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Substantial degradation can occur to warm permafrost due to changes in surface conditions resulting from infrastructure development and climate warming. The associated geohazards, including differential settlement, slope instability, and liquefaction of degraded, unconsolidated materials in seismically active warm permafrost regions, pose substantial threats to the built infrastructure. Among them, seismic hazards of degraded permafrost have received little attention. This paper aims to provide a case study of an airport built on warm permafrost about 80 years ago, focusing on climate changes, permafrost degradation, and observed seismic hazards during a strong earthquake. The study site, that is, the Northway Airport, is located in a discontinuous permafrost area in Interior Alaska. Geotechnical data from 1973, 1991, and 2005 were compiled and analyzed to reveal permafrost degradation at various surface conditions, and are compared with the well-known degradation data from a site in Fairbanks. Furthermore, the responses of the airport runway during the 2002 Denali earthquake (Mw = 7.9), including liquefaction and lateral spreading displacements, are described and analyzed. And the seismic hazards of civilian airports built on permafrost across Alaska are surveyed. Distinct trends are revealed in two periods, namely, from 1943 to 1975 and from 1976 to 2021, for air temperature, precipitation, and wind speed. Permafrost tables were observed to drop with time at various rates for different surface conditions. Liquefaction and lateral spreading were observed extensively during the earthquake. The locations of observed liquefaction at the airport are mapped, and the lateral spreading displacements are estimated based on available photos. The standard penetration test data collected during geotechnical investigations are analyzed, and a liquefiable layer is identified at the talik between the active layer and the permafrost table. Moreover, 55% of Alaska's civilian airports are in permafrost areas. Among them, two-thirds fall within seismic zones with a risk level of 3 or above. This study demonstrates the high seismic risks of degraded permafrost and its potential impact on the built infrastructure. [ABSTRACT FROM AUTHOR]

Brittle failures were observed in pile foundations during past earthquakes due to seasonally frozen ground. This paper introduces a new geosynthetic material derived from waste tires, i.e., polyurethane-bonded rubber particles and sand, termed PolyBRuS, for application around deep foundations to improve their seismic performance in cold regions. Cyclic triaxial tests were carried out at various temperatures, confining pressures, and freeze–thaw cycles to assess the cold-weather dynamic characteristics of PolyBRuS. The results show that the material behaves as a nonlinear viscoelastic material at an axial strain of less than 1%. Its dynamic elastic modulus rises after freezing and continues to increase as temperature drops, but it is much less sensitive to confining pressures and freeze–thaw cycles; its damping ratio rises significantly with increasing axial strains and decreasing subfreezing temperatures and declines moderately with increasing freeze–thaw cycles. Compared with natural soils, its dynamic elastic modulus is similar to those of unfrozen fine-grained soils and is much less sensitive to subfreezing temperatures; its damping ratio is comparable to that of fine-grained unfrozen soils and is substantially higher than frozen soils at subfreezing temperatures. These characteristics make this material an excellent candidate to replace local soil around deep foundations for vibration reduction and seismic hazard mitigation in cold regions. [ABSTRACT FROM AUTHOR]

This paper presents a work to define four fundamental concepts, namely, buoyant force, submerged unit weight, seepage force, and critical hydraulic gradients, for saturated geomaterials including soils, rocks, and concrete under normal and high pressures using the general effective stress (GES) concept along with Terzaghi's effective stress. In particular, four typical GES expressions are used for this purpose, and their impacts on the definition of the four concepts are compared based on available experimental evidence in the literature. The results suggest that (1) Terzaghi's effective stress can be physically validated in the context of Archimedes' principle for soils under normal conditions; (2) the generalized buoyant force on the unit volume of saturated geomaterials is the product of the unit weight of pore fluid and the GES coefficient tensor; and (3) the generalized seepage force theoretically acts in the direction of pore fluid flow only when the GES coefficient tensor is proportional to the permeability coefficient tensor. These four fundamental concepts have a profound significance for geotechnical applications with GES and thus merit further validation with adequate laboratory and in situ observations. [ABSTRACT FROM AUTHOR]

Soil-structure interaction may play a major role in the seismic response of a bridge structure. Specifically, soil layers of low stiffness and strength may result in permanent displacement of the abutments and foundations, thus imposing important kinematic conditions to the bridge structure. A study to illustrate such phenomena is undertaken based on three-dimensional nonlinear dynamic finite-element (FE) modeling and analysis (for a specific bridge configuration under a given seismic excitation). A bridge-foundation-ground model is developed based on the structural configuration and local soil conditions of the Humboldt Bay Middle Channel Bridge. The FE model and nonlinear solution strategy are built in the open-source software platform OpenSees of the Pacific Earthquake Engineering Research Center. Based on the simulation results, the overall system seismic response behavior is examined, as well as local deformations/stresses at selected critical locations. It is shown that permanent ground deformation may induce settlement and longitudinal/ transversal displacements of the abutments and deep foundations. The relatively massive approach ramps may also contribute to this simulated damage condition, which imposes large stresses on the bridge foundations, supporting piers, and superstructure. CE Database subject headings: Bridges; Finite element method; Soil-structure interaction; Abutments; Seismic effects; Seismic analysis; California.

This paper presents the results of more than one year's monitoring efforts and analysis of the effects of environmental variables on the dynamic properties of a selected bridge in Anchorage, Alaska. A seismic monitoring system was installed on the bridge to study these effects. The dynamic properties of the bridge have been identified from the recorded time histories which include ambient noises, traffic-induced vibrations, and small-magnitude earthquakes. Hourly air temperature data from nearby meteorological station during the period of study were collected to estimate the frozen soil depth for modeling purpose. A finite-element model and multiple-input autoregressive model were applied to study the effects of environmental variables on the dynamic properties. The results show that the environmental variables can significantly affect the dynamic properties by modifying the stiffness of the bridge system and the seasonal frost is found to have the dominating effects over air temperature on the bridge dynamic properties in cold regions. The results show that the models explain well the variation of dynamic properties with environmental variables. DOI: 10.1061/(ASCE) 0887-381X(2007)21:4(108) CE Database subject headings: Frost; Soil-structure interaction; Dynamics; Finite element method.

One-dimensional nonlinear ground response analyses provide a more accurate characterization of the true nonlinear soil behavior than equivalent-linear procedures, but the application of nonlinear codes in practice has been limited, which results in part from poorly documented and unclear parameter selection and code usage protocols. In this article, exact (linear frequency-domain) solutions for body wave propagation through an elastic medium are used to establish guidelines for two issues that have long been a source of confusion for users of nonlinear codes. The first issue concerns the specification of input motion as 'outcropping' (i.e., equivalent free-surface motions) versus 'within' (i.e., motions occurring at depth within a site profile). When the input motion is recorded at the ground surface (e.g., at a rock site), the full outcropping (rock) motion should be used along with an elastic base having a stiffness appropriate for the underlying rock. The second issue concerns the specification of viscous damping (used in most nonlinear codes) or small-strain hysteretic damping (used by one code considered herein), either of which is needed for a stable solution at small strains. For a viscous damping formulation, critical issues include the target value of the viscous damping ratio and the frequencies for which the viscous damping produced by the model matches the target. For codes that allow the use of 'full' Rayleigh damping (which has two target frequencies), the target damping ratio should be the small-strain material damping, and the target frequencies should be established through a process by which linear time domain and frequency domain solutions are matched. As a first approximation, the first-mode site frequency and five times that frequency can be used. For codes with different damping models, alternative recommendations are developed. DOI: 10.1061/(ASCE) 1090-0241 (2007) 133:11(1385) CE Database subject headings: Earthquakes; Ground motion; Wave propagation; Seismic effects; Damping.

This paper presents results of the finite element study on the behavior of a single pile in elastic-plastic soils. Pile behavior in uniform sand and clay soils as well as cases with a sand layer in a clay deposit and a clay layer in a sand deposit were analyzed using finite element modeling. Finite element results were used to generate p-y response curves, which were cross compared to investigate the soil layering effects. CE Database subject headings: Layered soils; Lateral loads; Piles; Finite element method; Elastoplasticity.

A highly instrumented centrifuge experiment was conducted at the Univ. of California at Davis, to investigate the seismic response of a saturated dense sand stratum. Nevada sand at about 100% relative density was employed in a laminated (flexible shear beam) container to simulate one-dimensional site response. Among the total of 27 imparted earthquake-like shaking events, peak accelerations near ground surface ranged from 0.03 to 1.7g (in prototype scale), covering linear to highly nonlinear scenarios. This comprehensive set of recorded downhole accelerations is utilized herein to identify variation of shear modulus and damping ratio with shear strain amplitude. The estimated modulus reduction and damping ratio display a confinement dependence. At shear strains below about 0.2%, modulus variation is found in reasonable agreement with the formulae of Hardin-Drnevich and the modulus reduction bounds of Seed-Idriss, while damping is generally higher. At shear strains larger than 0.2%, the shear-induced dilation tendency maintained secant shear modulus at about 20% of its initial value, with a 20% damping ratio approximately. In earlier laboratory experimental studies on loose to medium-dense sands, Vucetic and Matasovic also reported similar trends. Based on the findings, a two-phase (solid and fluid) fully coupled nonlinear finite element program is calibrated and used to conduct numerical simulations of representative weak to strong shaking events. The computational results are in good agreement with the recorded counterparts, and satisfactorily reproduce the important dilation effects. CE Database subject headings: Sand; Saturated soils; Centrifuge model; Damping ratio; Dilatancy; Soil dynamics; Amplification.

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. DOI: 10.1061/(ASCE)0733-9399(2004)130:10(1168) CE Database subject headings: Dams, earth; Dam foundations; Liquefaction; Soil compaction; Numerical models; Earthquakes.

In this paper, we investigate the behavior of elastic-plastic specimens during testing in a triaxial apparatus. In particular, an investigation of the influence of a number of imperfections on the observed behavior of a specimen is performed. To this end, we present influences of end platen friction, end platen inclinations, and the shape of specimen on what we broadly understand by 'constitutive behavior.' We investigate the issues related to the constitutive as opposed to boundary value behavior or elastic-plastic specimens. We present a number of examples to illustrate the differences between different types of response, which are usually, and wrongly, just called the constitutive behavior. CE Database subject headings: Elastoplasticity; Constitutive relations; Geomaterials; Laboratory tests.

In saturated clean medium-to-dense cohesionless soils, liquefaction-induced shear deformation is observed to accumulate in a cycle-by-cycle pattern (cyclic mobility). Much of the shear strain accumulation occurs rapidly during the transition from contraction to dilation (near the phase transformation surface) at a nearly constant low shear stress and effective confining pressure. Such a stress state is difficult to employ as a basis for predicting the associated magnitude of accumulated permanent shear strain. In this study, a more convenient approach is adopted in which the domain of large shear strain is directly defined by strain space parameters. The observed cyclic shear deformation is accounted for by enlargement and/or translation of this domain in deviatoric strain space. In this paper, the model formulation details involved are presented and discussed. A calibration phase is also described based on data from laboratory sample tests and dynamic centrifuge experiments (for Nevada sand at a relative density of about 40%). DOI: 10.1061/(ASCE)1090-0241(2003)129:12(1119) CE Database subject headings: Liquefaction; Constitutive models; Cyclic plasticity; Soil dynamics; Centrifuge models.

The first articulation of the second type of dilatational wave propagating through fluid-saturated geomaterials has been traced to Heinrich's formulation built on Fillunger's framework of the mixture theory and Terzaghi's principle of effective stress. Although this Fillunger–Heinrich theory (FHT) precedes the celebrated Biot's wave theory and Frenkel's theory, research has yet to systematically investigate the FHT's predictive ability. To value the scientific heritage, the original formulation of FHT was first revisited with minor corrections and then reformulated in a dimensionless form. Using the method of separation of variables, an analytical solution was developed for the dimensionless FHT in the context of consolidation under instantaneously applied surcharge and with one-way drainage at the top boundary of the consolidating stratum. The predictive power of FHT was validated against available wave measurements; the proposed solution was verified against the finite-difference method with nonclassical Newmark's integration schemes. The parametric analysis conducted herein further suggests that FHT can qualitatively interpret observed complex phenomena, including the consolidation delay effect, the top-down progressive pattern, and the initial settlement overestimation. FHT significantly fills the knowledge gap between Terzaghi's classic theory and Biot's theory, thus enabling engineers to analyze the one-dimensional dynamic behavior of saturated geo-/poro-materials with incompressible constituents. [ABSTRACT FROM AUTHOR]

Permeability of a liquefiable soil profile may affect the rate of pore-pressure buildup and subsequent dissipation during and after earthquake excitation. Consequently, effective soil confinement and available resistance to shear deformations may be significantly dependent on permeability in many practical situations. If present, spatial variation in permeability may even have a more profound impact on available overall shear resistance. Indeed, case histories and experimental evidence (shake table and centrifuge tests) suggest that spatial permeability variation in stratified liquefiable deposits can highly influence the nature and extent of associated lateral deformation. In such situations, the onset of liquefaction-induced densification may result in water or water-rich thin interlayers trapped below overlying low-permeability strata. The presence of these low-shear-strength interlayers may trigger excessive (or even unbounded) localized shear deformations (flow failure mechanism). In this paper, numerical modeling is employed in order to investigate the influence of permeability and the spatial variation thereof on liquefaction-induced shear deformations. The involved response characteristics are numerically simulated using a fully coupled two-phase (solid-fluid) Finite Element program. DOI: 10.1061/(ASCE)0733-9399(2002)128:7(720) CE Database keywords: Permeability; Shear deformation; Liquefaction; Earthquakes; Sand boils.

Roads and other infrastructure in Western Alaska are difficult to design and build owing to the high cost of construction materials and the ice-rich permafrost foundation. The present study explores methods to treat locally available frozen materials for satisfactory engineering applications. Stabilizing agents including cement, perlite, nanosilica, and polypropylene fiber (PP-fiber) were used at various mix ratios to treat pulverized frozen silty sand. Subsequently, a suite of laboratory tests was performed on thawed and/or cured specimens to assess the thaw strain, shear-strength parameters, elastic wave velocities, and thermal conductivity of the treated soil. Scanning electron microscopy images were obtained to reveal the microstructure of the stabilized frozen soil. It was found that the addition of cement, perlite, nanosilica, and PP-fiber greatly reduces the thaw strain and improves the shear strength of the stabilized soil. A combination of cement and perlite at 3% each can be very effective and economical in reducing the thaw strain, enhancing the shear strength, and decreasing the thermal conductivity, and is recommended for field trial. [ABSTRACT FROM AUTHOR]

In cold regions, snow and ice cause serious safety problems to the transportation system. South central Alaska, particularly Anchorage, is susceptible to a number of icing events resulting from frequent freeze/thaw cycles in the winter season. Traditionally, deicing has been accomplished by mechanical, chemical, and thermal methods. However, these methods cause problems such as damage to pavement, pollution in the environment, corrosion to vehicles and reinforcing steel in concrete, or being too expensive. A new type of roadway deicing system on the basis of commercially available carbon fiber tape is proposed. This paper presents the design of a deicing heating panel, the layout and construction of the test sidewalk, experimental results and analyses, and cost comparison with other deicing systems. Experimental results including system performance, deicing time, energy consumption, deicing cost, and temperature variation with time and location are presented. The sensitivity of the deicing cost to ambient air temperature, wind chill, and snow density is also analyzed. Finally, this system is compared with other deicing systems in annual operating cost, unit cost, power density, and installation cost. The cost comparison shows that the present deicing system demonstrates higher energy efficiency and lower installation cost among the systems compared and has great potential for applications in cold regions. [ABSTRACT FROM AUTHOR]

Traditional deicing approaches such as salting pollute the environment and corrode reinforcing steel bars in concrete. Meanwhile, recently emerging carbon nanofiber material has improved electrical conductivity, a large heating capacity at low voltage, high strength, and, in particular, natural immunity to corrosion. This material offers an excellent alternative as the heating element in electrical resistive deicing systems. This paper aims to assess the effectiveness of a deicing system that has embedded carbon nanofiber paper heating elements and to evaluate the effects of several key parameters on the performance of such a deicing system. A physics-based finite-element model was built, validated by test results, and used to assess the performance of such a deicing system when applied to roadway conditions. Factors considered include air temperature, wind speed, pavement and insulation layer thicknesses, and heating input. Results show that the proposed system can be very effective for roadway deicing. Future research is needed to validate its feasibility and effectiveness in a field experiment. [ABSTRACT FROM AUTHOR]