Multilayer Soil Structure Research Articles

Kernel Function-Based Inverting Algorithm for Structure Parameters of Horizontal Multilayer Soil

A multilayer soil structure model is fundamental to design grounding systems. A new method is presented to invert the structure parameters of horizontal multilayer soil. The structure parameters of soil are determined by analyzing the kernel function of the integral equation of the apparent resistivity. The essence of the proposed method avoids the difficulties encountered in general optimization methods; namely, the calculation of the apparent resistivity and its derivative.

Investigation of acoustic waves behavior of an underground tunnel in a multilayer soil

Understanding the acoustic behavior of buried tunnels is valuable for locating them and monitoring their structure health. This research focuses on the acoustic behavior of buried tunnels in multilayer soil structures. The reflected and transmitted acoustic wave pressure variations are investigated exclusively for a multilayer soil buried tunnel. The tunnel system's 3D finite element model is presented, which contains the tunnel lining, surrounding soil, and the air inside the tunnel and at the ground surface. A free air explosion is used as the acoustic wave source. The reflected and transmitted waves' pressure values are measured to evaluate the effects of mechanical characteristics of soil layers, tunnel buried depths, and lining concrete types on the acoustic wave behavior of the tunnel. In addition, a utility line is introduced to the system in different positions related to the main tunnel to investigate its effect on the main tunnel’s acoustic wave behavior. The results indicate that in a multilayer soil structure, the relative position of the soil layers and the tunnel (whether the main tunnel or the utility line) significantly impacts the acoustic pressure value, particularly the transmitted wave pressure. When changing the tunnel buried depth and the lining concrete type, multiple pressure peaks are observed in reflected acoustic wave pressure–time history exclusive to a tunnel surrounded by a multilayer soil structure. The findings can be used to precisely interpret the recorded signals for structural health monitoring and locating underground structures, especially in a media with multilayer soil structures.

Impact of Earthing System Designs and Soil Characteristics on Tower Footing Impedance and Ground Potential Rise: A Modelling Approach for Sustainable Power Operation

Improving a tower earthing system by reducing the impedance is an effective solution to prevent back flashover from occurring and thus maintaining the sustainable operation of power supply. Knowledge of the soil and earthing structure is an important element when designing an earthing system and to determine the parameters of a transmission line (TL). This paper presents the computation of soil structure interpretation based on several earthing designs using current distribution, electromagnetic interference, grounding, and soil structure analysis (CDEGS) software. The results showed that each tower has a multi-layer soil structure and it was also found that the soil resistivity at the surface layer strongly affected the earthing impedance. Subsequently, it was demonstrated that soil structure and the earthing design arrangement are the two parameters that significantly affected the ground potential rise (GPR). This aspect affects the resistance and impulse impedance of a tower and thus influences the performance of the TL system when subjected to lightning strike, which is undoubtedly one of the major culprits of power outages in Malaysia.

Accounting for field-scale heterogeneity in the ecohydrological modeling of large arid river basins: Strategies and relevance

It remains a great challenge to represent field-scale (e.g., meters to tens of meters) heterogeneity in the ecohydrological modeling of large river basins due to the tradeoff between spatial resolution and computational cost. This study improved an existing ecohydrological model, HEIFLOW, by introducing the subgrid structure of land cover, multilayer soil water simulation and accurate spatial coverage of irrigation within the grid. These improvements enable the model to provide reliable simulations over a wide spectrum of spatial scales, from the field scale to the large-basin scale (i.e., 104 to 105 km2). The new model was implemented in the Heihe River Basin, the second largest endorheic river basin in China, with a grid size of 1 km by 1 km for a modeling domain of approximately 90,589 km2. The major study findings include the following. First, in arid areas with sparse vegetation, ignoring the subgrid characteristics of land surfaces will lead to significant errors that may be further propagated when the modeling results are used to support management or scaled up for larger-scale climate modeling. Second, the multilayer soil structure can improve ecohydrological simulations in terms of temporal variations, and it is necessary to separate a thin surface layer from the soil zone in arid areas. In the case study, a single-layer soil structure would introduce greater than 10% error in simulating the annual maximum leaf area index (LAI). Third, considering the accurate spatial coverage of irrigation within the grid cell is critical for successful simulations of ecohydrological processes in arid areas. In the case study, accurate spatial coverage would lead to −31%, +46%, and +13% changes in the simulated average soil evaporation, transpiration and LAI, respectively, over the entire area with irrigation. Overall, this study provides a unique perspective to address the scale issue in ecohydrological modeling and reveals the importance of field-scale heterogeneity to the management of water resources and ecosystems based on ecohydrological modeling.

Multilayer Earth Structure Approximation by a Homogeneous Conductivity Soil for Ground Return Impedance Calculations

This paper proposes a technique to approximate a multi-layer earth structure by a homogeneous conductivity soil in ground return impedance calculations. An equivalent real-valued conductivity parameter is obtained, which can be used with reasonable accuracy in a simpler expression or in commonly available EMTP software, such as the Line Constants routine of the Alternative Transients Program (ATP). Several actual soil models are evaluated at frequencies ranging from 1 Hz to 2 MHz. Results show that the proposed method is accurate for modeling most power system problems, from steady-state conditions to transients commonly verified in electrical systems. The proposed expression is easy to use and introduces a considerable performance gain in terms of floating-point operations, compared to the analytical formulation of the general multi-layer soil structure.

Load–settlement response of shallow foundations resting on granular soil

Proper estimation of settlement of shallow foundations resting on granular soil deposits has a significant role in the design and construction of buildings and other related structures. While several procedures are available in the literature, discrepancies still exist between the predicted and observed responses. Furthermore, there is a decoupling between bearing capacity and settlement assessment for the same foundation and soil type. This paper presents a new model which was developed to assess load–settlement response up to ultimate soil failure. The model utilizes Mohr–Coulomb criteria coupled with a stress–strain relationship that captures the behavior of granular soil up to large strains. The model has been verified using documented results reported in the literature. Furthermore, two full-scale plate load experiments were recently performed at the University of Nevada, Reno (UNR), utilizing a large soil box 10 ft. (3.048 m) × 10 ft. (3.048 m) × 7 ft. (2.134 m). The experiments modeled single-layer and multi-layer soil structure. The load-settlement responses up to bearing capacity failure are reported for both experiments.

Spatial distributions of pore water pressure and effective stress in vertical seepage flow through multi-layer soil structure

Spatial distributions of pore water pressure and effective stress in vertical seepage flow through multi-layer soil structure

Multiband Software Defined Radar for Soil Discontinuities Detection

A multiband Software Defined Radar based on orthogonal frequency-division multiplexing technique is proposed in this work for an accurate soil discontinuities detection, taking into account also the dispersive behavior of media. A multilayer soil structure is assumed as a validation test to demonstrate the effectiveness of the proposed approach, by accurately retrieving the unknown thicknesses and permittivities of the soil layers.

Mesh voltages at earthing grids buried in multi-layer soil

Expressions for the mesh voltages caused by earth fault currents leaking from earthing grids buried in uniform, two- and three-layer soils are proposed based upon the examination of a large set of grids and soil structures using the finite element approach. Simple empirical correction factors are developed to modify the mesh voltage formulae for uniform soil to take into account the multi-layer soil structure. A comparative analysis of available expressions for uniform and two-layer soils is performed in order to check their applicability in various cases.

Resistance to earth of earthing grids buried in multi-layer soil

Expressions for the resistance to earth of earthing grids buried in uniform, two- and three-layer soils are proposed based upon the examination of a large set of grids and soil structures using the finite-element approach. Simple empirical correction factors are introduced to modify the earth resistance formulae for uniform soil to account for the multi-layer soil structure. A comparative analysis of available expressions for uniform and two-layer soils is performed in order to check their applicability in various cases.

Two-Stage Algorithm for Inverting Structure Parameters of the Horizontal Multilayer Soil

The multilayer soil structure model is the fundament to design grounding systems. A fast algorithm is presented to invert the structure parameters of the horizontal multilayer soil. The procedure is divided into two independent stages. First, Fredholm equation of the first kind with respect to the apparent resistivity is solved by using the technology of decay spectrum, which can reduce the computation time greatly. Second, the structure parameter of soil is determined by the generalized Newton-Kantorovich method, which is more robust and less noise sensitive because of using the generalized inverse algorithm to solve the nonlinear equation system. The numerical results show the validities and main features of the proposed approach. The numerical results by using the proposed method are in a good agreement with ones from geophysical exploration.