Analyzing Dynamic Behavior of Geosynthetic-Reinforced Soil Retaining Walls

An advanced generalized plasticity soil model and bounding surface geosynthetic model, in conjunction with a dynamic finite element procedure, are used to analyze the behavior of geosynthetic-reinforced soil retaining walls. The construction behavior of a full-scale wall is first analyzed followed by a series of five shaking table tests conducted in a centrifuge. The parameters for the sandy backfill soils are calibrated through the results of monotonic and cyclic triaxial tests. The wall facing deformations, strains in the geogrid reinforcement layers, lateral earth pressures acting at the facing blocks, and vertical stresses at the foundation are presented. In the centrifugal shaking table tests, the response of the walls subject to 20 cycles of sinusoidal wave having a frequency of 2 Hz and of acceleration amplitude of 0.2g are compared with the results of analysis. The acceleration in the backfill, strain in the geogrid layers, and facing deformation are computed and compared to the test results. The results of analysis for both static and dynamic tests compared reasonably well with the experimental results.     

New Structure-Based Model for Estimating Undrained Shear Strength

This paper presents an experimental study of the strength in anisotropic clays by means of centrifuge model, cone penetration, and vane shear tests. To understand the effects of void ratio, overconsolidation ratio, and testing rate on the undrained shear strength (Su) of anisotropic Speswhite clay, a new centrifugal testing technique is designed to obtain constant overconsolidation ratio (OCR) profiles with varying void ratios (e), called the “descending gravity test.” The parameters controlling the generation of peak shear strength are quantified. As a result of this function, a new material and rate-dependent surface is defined in the e-OCR-Su space, which is identified as a “structural state capacity surface” since it relates the anisotropic structure to structure inherent capacity and properties. A new function for the estimation of excess pore pressure (uex) generated by cone penetration is found. By combining the strength and pore pressure functions a new model is proposed, called the “CU model.” The CU model is a structure-based model that provides reliable estimates of shear strength for in situ saturated clays using the knowledge of void and overconsolidation ratios. Finally, by combining Su-e-OCR and uex-e-OCR relationships, it estimates the void ratio and OCR profiles of anisotropic clays from piezocone penetration test results.     

Numerical Modeling of Seismic Response of Rigid Foundation on Soft Soil

A numerical model was developed to simulate the response of two instrumented, centrifuge model tests on soft clay and to investigate the factors that affect the seismic ground response. The centrifuge tests simulated the behavior of a rectangular building on 30?m uniform and layered soft soils. Each test model was subjected to several earthquakelike shaking events at a centrifugal acceleration level of 80g. The applied loading involved scaled versions of an artificial western Canada earthquake and the Port Island ground motion recorded during the 1995 Kobe Earthquake. The centrifuge model was simulated with the three-dimensional finite-difference-based fast Lagrangian analysis of continua program. The results predicted with the use of nonlinear elastic–plastic model for the soil are shown to be in good agreement with measured acceleration, soil response, and structural behavior. The validated model was used to study the effect of soil layering, depth, soil–structure interaction, and embedment effects on foundation motion.     

Seismic Deformation of Bar Mat Mechanically Stabilized Earth Walls. II: A Multiblock Model

A relatively simple rigid plastic multiblock computational model has been developed to predict the permanent seismic displacement of mechanically stabilized earth (MSE) walls. The model formulation was based on many observations made from a series of centrifuge tests carried out on many different configurations of MSE walls. The proposed model is similar to the sliding block method of Newmark. The approach accounted for the variation in acceleration within the backfill and the nonuniform nature of the permanent wall face deformation. The predictive capability of the proposed model has been verified using centrifuge test results obtained for four MSE walls each subjected to three earthquake excitations with strength varying between 0.48 and 0.9g. The analytical model captures many aspects of the characteristic deformation behavior of MSE walls observed in the centrifuge tests. In each of the eleven wall displacement cases studied, the backfill friction angle that yielded a good match between the computed and measured maximum wall displacement was consistent with the corresponding laboratory measured values.     

Centrifuge Modeling of LNAPL Transport in Partially Saturated Sand

Model tests were performed at the Geotechnical Centrifuge Facility of Delft University of Technology, The Netherlands, to examine the mechanics of light nonaqueous phase liquid (LNAPL) movement in a partially saturated porous granular medium. The experiment simulated a 2D spill of LNAPL in an unsaturated sand prepared at two values of porosity. The duration of the centrifuge model tests corresponded to a prototype equivalent of 110 days. The choice of modeling a 2D flow together with the use of a transparent container enabled direct visual observation of the experiments. Scaling laws developed in connection with other centrifuge modeling studies were used to support the test results. Tests were conducted at two different centrifuge accelerations to verify, by means of the “modeling of models technique,” the similitude between the different experiments. The paper presents details of the experimental methodologies and the measuring techniques used to evaluate the final distribution of water and LNAPL content in the soils.     

Construction Effect on Load Transfer along Bored Piles

The load transfer behavior along bored piles is affected by details of pile construction particularly those imposing stress and moisture changes to the surrounding soils. An investigation involving moisture migration tests, in situ horizontal stress measurements, and borehole shear and pressuremeter tests shows clear effects of construction that lead to subsequent changes in soil properties. The construction of bored piles in Singapore and the region often involves casting of concrete either in unsupported “dry” boreholes or in “wet” boreholes filled with water. It is necessary to differentiate these two extreme construction conditions in bored pile design. Based on triaxial compression and pressuremeter tests on the residual soil of the Jurong Formation in Singapore, the variation of soil modulus with shear strain can be described by a hyperbolic function. A procedure is recommended for assessing the combined effect of stress relief and soaking on soil modulus by introducing a modulus reduction factor. Modulus degradation curves from pressuremeter tests with the borehole conditions properly simulated are found capable of producing load transfer curves that are comparable to those deduced in the field.     

Tunneling beneath Buried Pipes: View of Soil Strain and Its Effect on Pipeline Behavior

The paper examines the problem of tunneling beneath buried pipelines and the relationship between soil strains and pipeline bending behavior. Data are presented from centrifuge tests in which tunnel volume loss was induced in sand beneath pipelines of varying stiffness properties. The model tunnel and pipelines were all placed at a Perspex wall of the centrifuge strong box such that image-based deformation analyses could be performed. The method provided detailed data of subsurface soil and pipe displacements and illustrated the soil-pipe interaction mechanisms that occurred during tunnel volume loss, including the formation of a gap beneath the pipes. The relationship between tunnel volume loss, soil strain, and pipe bending behavior is illustrated. Experimental results of pipe bending moments are compared against predictions: (1) assuming the pipe simply follows greenfield displacements; (2) using an elastic continuum solution; and (3) using a new method in which an “out-of-plane” shear argument, due to soil-pipe interaction, is introduced into the elastic continuum solution. It is shown that the new method gives the best prediction of experimental pipe bending moments.     

Strength Loss and Localization at Silt Interlayers in Slopes of Liquefied Sand

The role of void redistribution in the liquefaction behavior of saturated sand slopes with and without silt interlayers was investigated using a series of dynamic centrifuge model tests. Twelve centrifuge model tests are described that represent four different simple slope configurations, a range of initial relative densities (DR), and three different input motions with different sequences of application. These experimental results demonstrate that the potential for void redistribution induced shear localizations and slope instability depends on the sand’s initial DR, slope geometry (silt layer shape, sand layer thickness), and shaking characteristics (duration, intensity, and history). The archived experimental data set provides a good basis for assessing the ability of numerical modeling methods to distinguish between conditions leading to localization or not. Apparent residual shear strengths mobilized in the models were backcalculated using techniques common to practice. The experimental and analytical results demonstrate that the apparent residual shear strength is unlikely to correlate closely to pre-earthquake penetration resistance alone, but rather is a function of the initial shear stresses and numerous factors affecting the process of void redistribution and localization.     

Earth Dam on Liquefiable Foundation and Remediation: Numerical Simulation of Centrifuge Experiments

A series of four dynamic centrifuge model tests was performed to investigate the effect of foundation densification on the seismic performance of a zoned earth dam with a saturated sand foundation. In these experiments, thickness of the densified foundation layer was systematically increased, resulting in a comprehensive set of dam-foundation response data. Herein, Class-A and Class-B numerical simulations of these experiments are conducted using a two-phase (solid and fluid) fully coupled finite element code. This code incorporates a plasticity-based soil stress–strain model with the modeling parameters partially calibrated based on earlier studies. The physical and numerical models both indicate reduced deformations and increased crest accelerations with the increase in densified layer thickness. Overall, the differences between the computed and recorded dam displacements are under 50%. At most locations, the computed excess pore pressure and acceleration match the recorded counterparts reasonably well. Based on this study, directions for further improvement of the numerical model are suggested.     

油罐爆炸作用下隧道衬砌动力响应数值模拟研究

为准确分析油气爆炸下隧道及采矿巷道等地下工程的结构稳定性,采用FLACS软件计算LPG爆炸荷载,基于LS-DYNA软件将爆炸冲击荷载施加于结构表面,进而计算爆炸荷载作用下衬砌结构动力响应。研究结果表明：隧道的“角状结构”对冲击波反射具有强化作用,致使相应位置形成应力集中,应力波强度衰减缓慢,随着传播距离的增加,衬砌所受应力逐渐减小且同一截面应力值趋于一致;同一截面不同测点处的速度、位移值受爆心距和隧道几何结构的共同影响,当爆心距大于12 m时,速度和位移值变化趋于稳定;顶部衬砌和底部结构更易发生破坏,边墙位置损伤程度较小。该研究成果为地下工程安全稳定性分析提供了方法依据,也为巷道抗爆设计及支护优化提供了理论参考。     

Simulation of Shield Tunneling Behavior along a Curved Alignment in a Multilayered Ground

The kinematic shield model has been proposed to simulate shield behavior during excavation based on equilibrium condition, taking into account ground displacement around the shield. The model has been validated by the simulation of an earth pressure balanced shield behavior in a straight alignment for a single ground layer. To verify the model performance for shield tunnel excavation at curved alignment in multilayered ground, the slurry shield behavior is simulated in this study using the in situ data, and the immediate ground movements around the shield are computed by three-dimensional FEM employing the enforced displacement, which is obtained from the shield behavior simulation. As a result, it is found that the simulated shield behavior and the computed immediate ground movements around the shield during shield tunneling are in good agreement with the observations. Furthermore, the results reveal that the excavated area including the area generated by copy cutter is a predominant factor affecting the shield behavior, and the ground displacement, at the excavated surface plays an important role in the surrounding ground movements during shield tunneling.     

Centrifuge Modeling of Light Nonaqueous Phase Liquids Transport in Unsaturated Soils

Centrifuge modeling appears useful for studying geo-environmental problems such as pollutant migration in subsurface systems. In this study, centrifuge tests were conducted to simulate a gasoline spill from a leaking underground storage tank (UST) and the subsequent subsurface migration of the gasoline. When the centrifugal acceleration reached the desired g level, the gasoline was released from the UST and then it migrated in the unsaturated soil for a prototype time equivalent to 1 year. After the centrifuge tests, soil samples were collected using sampling tubes and the concentrations of individual constituents in the light nonaqueous phase liquids (LNAPLs) were directly measured by means of gas chromatograph analysis. Two types of unsaturated soils were used to study the migration patterns of LNAPLs in unsaturated porous media. Centrifuge test data show that the migration pattern of LNAPLs is related to the soil type and the physical properties of individual constituents in the LNAPLs.     

Centrifuge Simulations of Large-Scale Shaking Table Tests: Case Studies

This paper documents three case studies that involve dynamic centrifuge tests that simulated large-scale shaking table tests on soil–pile-structure systems. The large-scale shaking table tests were performed using the world’s largest laminar shear box with depth of 6 m and plan dimensions of 11 m and 3.5 m. Life-size steel and prestressed concrete piles were used in these tests. The large-scale tests involved intense shaking that produced strong nonlinear stress–strain effects and degradation of soil stiffness due to liquefaction in the foundation soil models. The dynamic centrifuge tests treated the large-scale models as their prototypes. Only essential information about the large-scale test models and the testing conditions were available to design and perform the dynamic centrifuge tests. The three case studies showed that carefully designed performed centrifuge tests could reproduce the key features of the responses of the large-scale models. However, some differences were also found in the results from these two types of tests.     

Seismic Soil-Pile-Structure Interaction Experiments and Analyses

A dynamic beam on a nonlinear Winkler foundation (or “dynamic p-y”) analysis method for analyzing seismic soil-pile-structure interaction was evaluated against the results of a series of dynamic centrifuge model tests. The centrifuge tests included two different single-pile-supported structures subjected to nine different earthquake events with peak accelerations ranging from 0.02 to 0.7g. The soil profile consisted of soft clay overlying dense sand. Site response and dynamic p-y analyses are described. Input parameters were selected based on existing engineering practices. Reasonably good agreement was obtained between calculated and recorded responses for both structural models in all earthquake events. Sensitivity of the results to dynamic p-y model parameters and site response calculations are evaluated. These results provide experimental support for the use of dynamic p-y analysis methods in seismic soil-pile-structure interaction problems.     

2500 m3新2号高炉长寿烘炉新工艺

为消除高炉冷却壁铸造内应力对壁体工作的破坏性影响,对马钢2 500 m3新2号高炉实施了利用高炉烘炉过程来实现既烘干水分保护耐材,同时又消除内应力的工业应用.采用与工业高炉同材质、同制作工艺的铜、灰铁和球铁实验冷却壁,使用力学性能及X射线应力测试、金相微观组织分析等方法,在实验室进行了系列热态模拟实验,取得的优化工艺条件在2号高炉烘炉过程中应用.结果表明,有效消除铸铁冷却壁内应力平均达93%以上,同时壁体的力学性能平均提高12%以上.     

Effects of Layer Thickness and Density on Settlement and Lateral Spreading

This paper presents the results of six large-scale centrifuge model tests that were performed to study the effect of relative density and thickness of sand layers on the amount of settlement and lateral spreading. The models included a “river” channel with clay flood banks underlain by layers of loose and dense sand of variable thickness, and a bridge abutment surcharge on one of the banks. The model container was tilted to provide an overall slope to the model. Each model was subjected to three or four significant ground motion events, which were obtained by scaling the amplitude of recordings of the Kobe (1995) and Loma Prieta (1989) earthquakes. Several measurements of acceleration, pore water pressure, settlement, and lateral movement are presented. The liquefaction potential index and a deformation index, which combine the influences of depth, density, and layer thickness, were found to correlate reasonably well with liquefaction induced settlements and lateral deformations for the range of models tested and indicate that centrifuge results are consistent with field observations.     

塑料模具钢镦粗过程内部空洞缺陷的有限元模拟

摘要：利用JmatPro软件模拟计算718类塑料模具钢（3Cr2MnNiMo）热物性参数。应用ABAQUS有限元模拟软件建立模具钢镦粗过程中孔洞模型，模拟不同压下率条件下孔洞的闭合规律。模拟结果表明：孔洞闭合分为开始闭合、闭合加速和闭合减速3个阶段；孔洞闭合的2个主要影响因素为孔洞表面等效应变εe、静水压力与等效应力之比σm/σe；随着孔洞所处位置不同，孔洞闭合度不同，根本原因为孔洞所处位置的等效应变不同。所得结果对于塑料模具钢实际锻造生产过程具有指导意义。     

Centrifugal Modeling of Seismic Behavior of Large-Diameter Pipe in Liquefiable Soil

This study focused on the behavior of a large-diameter burial pipe with special reference to its stability against flotation subject to soil liquefaction. Centrifugal modeling technique was used where the results are presented for a total of eight shaking table tests conducted on the burial pipe in a laminar box under 30g gravitational field. The ground was prepared with Nevada sand at a relative density of 38% and shaken with a sinusoidal wave at an amplitude of 0.5g. The use of a viscous fluid in a saturated soil deposit satisfied the time scaling relationships of both dynamic and dissipation phenomena. The centrifugal modeling technique simulated flotation of pipeline as the soil liquefied. A technique that used gravels and geosynthetic material was used to mitigate flotation. The response of the soil deposit, in terms of acceleration and excess pore pressure, was investigated. The uplifting of the pipe, earth pressure response and ground surface deformation were also presented. Based on the test results, a design procedure was proposed for the burial pipe in resisting flotation due to soil liquefaction. The deadweight and stiffness of the gravel unit, which was confined by geosynthetic, were important items in design.     

Strength of Undisturbed versus Reconstituted Silt and Silty Sand Specimens

The differences in undrained stress-strain-strength behavior between “undisturbed” and reconstituted silt and silty sand specimens tested at the same void ratio and initial stress state may be dramatic. In all tests reported herein the undisturbed specimens showed dilative and ductile behavior, whereas in all but a very few cases the accompanying reconstituted specimens at the same (or lower) density showed contraction, much lower undrained strength, and brittle behavior. The test series included samples from a natural fluvial silt deposit as well as from silty sand hydraulically placed in a tailings dam. When reconstituting specimens for laboratory testing, it is not sufficient to only satisfy the criteria of correct density and grain size distribution, but somehow the same fabric also must be reproduced. Otherwise, deformation and stability analyses based on the results of reconstituted specimens, or on in situ tests calibrated against such results, may be misleading. Most of the reconstituted specimens tested herein were prepared by moist tamping, but other methods were also used and the results compared. The reconstitution of silty sand specimens by water pluviation seems to be the most promising preparation method.     

盾构机轴承用钢的开发与质量控制

 随着中国工业化进程及基础设施建设的需要,大量的交通隧洞、城市地下铁道、供排水隧道和电缆隧道等工程建设需要使用大型掘进设备盾构机。由于盾构机的特殊使用环境,对盾构机轴承的使用寿命和可靠性要求非常高。大型盾构机轴承用钢的开发和质量控制是影响盾构机寿命以及整个施工安全的重要因素。通过对盾构机轴承的使用环境以及性能要求进行分析,分别研究了大型盾构机轴承滚动体以及套圈用钢的钢种选择问题,并提出了在盾构机轴承质量控制过程中的关键措施。对轧材或锻材的质量来说,钢质纯净化是基础,铸态组织的均匀化和形变组织的精细化是关键。后续热处理的综合组织性能控制,包括淬硬层控制、马氏体组织控制、残余碳化物控制以及残余奥氏体控制是保证满足盾构机轴承强韧化的重要措施。