The shear strength index of seasonally frozen soil is significantly affected by the freezing-thawing and water replenishment methods. To simulate the actual freeze-thaw and water replenishment process in seasonally frozen soil, a new method called the unidirectional freeze-thaw and natural water replenishment method was proposed. A test device was developed to facilitate this method. By using soil as the medium for water migration, the temperature change and water migration characteristics during the freeze-thaw process were investigated. The study also considered the influence of the samples' water content and the gradient between the water content of the test samples and the water replenishment soil layer. The changes in the soil stress-strain curve, static strength, and shear strength index under freeze-thaw were analyzed based on triaxial tests. The results revealed that the temperature change during the test process can be divided into six stages: rapid cooling, slow cooling, temperature stability, slow heating, continuous phase change around 0 degrees C, and positive temperature stability. After freeze-thaw, the sample water content without gradient increased by approximately 0.6%, while the sample water content with a gradient increased by about 1.5%. However, the distribution characteristics of the water content were different. The static strength, cohesive force, and internal friction angles were all lower after freeze-thaw under different water content conditions. The maximum static strength and cohesion decreased by approximately 50% and 60%, respectively, under freeze-thaw, while the internal friction angle showed a slight decrease. The new freeze-thaw and natural water supplement method can serve as a basis for selecting the shear strength index of seasonally frozen soil.

The influence of cyclic loading on frozen soil may be reflected by the variation of soil temperature. To uncover this process, dynamic triaxial tests were performed in this study on saturated warm frozen soil, during which the temperature changes inside the specimens were monitored. The effects of initial dry density, test temperature, dynamic stress amplitude and vibration frequency on temperature change were studied. The results universally manifested a rise in specimen temperature under cyclic loading. The higher dynamic stress, vibration frequency, testing temperature and initial dry density was responsible for the faster heating rate. The mechanism controlling the temperature variation inside the specimens could be explained by the heat production as a result of friction and extrusion between soil grains when subjected to dynamic loading. This temperature rise could be compromised by the heat transfer with the thermal environment where the specimen was in. A colder environment would cause the specimen temperature to drop back. This study provides an experimental foundation for deeply understanding how the mechanical behavior of frozen soil degrades under dynamic loading.

The internal replacement pipe (IRP) is a developing trenchless system utilised for restoring buried steel and castiron legacy pipelines. It is crucial to ensure that this advanced system is appropriately designed to reinstate the functionality of damaged pipelines effectively and safely. The present paper investigates the structural response of IRP systems used in repairing pipelines with circumferential discontinuities subjected to seasonal temperature changes. Analytical and numerical approaches verified via experimental data and available closed-form solutions were implemented to analyse a total of 180 linear and nonlinear finite element (FE) simulations. A set of analytical expressions was developed to describe the loading and induced responses of the system. Based on an extensive FE parametric study, five modification factors were derived and applied to developed analytical expressions to characterise the structural response incorporating the effects of soil friction. Results showed that there is a major difference between the results of linear and nonlinear analyses highlighting the importance of including the material nonlinearities in the FE analysis. A significant difference was observed between the discontinuity openings with and without the consideration of soil friction implying that appropriate inclusion of soil friction in the FE model is crucial to get realistic system responses subjected to temperature change. Although the application of IRP holds immense promise as a trenchless solution for rehabilitating legacy pipelines, the lack of established design procedures and standards for these technologies has restricted their application in gas pipelines. Results obtained from numerical and analytical models developed in the present research will provide valuable insights for the design and development of safe and efficient IRP systems urgently needed in the pipeline industry.

It is frequently observed that the stress-strain behaviour of soft clayey soils is affected by temperature changes. Development and verification of a reliable constitutive model with consideration of variable temperature conditions are necessary. Due to the significant rheological and other nonlinear properties of clayey soils, the coupled effects of temperature, time dependency, structuration, nonlinear creep, and anisotropy should be considered in the constitutive model. In this study, a new threedimensional (3D) thermal elastic visco-plastic model is established and verified for the time-dependent stress-strain behaviour of clayey soils considering temperature changes. The model is developed based on the existing elastic visco-plastic models with the equivalent time concept, the overstress theory, and the critical state model. The thermal elastic line and virgin heating line are introduced and generalized to construct constitutive equations for both thermal elastic and thermal visco-plastic behaviour of clayey soils in general stress conditions. After establishing the 3D basic model, further refinement is introduced to consider the nonlinear creep behaviour and structuration for natural and reconstituted clayey soils. Finally, the model is successfully validated by a series of laboratory test data on different clayey soils under variable temperature paths with reasonably good accuracy.

The transport sector emits a wide variety of gases and aerosols, with distinctly different characteristics which influence climate directly and indirectly via chemical and physical processes. Tools that allow these emissions to be placed on some kind of common scale in terms of their impact on climate have a number of possible uses such as: in agreements and emission trading schemes; when considering potential trade-offs between changes in emissions resulting from technological or operational developments; and/or for comparing the impact of different environmental impacts of transport activities. Many of the non-CO2 emissions from the transport sector are short-lived substances, not currently covered by the Kyoto Protocol. There are formidable difficulties in developing metrics and these are particularly acute for such short-lived species. One difficulty concerns the choice of an appropriate structure for the metric (which may depend on, for example, the design of any climate policy it is intended to serve) and the associated value judgements on the appropriate time periods to consider; these choices affect the perception of the relative importance of short- and long-lived species. A second difficulty is the quantification of input parameters (due to underlying uncertainty in atmospheric processes). In addition, for some transport-related emissions, the values of metrics (unlike the gases included in the Kyoto Protocol) depend on where and when the emissions are introduced into the atmosphere - both the regional distribution and, for aircraft, the distribution as a function of altitude, are important. In this assessment of such metrics, we present Global Warming Potentials (GWPs) as these have traditionally been used in the implementation of climate policy. We also present Global Temperature Change Potentials (GTPs) as an alternative metric, as this, or a similar metric may be more appropriate for use in some circumstances. We use radiative forcings and lifetimes from the literature to derive GWPs and GTPs for the main transport-related emissions, and discuss the uncertainties in these estimates. We find large variations in metric (GWP and GTP) values for NOx, mainly due to the dependence on location of emissions but also because of inter-model differences and differences in experimental design. For aerosols we give only global-mean values due to an inconsistent picture amongst available studies regarding regional dependence. The uncertainty in the presented metric values reflects the current state of understanding; the ranking of the various components with respect to our confidence in the given metric values is also given. While the focus is mostly on metrics for comparing the climate impact of emissions, many of the issues are equally relevant for stratospheric ozone depletion metrics, which are also discussed. (C) 2009 Elsevier Ltd. All rights reserved.

We integrated experimental and natural gradient field methods to investigate effects of climate change and variability on flowering phenology of 11 subalpine meadow shrub, forb, and graminoid species in Gunnison County, Colorado (USA). At a subalpine meadow site, overhead electric radiant heaters advanced snowmelt date by 16 d and warmed and dried soil during the growing season. At three additional sites, a snow removal manipulation advanced snowmelt date by 7 d without altering growing season soil microclimate. We compared phenological responses to experimental climate change with responses to natural microclimate variability across spatial gradients at small and landscape scales, as well as across a temporal gradient from a separate study. Both manipulations significantly advanced timing of flowering for the group of species and for most species individually, closely paralleling responses of timing to natural spatial and temporal variability in snowmelt date. Snowmelt date singularly explained observed shifts in timing only in the earliest flowering species, Claytonia lanceolata. Among all other species except Artemisia tridentata var. vaseyana, the latest flowering species, a consistent combination of temperature-related microclimate factors (earlier snowmelt date, warmer soil temperatures, and decreased soil degree-days) substantially explained earlier timing. Both manipulations also extended flowering duration for the group of species, similar to species' responses to natural snowmelt variability at small spatial scales. However, only early flowering species displayed consistent, significant changes in duration, with extended duration related to earlier snowmelt or warmer spring soil temperatures. Soil moisture was generally not a significant explanatory factor for either timing or duration of flowering. Best-fit microclimate models explained an average of 82% of variation in timing but only 38% of variation in duration across species. Our research demonstrates the value of comparing and synthesizing results of multiple field methods within a single study. This integrated approach makes it easier to identify robust community-wide trends, as well as species-specific responses of phenology to climate change. The predicted short-term flowering phenology responses to temperature-related aspects of climate change may lead to longer term asynchronies in interspecific interactions, potentially altering population and evolutionary dynamics, community structure, and ecosystem functioning.