In energy geostructures, the soil-structure interface is subjected to thermo-mechanical loads. In this study, a non-isothermal soil-structure interface model based on critical state theory is ...developed from a granular soil-structure interface constitutive model under isothermal conditions. The model is capable of capturing the effect of temperature on sand/clay-structure interfaces under constant normal load and constant normal stiffness conditions. First, the developed model was verified for sand-structure interface in isothermal conditions. Then, it was calibrated for clay-structure interface under non-isothermal conditions. On one hand, a well-defined peak shear stress for the clay-structure interface and, on the other hand, the effect of temperature on the void ratio of the clay-structure interface were captured and reproduced by the model. The importance of interface thickness determination and some differences between the interface thicknesses of clay-structure and sand-structure interfaces are discussed in detail. The additional parameters have physical meanings and can be determined from laboratory tests. The modeling predictions are in good agreement with experimental results, and the main trends are properly reproduced.
This paper assesses the performance of an embankment constructed in 2010 with a stabilised expansive soil. Two types of treatment were employed at construction time: 4% lime and a mix of 2% lime and ...3% cement. A sampling campaign was carried out in 2021 to evaluate the long-term performance of the stabilised soil properties. To assess the compressibility of the soil, oedometer tests were carried out on samples from different parts of the embankment. The results were compared to the compression curve of the untreated soil, also sampled in the same embankment. Complementary shrinkage tests were performed to investigate the effect of the treatment on swelling and shrinkage. The obtained results show that the yield stress of the material from the outer part was inferior to 100 kPa, similarly to the yield stress of the untreated soil, demonstrating a strong alteration in the effect of both treatments over time. This alteration was noticeable to a distance of approximately 2 m from the external surface. Beyond this distance, the performance of the soil was comparable to the behaviour of recently treated soil, with yield stresses close to 1000 kPa. These observations, similar for each treatment dosage, raise questions as to the durability of the treatment on the outer part of the backfill.
The positive effects of lime or cement treatment could be altered by weathering in the very long term. In this context, the main purpose of this study is to examine the impact of wetting/drying ...cycles on the strength and the hydraulic conductivity of a compacted soil treated with lime and cement. Compacted specimens were cured for 90 days before being exposed up to twelve wetting and drying cycles. A special concern of the study was the experimental method to impose the wetting and drying cycles. Two protocols were employed: one relied on relative humidity control to dry the samples, while the other was based on oven drying. The impact of the cycles was quantified by comparing the performance of the samples exposed to the cycles to the performance of the unsolicited samples. The results showed that the cycles induced a major alteration of the strength of the samples, with both methods. This degradation is associated to a significant increase of the hydraulic conductivity of the samples with the number of cycles.
The compacted clay barrier of shallow depth repositories for wastes would be subjected to temperature variations. Consequently, the hydro-mechanical properties of compacted clays could be ...progressively modified, and thus affect the performance of repositories. The influence of effective stress and temperature on the creep behavior of a saturated compacted clayey soil was experimentally investigated by performing a series of incremental loading creep tests using a temperature-controlled oedometer. Applied effective vertical stress varied from 10 to 1300 kPa within a large temperature range of 5 °C to 70 °C. The results showed that the compression and swelling indices appear not to be affected by temperature, whereas the yield stress decreases as the temperature increases. The secondary compression is time-dependent; creep strains decrease with time till reaching a stable value corresponding to a period of 10 days. The creep coefficient Cαe increases with the increase of the effective stress and temperature. Moreover, relationships between the creep coefficient Cαe, incremental compression index Cc∗, effective stress and temperature were further analyzed. A linear relationship between Cαe and Cc∗ was observed in the considered stress range and the (Cαe/Cc∗) ratio appears to be temperature dependent. Finally, the main results were discussed and interpreted in the light of a suitable constitutive framework.
•Compressibility soil increases with temperature increase.•Creep coefficient increases with vertical stress and temperature increasing.•Linear relationship between Cαe and Cc∗ in the considered range of Cc∗.•Concept of constant ratio Cαe/Cc∗ is applied to the studied clayey soil.
In geotechnical engineering, thermal energy storage in embankments can be considered as a new economically efficient, and environmentally friendly structure for space heating. In these structures, ...horizontal heat exchanger tubes can be installed inside the different layers of compacted soil to store the heat in the medium during the summer, to be extracted in the winter. Seasonally temperature variations caused by heat exchangers can affect Thermo-Hydro-Mechanical (THM) properties of the compacted soil in the embankment. Both the short and long term behavior of this compacted soil should be investigated. The aim of this study was to investigate the effect of temperature variations in the range of 5° to 50 °C, on THM behavior of a compacted sandy lean clay in saturated state. To achieve this, temperature-controlled œdometric and direct shear tests were performed. The results showed that, the effect of the temperature on mechanical properties are more pronounced under a vertical stress higher than the preconsolidation pressure. Heating changed the void ratio during consolidation phase but has a negligible effect on the shear characteristics. The results also showed that the cooling slightly changed the shear parameters.
PURPOSE: Sustainable development principles are leading earthwork companies to use all-natural materials extracted from the construction site to build the infrastructure. Natural materials with low ...characteristics must be improved. For dry soils, the common solution is to increase the compaction energy or add important quantities of water to reach the target dry density and bearing capacity. To reduce the environmental impact of their activities, the use of industrial organic products has been proposed. The aim of this study was to assess the potential benefits that could be expected from the use of these non-traditional treatments in earthworks with a well-recognised environmental impact assessment methodology. METHODS: Three non-traditional products were selected as follows: an acid solution (AS), an enzymatic solution (ES) and a calcium lignosulfonate (LS). For each of these categories, geotechnical properties such as compaction, bearing capacity, unconfined compressive strength and stiffness were first determined. Based on these results, the construction strategy for which non-traditional additives lead to greater improvement of soil properties was defined. The environmental balance of each option was then determined via a comparative process life cycle assessment study that considered ten impact categories. RESULTS AND DISCUSSION: An experimental study showed the ability of enzymatic and lignosulfonate additives to improve soil characteristics with significant savings of water at the construction stage. The purpose of the study was also to compare the global environmental impact of each treatment strategy defined from laboratory investigations. The life cycle assessment results showed that some construction strategies lead to a significant reduction in the environmental impact compared with the reference strategy. However, these environmental improvements are strongly linked to the choice of the construction strategy and site conditions as discussed in the sensitivity analysis. CONCLUSIONS: Within the three tested non-traditional additives, enzymatic and lignosulfonate treatments showed an association of technical and environmental interest for the compaction of dry soils. As demonstrated in the sensitivity analysis, these benefits are achieved when the production and transport steps have limited environmental impact. Thus, despite an important transportation distance for enzymatic additive, the small quantities that must be used (0.002Â % by dry weight) have a limited contribution on the global environmental impact. In contrast, the production step strongly impacts the treatment with lignosulfonates. Moreover, environmental interest remains strongly dependent on the site conditions and construction strategy, which is why the adopted methodology can accurately perform an initial evaluation before implementing a soil treatment with a non-traditional product.
A well-known backfill soil was considered to be used as the backfill substitutive material. The hydrothermal properties of the backfill material were estimated in laboratory and then injected in a ...numerical framework considering the atmosphere-soil-HGHE interaction. Numerical simulations were performed for a HGHE installed in the compacted backfill soil and the local materials. Two heat storage scenarios at three different installation depths were also investigated. The results show that an inlet fluid temperature of 50°C in summer increases highly the system performance (13.7% to 41.4%) while the improvement is less significant (0% to 4.8%) for the ambient inlet temperature scenario. A deeper installation depth increases also the system performance.
In energy geostructures, which exploit the heat in soil using earth contact elements, the interface is subjected to cyclic thermo-mechanical loads. Monotonic and cyclic constant-volume ...equivalent-undrained (CVEU) direct shear tests were performed on clay-clay and clay-structure interface at different temperatures (22 and 60 °C). Different cyclic and average stress ratios (CSR and ASR) were applied to the kaolin clay-structure interface under 300 kPa of normal stress. The results showed that, the number of cycles to failure for the clay-structure interface test was lower than that for the clay-clay case in the same range of cyclic and average shear stress ratios. In cyclic clay-structure tests, decreasing the cyclic stress ratio, increased the number of cycles to failure; however, decreasing the average shear stress ratio decreased the number of cycles to failure. Increasing the temperature, decreased the rate of strain accumulation and the number of cycles to failure increased by 2-3 times. The rate of degradation (degradation parameter, t) decreased by 16% with heating from 22 to 60 °C for the different cyclic stress ratios tested.
The mechanical behaviour of the soil-structure interface plays a major role in the shear characteristics and bearing capacity of foundations. In thermo-active structures, due to non-isothermal ...conditions, the interface behaviour becomes more complex. The objective of this study is to investigate the effects of temperature variations on the mechanical behaviour of soils and soil-structure interface. Constant normal load (CNL) and constant normal stiffness (CNS) tests were performed on soil and soil-structure interface in a direct shear device at temperatures of 5, 22 and 60 °C. Kaolin clay was used as proxy for clayey soils. The results showed that, in clay samples the temperature increase, increased the cohesion and consequently the shear strength, due to thermal contraction during heating. The temperature rise had less impact on the shear strength in the case of the clay-structure interface than in the clay samples. The adhesion of the clay-structure interface, is less than the cohesion of the clay samples.
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