Effective Stress Analysis Method Research Articles

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.

Seabed Liquefaction around Pipeline with Backfilling Trench Subjected to Strong Earthquake Motions

As an indispensable part of the lifeline for the offshore gas and oil industry, submarine pipelines under long-term marine environmental loadings have historically been susceptible to earthquakes. This study investigates the impact of trench backfilling on the residual liquefaction around a pipeline and the induced uplift of a pipeline under the combined action of an earthquake, ocean wave and current loading. A fully coupled nonlinear effective stress analysis method, which can consider the nonlinear hysteresis and the large deformation after liquefaction of the seabed soil, is adopted to describe the interaction between the seabed soil and the submarine pipeline. Taking a typical borehole in the Bohai strait as the site condition, the nonlinear seismic response analysis of the submarine pipeline under the combined action of seismic loading and ocean wave and current is carried out. The numerical results show that trench backfilling has a significant impact on the seismic response of the pipeline. The existence of trench backfilling reduces the accumulation of the residual excess pore water pressure, so that the seabed liquefaction around the pipeline is mitigated and the uplift of the pipeline is also decreased.

Numerical analysis of the anti-liquefaction performance of a water reservoir dam under self-weight consolidation

The embankment dam on the Qingcaosha Reservoir in Shanghai, China, was constructed on slightly or moderately liquefiable ground without a special foundation treatment. The designers considered to use the self-weight consolidation from the dam to improve its anti-liquefaction performance. To assess the liquefaction mitigation effects of this simple method, an effective stress analysis method was utilized to simulate the seismic responses of the reservoir dam. The numerical method was first validated using a centrifuge test. The dynamic performance of the dam was then analyzed for three cases: during a free-field period without dam construction (case 1), during completion of the construction of the dam in a short period of time (case 2), and 5 years after construction of the dam (case 3). The effects of liquefaction remediation were analyzed based on the excess pore water pressure ratio (EPWPR), the vertical and lateral displacements, the effective stress path, and stress-strain relationships. The remediation method, done using self-weight consolidation, reduced the EPWPR generated within the foundation soil, decreased the vertical settlement (from 27 to 20 cm) and the lateral displacement (from 21 to 20 cm) of the dam structure, and increased the stiffness of the foundation soil. In addition, the mechanisms underlying the remediation effects were also elucidated.

A study into the behaviour of the formation level of an excavation under different unloading patterns in soft deposits

The construction of basements in urban areas is often associated with the possible damage to existing structures and services. The varying construction processes inevitably lead to different stress unloading patterns and therefore the dissipation of these excess pore-water pressures may lead to non-standard deformation profiles. The three main types of basement construction processes are layered excavation (LE), basin excavation (BE) and island excavation (IE). The effect of the various unloading patterns has been investigated by a three dimensional (3D) effective stress analysis method using the developed computer program 3DBCPE4.0. An excavation of length 50 m, width 50 m and depth 9 m in a certain homogenous and isotropic saturated soft soil was modelled. This included a diaphragm wall of 800-mm thickness embedded 18 m deep into the soft soil. The different excavation deformation profiles under different excavation patterns were related to the different unloading process, the exposure time of excavation face and the dissipation of negative excess pore-water pressures. The most favourable process for controlling the horizontal deformation of a retaining wall or the heave deformation of the formation level is suggested. The ground water potentials within the formation level are also presented.

Study on Dynamic Analysis Methods Verification of Earth-Rock Fill Dam Using Large-Scale Shaking Table Model Test

The large-scale models of core rock-fill dam were constructed firstly, and the model dams were vibrated on large shaking table. In this paper, the dynamic analysis methods of earth-rock fill dam were verified base on the results of large-scale shaking model test, including the equivalent linear analysis method base on equivalent linear visco-elastic model and the effective stress analysis method of earth-rock fill dam. Study results show that: the value of natural vibration frequency of model dam which was calculated though characteristic value method using maximum dynamic shear modulus is close to the value which obtained from shaking model test; the acceleration response of the model dam under earthquake were simulated well by the equivalent linear analysis method base on equivalent linear visco-elastic model, and the calculated acceleration response values of model dam are close to the experiment results; because the finite element method (FEM) base on continuum media theory can not well reflect the loosening phenomenon of soil in vibration, the calculated acceleration response values are lower than experiment results; the effective stress analysis method of earth-rock fill dam can consider the dissipation and diffusion of dynamic pore water pressure during earthquake, and the calculated acceleration response values of model dam are close to the experiment results when the reservoir before dam was full of water.

Seismic performances of dyke on liquefiable soils

Various field investigations of earthquake disaster cases have confirmed that earthquake-induced liquefaction is a main factor causing significant damage to dyke, research on seismic performances of dyke is thus of great importance. In this paper, seismic responses of dyke on liquefiable soils were investigated by means of dynamic centrifuge model tests and three-dimensional (3D) effective stress analysis method which is based on a multiple shear mechanism model and a liquefaction front. For the prototype scale centrifuge tests, sine wave input motions with peak accelerations 0.806m/s2, 1.790m/s2 and 3.133m/s2 of varied amplitudes were adopted to study the seismic performances of dyke on the saturated soil layer foundation with relative density of approximately 30%. Then, corresponding numerical simulations were conducted to investigate the distribution and variations of deformation, acceleration, excess pore-water pressure (EPWP), and behaviors of shear dilatancy in the dyke and the liquefiable soil foundation. Moreover, detailed discussions and comparisons between numerical simulations and centrifuge tests were also presented. It is concluded that the computed results have a good agreement with the measured results by centrifuge tests. The physical and numerical models both indicate that the dyke hosted on liquefiable soils subjected to earthquake motions has exhibited larger settlement and lateral spread: the stronger the motion is, the larger the dyke deformation is. Compared to soils in the deep ground under the dyke and the free field, the EPWP ratio is much smaller in the shallow liquefiable soil beneath the dyke in spite of large deformation produced. For the same overburden depth soil from free site and the liquefiable foundation beneath dyke, the characteristics of effective stress path and stress–strain relations are different. All these results may be of theoretical and practical significance for seismic design of the dyke on liquefiable soils.

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.

Characteristics of seismic responses at liquefied and non-liquefied sites with same site conditions

To understand the characteristics of seismic response at liquefied sites, a liquefiable site and a non-liquefiable site were selected, separated by about 500 m and having the same site conditions as Class D in the National Earthquake Hazards Reduction Program (NEHRP). A suite of earthquake records on rock sites are selected and scaled to the spectrum of the Joyner, Boore, and Fumal (JBF) attenuation model for a magnitude 7.5 earthquake at a distance of 50 km. The scaled records were then used to excite the two sites. The effect of pore-water pressure was investigated using the effective stress analysis method, and nonlinear soil behavior was modeled by a soil bounding surface model. Comparisons for spectra, peak ground acceleration (PGA), peak ground displacement (PGD) and permanent displacement were performed. Results show that the mean ground response spectrum at the non-liquefied site is close to the estimated ground response spectrum from the JBF model, but the mean ground response spectrum at the liquefied site is much lower than the estimated ground response spectrum from the JBF model for periods of up to 1.3 s. The mean PGA at the non-liquefied site is about 1.6–1.7 times as large as that at the liquefied site, but the mean peak ground displacement (PGD) at the non-liquefied site has a slight difference with that at the liquefied site. The mean permanent displacements at the liquefied site are larger than those at the non-liquefied site, particularly at the liquefied layer.

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.

3D Numerical Analysis of Seismic Performances of Dyke on Liquefiable Soils

Many field investigations of earthquake disaster cases confirm that earthquake-induced liquefaction is a main factor resulting in large damages to dyke. Consequently to ensure seismic safety of dyke on the liquefiable foundation, the research on seismic performances of dyke is of great importance. Herein seismic responses of dyke on the liquefiable soils were discussed by means of three dimension effective stress analysis method using a multiple shear mechanism model and liquefaction front. Two numerical models, in which the liquefiable foundation both consisted of saturated fine silica sand of 30% relative density and scenario waves with peak amplitude of 0.8056 and 3.133 m/s2 were used input waves, were conducted to investigate the distribution principles and the changing rules of deformation, acceleration, express pore water pressure, and shear dilatancy behavior in the dyke and the liquefiable foundation. The computed results do good agreements with the measured results from centrifuge tests. And these results may be of theoretical and realistic significance for seismic design of dyke on liquefiable soils.

Numerical analysis of deformation behaviour of quay walls under earthquake loading

In the last 50 years, there have been many incidences of failure of gravity quay walls. These failures are often associated with significant deformation of liquefiable soil deposits. Gravity quay wall failures have stimulated great progress in the development of deformation-based design methods for geotechnical structures. In this paper, the effective-stress analysis method has been used in conjunction with a generalised elasto-plasticity constitutive model implemented into a finite element procedure. Various monotonic and cyclic triaxial paths are simulated in order to demonstrate the capabilities of the constitutive model. The FEM is validated by back analysis of a typical Port Island PC1 caisson type quay wall, which was damaged during the 1995 Hyogoken-Nanbu earthquake. The numerical results are compared with the observed data obtained consisting of seaward displacement, settlement and tilting. In addition, both the influence of permeability, on the generation of pore water pressure and the influence of the relative density of the backfill and foundation layers, on the residual deformation of gravity quay walls are investigated.

Effective stress analysis method of seismic response for high tailings dam

Based on the analysis method for tailings dam in upstream raising method presently used in metallurgy and nonferrous metals tailings depository in the world, an effective stress analysis method of seismic response for high tailings dam was developed according to the results of engineering geological exploration, static and dynamic test and stability analysis on Baizhishan tailing dam 113.5 m high. The law of generation, diffusion and dissipation of seismic pore water pressure during and after earthquake was investigated, and the results of tailings dam’s acceleration, seismic dynamic stress and pore water pressure were obtained. The results show that the seismic stability and liquefaction resistance of high tailings dam are strengthened remarkably, and the scope and depth of liquefaction area at the top of dam are reduced greatly. The interior stress is compressive stress, the stress level of every element is less than 1.0 and the safety coefficient of every element is greater than 1.0. The safety coefficient against liquefaction of every element of tailing dam is greater than 1.5 according to the effective stress analysis of seismic response by finite element method. The calculated results prove that liquefaction is the main reason of seismic failure of high tailing dams, and the effect of seismic inertia forces on high tailing dams’ stability during earthquake is secondary reason.

Verification of predicted non-linear site response during the 1995 Hyogo-Ken Nanbu earthquake

The linear and non-linear responses of surface soil layers have been predicted through the simultaneous simulation test against the observed ground motions at the six sites in Kobe City during the 1995 Hyogo-ken Nanbu earthquake. The total stress analysis method and the effective stress analysis method have been applied for the rough and detailed verification of the predicted non-linear dynamic behavior at the PIS and RKI sites including the liquefaction phenomenon. The shear strain distribution along depth, the ratio of excess pore water pressure to initial effective stress, the liquefaction strength parameters to initial effective stress, and the stress–strain curve during the earthquake at the PIS site have been investigated when the predicted ground motion could simulate successfully the observed acceleration time histories and response spectra in the non-linear range.

Effective Stress Analysis of Seismic Response and Liquefaction: Theory

An effective stress method is presented for analysis of seismic response and liquefaction of horizontally layered saturated sand deposits, based on solution of the fully coupled equations for the granular solid and the pore fluid. A new material model for hysteretic behavior of sands and a new effective stress path rule are presented. The shear modulus reduction and damping of the proposed model are compared with other experimentally based relations. The proposed effective stress analysis method is used to simulate shaking table tests, with results in reasonably good agreement with experimental results. The proposed method of analysis is compared with a number of other well‐known methods.

Behaviour of friction piles in soft sensitive clays : Blanchet, R; Tavenas, F; Garneau, R Can Geotech J, V17, N2, May 1980, P203–224

During the construction of heavy structures, such as bridges and overpasses, on soft clays on the north shore of the St. Lawrence Valley, a detailed load test program on friction piles was performed to establish the characteristics of the most suitable type of pile and to study its long-term behaviour. Three types of piles, timber, steel pipe with closed end, and precast concrete Herkules H-420 piles, were tested. Four timber piles driven in a group and submitted to a 712 kN load served to study the long-term settlement of a small group of piles. Three deep settlement gauges were installed in the centre of this group for measuring settlements in clay at various depths. This test program was completed by the instrumentation of two bridge piers in order to verify the behaviour of larger groups of piles. The paper presents the results of the test piles, the long-term behaviour (4 years) of the bridge pier foundations resting on friction piles in soft clay, and the interpretation of the results. This study shows that the pore pressures induced by pile driving are related to the preconsolidation of the clay and that they are much larger for tapered piles. It is demonstrated that the effective stress analysis method proposed in 1976 by Meyerhof determines adequately the ultimate pile bearing capacity, but that the effect of the timber pile taper doubles the skin friction. The settlement analysis of pile groups shows that settlements are due to the reconsolidation of the clay and shear creep deformations in the clay close to the pile wall.

Behaviour of friction piles in soft sensitive clays

During the construction of heavy structures, such as bridges and overpasses, on soft clays on the north shore of the St. Lawrence Valley, a detailed load test program on friction piles was performed to establish the characteristics of the most suitable type of pile and to study its long-term behaviour. Three types of piles, timber, steel pipe with closed end, and precast concrete Herkules H-420 piles, were tested. Four timber piles driven in a group and submitted to a 712 kN load served to study the long-term settlement of a small group of piles. Three deep settlement gauges were installed in the centre of this group for measuring settlements in clay at various depths.This test program was completed by the instrumentation of two bridge piers in order to verify the behaviour of larger groups of piles.The paper presents the results of the test piles, the long-term behaviour (4 years) of the bridge pier foundations resting on friction piles in soft clay, and the interpretation of the results.This study shows that the pore pressures induced by pile driving are related to the pre-consolidation of the clay and that they are much larger for tapered piles. It is demonstrated that the effective stress analysis method proposed in 1976 by Meyerhof determines adequately the ultimate pile bearing capacity, but that the effect of the timber pile taper doubles the skin friction.The settlement analysis of pile groups shows that settlements are due to the reconsolidation of the clay and shear creep deformations in the clay close to the pile wall.