Soil-structure System Research Articles

Investigation of Small-Scaled Soil Structure Model under Earthquake Loads via Small Shaking Table Tests

This paper aims to determine the appropriate scaling coefficient rigorously in the dynamic analysis of structures via small shaking table tests to represent the full real case while considering the soil-structure interaction problem. In addition, we investigate the seismic effects of the superstructure with flexible and fixed bases. To achieve this purpose, seven stories of concrete moment-resisting frames supported on silty clay soil were scaled. According to the shaking table specifications, a small-scaled soil-structure model was executed with a scaled factor of 1 : 50. Consequently, the scale steel skeleton model was built to represent the real superstructure. In addition, the laminar soil container for the soil block was constructed to reduce undesirable boundary effects. Three earthquakes have been applied at the superstructure base as a fixed base and at the bottom of the soil block in the soil structure system as a flexible base. The numerical simulations are implemented for scaled and real models. According to obtained results from experimental and numerical investigations, the numerical model achieved good results with experimental observation. In addition, the small scaling factor of 1 : 50 can represent the seismic response of full construction conditions with acceptable precision. It is observed that the flexible base has overestimated in lateral displacement of the real superstructure compared with a fixed base, in which the maximum amplification percentage at the roof floor level reaches up to 98% under seismic load. Otherwise, the shear force distribution along the height and base shear of the superstructure with a flexible base decreases compared with a fixed base. The maximum reduction percentage is 38% under seismic load. Consequently, the safety and cost of the superstructure are affected.

Constrained Mode–Damping Solvent Extraction Combined Method for the Soil Incorporation into a Real-Time Hybrid Test of the Soil–Structure System

The real-time hybrid test is an effective testing method for soil–structure interaction research. Due to the data interaction time requirement and formula derivation method, the traditional real-time hybrid test of soil–structure interaction mostly employs a simple numerical substructure model. This study investigated the model construction and numerical simulation of a finite element soil substructure with high simulation accuracy and calculation efficiency. The soil was subdivided into near-field and far-field zones. A constrained mode–damping solvent extraction combined method was applied to the latter zone, reducing the soil’s computational scale and simulating the far-field energy dissipation effect. Then, the basic formula of the near-field zone–structure system was derived using the branch mode method, and the motion equation of the soil–structure system applied to real-time hybrid test was obtained. The soil’s numerical model was realized by the joint application of ANSYS and MATLAB software packages and verified through the real-time hybrid test of the soil–structure system. The results show that the proposed constrained mode–damping solvent extraction combined method had high calculation efficiency and good accuracy. It satisfied the requirements of the soil numerical substructure in real-time hybrid tests.

Seismic performance and fragility analysis of underground subway station with rubber bearings

In this paper, a comparative study of the seismic response and fragility of a station structure before and after being retrofitted with an LNB installed on the top of its columns is conducted to evaluate the effectiveness of retrofitting measures in reducing risk probability employing, for the first time, a probabilistic approach. The Daikai subway station was adopted as a case study, and two-dimensional finite element models of soil-structure system with and without LNB were established. Incremental dynamic analyses (IDA) of original and retrofitted structures were conducted to evaluate their seismic responses under different ground motion intensities and considering the uncertainty of ground motion. Further, the IDA curve cluster and quantile lines of station structure and rubber bearing were constructed. Finally, the seismic fragility curves of structure and LNB were established for the risk assessment under different performance levels based on the structural performance index. The results demonstrated that the horizontal deformation, shear force and bending moment of the central column fitted with rubber bearings are greatly reduced compared with the actual Daikai station structure, which is more pronounced for lower ground motion intensity. In addition, the failure probability of the retrofitted structure corresponding to different damage levels is much lower than that of the original structure under the same ground motion intensity. Meanwhile, the probability of moderate to severe damage for the underground station structure is greatly reduced after retrofitting with the rubber bearings. The overall seismic performance of the structure is significantly improved and post-earthquake repair-demand is greatly decreased.

Seismic Response of a Two-Story Three-Span Subway Structural Model under High-Accelerated Geotechnical Centrifuge Shaking Table Test

The seismic response of underground structures such as subway stations is critical. However, the complex underground structure experiments under a dynamic centrifuge shaking table are significantly limited. This study conducts a shaking table test of a two-story three-span underground structure under 50 g gravitational centrifuge acceleration to investigate soil–structure interaction effects (SSI). The test is performed on a sand soil-structural model using a laminar shear box with depths of 2.5 m, and the input motion is a Parkfield wave. The experimental results indicate that the central column of the two-story three-span underground structure is the weak component during the earthquake. In addition, the numerical simulations of the soil–structure system are carried out to study the effect of buried depth and foundation soil type on the seismic response of the underground structures. The experimental and numerical results proved that the performed centrifuge test can reproduce the key seismic response characteristics of the SSI in the prototype underground structure and provided guidelines to design a similar underground structure in the future development of the urban subway systems.

Modelling the sequential earthquake–tsunami response of coastal road embankment infrastructure

Abstract. Transport networks in coastal, urban areas are extremely vulnerable to seismic events, with damage likely due to both ground motions and tsunami loading. Most existing models analyse the performance of structures under either earthquakes or tsunamis, as isolated events. This paper presents a numerical approach that captures the sequential earthquake–tsunami effects on transport infrastructure in a coastal area, taking into consideration the combined strains of the two events. Firstly, the dynamic cyclic loading is modelled, applied to the soil-structure system using a finite-difference approximation to determine the differential settlement, lateral displacement and liquefaction potential of the foundation. Next, using a finite-volume method approach, tsunami wave propagation and flooding potential are modelled. Finally, the hydrostatic and hydrodynamic loads corresponding to the wave elevation are applied to the post-earthquake state of the structure to obtain a second state of deformation. The sequential model is applied to an embankment in Manzanillo, Mexico, which is part of a main urban road; the response is analysed using ground motion records of the 1995 Manzanillo earthquake–tsunami event.

Seismic design of self-centering bridge piers considering soil-structure interaction

This paper presents the seismic design method for self-centering (SC) bridge piers considering soil-structure interaction (SSI) based on the inelastic displacement ratios (CR). The pier is simplified to a single-degree-of-freedom (SDOF) system characterized by flag-shaped hysteretic behavior. The cone model is adopted to simulate the dynamic behavior of the elastic homogeneous soil half-space below the foundation. Firstly, nonlinear time history analyses are conducted by subjecting the soil-structure interaction systems to 20 synthetic ground motions matched to the design response spectra. The effects of different parameters including the fundamental period of the fixed-base superstructure Tfix, strength reduction factor R, secondary stiffness ratio α, energy dissipation ratio of the flag-shaped model β, structure-to-soil stiffness ratio a0, and the height of the pier hs on the inelastic displacement ratios are studied. The analysis results show that the inelastic displacement ratio of the self-centering pier is generally underestimated when SSI is ignored. Specifically, the analytical relationship among CR, R, and Tfix is developed through regression analysis and used to estimate the inelastic displacement demands of the soil-structure systems during the design process. Next, the effects of soil on the elastic structural base shear force are investigated using the base shear effect coefficient RSSI and a simple equation is developed through regression analysis to estimate the RSSI value. A seismic design procedure of the self-centering piers considering soil-structure interaction is then proposed. Finally, a design example demonstrates the application of the proposed.design procedure, and 12 natural ground motions are used to perform nonlinear time history analyses of the designed self-centering pier. The analysis results verify the effectiveness of the proposed seismic design method.

Seismic Performance Assessment of Wide Pile-Supported Wharf Considering Soil Slope and Waveform Duration

Pile-supported wharf (PSW) is one of the primary port structures and is often damaged by earthquakes. To mitigate the risk of seismic damage to a PSW, its seismic performance should be thoroughly assessed. This study aimed to examine the impact of ground displacement on the seismic performance of PSW with a mild soil slope. We performed soil-structure system finite element analysis targeting a wide PSW. The analysis is divided into two scenarios. In the first scenario, the PSW was modeled without regard for the soil slope, whereas the second scenario considered the soil slope. Two waveforms that matched the target spectral acceleration were used to study the effects of the waveform duration on the seismic response of PSW. The analysis results revealed substantial influences of soil slope displacement as well as differences in waveforms on PSW’s seismic performance.

Soil–Foundation–Structure Interaction of Inelastic Structural Systems on Unsaturated Soil Layers

Recently, progress has been made toward understanding the seismic response of structures placed on unsaturated soil layers. A missing link, however, involves the influence and assessment of the underlying soil saturation conditions on the expected superstructure seismic demands. Simplified soil–structure interaction procedures that can be used to predict superstructure seismic demands have not been explicitly extended to incorporate the influence of unsaturated soil on the system response. In this paper, results from a series of six centrifuge tests are compared. In each test, an inelastic single-degree-of-freedom physical model was shallowly embedded in a sandy silt with a distinct water table elevation or a completely dry soil condition. The soil-structure system was subjected to a series of earthquake motions. The response of the system was evaluated to assess the influence of the soil saturation condition on the seismic response. Specifically, a conventional analytical procedure for predicting the influence of inertial interaction on the seismic response of the structure was extended to consider the water table elevation and underlying soil saturation condition and evaluated for its reliability. Analytical flexible-base modal parameters were compared with those determined from experimental results to judge the potential of the analytical procedure to be used in practice. Experimental results suggest that as the water table elevation was lowered from the fully saturated condition, both the flexible-base system period and damping ratio reduced. Therefore, the system behaved stiffer in the unsaturated soil compared with the dry and fully saturated conditions. The stiffer response reduced the seismically induced foundation settlements and rotations but amplified superstructure seismic demands in the form of accelerations, flexural drifts, and bending strains.

Deficient irrigation of vegetable crops

Water is one of the main factors for the production of vegetable crops due to its crucial role in the absorption and transport of nutrients, temperature regulation and some physiological processes, including photosynthesis. Considering the growing needs of a growing population for food and nutrients, a significant part of agricultural research is focused on improving the use efficiency (WUE - Water use efficiency) and saving water without reducing yields. Given the difficulty of increasing WUE through selection due to the tradeoff between photosynthesis and transpiration, agronomic strategies are needed. Due to the shallow root system and the fresh sale of vegetable products, vegetable crops are relatively more sensitive to moisture than field crops. Deficit irrigation (DI) is a direct approach to saving water by reducing irrigation to increase water productivity (WP - Water productivity). Regulated deficit irrigation (RDI) and partial root drying (PRD) are two widely used DI planning methods along with the classic DI approach. We searched the peer-reviewed literature for studies reporting yield differences in vegetable crops subjected to irrigation deficits. The search was conducted on Google Scholar and Web of Science using various combinations of the following keywords: vegetable crop yield and irrigation deficit or moisture shortage or water shortage or drought. Moderate levels of water stress (<65% FI) adversely affect vegetable yields regardless of external factors such as soil structure, climate and production system. This level of irrigation is justified for regions where water restrictions are already in place or forecast. Based on WP growth, irrigation levels as low as 35–50% FI for tomato and pepper, and 50–65% FI for onions and <35% FI for eggplant and watermelon are optimal for areas with severe water scarcity. However, a higher water deficit may also have an adverse effect on quality in terms of reduced fruit/root/bulb size.

Seismic assessment of irregular RC frames with tall ground story incorporating nonlinear soil–structure interaction

This paper is dedicated to evaluate the nonlinear Soil–Structure Interaction (SSI) impact on the earthquake-based response of vertically irregular reinforced concrete (RC) moment resisting frames. The main contribution of this paper is to evaluate the seismic performance of RC structures with 5 and 10 stories considering a number of key parameters including irregularity ratio, soil type and the vertical safety factor (FSv) of the foundation. In this regard, the beam on nonlinear Winkler foundation (BNWF) scheme is used for the modeling of shallow foundations resting on a semi-infinite sandy medium. Vertical irregularity is considered by using a tall ground story in the RC frames. The models are subjected to 15 earthquake ground motions for conducting nonlinear dynamic time-history analyses to capture the seismic demands of soil–structure systems. The results demonstrate that considering SSI influence reduces the seismic demands in the lower stories, which is more evident in the case of soft soils (site class E). Moreover, a rational relationship between the maximum inter-story drifts and the response of the foundations is observed. It is also concluded that for both regular and irregular structures, lower values of the FSv lead to a considerable decrease in the structural demands (story drifts) and an impressive growth in transient and residual foundation settlements.

Time Domain Implementation of Consistent Boundaries for Continuum Two-Dimensional Wave Propagation Problems Using ABAQUS User-Defined Elements

The present paper details the finite element implementation procedure for applying consistent boundaries for two-dimensional continuum soil-structure interaction systems. Consistent boundary conditions are ensured by applying rigorously calculated interaction forces at the truncated soil-structure interface. These calculations involve the evaluation of convolution integral on acceleration unit-impulse response functions for all boundary degrees of freedom for all time steps. The interactive or run-time evaluation of the interaction forces based on the past response history, is successfully carried out using user-defined element formulation in ABAQUS. This precise implementation of this boundary element procedure is demonstrated through benchmark problems and demonstrated through typical stress-wave propagation problems.

The effects of various tillage systems on soil structure and root system development in wheat (Triticum durum Desf.).

The objective of our study is to compare the effect of agricultural soil preparation on the physicomechanical properties of the soil and the consequences on the root system of wheat. To achieve these goals, three technical tillage chains (chain 1: deep tillage, chain 2: agronomic tillage, chain 3: no-tillage), were compared in the same pedoclimatic and historical situations. The experiment was carried out on silty clay soil in the experimental station of the National Higher School of Agronomy (Algiers). The results show that the techniques affect soil’s proprieties and the root system differently. The agronomic tillage has the best favorable effect on soil humidity, Bulk density, and soil Penetration resistance (11,1%; 50%; 0.6 MPa) (p-value :0,0001). Concerning the roots, the density, the diameter, and length were better when the soil is deeply tilled, non-tilled, or agronomical tilled, respectively (CH1:3.37 g/dm³; CH3:1.38 mm; CH2:12.23 cm). Examining all the results of this study has shown how tillage is reflected in and contributes to the farmer's orientation towards the right choice to optimize and conserve soil and water at the same time. Thus, under this study's experimental conditions, the technical itinerary of tillage with agronomic ploughing seems to be an alternative to conventional ploughing. This method of tillage is easily feasible from a technical point of view. Besides, it can generate economic gains compared to ploughing. However, its impacts on the soil and crop yields need to be studied in the longer term.

Effect of Embedded Basement Stories on Seismic Response of Low-Rise Building Frames Considering SSI via Small Shaking Table Tests

The dynamic soil-structure interaction is a combination of phenomena caused by the flexibility of soil foundation in structure response. The structure response may be changed by embedded basement stories. Thus, this study seeks to assess the dynamic response of seven-story concrete frame type buildings without a basement, one basement story, and two basement stories, considering fixed and flexible bases. For this purpose, the experimental tests on the small shaking table were executed with a small scaling coefficient of 1:50. Consequently, three scaled models of steel skeleton structures with variable embedded depths have been constructed with fixed and flexible bases. These models are exposed to three seismic input motions: Northridge (1994), Kobe (1995), and Chi-Chi (1999) at the base of the structure as a fixed base and the bedrock level in the soil structure system as a flexible base. The finite element technique is carried out for scaled and real models. Both the scaled and real numerical models are in good agreement with the obtained experimental observations with reasonable accuracy. It is concluded that the lateral deflections are overestimated by excluding embedded depths of structural elements. In the flexible prototype model, the lateral deflections of the superstructure with embedded depths (3 m, 6 m) decrease compared with no embedded depth, in which the maximum reduction percentages of 7-story with embedded depths 3 m and 6 m at the roof floor level are 21% and 42% compared with no embedded depth, respectively, under Northridge earthquake. Otherwise, ignoring the SSI effects (fixed base case), the lateral displacements are underestimated compared with the flexible base. The maximum amplification percentages at the roof floor level between flexible and fixed bases models with variable embedded depths are 35%, 37%, and 65% under Northridge, Kobe, and Chi-Chi earthquakes, respectively. The amplification and reduction percentages may be high or low, mainly depending on soil condition (fixed, flexible), variable embedded depths, characteristics of seismic motion, travel pass, and source of seismic motion. These items are summarized as the frequency domain of the coupled system compared with the frequency domain of the earthquake motion.

Effects of adjacent paleochannel sedimentary on the seismic response of structure with incident SH-wave

This paper combines the indirect boundary element method and the idea of “region-matching technique” to study the impact of adjacent paleochannel on structures in a layered half-space with incident SH-wave. It decomposes the model into paleochannel closed region, layered half-space open region, and rigid foundation-elastic structure. Wave field in the closed region only have scattered wave, and wave field in the open region includes scattered and free field. The scattered and free field are simulated by the dynamic Green's function and the direct stiffness method, respectively. Then, response of soil-structure system is solved by employing the boundary continuity conditions and dynamic equilibrium of structure. After verification of the method, seismic response of structure under the influence of adjacent paleochannel shape, distance between the paleochannel and structure, and shear wave velocity ratio of the paleochannel were analyzed. Results show: All three paleochannel shapes (ellipse, trapezoid, triangle) are adverse to the structure compared to the case of no paleochannel, and ellipse is the most unfavorable shape; Effect of paleochannel should be taken into account when paleochannel distance L/a<100; Higher shear wave velocity ratios result in larger peak of structural displacement; Structural response is more amplified in oblique incidence than vertical incidence.

Soil-Structure Interaction Effects on Dynamic Behaviour of Transmission Line Towers

As inferred from earthquake engineering literature, considering soil structure interaction (SSI) effects is important in evaluating the response of transmission line towers (TLT) to dynamic loads such as impulse loads. The proposed study investigates the dynamic effects of SSI on TLT behavior. Linear and non-linear models are studied. In the linear model, the soil is represented by complex impedances, dependent of dynamic frequency, determined from numerical simulations. The nonlinear model considers the soil non-linear behavior in its material constitutive law and foundation uplift in a non-linear time history analysis. The simplified structure behavior of a typical lattice transmission tower is assessed. The analysis of frequency and time domain are followed through varying soil stiffness and damping values. Three different shock durations are investigated. The soil-structure system with equivalent dynamic properties is determined. The behaviors achieved utilizing a rigid and a flexible base for the structures is compared to estimate the impact of taking SSI into account in the calculation. The current mainstream approach in structural engineering, emphasizing the importance of the SSI effect, is illustrated using an example where the SSI effect could be detrimental to the structure. Furthermore, the non-linear analysis results are analyzed to show the linear approach’s limitations in the event of grand deformations.

Investigating the Effect of Soil Layering on Soil-structure Interaction under Seismic Load

Considering soil layering is a crucial and effective issue in investigating the seismicity of structures. However, previous studies have not examined the presence of a rock layer in soft soil. So, in the present paper, the effect of the rock layer in soft soil on the forces and displacements created in the low-and mid-rise steel moment frame was investigated. Thus, several numerical calculations were performed on 12 different sizes of rock layers at three different depths. Finite element models were analyzed using ABAQUS Software and considering the interaction of structure and soil. Results of the studies showed that the value of force and displacement depends on the frequency of the structure, the frequency of the soil-structure system, dominant earthquake frequency, the rock weight, and the stiffness of the structure. Two new parameters are defined that have a linear relationship with force and displacement. Results show that the thickness and length of the rock layer affect the value of force and displacement. Also, the presence of a rock layer in the soil may not be reliable and may increase the shear force by up to 27%, the axial force by up to 10%, and the moment by up to 19%. The effect of the presence of a rock layer on the displacement is more than on the force and increases the lateral displacement by up to 31% and the relative vertical displacement of the foundation by up to 59%.

Improvement of the Technique for Seismic Analysis in the Soil-Structure System of an Arched-Gravity Dam

Improvement of the Technique for Seismic Analysis in the Soil-Structure System of an Arched-Gravity Dam

2D and 3D techniques to assess the structure and porosity of Oxisols and their correlations with other soil properties

Structure and porous geometry are dynamic soil parameters that control several soil processes and functions. This study details the differences in the structure of typical Oxisols regarding the clay amount, biological activity, and mineralogy. Combining 2D and 3D image analysis can provide detailed information about the soil structure and porous system. The objectives of this study were: (i) to describe the soil microstructure and degree of microaggregation; (ii) to quantify porosity, soil pore types, and soil pore size distribution using 2D and 3D techniques; and (iii) to better understand the relationship between the porous system and the biological, chemical, mineralogical, and physical properties of the soil. The study considered four Oxisols: Xantic Kandiustox (P1), Rhodic Haplustox (P2), Anionic Acrustox (P3), and Typic Hapludox (P4). The results showed that all Oxisols have some degree of microaggregation. The Rhodic Haplustox (P2) had the most pronounced degree of microaggregation, which reflects the greater biological activity and gibbsite/kaolinite ratio, and lower hematite/(hematite + goethite) ratio compared to the other Oxisols. The pore types found by 2D analysis were complex pores in P1 and P2 and rounded pores in P3 and P4. The 3D analysis showed that P2 and P3 have a more connected porous system compared to the other Oxisols, evidenced by the lower value of the Euler number. The best connectivity values of the porous system were congruent to improved saturated hydraulic conductivity measured in a separate sample set.

Fragility analysis of nonlinear soil-structure systems including foundation uplifting and soil yielding

Fragility analysis of nonlinear soil-structure systems including foundation uplifting and soil yielding

Seismic mitigation performance analysis of underground subway station with arc grooved roller bearings

A seismic mitigation control technology involving arc groove roller bearings (AGRB) for shallow buried underground frame structures is proposed for reducing the horizontal deformation of the central column. Firstly, the working mechanism of AGRB component is described and its mechanical properties are analyzed through pseudo-static analysis. The results show that AGRB offers good vertical bearing capacity and horizontal deformation performance. Secondly, the finite element models of the soil-structure system for subway stations with and without AGRB are established for implementing the nonlinear dynamic time-history analysis. Compared with the observed response of the structures without AGRB, the horizontal deformation, shear force and bending moment of the central column fitted with AGRB are greatly reduced and the maximum seismic mitigation rate is above 80%. In addition, the results demonstrated that utilizing AGRB could greatly reduce the plastic damage area and damage degree of the supporting column, and avoid the occurrence of plastic hinges and shear failure due to insufficient lateral deformation resistance of the central column under high axial compression. Thus the AGRB can be used as an effective design scheme to achieve seismic mitigation control for underground structures.