Large Permanent Displacements Research Articles

Experimental study on forced response characteristics and anti-dislocation performance of articulated tunnel structure under dislocation action of normal fault

The stick–slip dislocation of normal faults will produce large permanent displacement. The tunnel lining structure crossing active normal faults is easily affected by fault dislocation. It is necessary to study the mechanical behavior of tunnel lining structure under fault dislocation. Therefore, taking the subway tunnel of Urumqi Rail Transit Line 1 crossing the Jiujiawan fault project as an example, based on the optimal mix ratio determined by the indoor similar material ratio test, the self-designed large-scale active fault dislocation simulation loading system is used to carry out the stick–slip dislocation model test of normal fault with 60° dip angle. The mechanical behavior difference between the conventional tunnel structure and the flexible articulated tunnel structure is compared and analyzed, and the cracking range, damage characteristics and failure mode of the tunnel lining structure are defined. The results show that: (1) The failure modes of the conventional tunnel structure and the flexible articulated tunnel structure are basically the same, including the large eccentric failure of the inverted arch and the wall foot, and the compression shear failure at the fault plane, which are longitudinal cracks and oblique cracks respectively. In addition, there are longitudinal cracks in the inner side of the invert and the lateral side of the wall foot, but few circumferential cracks. (2) Because the flexible articulated structure increases the overall longitudinal flexibility of the tunnel, the flexible joints between segments can share part of the fault dislocation displacement, so the deformation range, failure degree and number of cracks of the articulated tunnel structure are significantly reduced compared with the conventional tunnel structure, and the anti-dislocation performance is better. (3) Considering the influence of fault dislocation on tunnel structure, the loose area and empty area should be investigated and repaired in the rapid repair and reinforcement of post-disaster tunnel. At the same time, the case study ideas and test methods in this paper can provide some reference value and guidance for other similar tunnel engineering studies in the future.

Earthquake response and sliding displacement of submarine sensitive clay slopes

Many submarine landslides occur through marine sensitive clay layers, and the strain softening behavior plays a key role. The changing soil properties induced by various disturbances will have marked impact on earthquake performance of submarine clay slopes. In the present study, undrained triaxial compression tests on reconsolidated samples of a soft sensitive marine clay were conducted, and a soil disturbance dependent simple constitutive model is proposed for describing post-peak nonlinear strain softening behavior of sensitive clays based on experimental results, and then is implemented in QUIVER code to perform one-dimensional seismic response analysis of mild infinite slopes, to address the relative importance of soil disturbance effect on the site response and sliding displacement of submerged slopes during seismic loading. Detailed laboratory test descriptions and results of a soft sensitive marine clay, model formulations and comprehensive computational efforts are presented. Parametric study of site response analysis focusing on the effects of soil disturbance degree and depth on generic clay grounds with varying sloping angles subjected to harmonic and earthquake loadings are performed. The predicted acceleration amplification, maximum shear strains and permanent displacements provide insight of earthquake performance of submarine sensitive clay slopes.The main findings are drawn based on several key concepts. First, undisturbed sensitive clay is typically stiffer and stronger than disturbed clay consolidated at the same stress level and hence, unless strain softening is triggered, structured sensitive clay will perform better than insensitive clay of the same residual strength. Second, post-peak softening at shallow depth will lead to strain localization on a thin layer, which is the main cause of sudden change of upward wave propagation characteristics and large permanent displacement at seabed surface of mild submarine clay slope. Thirdly, soil disturbance degrees and depths have very marked effects on seismic response and displacement performance of sensitive clay slopes, and such effect will be further enhanced by slope angle or earthquake intensity, which should be cautiously treated in engineering design.

A GLE-based model for seismic displacement analysis of slopes including strength degradation and geometry rearrangement

Seismic performance of natural slopes, earth structures and solid-waste landfills can be evaluated through displacement-based methods in which permanent displacements induced by earthquake loading are assumed to progressively develop along the critical sliding surface as a result of transient activation of plastic mechanisms within the soil mass. For sliding mechanisms of general shape the earthquake-induced displacements should be computed using a model that provides a closer approximation of sliding surface. When large permanent displacement are induced by seismic actions, due to substantial shear strength reduction, and significant changes in ground surface occur, an improved estimate of permanent displacement can be obtained using a model which accounts for shear strength reduction and mass transfer between adjacent portions of the slope resulting from geometry changes of ground surface during the seismic event.In this paper, a GLE-based model is proposed for seismic displacement analysis of slopes that accounts for shear strength degradation and for geometry rearrangement. Model accuracy is validated against experimental results obtained from shaking table tests carried out on small scale model slopes. Comparison of computed and experimental results demonstrates the capability of the proposed approach in capturing the main features of the observed seismic response of the model slopes.

Rigid Block Sliding to Idealized Acceleration Pulses

AbstractNew analytical solutions are derived for the frictional sliding of rigid blocks to idealized ground acceleration pulses. These excitations are indicative of near-fault earthquake motions affected by forward fault-rupture directivity, which may inflict large permanent displacements in the absence of substantial frictional resistance at the sliding interface. The scope of this study is threefold: (1) to derive analytical solutions for a wide set of idealized pulses; (2) to investigate the effects of symmetric and asymmetric sliding under both unilateral and bilateral excitation conditions; and (3) to explore alternative normalization schemes of peak sliding with reference to peak pulse acceleration, velocity, duration, and shape. A generalized exponential function, capable of simulating an infinite number of pulse waveforms based on a single parameter, is employed to this end. Results are presented in the form of dimensionless closed-form expressions and graphs that provide insight into the physics ...

Inelastic demand spectra for bi-linear seismic isolation systems based on nonlinear time history analyses and the response of lead-rubber bearing isolation systems subjected to near-source ground motions

In this study, we present an inelastic demand spectrum for the design of seismically-isolated structures using lead-rubber bearings or other types of isolators with bi-linear hysteresis loops and the inelastic spectrum can be used in the design of seismically-isolated structures in a very similar manner to capacity spectrum method. The inelastic demand spectrum is a very useful design tool for visual selection of optimal isolation parameters, and eliminates the use of equivalent linear-elastic substitute structures as the displacement demand is obtained from nonlinear time history analysis. The responses of seismically-isolated structures subjected to near-source ground motions with either large forward-directivity pulses or fault-fling pulses are presented. Our analyses suggest that seismic isolation can be used to protect structures subjected to recorded ground motions currently available to us, with acceptable levels of base shear coefficient and isolator displacement, except for one component of the TCU068 record from the 1999 Chichi, Taiwan, earthquake (which contained a large permanent displacement of nearly 10 m).

Influence of vertical ground motion on seismic-induced displacements of gravity structures

A method enabling assessment of seismic-induced movements of gravity block is proposed. This method is based on dynamic analysis of the block subjected to both horizontal and vertical ground accelerations, and resultant forces acting on the block. There are two kinds of the motion. The first one is trivial, as it is a common motion of the block and subsoil. The second is a relative motion of the block with respect to subsoil, depending on combination of ground accelerations and the resultant of horizontal forces. Attention is focused on the influence of vertical ground motion on seismic-induced displacements of the structure. Experimental investigations performed in order to validate a numerical algorithm are described, and then experimental data are compared with numerical predictions. A good agreement is obtained. Then, the dynamics analysis of the block is presented for harmonic and pseudo-stochastic ground motions in order to illustrate the algorithm proposed. The results of computations show that, for some typical data and ground accelerations corresponding to strong earthquakes, large permanent displacements of the block take place, as observed in real conditions.

Engineering assessment of seismic hazard and long period ground motions at the Bolu Viaduct Site following the November 1999 earthquake

The Mw 7.1 earthquake of November 12, 1999 severely damageda 2.5 km long viaduct on a stretch under construction of theIstanbul-Ankara motorway, 18 km W of Bolu. The fault rupture crossedthe viaduct with an observed offset close to 1.5 m; the viaduct decksuffered large permanent displacements but did not collapse.Seismic hazard at the site appears to be governed by characteristicearthquakes occurring every few hundred years both on the Duzce faultand on the main stretch of North Anatolian fault (NAF). Smaller activefaults near the site also contribute to the hazard.We investigate how a reliable design response spectrum of displacement canbe constructed for the viaduct site using both probabilistic and deterministictools. After checking the applicability of known attenuation relations againstrecorded data, we illustrate a hazard analysis that incorporates acharacteristic earthquake model for the relevant faults, and accounts forstatistical directivity effects on the Duzce fault. Constant-risk responsespectra up to 3 s are thus obtained for different return periods. Syntheticmotions at the site are generated next, using a known source model, inorder to explore the features of the displacement response spectrum atvibration periods in the range between 1s and 6 s, in which the dominantresponse of the viaduct deck, uncoupled from the piers, occurs. Adiscussion of results follows.

Characteristics of amplitude and duration for near fault strong ground motion from the 1999 Chi-Chi, Taiwan Earthquake

A great number of free-field ground motion records are obtained during the 1999 Chi-Chi, Taiwan, earthquake. Records from 130 near fault free-field stations within 55 km to the causative fault surface are used as database, and characteristics of earthquake peak ground acceleration, velocity, displacement and duration are analyzed. According to this study, near fault ground motions are strongly affected by distance to fault, fault rupture directivity, site condition, as well as thrust of hanging wall. Compared with empirical strong ground motion attenuation relations used in China, US and Japan, the PGAs and PGVs recorded in this earthquake are not as large as what we have expected for a large earthquake as magnitude 7.6. However, the largest PGV and PGD worldwide were recorded in this event, which are 292 cm/s and 867 cm, respectively. Caused by nonlinear site effects of soil, peaks and corresponding ratios on E-class site were markedly different from those on other sites. Just as observed in historic earthquakes, fault rupture directivity effects caused significant differences between peaks of ground motion of two horizontal components, but took very slight effects on the duration of ground motion. The significant velocity pulses associated with large PGVs and PGDs, as well as large permanent displacements, which may result from the large thrust of the hanging wall, became the outstanding character of this event. Based on this study, we point out that 3D waveform modeling is needed to understand and predict near fault ground motion of large earthquakes.

Cyclic Axial Loading of Drilled Shafts in Cohesive Soil

Medium- and large-size model drilled shafts up to 174 mm in diameter were constructed in laboratory-prepared cohesive soil deposits. The models were subjected to cyclic axial loading, and the resulting displacements and changes in capacity were determined, while the in-situ stresses at the foundation/soil interface were measured. The applied loading was designed to simulate realistic windstorm events, which are an important source of cyclic loading for foundations. Shaft response was found to depend critically on the type of cyclic loading. One-way uplift, in which the direction of loading is always upward caused large permanent displacements at high load levels but only small displacements at moderate load levels, while capacity reductions were modest. Two-way loading, in which the direction of loading reverses twice every cycle, caused minimal response at low load levels but a sudden degradation in displacement response at moderate load levels, with an associated substantial reduction in capacity. Critical levels of repeated load, below which shaft response remained stable, were established; and the mechanisms responsible for capacity reduction are discussed.

Balanced Seismic Design of Anchored Retaining Walls

Large permanent displacements of anchored retaining walls such as quay walls, sheet‐pile walls, and bulkheads are often reported in the literature after moderate to strong seismic activity. In most cases, liquefaction of the soil is cited as the reason for the large displacement or failures. In this paper, we examine an alternative mechanism, generated by inertial forces, which triggers large displacements of anchored retaining walls during moderate to strong earthquakes. Through this mechanism, we investigate whether substantial wall displacements or failures precede liquefaction. A limit equilibrium analysis, using the Mononobe‐Okabe seismic earth pressure equations, is performed to determine whether anchor failures lead to the general failure of anchored retaining walls during seismic events. Results of shaking‐table tests on aluminum walls with a dry cohesionless soil as the backfill confirm the analytical methodology. Based on the limit analysis, a balanced seismic design concept for anchored retaining walls is presented. We find that the balanced seismic design enhances the seismic resistance of anchored retaining walls at little additional expense. We use a typical design example to compare the balanced design procedure with current design practices.