Dynamic Effective Stress Analysis Research Articles

Dynamic effective stress analysis of centrifuge tests on pile foundations and liquefaction countermeasure utilizing densification method

Dynamic effective stress analysis of centrifuge tests on pile foundations and liquefaction countermeasure utilizing densification method

Seismic response of soil-shield tunnel systems in sandwiched liquefiable soil deposits

Long-extended underground structures such as shield-driven tunnels may be constructed through sandwiched liquefiable soil profiles, which can compromise their integrity during strong earthquakes. In this study, the influence of sandwiched liquefiable soil layer on the seismic response of shield tunnels under ground motions with different frequency contents is evaluated through nonlinear numerical simulations. Six soil-shield tunnel finite element models with different sandwiched liquefiable soil profiles are developed using the open-source software framework OpenSees. The solid–fluid fully coupled dynamic effective stress analysis method is adopted for the nonlinear seismic analysis of liquefiable soil. The numerical results demonstrate that the frequency contents of earthquake motion and the spatial location of the sandwiched liquefiable soil profile have great influence on the dynamic responses of the segmental tunnel. In all cases studied, the bottom half of the tunnel embedded in the liquefiable soil layer experienced the most unfavorable condition for the seismic performance. The deformations and internal forces of the segmental joints around the tunnel foot are remarkably higher than at other joints under the same ground motion intensity. Moreover, the Kobe motion with the low-frequency content would significantly amplify the seismic responses of both the site and the segmental tunnel compared to the Chi-Chi motion with the high-frequency content in different sandwiched liquefiable soil deposits. It is also found that the racking ratio of the non-liquefiable soil layer is greater than that of the liquefiable soil layer, which means that the surrounding soil with large shear deformation pushes the underground structure leading to larger adverse lateral deformation of the structure.

Pore Pressure Responses of Liquefied Numerical Sand Columns

The Palu 28 September 2021 M 7.5 Earthquake has brought several new challenges to the understanding of liquefaction and its following geotechnical phenomena. In addition, that main shock was followed by a series of aftershocks within a short time frame. The common geotechnical conditions of Palu area include layered soils conditions, and the associated variability of geotechnical conditions exists. This paper reports the dynamic effective stress analysis (ESA) study of four different liquefiable layered sand columns, and the above three conditions (layered soils, variability, aftershocks) are explicitly modeled. The dynamic ESA employs the PM4Sand constitutive model for liquefiable sands, implemented in the OpenSees platform. Three ground motion sets (“main shock only”, “main shock plus aftershock”, “aftershock” only) of variable amplitude, single frequency harmonic motions are used. The models are validated by comparing qualitatively their results against laboratory test results and field measurements. The saturated sand layers in all cases subjected to “main shock only” are liquefied with different detailed excess pore pressure (EPP) responses, highlighting the importance of the system response of liquefying sand columns. The cases subjected to “main shock plus aftershock” show a much a longer higher EPP state, while cases subjected to both “main shock plus aftershock” and “aftershock only” indicate a longer liquefaction state during the aftershock. The implication of the longer duration in the higher EPP state and the longer liquefaction state is that a longer duration of lower shear strength conditions would exist. The different EPP responses resulted from different geotechnical conditions represented by the four sand columns suggest that the variability of geotechnical conditions would have an important influence on the system response.

Dynamic effective stress analysis of a centreline tailings dam under subduction earthquakes

A case study was conducted to evaluate the seismic performance of a centreline tailings dam in the South American Andes through dynamic effective stress analyses with advanced constitutive models. The seismic demand at the dam site was evaluated through a probabilistic seismic hazard assessment (PSHA), from which deterministic and probabilistic-based seismic design criteria were derived. The PSHA results were used to select spectrally matched ground motions for the subsequent dynamic analyses. The plan is for the centreline tailings dam to be raised in stages to a height of 90 m; this was considered in establishing the initial stresses and pore pressures before seismic loading. The material properties were based on a large geotechnical characterisation programme considering the mine tailings to be stored in the deposit and other critical dam components. Dynamic analyses were performed using the UBCHYST constitutive model for materials that are not expected to generate significant excess pore pressures and the PM4Silt constitutive model for materials that may generate excess pore pressures due to cyclic loading. The results showed the deformation patterns in the centreline dam, after seismic loading, to be significantly affected by the presence of mine tailings. The results of this work will be useful in planning the overall operational management of the tailings facility.

Seismic performance of block-type quay walls with liquefiable calcareous sand backfill

Block-type gravity quay walls are widely used in remote oceanic regions due to their cost and construction efficiency, where backfill and foundation soil often consist of liquefiable calcareous coral sand. The lack of connection between blocks and hence structure integrity can result in poor seismic performance of block-type quay walls, especially in liquefiable soil. Based on laboratory element tests on calcareous sand, centrifuge shaking table test, and high-fidelity numerical simulation, this paper investigates the seismic performance of block-type quay walls with liquefiable calcareous sand backfill. Undrained cyclic torsional shear tests are conducted on South China Sea calcareous coral sand to determine its dynamic properties, which are used to calibrate the unified plasticity model for large post-liquefaction shear deformation of sand. A centrifuge shaking table test is conducted to obtain the basic physical seismic response of a block-type quay wall in liquefiable calcareous backfill sand. Utilizing the understanding from laboratory tests, fully coupled dynamic effective stress analysis using the calibrated constitutive model is conducted. The influence of seismic input, quay wall structure, and backfill sand properties on the seismic response of the quay wall is analyzed. Input motion intensity and frequency are shown to be influential to the seismic response of the quay wall. Increase of backfill soil density, permeability, and block to block connection can significantly improve the seismic performance of the quay wall.

Safety assessment for a shield tunnel in a liquefiable deposit using a practical dynamic effective stress analysis

Shield tunnels are widely constructed throughout urban areas with most of their sections being fully or partially embedded in liquefiable deposits. The possible damage to shield tunnels caused by soil liquefaction should be considered in their seismic design. Thus, this paper proposes a FDM-based analysis method to study this issue. Several dynamic time history analyses were performed for a shield tunnel embedded at different positions in ground with a liquefiable layer. It was found that the liquefied soil behaves like a fluid, and the tunnel uplifts due to buoyancy if the tunnel is fully embedded in a liquefied soil deposit. However, if the tunnel is only partially embedded in the liquefied deposit, with its top or bottom section in a non-liquefied deposit, the interaction behavior is quite complex and differs from that of a tunnel fully embedded in liquefied soil. To check the safety of the lining, the internal forces of the lining were monitored and compared with its strength curves throughout the shaking history. The proposed framework can be used as a reference for a practical engineer to consider the dynamic behavior of a shield tunnel in a liquefiable deposit.

Seismic damage of gravity abutment in liquefied ground

Purpose Abutment damage in liquefied ground is an important form of seismic damage of bridge structure. This paper aims to further research the effect of beam restriction on seismic damage mode of abutment in liquefied ground. Design/methodology/approach Based on the investigation of the seismic damage of Shengli Bridge in Tangshan earthquake, the finite element software dynamic effective stress analysis for ground (UWLC) is used to simulate the seismic damage of Shengli Bridge, and the results were compared with the actual seismic damage results. Then, the influences of the horizontal binding force of the beam, the liquefaction layer thickness, the top weight of the abutment, the peak acceleration, the liquefaction layer buried depth and the type of the foundation soil on the abutment seismic damage model are studied. Findings The results show that numerical simulation results are consistent with the actual seismic damage, and it is feasible to use UWLC software to simulate seismic damage. The results show that the seismic failure mode of the gravity abutment in liquefied ground is slip–rotation coupling type, not single slip type or rotation type. The large deformation of abutment bottom layer, horizontal binding force of the beam and post-stage soil pressure are the main reasons for abutment rotation or even destruction. Research limitations/implications A series of basic assumptions are used in the calculation process in this paper. The gravity abutment is defined as the elastic body and neglects its local deformation. The soil layer is a homogeneous isotropic. The consolidation process and the drainage boundary problem are not considered in the calculation process. Therefore, the paper may have some limitations. Originality/value To further research the seismic damage mode and influencing factors of abutment in liquefied ground, in this paper, based on the investigation of the seismic damage of Shengli Bridge in Tangshan earthquake, the finite element software UWLC is used to simulate the seismic damage of Shengli Bridge, and the results were compared with the actual seismic damage results. The seismic damage mode and influencing factors of gravity abutment in liquefied ground have been studied.

Interpreting the deformation phenomena of a levee damaged during the 2012 Emilia earthquake

The May 20th, 2012 Emilia earthquake triggered significant fractures, deformations and liquefaction occurrences along a number of riverbanks located close to the epicentre area. One of the most severely damaged earth structures was a levee of an irrigation channel, where large, longitudinally-oriented ground cracks were observed along a 3 km stretch. The ground fissuring was apparently associated to a lateral spreading mechanism causing structural damage to the buildings settled on the bank crown.An extensive study, including in-situ and laboratory investigations permitted a detailed definition of the geotechnical model and to back-figure the reference input motion at the deep bedrock. On such a basis, a dynamic effective stress analysis was carried out on a representative cross-section of the dyke showing that liquefaction occurred within the soil constituting the foundation of the levee. The results of the analysis allowed also for computing the permanent displacement along the critical sliding surface, which turned out to be compatible with the observed damage.

3-D Seismic Response Analysis Methods of High Core Rockfill Dams

Based on dynamic triaxial test data of dam materials, a dynamic constitutive model is suggested. Combining with construction of a high core rock-fill dam, several key issues, such as dam seismic response, seismic slope stability, dam permanent deformation, filter layer anti-liquefaction, and dynamic strength of the core wall are analyzed using 3-D dynamic effective stress analysis method. Some useful conclusions and regularity are obtained in aspects of seismic response and anti-seismic properties. The analysis method and conclusions could be referred to the analogous engineering.

The Dynamic Response and Stability Analysis of Nuclear Power Station Water Intake Diversion Dike

This paper uses the equivalent linear model of Hardin-Drnevich and the dynamic effective stress analysis method, gets the safety coefficient of stability, the liquefaction zone distribution and seismic residual deformation of diversion dike under the seismic action of SL1 and SL2. The paper also uses the minimum safety coefficient and average minimum safety coefficient of the whole process of earthquake to evaluate the stability of diversion dike under different seismic action and compares the results. Compared with SL2, the diversion dike foundation liquefaction range is smaller than under the SL1 seismic action, so it is does not affect the normal use of diversion dike structure. When meet the seismic action of SL2 which is appears about one time in a ten thousand, diversion dike will produce bigger deformation, but the integral slip to the heart of canal will not happen, so the use of water of the nuclear power plant is safe. The result has a certain reference value and guiding significance for the similar engineering design.

Seismic Response Analysis Method of High Core Rockfill Dam

A dynamic constitutive model is suggested based on dynamic triaxial test data of dam materials. Combining with construction of a high core rock-fill dam, several key issues, such as dam seismic response, dam permanent deformation, filter layer anti-liquefaction, dynamic strength of the core wall are analyzed by using 3-D dynamic effective stress analysis method. And some useful conclusions and regularity are obtained in the aspects of seismic response and anti-seismic properties. The analysis method and conclusions could be referred to the analogous engineering.

Study about Behavior of Fill Type Dams during Liquefaction by Dynamic Effective Stress Analysis

Study about Behavior of Fill Type Dams during Liquefaction by Dynamic Effective Stress Analysis

Seismic Response Analysis of Pile Foundations

A method is presented for the dynamic effective stress analysis of pile groups including nonlinear stress-strain response of the foundation soils and pile-to-pile interaction. The method is used to evaluate the behaviour of a large bridge foundation under strong earthquake shaking, and to demonstrate the importance of including the effects of inertial interaction in the determination of stiffness.

DEVELOPMENT OF EARTHQUAKE REINFORCEMENT METHOD FOR GRAVITY-TYPE QUAYWALL BY SHEET PILE INSTALLED AT THE FOOT OF THE CAISSON

The objective of this development is to increase the earthquake resistance performance of gravity caisson quay wall by employing sheet pile at the foot of the caisson. Gravity caisson quay wall with sheet pile realizes the 0.05 point increase of seismic coefficient by comparing usual gravity caisson quay wall. This method can apply existing gravity caisson quay wall which is short of sliding resistance during earthquake. Quay wall structure becomes hybrid type by connecting the head of sheet pile and the caisson and shows both advantages of gravity type structure and sheet pile structure. Underwater shaking table test and 2D dynamic effective stress analysis were done for the proposed hybrid type quay wall structure. Gravity caisson quay wall was designed at the condition of 0.15 design seismic coefficient and 10m water depth at the foot of the structure. The result shows the necessity of 900mmdia. steel sheet pile for the condition of 0.2 design seismic coefficient. 50 percent reduction of caisson crest displacement during earthquake is also obtained. Design criteria for this hybrid quay wall structure is also proposed.

Liquefaction analyses of sandy ground improved by sand compaction piles

The two-dimensional finite element program NUP2 of dynamic effective stress analysis is developed based on the two-phase mixture theory of Biot and the strain space plasticity theory of soil. The numerical analyses are performed to investigate the liquefaction behavior of sandy ground improved by the sand compaction piles. The good performance of the numerical procedure used here is proved by the comparison of numerical and experimental results. It is also demonstrated that the numerical results provide substantial information which aid in the understanding of the liquefaction mechanisms of improved soil ground. The results of numerical and experimental investigation show that there may exist unstable zones in the compacted area near the unimproved area and an optimum compaction width to resist liquefaction of the ground for design purposes.

Comparative assessment of methods for dynamic effective stress analysis : Finn, WDL; Yogendrakumar, M; Yoshida, N Proc 3rd International Symposium on Numerical Models in Geomechanics (NUMOG III), Niagara Falls, 8–11 May 1989P330–339. Publ London: Elsevier Applied Science, 1989

Comparative assessment of methods for dynamic effective stress analysis : Finn, WDL; Yogendrakumar, M; Yoshida, N Proc 3rd International Symposium on Numerical Models in Geomechanics (NUMOG III), Niagara Falls, 8–11 May 1989P330–339. Publ London: Elsevier Applied Science, 1989

Liquefaction potential of level ground: Deterministic and probabilistic assessment

Two important aspects of the liquefaction of level ground are discussed; the liquefaction potential of a site due to specified earthquake motions and the total probability of liquefaction at a site due to the entire seismic environment surrounding the site. Dynamic effective stress analysis is used to explore two important case histories of liquefaction due to specified ground motions. The probability of liquefaction is assessed by a method which estimates the joint probability of occurence of earthquake magnitude and acceleration amplitude sufficient to cause liquefaction.

Simulation analysis of ground liquefaction induced by earthquake

A dynamic effective stress analysis with the finite element method has long been recommended to predict the liquefaction phenomena of sandy soil by authors and Zienkiewicz et al. as well as the similar approaches by the others. Our approach of the analysis is summarized in the first. Until recently, however, these approaches has not commonly been used as the means of design, although its capability of prediction is appreciated by geotechnicians. This method has been neglected because of the lack of verification studies of soil models of sand and mathematical formulation for boundary problems of liquefaction phenomena. Therefore the verification of the numerical method to evaluate liquefaction potential are urgent requirement of the recent engineering practice. To respond this requirement, extensive numerical studies on the liquefation simulations are performed by DIANA program for shaking table tests which have been conducted by the authors. The test models are soil-structure type models with combination of homogenous ground and partially improved ground by compaction. The good performance of our approach is proved by the results of numerical simulation showing good agreement with experimental data in terms of response acceleration, excess pore pressure, and deformation profile. It is also demonstrated that the numerical results can provide substantial information to understand the mechanisms of soil ground behavior which is not easily obtained by experiments. The procedure to identify soil constants for the reflecting surface model is also reported in details.

Seismic soil-structure interaction: Analysis and centrifuge model studies

A method for nonlinear dynamic effective stress analysis applicable to soil-structure interaction problems is introduced. Full interaction including slip between structure and foundation is taken into account and the major factors that must be considered when computing dynamic soil response are included. An experimental investigation using simulated earthquake tests on centrifuged geotechnical models was conducted to obtain prototype response data of foundation soils carrying both surface and embedded structures and to validate the dynamic effective stress analysis. The centrifuge tests were conducted in the Geotechnical Centrifuge at Cambridge University, England. Horizontal and vertical accelerations were measured at various points on structures and in the sand foundation. Seismically induced pore water pressure changes were also measured at various locations in the foundation. Computer plots of the data were obtained while the centrifuge was in flight and representative samples are presented. The results clearly show the pronounced effect of increasing pore water pressures on dynamic response. It is demonstrated that a coherent picture of dynamic response of soil-structure systems is provided by dynamic effective stress nonlinear analysis. On the basis of preliminary results, it appears that the effects of pore water pressure can be predicted.

An Effective Stress Model for Liquefaction

The important factors affecting the dynamic response of saturated sand layers to earthquake motions are: (1)The initial shear modulus in situ; (2)the variation of shear modulus with shear strain; (3)contemporaneous generation and dissipation of pore-water pressures; (4)changes in effective mean normal stress; (5)damping; and (6)hardening. Constitutive relations are formulated that take all these factors into account and these are incorporated into a nonlinear method for the dynamic effective stress analysis of saturated sands. The method predicts the phenomenological features of the dynamic response of saturated sand layers that commonly occur as the pore-water pressure rises in the sand during earthquake shaking. It allows the distribution of pore-water pressure and the effects that drainage and internal flow have on the location and time of liquefaction to be determined quantitatively.