Shaking table performance of reinforced soil retaining walls with different facing configurations

In this paper, a new type of MSE wall facing, termed as hybrid facing, is introduced and studied, which is built using a combination of concrete modular blocks and cast-in-place concrete. Two shaking table tests were carried out to compare seismic performances of model reinforced soil retaining walls with full-height vs. hybrid facing configurations. Results of this study show that the stability and performance of the hybrid facing model were similar to those of the full-height panel wall for peak input acceleration magnitudes less than 0.40 g. The amplification factors along the height of the facing were more uniform and smaller in the hybrid facing model as compared to the full-height panel wall, especially at higher peak acceleration amplitudes. Dynamic increment of lateral earth loads acting on the facing in both cases were found to be only 20% of the values calculated using pseudo-static methods. Connection loads in the hybrid facing model were smaller than those in the full-height panel wall, which was attributed to its smaller facing displacements.     

Reinforcement load and deformation mode of geosynthetic-reinforced soil walls subject to seismic loading during service life

A Finite Element procedure was used to investigate the reinforcement load and the deformation mode for geosynthetic-reinforced soil (GRS) walls subject to seismic loading during their service life, focusing on those with marginal backfill soils. Marginal backfill soils are hereby defined as filled materials containing cohesive fines with plasticity index (PI) >6, which may exhibit substantial creep under constant static loading before subjected to earthquake. It was found that under strong seismic loading reinforced soil walls with marginal backfills exhibited a distinctive “two-wedge” deformation mode. The surface of maximum reinforcement load was the combined effect of the internal potential failure surface and the outer surface that extended into the retained earth. In the range investigated, which is believed to cover general backfill soils and geosynthetic reinforcements, the creep rates of soils and reinforcements had small influence on the reinforcement load and the “two-wedge” deformation mode, but reinforcement stiffness played a critical role on these two responses of GRS walls. It was also found that the “two-wedge” deformation mode could be restricted if sufficiently long reinforcement was used. The study shows that it is rational to investigate the reinforcement load of reinforced soil walls subject to seismic loading without considering the previous long-term creep.     

Shaking table tests on polymeric-strip reinforced-soil walls adjacent to a rock slope

This research adopts the approach to constructing reinforced-soil walls on rock slope, where the extent of reinforced zone has to be constrained since excavation of the relatively rigid zone may not be economical and may disrupt the traffic. To examine the seismic behavior of these structures, a series of 1-g shaking table tests using variable-amplitude harmonic excitations was conducted on 0.8m-high polymeric-strip reinforced-soil walls (PSWs) on rock slope under a scenario of waves with different intensities. Rock slope appeared to have a satisfactory dynamic response compared to the soil base as the rock behind the reinforced zone controls the development of active wedge failure and prevents higher amplification and progressive deformation. The results illustrated that the confining pressure and reinforcement length considerably affect the shear modulus and damping ratio. Also, it was found that in PSWs on rock with L/H ratio of 0.3 for bottom strips, the lowest facing panel, having the maximum horizontal displacements after failure, and lower maximum shear modulus (G_max), and damping ratio (D), is the most crucial one despite having the highest confining pressure representing the profound effect of L/H ratio when it equals 0.3.     

Equivalent seismic coefficient in geocell retention systems

Ideal design of an earthquake resistant earth structure would consider the time records of future seismic events. Objectively, such time records are difficult to predict especially when compared with prediction of the design peak ground acceleration (PGA), a single-value parameter. Furthermore, relevant soil properties are not easily obtainable in the field. Consequently, in routine stability designs, the state of practice utilizing a pseudostatic analysis has not changed for many years. To reduce the inherent conservatism of the pseudostatic approach, it is common to use a fraction of PGA in the stability analysis. For earth structures such as slopes, existing standards suggest a value of this fraction, typically varying between 0.3 and 0.5 times PGA. While one hopes that such values are calibrated against case histories, it is doubtful if there is sufficient field data for a value corresponding to geocell gravity walls and geocell reinforced slopes. Reported here are relevant results of shake table tests on five different geocell structures, each 2.8 m high, subjected to an excitation simulating the Kobe earthquake. Exhumation enabled the tracing of slip surfaces that developed during the shaking. Back-analysis resulted in the fraction of the applied PGA needed to establish a slip surface. The formation of slip surfaces in the context of this work should not be interpreted as collapse or catastrophic failure; rather it signifies the development of an active wedge. Hence, the equivalent coefficients in this work are an upper bound value for the magnitude and intensity of the ground motion applied in the analysis. It was found that for geocell gravity walls, essentially flexible structures, the upper bound seismic coefficient for the applied motion is about 0.4 times PGA. For reinforced geocell walls the upper bound coefficient would be 0.3 times PGA.     

多级拼装悬臂式挡墙地震响应振动台模型试验

多级拼装悬臂式挡墙是一种可用于高填方工程的新型轻型支挡结构.为确定墙-坡系统的地震动力响应特征,进行几何、重度和时间相似比分别为1 ∶ 10,1 ∶ 1和1 ∶ 3.162的三级拼装悬臂墙支挡边坡的水平振动台模型试验.结果表明:坡体加速度沿墙高呈明显的非线性放大效应;墙后静止土压力和动土压力均呈"三峰型"分布模式,各级...     

Dynamic behavior of reinforced walls - Horizontal displacement response

A series of uni-axial shaking table tests using step-wise intensified sinusoidal waves is performed on plane-strain geosynthetic-reinforced slopes to investigate the effects of wave frequency and amplitude to the seismic displacements of geosynthetic-reinforced slopes. The geosynthetic-reinforced model slope is backfill with uniform steel rods with a known Coulomb friction angle. A comparative study on the normalized slope displacement based on Newmark’s sliding-block theory shows that the normalized displacement curves obtained here fall to the right of analytical and empirical curves reported in the literature, suggesting that a plastic displacement of the slope prior to the yielding of the slope has been ignored in conventional displacement evaluation for geosynthetic-reinforced slopes. Furthermore, no amplified acceleration response at the crest of the slope was found for the post-yield geosynthetic-reinforced slopes subjected to a relatively intensive input base acceleration of 0.4-0.6 g, or subjected to a maximum wall displacement greater than 1.9-3.9% of the wall height.     

Assessment of deformation modulus of weak rock masses from pressuremeter tests and seismic surveys

The deformation modulus of intact rock can be determined through standardized laboratory tests for heavily jointed rock masses but this is very difficult, while in situ tests are time-consuming and expensive. In this study, the deformation modulus of selected heavily jointed, sheared and/or blocky, weathered, weak greywacke, andesite and claystone were assessed, based on pressuremeter tests, geo-engineering characterization and seismic surveys. Empirical equations based on GSI and RMR values are proposed to indirectly estimate the deformation modulus of the greywackes. For the andesites, the spacing of the discontinuities is greater than the length of the pressuremeter probe hence the intact rather than rock mass deformation modulus is obtained. The pressuremeter test results from the claystones could not be correlated with the field data; the relationship between the ratio of rock mass modulus to intact rock modulus and RQD appears to give a better estimation of the deformation modulus.      

Experimental evaluation of steel slit panel-frames for seismic resistance

The steel slit panel-frame is a new system for seismic resistance of buildings. The steel slit panels are bolted to beams which are simply connected to the columns. The steel slit panels are steel plates with rows of vertical slits forming a series of flexural members within the plate. The steel slit panels are designed to resist the entire lateral load and provide all the stiffness and energy dissipation in the system. The steel slit panel-frame system was studied via an experimental program, divided into two series of testing. The first series studied the fundamental characteristics of the steel slit panels, while the second series studied the behavior of the steel slit panels within the frame (i.e., behavior of the steel slit panel-frames). A concise introduction to the system is presented first, followed by the findings from the experimental study.     

Experimental investigation on the performance of multi-tiered geogrid mechanically stabilized earth (MSE) walls with wrap-around facing subjected to earthquake loading

Construction of mechanically stabilized earth (MSE) walls in multi-tiered configurations is a promising solution for increasing the height of such walls. The good performance of this type of walls after recent major earthquakes was reported in a number of technical studies. In the present study, an experimental approach was adopted to compare the seismic performance of single-tiered and multi-tiered MSE walls using physical modeling and through conducting a series of uniaxial shaking table tests. To do so, several geogrid-reinforced soil walls with wrap-around facing (i.e., three-, two-, and single-tiered) with a total height of 10 m were designed in the form of prototypes of 1-m-height wall models. The step-wise intensified sinusoidal waves were applied to the models in 14 typical forms. Comparing the shaking table test results confirmed the post-earthquake advantages of multi-tiered MSE walls. The results revealed that tiered walls exhibited better behaviors under earthquake loading in terms of the seismic stability of the wall, displacement of the wall crest, horizontal displacement of the wall facing, deformation mode and failure mechanism of the wall, settlement of backfill surface, and seismic acceleration responses.     

Effect of reinforcing technique on strain-dependent dynamic properties of reinforced earth walls

Due to lack of sufficient understanding of the strain-dependent dynamic properties of reinforced mass, existing soil and reinforcement models are not capable of accurately representing the seismic response of reinforced soil structures in numerical and analytical analyses. In the present study, to evaluate the effect of reinforcing technique on strain-dependent dynamic properties of reinforced earth walls, the values of equivalent shear modulus (G_e) and damping ratio (D) were estimated for soil-nailed wall (SNW) and steel-strip reinforced-soil wall (SSW) as a function of shear strain level using 1-g shaking table tests. The results obtained showed that the variation trend of G_e and D versus γ is strongly influenced by the type of reinforcing technique and confining pressure, so that the variation trend of these two parameters versus shear strain can be well expressed as an exponential equation with a high correlation coefficient for each type of reinforced earth wall.     

Exploring the possibility of assessing the damage degree of liquefaction based only on seismic records by artificial neural networks

This study presents a new approach to determine the damage degree of liquefaction caused by a large earthquake. We propose an artificial neural network (ANN) model based only on the seismic records of ground and define the degree of liquefaction “DDL” as a damage index. This ANN model predicts the degree of excess pore water pressure increase as the correct output label based on the seismic records obtained from the three-dimensional shaking table test. The proposed model achieved high accuracy, and the outcomes from training data indicated that the ANN model is suitable to function as a liquefaction assessment system. Further, to evaluate the applicability of the proposed ANN model in the real world, the datasets of waves from three actual seismic records were input to the ANN as validation data. The DDL judgment obtained was a good fit with the real phenomena observed.     

高强型钢高性能混凝土剪力墙抗震性能研究

设计了4片高强型钢高性能混凝土剪力墙试件,对其进行了低周反复加载试验。分析了试件在压、弯、剪共同作用下的破坏过程和破坏机理,讨论了含钢率、配箍特征值等参数对这种剪力墙的破坏形态、荷载-位移滞回曲线、骨架曲线、位移延性、刚度退化和耗能能力以及承载力的影响。研究结果表明,轴压比、配钢率、配箍率以及边缘约束区长度等对这种剪力墙的破坏形态、承载力、延性、滞回特性等均有影响,按《型钢混凝土组合结构技术规程》(JGJ 138—2001)中型钢混凝土剪力墙承载力计算公式所得结果与试验结果吻合较好。     

土样回弹及再压缩变形特征的试验研究

通过固结回弹试验对土体的回弹变形规律进行研究,提出回弹比率的概念,更为清晰地反映出了回弹变形随卸荷比变化的发展过程:当卸荷比小于0.4时,土样卸荷产生的回弹量不到总回弹量的10%;而当卸荷比在0.9～1.0之间时,土样卸荷产生的回弹量占到总回弹量的40%～60%。将原有的卸荷比—回弹模量分析方法中的R-Ec与R-lgEc方法相结合应用,得出土体回弹变形发展的3个阶段,为回弹变形的计算提供参考,同时通过对卸荷比—回弹模量关系曲线进行拟合分析,可得到在任一卸荷比下土体的回弹模量。试验结果表明:土体回弹率与固结压力、卸荷比密切相关,反映了土体回弹变形的基本特征;在土样的再压缩过程中,再压缩变形大于回弹变形。结合模型试验实测结果,对土样的再压缩变形进行了研究。     

Dynamic properties of calcareous and siliceous sands under isotropic and anisotropic stress conditions

The strain-dependent dynamic properties of sand are generally described by their relative density and mean effective stress, while the contribution of other factors, like soil origin, mineralogy, grain morphology, and initial stress anisotropy, have not been fully recognized. This paper presents the results of an experimental study on the shear modulus and damping ratio of calcareous and siliceous sands of different origins and their identical grain size distribution and stress-density states. Resonant column and cyclic triaxial tests were conducted on reconstituted samples of these two sands obtained from coastal areas. The significance of the initial effective confining pressure and stress anisotropy on the dynamic properties of the sands is evaluated and compared. It is demonstrated that the small-strain shear modulus of the calcareous sand is more affected by an increase in mean effective confining pressure than the siliceous sand. However, the effect of the initial shear on the secant shear modulus of the sands is unique. Based on the test data, a rigorous correction factor is proposed to account for the influence of the initial stress anisotropy on the small-strain shear modulus of the sands. A comparison between the strain-dependent dynamic properties of the calcareous and siliceous sands reveals that the calcareous sand has a higher secant shear modulus, lower damping ratio, and higher linear and volumetric threshold strain. Since the stress-density states and grain size distribution of the two sands were identical in the experiments, the discrepancy in the dynamic properties can be attributed to other factors, including sand origin, grain angularity, mineralogy, and formation processes, which are not commonly taken into account in the current practice.     

Numerical simulation of geosynthetic-reinforced soil walls under seismic shaking

This paper presents the results of numerical simulation of three full-scale geosynthetic-reinforced soil walls that were seismically loaded by a shaking table. Material model parameters were determined from the available laboratory data. In particular, the backfill was simulated with a cap model with parameters dependent of stress level. Hardening parameters of cap model were determined from hyperbolic relation derived from the relevant hydrostatic compression tests. A discussion on the calibration of modeling parameters is presented. Responses compared include (a) maximum wall displacement, (b) maximum backfill settlement, (c) maximum lateral earth pressure, (d) maximum bearing pressure, (e) maximum reinforcement tensile load, (f) absolute maximum acceleration in reinforced soil zone, and (g) absolute maximum acceleration in retained soil zone. Qualities of simulations were evaluated and are discussed. It was found that not all the calculated results agree well with the measured data. However, strong inference or high confidence is anticipated for the closely matched responses such as lateral earth pressure and horizontal displacement utilizing the calibrated model described herein. As indicated by the calculated results, seismic wall displacement decreases with decreasing reinforcement spacing. Factors responsible for comparison discrepancy are discussed. Variability within the measured data is thought to have contributed to some of the comparison discrepancies.     

An investigation on the accuracy of pushover analysis for estimating the seismic deformation of braced steel frames

This paper investigates the potentialities of the pushover analysis to estimate the seismic deformation demands of concentrically braced steel frames. Reliability of the pushover analysis has been verified by conducting nonlinear dynamic analysis on 5, 10 and 15 story frames subjected to 15 synthetic earthquake records representing a design spectrum. It is shown that pushover analysis with predetermined lateral load pattern provides questionable estimates of inter-story drift. To overcome this inadequacy, a simplified analytical model for seismic response prediction of concentrically braced frames is proposed. In this approach, a multistory frame is reduced to an equivalent shear-building model by performing a pushover analysis. A conventional shear-building model has been modified by introducing supplementary springs to account for flexural displacements in addition to shear displacements. It is shown that modified shear-building models have a better estimation of the nonlinear dynamic response of real framed structures compared to nonlinear static procedures.     

Numerical study on dynamic behavior of slope models including weak layers from deformation to failure using material point method

This paper describes numerical studies on the dynamic behavior of experimental slope models, including various inclined weak layers. These studies were conducted by simulation of shaking table tests using the material point method (MPM), which allows seamless treatment of various considerations, from elastic behavior to discontinuous collapse behavior of slopes, on the basis of an elasto-plastic constitutive law. The simulation results showed that the failure modes, progressive deformation and downward sliding of the numerical slope models, which were similar to that observed in the shaking table tests, can be obtained using the numerical method. In addition, sensitivity analyses of the numerical models used in this study were performed to determine the effects of mesh size, number of particles per cell (PPC) and damping constants on the simulation results. The results of these analyses indicated the use of fine meshes and high damping constants seems to produce sensible results and reduce numerical noises, respectively.     

配筋页岩空心砖墙体抗震性能试验研究

为研究空心砖体系的抗震性能,对3种砌筑形式的6片页岩空心砖墙体进行了低周反复荷载试验。阐述了试件的破坏过程,探讨了墙体的破坏特征、承载能力、滞回性能、刚度退化、延性、能量耗散等问题。研究结果表明:配置水平钢筋不仅可以提高墙体的承载能力,而且可以大大提高墙体的抗震能力和变形性能。水平钢筋对墙体可起到有效的约束作用,使破坏的墙体不倒塌,在实际工程中设置水平钢筋是非常必要的。     

型钢水泥土墙中水泥土对型钢的约束反力试验研究

通过型钢水泥土中水泥土对型钢的约束反力和位移关系的试验,描绘出了约束反力与位移的关系曲线,进一步拟合出了水泥土对型钢的约束反力与位移的关系式,利用关系式得到了约束反力系数,并分析了水泥土强度对约束系数的影响,通过约束反力系数可以量化水泥土对型钢的约束程度,对实际工程有一定的借鉴意义。