Surface Of Soil Profile Research Articles

Seismic site response analysis of liquefiable soil deposits focusing on the ground surface response spectrum

A numerical algorithm is developed for conducting one-dimensional non-linear ground response analysis of layered sites, capable of reproducing liquefaction phenomena and accounting for the simultaneous dissipation of excess pore water pressure through soil grains. Τhe shear wave propagation algorithm is based on the plasticity constitutive model for sand Ta-Ger, expressed in a one dimensional p-q space form. This model demonstrates remarkable versatility in representing complex patterns of the cyclic behavior of sand, such as stiffness decay and strength reduction due to pore-water pressure buildup. The calibration of the model is based on shear modulus reduction and damping curves for drained loading conditions, as well as liquefaction resistance curves for undrained conditions. A detailed presentation of the numerical model formulation is provided, outlining the numerical approach for solving the wave propagation and consolidation differential equations. To validate model predictions, the recorded seismic ground response of the Port Island array during the 1995 Kobe earthquake is utilized. Furthermore, the model is applied to estimate the elastic response spectra at the surface of soil profiles with liquefiable layers (ground type S2) as per EC8:2004. The investigation involves the ground response analysis of various soil p3rofiles, all including a liquefiable zone, excited by a suite of earthquake motions at their base. The acceleration time histories are extracted from the PEER Ground Motion Database, having characteristics compatible with the NGA-estimated response spectrum at the bedrock as well as key seismological parameters such as the earthquake magnitude Mw and the horizontal distance from the fault RJB. Two different methods are employed for selecting the base excitations: amplitude-scaled records to match a target response spectrum and spectral-matched records. From the results, an idealized response spectrum is derived in terms of the design spectrum parameters S, η, ΤΒ and TC. The findings demonstrate that the idealized ground surface response spectrum is minimally sensitive to the method used for base excitation selection.

Impact of municipal wastewater reuse through micro-irrigation system on the incidence of coliforms in selected vegetable crops

The incidence of coliforms in soil and agricultural produce was evaluated in two vegetable crops, namely, cauliflower and eggplant, which were grown using wastewater for irrigation. Field experiment was conducted at Indian Agricultural Research Institute (IARI), New Delhi, India. In the field experiments to irrigate the crop, municipal wastewater was applied through drip system. The filtration of irrigation water was done through sand media, disk media and their combination. The laterals were placed at surface and subsurface of soil. All filtration processes significantly reduced total coliforms (12–20%) and E. coli (15–25%) populations when evaluated against untreated wastewater. The population dynamics of coliforms in soil profiles indicated that the maximum population of E. coli was estimated on the surface of soil profile when using surface drip, which decreased with soil depth under subsurface placement of drip lateral. After crop harvesting, E. coli in the soil reduced until 20 days after the cessation of irrigation and was highly correlated with soil moisture. E. coli and total coliforms availability were noticed on the surface and in the tissues of leaf and fruit, the coliform count is higher on the surface of plants under surface placement of drip lateral. The concentration of coliforms was lower with eggplant in comparison to cauliflower due to the smooth fruit surface of eggplant. Our study reveals the critical role of subsurface drip irrigation in reducing the load of coliform both in the soil and the crop produce ensuring safety of the consumers against health hazards. In another way protect the environment from wastewater disposal and reduce the burden on synthetic fertilizers as well as shrinking freshwater resources.

Nonlinear seismic response for the 2011 Tohoku earthquake: borehole records versus one-directional three-component propagation models

The seismic response of surficial multilayered soils to strong earthquakes is analysed through a non-linear one-directional three-component (1D-3C) wave propagation model. The three components (3C-polarization) of the incident wave are simultaneously propagated into a horizontal multilayered soil. A 3-D non-linear constitutive relation for dry soils under cyclic loading is implemented in a quadratic line finite element model. The soil rheology is modelled by mean of a multisurface cyclic plasticity model of the Masing-Prandtl-Ishlinskii-Iwan type. Its major advantage is that the rheology is characterized by few non-linear parameters commonly available. Previous studies showed that, when comparing one to 3C unidirectional wave propagation simulations, the soil shear modulus decreases and the dissipation increases, for a given maximum strain amplitude. The 3-D loading path due to the 3C-polarization leads to multiaxial stress interaction that reduces soil strength and increases non-linear effects. Non-linearity and coupling effects between components are more obvious with decreasing seismic velocity ratio in the soil and increasing vertical to horizontal component ratio for the incident wave. This research aims at comparing computed ground motions at the surface of soil profiles in the Tohoku area (Japan) with 3C seismic signals recorded during the 2011 Tohoku earthquake. The 3C recorded downhole motion is imposed as boundary condition at the base of soil layer stack. Notable amplification phenomena are shown, comparing seismograms at the bottom and at the surface. The 1D-3C approach evidences the influence of the 3-D loading path and input wavefield polarization. 3C motion and 3-D stress and strain evolution are evaluated all over the soil profile. The triaxial mechanical coupling is pointed out by observing the variation of the propagating wave polarization all along the duration of seismograms. The variation of the maximum horizontal component of motion with time, as well as the influence of the vertical component, confirm the interest of taking into account the 3C non-linear coupling in 1D wave propagation models for such a large event.

Strong Ground Motion in the 2011 Tohoku Earthquake: A One-Directional Three-Component Modeling

Local wave amplification due to strong seismic motions in surficial multilayered soil is influenced by several parameters such as the wavefield polarization and the dynamic properties and impedance contrast between soil layers. The present research aims at investigating seismic motion amplification in the 2011 Tohoku earthquake through a one-directional three-component (1D-3C) wave propagation model. A 3D nonlinear constitutive relation for dry soils under cyclic loading is implemented in a quadratic line finite element model. The soil rheology is modeled by mean of a multi-surface cyclic plasticity model of the Masing-Prandtl-Ishlinskii-Iwan (MPII) type. Its major advantage is that the rheology is characterized by few commonly measured parameters. Ground motions are computed at the surface of soil profiles in the Tohoku area (Japan) by propagating 3C signals recorded at rock outcrops, during the 2011 Tohoku earthquake. Computed surface ground motions are compared to the Tohoku earthquake records at alluvial sites and the reliability of the 1D-3C model is corroborated. The 1D-3C approach is compared with the combination of three separate one-directional analyses of one motion component propagated independently (1D-1C approach). The 3D loading path due to the 3C-polarization leads to multiaxial stress interaction that reduces soil strength and increases nonlinear effects. Time histories and spectral amplitudes, for the Tohoku earthquake, are numerically reproduced. The 1D-3C approach allows the evaluation of various parameters of the 3C motion and 3D stress and strain evolution all over the soil profile.