situ Direct Shear Device” with the cross-sectional dimensions 122 × 122 cm. In spite of difficulties related to conducting tests such as potential exposure to various contaminations and the lack of specific equipment in the beginning, it provided more realistic results of the geotechnical behavior of municipal solid waste compared to other methods. Moreover, the in situ unit weight, physical analysis, moisture and organic content at different ages were evaluated to better understand the mechanical response with increase in the age of MSW. The results showed the cohesion and friction angle of 5- and 16-year-old MSW was estimated as 1.17, 2.215 kPa and 31.51°, 21.51°, respectively; According to the results, the shear strength of 5- and 16-year-old MSW is mainly controlled by the friction angle which seems due to the MSW composition as a function of the consumption pattern. The physical analysis of fresh MSW from 2005 to 2017 showed an increase in the fiber content including plastics and textiles. Moreover, studies on MSW mechanical responses over the time revealed a decrease in the shear strength because of the raise in the fiber and plastic content.

    Keywords: Shear strength, Municipal solid waste, Landfill, Mechanical response, Aging
  • Lateral Response of Drilled Shafts in A Moving Cohesive Soil
    Mohammad M. Yamin*, Mousa F. Attom, Zahid Khan Pages 735-742

    Three-dimensional finite element (FE) analysis was carried out to investigate the behavior of a single row of drilled shafts installed in an unstable slope and to determine the soil pressures acting on the shafts. ABAQUS program was used and the built-in Mohr–Coulomb constitutive model was employed to model the elastic–plastic behavior of the purely cohesive soil, while the drilled shaft was assumed to behave as linear elastic. The length of the drilled shaft is 10 m with a diameter of 1 m. The center-to-center spacing between drilled shafts was taken as 2 m. Slope movement was simulated by imposing a uniform horizontal movement of the soil adjacent to the shaft. Soil pressures along the shaft were recorded at several uniform lateral soil movements until the ultimate soil movement was reached. Cohesion of soil was varied in the FE simulations from 30 to 100 kPa to study its influence on the soil pressure profiles. The effect of shaft stiffness on soil pressures was also included in the study through the relative shaft/soil flexibility factor KR. Two cases of drilled shafts were considered: (1) stiff shaft with KR = 2.9; and (2) flexible shaft with KR = 0.00004. Soil pressures from FE analyses were idealized and simplistic equations were developed and presented which will allow prediction of soil pressures acting on flexible and stiff shafts. The computed ultimate soil pressures agreed well with those from the literature. The computed soil movement to fully mobilize the ultimate contact pressure was found to vary from 10 to 35% of drilled shaft diameter (D) for flexible shafts and from 7 to 15% of the drilled shaft diameter for stiff shafts depending on soil cohesion. The relative displacement between the moving soil and the moving drilled shaft for the contact pressure to be fully mobilized at the soil/shaft interface was found to range from 3 to 15% of the shaft diameter.

    Keywords: Drilled shafts, Cohesive soil, FEM, Soil movement
  • Experimental Study on Connected and Non-connected Piled Raft Foundations Subjected to Eccentric Loading
    Alireza Saeedi Azizkandi *, Reza Taherkhani Pages 743-761

    Piled raft foundations are sometimes used when the supporting soil has no adequate bearing capacity and the raft settlements exceed allowable values. This research investigates the bearing capacity of a foundation subjected to eccentric loads in both connected and non-connected piled raft foundations under 1 g. The load-settlement curves of a strip, square and circular raft are compared. The results illustrate that piled raft behavior is influenced by various factors such as pile length, spacing, shape, and eccentricity ratio in connected and non-connected cases. Test results indicate that connected foundations have greater bearing capacities and lesser settlements in larger pile spacing (S/D = 6), while non-connected foundations have higher bearing capacities and lesser settlements in lesser pile spacing (S/D = 3). Moreover, both the pile length in a connected piled raft system and pile spacing in a non-connected system affected the bearing capacity remarkably. The bearing capacity of the square and circular foundations at S/D = 3 was greater for the non-connected pile (19.8 and 15.8 kg/cm2 receptivity) than the connected pile (18 and 14.1 kg/cm2), while at S/D = 6, the bearing capacity of the foundations was greater for the connected pile than the non-connected pile. However, in both cases, the bearing capacity was enhanced and the settlements were reduced. The effect of various parameters is also evaluated and discussed in this study.

    Keywords: Connected piled raft, Non-connected piled raft, Settlement, Bearing capacity, Eccentric load
  • Influence of Motion Energy and Soil Characteristics on Seismic Ground Response of Layered Soil
    Angshuman Das, Pradipta Chakrabortty* Pages 763-782

    The present study focuses on assessing local site effects (especially large-scale soil heterogeneity) and motion characteristics on seismic ground response using nonlinear one-dimensional numerical analysis. All nonlinear and curve-fitting parameters used for soil models were verified using the Class C1 prediction of centrifuge test results available in the literature. The comparison demonstrates that the available MKZ (pressure dependent Modified Kondner Zelesko) formulation with non-Masing hysteresis loading and unloading rule can reliably compute the 1-D ground response of cohesionless soil. Horizontal soil layers with different relative densities were considered next in various hypothetical models to assess the effect of subsurface properties on responses. One novel aspect of this study is that 51 different ground motions with a wide range of variation in their spectral accelerations, frequency contents, and duration characteristics were used to evaluate the effect of ground motion characteristics on the soil response. The results reveal that layering conditions play a significant role in modifying the seismic ground response of heterogeneous soil, especially when the loose liquefiable sand layer is sandwiched between two non-liquefiable soil layers. Relations were obtained to quantify the effect of different seismic inputs and varying site conditions on seismic ground response. The best correlation was obtained between the maximum excess pore water pressure (EPWP) development and the damage potential (Arias intensity) of an input ground motion. These relations can be used for estimating seismic ground response of an identical soil profile to that used in the present study for known design motion characteristics.

    Keywords: Lumped mass model, Nonlinear analysis, Large-scale heterogeneity, One-dimensional model, Numerical analysis
  • Shaking Table Experiments to Evaluate the Boundary Effects on Seismic Response of Saturated and Dry Sands in Level Ground Condition
    Yaser Jafarian*, Hamed Taghavizade, Sadra Rouhi, Saeed Shojaemehr, Pouria Esmaeilpour Pages 783-795

    The laminar shear boxes (LSBs) are commonly preferred for geotechnical physical modeling over the fixed wall boxes; the latter may suffer from problems associated with wave reflection. This paper mainly describes the seismic response of a uniform layer of loose saturated and dry sands in rigid and flexible boundary conditions. A lightweight LSB was recently designed and fabricated by the authors for physical modeling of geotechnical earthquake engineering problems. To investigate the boundary effect on the seismic response of level ground, a series of shaking table tests were conducted with both LSB and rigid wall containers in identical conditions. The seismic performance of the free-field ground in the experiments is evaluated in terms of time histories, shear stress–strain hysteresis loop, and dynamic soil properties. The dynamic movements of all layers in the LSB, captured by image processing techniques, are compared with that of the rigid end-wall condition. The results demonstrate that acceleration and settlement of the ground surface are highly affected by artificial boundaries in both dry and saturated sands. It is shown that the hysteresis loops estimated from the LSB tests are more compatible with the cyclic behavior of sands, compared with those of the rigid box tests.

    Keywords: Shear box, Shaking table test, Boundary effects, Level ground, Dry, saturated sands
  • Extraction of Isfahan’s Seismic Geotechnical Model Using Ambient Noise and Numerical Modeling
    H. Hashemifesharaki, E. Haghshenas, M. Kamalian*, M. Mirmohamadsadeghi Pages 797-815

    A preliminary seismic geotechnical model of Isfahan is extracted using advanced microtremor measurements as well as 2D site response analysis. Single-station microtremor measurements were performed at 25 stations throughout the study area and analyzed using the H/V method as well as the concept of ellipticity of Rayleigh waves. Seismic microzonation maps including the distribution of natural site period, depth to seismic bedrock as well as the soil type throughout the study area were extracted, providing a useful basis for land-use planning in Isfahan. The shear wave velocity of sub-surface soil layers varies from less than 250 m/s near the ground surface to more than 1200 m/s throughout the study area. In the northern districts, the depth of seismic bedrock may exceed 100 m. The natural site period varies from less than 0.5 to more than 1.0 s throughout the study area. It increases from south to north, whereas in the E–W direction, the changes are much less.

    Keywords: Ambient noise, H, V method, Isfahan, Seismic geotechnical model, Ellipticity of Rayleigh waves
  • Bearing Capacity Failure of Supported Cuts in the Presence of Seepage Flow by Coupled Finite Elements and Stress Characteristics Method
    Sina Fadaie, Mehdi Veiskarami* Pages 817-825

    The deep-seated failure caused by inadequate shear resistance against the weight of the surrounding soils is often the more probable mode of failure prior to other types of failure. In this research, stability of flexible supported vertical cuts in granular soils against the deep-seated failure, in the presence of the seepage flow, is investigated. First of all, the flow field is computed by the traditional finite elements method. It is then assumed that the soil in the proximity of the bottom of the cut is at the verge of the limiting equilibrium. Once the flow field solution is known as a steady-state solution, i.e., the background solution, the stress field at the limiting equilibrium subjected to this flow field has been calculated. The method of stress characteristics was used to solve the stress field. It is, therefore, possible to estimate the factor of safety against the deep-seated failure and to assess the overall stability of the system. Results reveal that in spite of quite good margin of safety in the absence of the seepage flow, the deep-seated failure becomes most likely to initiate when the seepage flow exists.

    Keywords: Stability, Deep-seated failure, Slip lines, Finite elements, Seepage flow
  • Post-cycling Interface Strength Test of Geogrids
    Gian Franco Napa Garcia, Paulo César Lodi* Pages 827-834

    Geosynthetic-reinforced soil structures are commonly used in seismic design in regions. The performance of GRES under seismic conditions can be found to range from very good to catastrophic. This paper presents the implementation of a test to evaluate the influence of pre-cycling on the post-cycling resistance of a soil–geogrid system. Tests were performed on a PVE uniaxial geogrid with a tensile strength of 400 kN/m and a clean sand with 89% compaction and friction angle of 37.5°. The system was subjected to cyclic pullout tests at 40 and 80% of the monotonic strength. After the pre-cycling, a posterior monotonic pullout test was performed to evaluate the influence of the previous cycling on the final post-cycling strength. A test protocol was established to apply 50, 100, 500 and 5000 cycles with 40% and 80% pullout resistance amplitudes. At the 40% amplitude, the system exhibited stable increasing behavior in terms of resistance and cyclic displacement. Failure was not reached during the pre-cycling stage at 40% amplitude. At the 80% amplitude, the system failed at 250 cycles, and cyclic displacement was found to be erratic for all pre-cycling cases. The results suggest a general tendency of the pre-cycling to increase the post-cycling resistance. However, a combination of high cyclic amplitude with large number of cycles may lead to failure. Exposure to seismic events could be considered in the design of GRES though a rationally chosen reduction factor is applied.

    Keywords: Geosynthetics, Geogrid, Pullout, Pre-cycling, Post-cycling strength