Soil Spring Research Articles

Analysis of seismic damage mechanism of simply supported girder bridges at near‐fault liquefaction sites

AbstractThis work uses the Yematan Bridge as an example to explore the seismic damage mechanism of simply supported girder bridges at near‐fault liquefaction site. It analyzes the bridge from the local portion to the complete bridge, considering the effects of the near‐fault and liquefied soil layers. First, a three‐dimensional model of the pile‐soil seismic action of Pier No.17 was created using simulated near‐field ground motion, and analysis was performed to simulate the action of the liquefied soil layers on the pile foundation, getting pile‐soil dynamic p‐y curves. After that, the accuracy of the pile spring parameters was verification by doing an equivalent static analysis. Finally, to identify the seismic damage mechanism of high‐damping rubber (HDR) bearings and the dynamic unseating process of the Yematan Bridge, a finite element model of the complete bridge was developed. During this procedure, the near‐field ground motion amplitude and soil spring parameters were iterated and optimized continually, such that the simulated earthquake damage was identical to the real one. The findings suggest that the bridge was destroyed by significant structural vibration. The near‐fault impulse effect and lack of equivalent limiting measures induced the entire collapsing girders to move consistently and destroyed the HDR bearings. Liquefied soil can cause some damage to pile foundations, and lateral spreading can cause the piers of the same span to perform differently.

Formulation and numerical applications of efficient pile–soil integrated element considering structural inelasticity

AbstractThe prediction of pile behavior under extreme loading is an essential consideration in the design. The pile behavior at a large displacement level is governed by the pile–soil interaction and the material inelasticity. The conventional numerical model using a large number of elements is inefficient for modeling the nonlinear pile–soil interaction and structural inelasticity in finite element analysis. To accurately and effectively evaluate the behavior of piles under extreme loading, this paper develops a pile–soil integrated element considering structural inelasticity. The pile–soil interaction force can be efficiently evaluated according to the soil resistance at the Gauss integration points. The different types of p‐y and t‐z curves can be applied in this element to represent soil properties at any soil depth. Zero‐length plastic hinges at the ends and middle of an element are used to capture the inelastic behavior of a pile. The plastic hinges and the soil springs are integrated into the proposed element formulations, and thus one element type is sufficient to conveniently simulate the nonlinear pile–soil interactions. Comparisons between the results of the elastic pile element and the data from published literature and field tests are provided to validate the accuracy and efficiency of the proposed method.

Changes in Soil Properties and Crop Yield under Sustainable Conservation Tillage Systems in Spring Wheat Agroecosystems

The cultivated soils in several semi-arid areas have very low organic matter due to climatic constraints that limit primary crop yield. Conservation tillage systems, outlined here as no tillage, no tillage with straw return and straw incorporation into the field, have been accepted as capable systems that preserve soil’s resources and sustain soil productivity. However, in semi-arid climates, there is presently no knowledge about the influence of different conservation tillage techniques on soil’s physical, chemical and biological properties at different soil depths in spring wheat fields and only little information about spring wheat yield in these management systems. Therefore, the present study was carried out with the objective of examining the impact of conservation tillage systems on soil properties (physical, chemical and biological) and spring wheat yield. The three conservation tillage treatments consisted of no tillage system (NT), wheat stubble return with no tillage (NTS) and straw incorporation with conventional tillage (CTS), as well as one conventional tillage (CT) control treatment, which were evaluated under randomized complete block design with three replications. The three conservation tillage treatments were compared with the conventional tillage control. Conservation tillage significantly increased the bulk density, gravimetric water content, water storage, hydraulic conductivity and soil aggregates and decreased the pore space and soil temperature compared to CT; however, no significant difference was found in the case of field capacity. Soil chemical properties in the 0–40 cm soil layer increased with conservation tillage compared to CT. Conservation tillage also notably increased the soil microbial counts, urease, alkaline phosphatase, invertase, cellulase and catalase activities relative to CT. Microbial biomasses (carbon and nitrogen) and wheat yield significantly elevated under conservation tillage compared to CT. Therefore, conservation tillage could significantly improve soil properties and maintain wheat yield for the research zone.

Dynamic response of OWTs under wind-wave loads considering 3D water-pile-soil interactions

A new three-dimensional (3D) integrated model of offshore wind turbine (OWT) is proposed, which considers the soil-monopile-water interactions and the accumulative deformation of foundations under cyclic loads. The effects of three different modelling methods on the dynamic response of wind turbine are discussed, where three modelling methods are the new WOT model, OWT model with a 3D soil-pile medium without a seawater domain and OWT model with API's spring-type foundation. The numerical results show that the use of API's soil spring may overestimate the fundamental frequency of OWT by up to 32.2%. This leads to inaccurate structural resonance. Meanwhile, a significant displacement drift of the tower top of the new model is observed due to the ratcheting effect, and the OWT with API's spring cannot correct this phenomenon. Consequently, the API method should be used with care in assessing dynamic performance under wind-wave loads. The added mass method considers only the water-structure interaction and excludes the soil-water interaction, and it may underestimate the responses of the tower, blades and monopile, which can render the design of wind turbines unsafe. Additionally, assumption of the parked condition underestimates the structural response, and the frequency of the blades may change during operation.

Deepened snow cover increases grassland soil carbon stocks by incorporating carbon inputs into deep soil layers.

Climate-induced changes in snow cover can greatly impact winter soil microclimate and spring water supply. These effects, in turn, can influence plant and microbial activity and the strength of leaching processes, potentially altering the distribution and storage of soil organic carbon (SOC) across different soil depths. However, few studies have examined how changes in snow cover will affect SOC stocks, and even less is known about the impact of snow cover on SOC dynamics along soil profiles. By selecting 11 snow fences along a 570 km climate gradient in Inner Mongolia, covering arid, temperate, and meadow steppes, we measured plant and microbial biomass, community composition, SOC content, and other soil parameters from topsoil to a depth of 60 cm. We found that deepened snow increased aboveground and belowground plant biomass, as well as microbial biomass. Plant and microbial carbon input were positively correlated with grassland SOC stocks. More importantly, we found that deepened snow altered SOC distribution along vertical soil profiles. The increase in SOC caused by deepened snow was much greater in the subsoil (+74.7%; 40-60 cm) than that in the topsoil (+19.0%; 0-5 cm). Additionally, the controls on SOC content under deepened snow differed between the topsoil and subsoil layers. The increase in microbial and root biomass jointly enhanced topsoil C accumulation, while the increase in leaching processes became critical in promoting subsoil C accumulation. We conclude that under deepened snow, the subsoil had a high capacity to sink C by incorporating C leached from the topsoil, suggesting that the subsoil, originally thought to be climate insensitive, could have a higher response to precipitation changes due to vertical C transport. Our study highlights the importance of considering soil depth when assessing the impacts of snow cover changes on SOC dynamics.

MSA-based seismic fragility analysis of RC structures considering soil nonlinearity effects and time histories compatible to uniform hazard spectra

In the present study, an updated ground motion simulation framework based on spectral compatible time histories is proposed for the evaluation of seismic performance of mid-rise reinforced concrete structures with multi-stripe analysis (MSA) based probabilistic seismic hazard analysis. The seismic fragility functions are generated for two numbers of three storied instrumented test buildings of which one is founded on individual flexible footings and other one is a base isolated building. The fragility analysis is carried out for different performance levels under a series of input ground motions (IGMs) by considering uncertainty in soil structure interaction and uncertainty in ground motion. IGMs are obtained from the uniform hazard response spectrum (UHRS) with different return period thus conserving the frequency content of input motion during the scaling of high intensity earthquakes. The UHRS compatible synthetic time histories are applied at rock level and amplified surface motion obtained from soil amplification studies considering soil nonlinearity are applied to the buildings supported on soil springs. Nonlinear time history analysis is performed by modelling hysteretic characteristic of columns using modified Takeda model. The fragility curves obtained from the proposed methodology are compared with that using simple scaling of accelerograms generally performed in literature. The proposed technique gives conservative result for structure with individual flexible footings while no marked differences are observed for base isolated structure.

Effects of Soil–Structure Interaction on Performance of Bridges During Earthquakes. Case Study: Integral Abutment Bridge in Pennsylvania, USA

Bridges are among the most important transportation elements that may be damaged by earthquakes. An integral abutment bridge (IAB) is a bridge linking the superstructure directly to the substructure. As soil piles, abutments, and superstructures act as a combined system to resist lateral loading on the bridge, soil stiffness has a major impact on load distribution. This research attempts to determine how the structure and soil parameters affect the IABs. The parametric study consists of four variables, namely bridge span (short, medium, and large spans were 18.3, 35.4, and 64.5 m, respectively), backfill height/pressure (3.1, 4.6, and 6.1 m, respectively), stiffness of soil mixture backfills (high, intermediate, and low), and soil density around the piles (high, intermediate, and low). Because of the small width–length ratio of the bridge, a 2D model of an IAB with soil springs around the piles and abutments was developed with finite element software. Findings show that the value of the backfill pressure affects girder axial forces and girder bending moments at the IAB. Also, the stiffness of soil mixture backfills is an important factor to change lateral displacements, while less movement is related to high stiffness of soil mixture backfills with intermediate clay around the pile. It is clear that the maximum axial girder moments at the superstructure generally decrease when the stiffness of the soil mixture behind the abutments and around piles increases, similar to pile deflection and abutment displacements. In addition to maximum abutment, the head moment decreases when abutment backfill is dense and increases when piles are located in hard clay, similar to pile moments. Lastly, dense sand backfill behind abutments is recommended since it decreases pile deflections, pile lateral forces, abutment displacements, abutment head moments, and particularly pile bending moments.

Integrated analysis of soil-structure interaction for statically indeterminate beams on spatially random soils

ABSTRACT This study aimed to develop an integrated approach to analyse the interaction between soils and beams. The research methods involved placing a statically indeterminate beam on spatially random soils, where soil springs acted as supports for the beam. The soil spring stiffness values were simulated using random field theory. This integrated approach was embedded in the Monte Carlo simulation framework to facilitate probabilistic assessment. This study concluded that the force method solution accurately determined the bending moment and shear diagrams for a beam supported by soil springs. Additionally, soil spatial variability had a significant impact on the beam responses, including the variations in footing settlements, support reactions, bending moment, and shear force. This study also identified a critical scale of soil fluctuation that coincides with the beam span, which resulted in the highest probability of structural bending failure. Overall, this study highlights the importance of accounting for soil spatial variability in an integrated geotechnical and structural design approach.

Seismic Response Analysis of Reinforced Concrete Frame Structures Considering Slope Effects

According to the seismic damage due to past events, buildings located on slopes can present a worse seismic performance. To explore this, this study established a finite element model based on a 6-story RC frame structure and soil models based on a practical slope using OpenSees software. Combining the superstructure model with the soil model through soil spring elements, three soil-structure interaction systems with different slope rates were set up. Twenty near-field seismic actions were used as input loads for dynamic time–history analysis. The analysis shows that in the process of seismic action, the deformation tendency of the structure is affected by the slope. There is a clear tendency for lateral displacement towards the slope, and it is more obvious with a greater slope ratio. Meanwhile, the slope has no impact on the shear force at the base of the structure or at the bottom of the column. In addition, there is no correlation between the degree of impact and the slope gradient on the peak value of internal forces and deformations of structure.

Application of Soil Structure Interaction on Building with Basement using Nonlinear Soil Springs

In a typical building design, the interaction between building and surrounding soils is often ignored. Since soil is deformable and has limited capacity to resist loads, this interaction, called soil-structure interaction (SSI), could alter building responses, especially during earthquake loadings for buildings with significant basement depths. In this study, a 10-story reinforced concrete building with 3-level basement was used to evaluate the effects of SSI on building during earthquakes. Dynamic time response analyses were performed using earthquake time histories scaled to a design response spectrum for a Surabaya, Indonesia, location. Soil responses during earthquakes were modeled using nonlinear hysteresis normal and elastic-perfectly plastic frictional soil springs, developed using the hardening soil with small strain stiffness model. Depth-varying ground motions were also applied along the basement depth. The results show inconclusive SSI effects, where some of the time histories produce greater base shears and inter-story drifts when SSI is considered, while others show the opposite results.

Analysis of the Effect of Local Foundation Scouring on the Structural Dynamic Effect of a Cable-Stayed Bridge Across The Sea

The foundation scour reduces the restraining effect of the foundation on the bridge foundation, resulting in the reduction of the lateral bearing capacity of the bridge foundation. For the cross-sea bridge, the dynamic effect of foundation scour on the bridge structure is more significant, thus affecting the safety of the structure. In this paper, the maximum possible local scouring depth of the foundation is first calculated to make the simulated foundation scouring condition conform. to the actual project. Then, the m-method is adopted to calculate the stiffness value of the foundation soil spring and establish an elastic restraint model that reflects the restraint of the foundation soil on the bridge foundation, thus setting up the finite element model of the bridge with regard to the foundation scouring. On this basis, taking Qiongzhou Strait cross-sea highway and railway dual-purpose cable-stayed bridge as an example, the effect of foundation scour on the dynamic effect of cross-sea cable-stayed bridges under the action of wind and waves is analyzed, and the influence law of the local scour depth of the foundation on the dynamic effect of the structure is determined. The maximum scour depth of 12m is considered to increase the displacement of the top of the tower by 14. 65%, mainly because the foundation scours reduces the restraint effect of the foundation soil on the bridge foundation, resulting in the reduction of the lateral bearing capacity of the bridge foundation. Therefore, for the cross-sea cable-stayed bridge without foundation soil treatment, the detection and monitoring of foundation scour should be strengthened or the preventive maintenance and reinforcement treatment of foundation soil should be done in advance to ensure the safe operation of the bridge structure.

Natural Frequency Analysis of Monopile Supported Offshore Wind Turbines Using Unified Beam-Column Element Model

Assessment of the natural frequency of the offshore wind turbine (OWT) system is a critical task in design to avoid resonance. The natural frequency of the monopile supported OWT may change during operation and needs to be calculated regularly. Conventional numerical methods separately model different components of the OWT system using various element types, which require tedious data manipulations and are inefficient to assess the changing natural frequency of the monopile supported OWTs. This paper develops a unified beam-column element by directly integrating the soil-pile interactions in element formulation. The proposed method is applicable for different components of the OWT system, including the rotor, the tower, the transition piece, and the monopile foundation, which enables an integrated and efficient OWT analysis by using only one type of element. The pile-soil interactions are directly considered in the element formulation. The tedious soil spring elements are avoided. Definitions and formulations of the proposed element are provided and the numerical solution procedure for the natural frequency analysis of OWTs is illustrated. The accuracy of the proposed element is validated against several closed-form solutions and the distributed spring model. The proposed method is also applied to analyze the natural frequencies of six OWTs in practice. The calculated results are consistent with the field measured data.

Lateral ground movement effects near a joint of MDPE gas distribution pipes

Buried medium-density polyethylene (MDPE) pipes are widely used for gas distribution systems in Canada and worldwide. When exposed to geotechnical hazards such as ground movements, these pipes can experience excessive distresses, leading to leaking or failure. This research investigates the effects of ground movement near a tee connection of MDPE gas distribution pipes. If the ground movement is parallel to a branch, the branch pipe experiences an axial force, and the main pipe experiences bending deformation/strains. The axial forces and the wall strains were investigated in this study using full-scale laboratory tests. Test results showed that the axial force on the branch and strains on the main pipe depend on the burial depth, backfill soil density, and the pipe diameter due to the effects on the shearing resistance of the soil. The soil shearing resistance was less for shallow buried pipes, resulting in a lower axial force in the branch but higher bending strain in the main pipe. The axial pullout resistance of the main pipe also contributed to the wall strains of this laterally loaded pipe at large displacements. The conventional beam-on-elastic foundation solution reasonably estimated the pipe wall strains within the linear range of deformations. Nonlinear analyses, including lateral and axial soil springs, are recommended to capture the nonlinear responses at large displacements.

Seismic Performance Assessment of Pile-Supported Wharfs: 2D Frame Analysis Method Considering Both Inertial and Kinematic Forces

Frame analysis (FA) is known for its efficiency and low computer resource requirements. However, compared to finite element analysis (FEA), the applicability of FA for the seismic performance assessment of pile-supported wharves (PSWs) is limited, particularly in the ability to account for the kinematic force caused by ground displacement during an earthquake. This study aimed to develop a two-dimensional FA method for PSW seismic response analysis that considers a combination of inertial and kinematic forces. We performed FA and FEA and compared the results. First, we targeted the PSW model without considering the soil slope and discussed the spectral acceleration (SA) evaluation method for calculating inertial force. As a result, an equation for estimating a damping coefficient to evaluate the SA in accordance with the PSW width and natural period was proposed. Next, we targeted the PSW model by considering the soil slope and proposed a method to evaluate the kinematic force based on the amount of ground displacement and the soil spring characteristics. The results revealed that using the proposed method, FA, by considering kinematic and inertial forces, could reproduce the bending moments of the piles comparable to those calculated using FEA. Therefore, solely considering the inertial force for a PSW on a soil slope may cause the bending moment to be underestimated.

Seismic response of column supported tanks considering uplift effect and soil‐structure interaction

AbstractIn this paper, the seismic responses of column supported tanks under horizontal earthquake are obtained by finite element method. Two types of structures are discussed including the anchored tank with columns fixed on the ground and the resilient tank whose columns can uplift. The uplift effect is realized by the contact algorithm to allow the column move upwards in a vertical direction and the soil‐structure interaction (SSI) is considered by equivalent soil springs. Different soil types and hard ground condition are adopted to study SSI effect on natural frequencies of tanks and seismic responses of the anchored tank, as well as coupling effect (both uplift and SSI effects) on seismic responses of the resilient tank. The structural displacement and acceleration, the stress of tank walls and columns, the base shear and the overturning moment, the uplift displacement of columns are discussed. The results of tanks in different conditions are compared with each other, which show that SSI has a significant impact on seismic responses of column supported tanks. As the stiffness of soil decreases, the tank has larger displacement, smaller natural frequency, and stress level of structural members especially when it is sited on softer soil type. Compared to the anchored tank, due to the combination of both uplift effect and foundation deformation, the resilient tank has smaller displacement to prevent its overall collapse and lower responses such as the base shear and the overturning moment. The resilient tank has better seismic performances regardless of soil conditions.

Regional‐scale seismic fragility, loss, and resilience assessment using physics‐based simulated ground motions: An application to Istanbul

AbstractUsing results from 57 large‐scale physics‐based fault‐rupture and wave propagation simulations, this research aims to evaluate the seismic risk, loss, and resilience of more than 16,000 reinforced concrete buildings in the Zeytinburnu district of Istanbul, Turkey. For each building and under each earthquake scenario, the spatially varying site‐specific simulated ground motions were used for performing three‐dimensional nonlinear time‐history analyses. The resulting structural responses—such as peak story drift ratios (PSDR) and peak floor accelerations (PFAs)—were utilized to conduct three region‐scale tasks: (i) building‐ and site‐specific seismic fragility analysis for both structural and nonstructural components of each building; (ii) intensity‐based seismic loss assessment using the FEMA P58 methodology and Monte Carlo simulations; and (iii) resilience evaluation based on the expected time of recovery predicted through FEMA P58. Moreover, both inertial and kinematic soil–structure interaction (SSI) effects were considered using a substructuring method for all three tasks. Site‐specific soil properties were utilized to compute the coefficients of soil springs and dashpots, as well as the foundation input motions. The SSI effects were investigated by comparing the fragility, loss, and resilience indices obtained with and without considering SSI.

Validation of earthquake analysis methodology of a suction-caisson foundation-structure through model testing

Suction caissons are one of the most widely used foundation solutions for subsea structures and wind farms. Seismic response of subsea structures is however seldom documented properly, often just treated as a foundation capacity issue applying a quasi-static acceleration and not considering the inertial interaction between the structure and the soil. The more relevant tasks to document are the motions of the unit and the response of the externally connected flowlines and equipment/systems on the unit.Based on a case study located in the Shah Deniz field in the Caspian Sea, model centrifuge tests and numerical modelling were carried out to validate the global response of a 4-caisson supported manifold structure subject to seismic motions in soft clay. The centrifuge tests were carried out at 58 g at the centre for geotechnical modelling at UC Davis. To simulate the soil-structure interaction, a series of non-linear springs defined by kinematic hardening models were used in analyses with the ABAQUS software. This development includes the algorithms for determining the required model parameters. A very good agreement between recorded response from the centrifuge test and calculated response from the FE-analyses was achieved.The development and validation of the soil model presented in this paper is an improvement in design methodology for caisson foundations subjected to earthquake loading. The non-linear soil springs are well suited to incorporate in more detailed structural analyses where an accurate representation of the foundation response is required. The paper also briefly describes how the subsequent earthquake design analyses were performed for the Shah Deniz manifold structures making use of the validated soil spring model and the added value it gave to the project.

Effect of Seismic Analysis Approach and Provision of Shear Walls on Parameters for Raft Foundation Design

The present work attempts to understand the effect of different methods of seismic analysis on the design of building raft foundation. The study also evaluates the role of shear wall on the foundation response. A ten storey building with raft foundation has been analyzed in STAAD Pro using three different seismic analysis methods, viz., Linear static analysis, Linear dynamic analysis and Non-linear dynamic analysis. Furthermore, building with two different arrangements of shear walls (peripheral and core region) are studied by Non-linear dynamic analysis and compared with the model without shear wall. The raft is modeled with plate elements supported by soil springs using Winkler's approach. To consider the effect of different soil and raft stiffness, three different soil spring values and two raft thickness values have been considered. It has been concluded from the study that linear static analysis yields lower values of all foundation design parameters (viz., base pressure, settlement, foundation bending moment and shear stress) as compared to dynamic analysis. Dynamic analysis yields higher variation in base pressure and settlement distribution, which suggests adopting dynamic analysis approach for obtaining more realistic response, especially for settlement sensitive structures. Further the provision of shear wall has negligible influence on base pressure and settlement of foundation, while maximum bending moment and shear stress in foundation increases. Hence, provision of shear wall may increase cost of foundation, however, considering its role in improving structural integrity, shear walls are deemed important. Further, the increase in soil stiffness and reduction in raft thickness yields higher maximum base pressure and variation in base pressure, which confirms the importance of considering the effect of soil-foundation interaction for design of foundation. It is opined that the findings of the study would help in more realistic foundation design to achieve better performance during its life cycle.

Study on Improvement of Pipe-Soil Spring Model in Mountain Slope Area

For the interaction between the pipeline and the soil under the condition of large surface displacement, the displacement load is often transmitted to the pipeline through soil springs. The selection of soil spring parameters is based on laboratory research results, which may not be effective for pipe-soil interface simulation. In addition, the load and soil spring coefficient of the pipeline in the slope should vary with space and time, and these factors are ignored by the resistance formula of the current general spring model. The adaptability and temporal load distribution of the pipe-soil spring model in regions of large surface deformation are largely unknown. In this paper, we deduced the soil spring resistance formula when the surface is inclined, established an improved soil spring model for the slope, and obtained the variation law of soil spring resistance in different directions at different slope angles. At the same time, a comparison of the improved soil spring model with the standard soil spring model recommended by international associations and codes was carried out. The rationality of the improved soil spring model proposed in this paper in the calculation of the pipe-soil interaction in the slope section is further verified by small-scale physical model tests. It has a certain guiding significance for the calculation of pipe-soil interaction in slope sections.

Force based Design Approach for Seismic Evaluation of Padma Multipurpose Bridge Pier at Different Performance Levels

The Padma Multipurpose Bridge (PMB) is one of the biggest megaprojects of Bangladesh connecting one third of the country with the capital city, Dhaka. The infrastructure is expected to produce considerable uplift on the nation’s transport system, the national and regional economy, employment, household income, and ultimately, poverty reduction. From construction and river management points of view, it is the most difficult and engineering innovation-intenstive project in the world. Hence the Padma Multipurpose Bridge (PMB) required analytical, computational and experimental studies. In this work, a 3D Finite Element (FE) model of the actual PMB containing a single (6x150m) 900m modules has been developed in MIDAS Civil, a commercial computer program for bridges. P-y soil spring model following API guideline has been developed to conform flexible support system of the bridge pier. Following BNBC 2020, the bridge's performance has been evaluated for the 475-year, 975 years, and 2475-year return periods for Service Level, Design Basis and the Maximum Credible Earthquake (MCE), respectively. The forced based design shows that the bridge pier reached only 28% and 36% of its axial and shear capacity respectively for an earthquake return period of 2475 years. On the other hand, the pier has reached a maximum of 41% of its total shear capacity for the same seismic level.