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.
Under a given compaction energy and procedure, it is known that maximum dry density of a soil is lowered due to lime addition. This modification of maximum dry density could alter the hydraulic ...conductivity of the soil. The main object of this study was to assess the impact of lime-stabilization on a silt soil microstructure and then on saturated hydraulic conductivity. An investigation at the microscopic level with mercury intrusion porosimetry showed that lime treatment induced the formation of a new small class, with a diameter lower than 3
×
10
3
Å in the compacted soil. This class is responsible for the difference in dry density between the treated and the untreated sample after compaction. It is shown that this small pores class was not altered by the compaction water content, the compaction procedure or the dry density. As in untreated soils, only the larger pores were modified by the compaction water content and the compaction procedure in the lime treated samples. The hydraulic conductivity appeared to be only related to the largest pores volume of the tested silt, regardless of lime treatment. Therefore, this study demonstrated that even if addition of lime resulted in a dramatic change of the maximum dry density of the tested silty soil, its effect on hydraulic conductivity is limited.
► Lime treatment induced the formation of a small pore class, with a diameter lower than 3
×
103 Å. ► This class explains the difference in dry density between the treated and the untreated sample after compaction. ► The hydraulic conductivity appeared to be only related to the macropore volume of the silt.
This study’s main goal was to examine how the wetting/drying solicitations affect the mechanical behavior of a cementtreated sand. A quantitative method based on the stress-dilatancy approach was ...used to assess the effects of two types of wetting and drying cycles of different intensities. The results showed that bonding is primarily altered by the wetting/drying cycles, leading to lower mechanical performances. It has been demonstrated that the weathering effect not only depends on the cement dosage, but also on the cycles’ intensity. The early cycles appeared to have the greatest impact on changes in mechanical performance on the samples treated with 4% cement. However, the accumulation of numerous cycles caused a more progressive degradation on the samples treated with 1% cement. The quantitative assessment of the treatment effect and the weathering progress with cycles was made possible through the evaluation of the bonding ratio. The importance of the imposed wetting/drying cycle protocol for a proper evaluation of the long-term performance of treated soils is highlighted. Further research is needed to define an appropriate weathering protocol that makes sense in light of the real solicitation faced by engineered structures.
This paper focuses on the performances of a treated expansive clayey soil sampled on an embankment constructed in 2010. Two types of treatment used during construction are considered: 4% lime as well ...as a mix of 2% lime and 3% cement. Oedometer tests were carried out on different parts of the embankment, to assess the compressibility of the soil. The results were compared to the compression curve of the untreated soil, also sampled in the same embankment. Several complementary aspects were also investigated (moisture content, dry density,…) to assess the ageing process of the embankment. The obtained results showed that the behaviour of the material from the outer part of the backfill is similar to the mechanical performances of the untreated soil, demonstrating a strong alteration of the effect of both treatments. This alteration is noticeable until a horizontal distance of about two meters from the surface. Beyond this distance, the performance of the soil is comparable to the mechanical behaviour of treated soil. These observations, similar for each treatment dosage, tend to question the durability of the treatment at the edge of the earth structure.
The mechanical efficiency of soil stabilization with cement is mainly controlled by various parameters, namely, the amount of binder, the compaction soil state and the curing conditions. The strength ...of the treated soil is the result of a complex combination of several factors that condition the physicochemical processes involved in cement hydration, which are difficult to monitor. The objective of this study is to identify the relevant parameters governing the bonding in cement-treated soil and suggest a predictive model for strength evolution using these parameters as input. To this purpose, an extensive testing program is presented to assess the impact of the initial water content (11–18%) and dry density (1.6–1.87 Mg/m3) as well as cement dosage (3 and 6%) in sealed curing conditions for 0, 7, 28 and 90 days. The water content variation, the total suction and the compressive strength were measured after different curing durations. The experimental results are first discussed in the parameters’ space, and then through a principal components analysis to overcome the complexity due to the parameters’ interdependency. The PCA revealed that the cement dosage explained 40% of the dataset variance, the remaining 60% being related to a combination of the initial state and curing time. Finally, a predictive model based on an artificial neural network was developed and tested. The predicted results were excellent, with an R2 of +0.99 with the training data and +0.93 with the testing data. These results should be improved by extending the dataset to include different soils and additional compaction conditions.
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.
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.
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