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1.
The soil fabric plays an important role in complex hydromechanical behaviour of the expansive soils. This article addresses the influence of the wetting and drying paths on the soil fabric of compacted bentonite and silt mixtures at two different initial dry densities corresponding to loose and dense states. To obtain the hydric response of the soil, two suction imposition techniques were used: osmotic technique for the suction range less than 8.5 MPa and the vapour equilibrium or the salt solution technique for the suction range between 8.5 and 287.9 MPa. Additionally, the soil fabric analysis was performed using mercury intrusion porosimetry (MIP) and nitrogen gas adsorption (BET) techniques. The dense samples produced cumulative swelling strains during the suction cycles, while shrinkage was observed for the loose samples. The suction cycles induced an equilibrium state indicative of the elastic behaviour of the samples. The soil fabric analysis showed that regardless of the soil's initial state (loose or dense), the samples obtained the same soil fabric at the equilibrium state. The experimental results illustrated also the existence of an elastic void ratio (e0el) where the compacted soils at this state present an elastic hydric behaviour during the successive suction cycles. 相似文献
2.
Hydromechanical behaviour of an expansive bentonite/silt mixture in cyclic suction-controlled drying and wetting tests 总被引：1，自引：1，他引：0
To further our knowledge of coupling between the hydraulic cycles and mechanical behaviour of the swelling soils, this paper presents an experimental study on a bentonite/silt mixture using an odometer with suction controlled by the osmotic technique. A loading/unloading cycle was applied to each of the samples at different constant suctions (0, 2, 3 and 8 MPa). Moreover, successive wetting and drying cycles were applied under constant vertical stress at a suction range of 0 to 8 MPa, followed by a loading/unloading cycle at similar suctions (0, 2, 3 and 8 MPa). Finally, the compression curves of the aforementioned suctions with and without the application of suction cycles were compared, so as to analyse the influence of hydraulic cycles on the soil fabric and the mechanical parameters. It is observed that the wetting and drying cycles applied to both the micro- and macrostructure significantly influenced the virgin compression index λ(s), the apparent preconsolidation stress p0(s) and the elastic compression index values κ. However, the hydraulic cycles imposed only on the micro- or macrostructure induce negligible changes in the mechanical parameters of the soil. 相似文献
3.
To further our knowledge of the coupling between the hydraulic and mechanical behaviours of the swelling soils, this paper presents an experimental study on a bentonite/silt mixture using an osmotic odometer. A loading/unloading cycle was applied to samples with different initial dry densities (1.27, 1.48, and 1.55 Mg m− 3) at different constant suctions (0, 2, and 8 MPa). We noted that the initial state of the soils after compaction significantly influenced the values of the apparent preconsolidation stress p0(s), the virgin compression index λ(s), and the elastic compression index κ.These experimental results provided a sufficient database to interpret the mechanical behaviour of the swelling soil and define three yielding surfaces:
- – the suction limit between micro- and macrostructure (sm/M) and the suction limit between nano- and microstructure (sn/m), which depend completely on the soil fabrics and the diameter separating the nano-, micro-, and macrostructure,
- – the Loading Collapse (LC) curve, representing the preconsolidation stress variation as a function of suction,
- – the Saturation Curve (SC), representing the variation of the saturation stress (Psat) as a function of suction.
4.
The Barcelona basic model cannot predict the mechanical behaviour of unsaturated expansive soils, whereas the Barcelona expansive model (BExM) can only predict the stress–strain behaviour of unsaturated expansive soils without the water‐retention behaviour being incorporated. Moreover, the micro‐parameters and the coupling function between micro‐structural and macro‐structural strains in the BExM are difficult to determine. Experimental data show that the compression curves for non‐expansive soils under constant suctions are shifted towards higher void ratios with increasing suction, whereas the opposite is true for expansive soils. According to the observed water‐retention behaviour of unsaturated expansive soils, the air‐entry value increases with density, and the relationship between the degree of saturation and void ratio is linear at constant suction. According to the above observation, an elastoplastic constitutive model is developed for predicting the hydraulic and mechanical behaviour of unsaturated expansive soils, based on the existing hydro‐mechanical model for non‐expansive unsaturated soil. The model takes into consideration the effect of degree of saturation on the mechanical behaviour and that of void ratio on the water‐retention behaviour. The concept of equivalent void ratio curve is introduced to distinguish the plastic potential curve from the yield curve. The model predictions are compared with the test results of an unsaturated expansive soil, including swelling tests under constant net stress, isotropic compression tests and triaxial shear tests under constant suction. The comparison indicates that the model offers great potential for quantitatively predicting the hydraulic and mechanical behaviour of unsaturated expansive soils. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
5.
Zhong-Sen Li Assia Benchouk Feth-Ellah Mounir Derfouf Nabil Abou-Bekr Said Taibi Hanène Souli Jean-Marie Fleureau 《Acta Geotechnica》2018,13(1):51-71
The main objective of this paper is to examine how different engineering soils react to environmental variations and to provide correlations to characterize their behaviour under null external mechanical stress. Two French and two Algerian soils with liquid limits ranging from 36 to 112 were prepared under both slurry and Proctor compaction conditions, and then subjected to drying–wetting paths with suction controlled from several kPa to several hundreds of MPa. Experimental results are presented in five diagrams to show globally and simultaneously the shrinkage–swelling, saturation–desaturation and water retention characteristics. A reasonable consistency was observed between the oedometric and drying curves of slurry, confirming the equivalence between hydraulic loading (suction) and mechanical loading (consolidation stress) on the volume change behaviour of different soils. As an intrinsic parameter of soil nature, liquid limit was found to have a significant influence on the shrinkage limit, air-entry suction and compressibility of both slurry and compacted samples. For that reason, correlations between these characteristics and liquid limit were set up, providing a good basis for a first estimation of the drying–wetting curves. At the micro-scale, new experimental results were obtained: either on drying or wetting path, the micro-pores were almost unaffected, whereas, when matrix suction increased from 0.1 to 8 MPa, the volume of macro-pores decreased to quasi-closure. At last, the analogy between the compaction and drying–wetting curves, and the comparison of different methods to determine the water retention curve were addressed. Such analogies and comparisons contribute to a better understanding of the mechanisms of mechanical stress and suction. 相似文献
6.
Expansive clay buffers in radioactive waste disposal designs experience cyclic drying and wetting paths during different stages of their design life. Clayey soils subjected to these processes develop swelling and shrinkage deformations, which give rise to the accumulation of compression or expansion strains during suction cycles. Experimental studies were undertaken using oedometer tests on an artificially prepared bentonite-sand mixture (80% bentonite by dry mass). In order to study these processes and to identify the most important features controlling soil behaviour, several wetting-drying cycles with suctions ranging between 130 and 4 MPa were applied using vapour equilibrium technique and covering a wide range of overconsolidation ratios (OCR). The tested samples showed cumulative shrinkage strains along the successive cycles, which became more significant at increasing vertical net stresses (low OCR values). However, no accumulation of expansion strains was detected at elevated OCR values. Test results were interpreted and predicted within the context of an elastoplastic model proposed by Alonso et al., 1999, [Alonso, E.E., Vaunat, J., Gens, A., (1999). Modelling the mechanical behaviour of expansive clays. Engineering Geology, 54, 173-183.] which takes into account the accumulation of strains. A good correspondence between measured soil response and model predictions was observed. The paper also presents the methodology to derive the constitutive parameters. 相似文献
7.
8.
为探讨水化状态对饱和压实膨胀土应力-应变-强度特征的影响,以压实度为95%的荆门弱膨胀土为研究对象,开展了2种典型水化状态下的固结与三轴试验,其中第1种水化状态采用常规饱和方法,第2种水化状态为试样自由膨胀至稳定状态。结果表明：（1）受变形约束条件与渗径的影响,不同水化状态下体膨胀率有较大差别;（2）第2种水化状态下的饱和压实膨胀土具有更大的硬化指数λ与膨胀指数κ、较小的弹性剪切模量,其有效内摩擦角为第1种水化状态下的77.2%,体现出膨胀土饱和强度的变动性;（3）2种水化状态下的固结曲线均呈现出明显的屈服现象,其屈服应力分别为123.2 kPa与94.5 kPa;（4）第1种水化状态下,低围压下试样应变软化与剪胀,高围压下应变强化与剪缩;第2种水化状态下试验围压范围内均发生剪缩和轻微的应变软化;（5）2种水化状态下试样在固结与剪切过程中均表现出超固结性,这种超固结性并非完全由先期固结压力所致,而是试样受荷过程中膨胀受到约束造成的;（6）不同水化饱和状态下初始孔隙比不同,膨胀势也不同,膨胀势与外部约束条件、排水条件、应力状态相互作用,造成其应力-应变-强度特征的差异性。 相似文献
9.
Compacted clay soils are used as barriers in geoenvironmental engineering applications and are likely to be exposed to salinization and desalinization cycles during life of the facility. Changes in pore fluid composition from salinization and desalinization cycles induce osmotic suction gradients between soil–water and reservoir (example, landfill/brine pond) solution. Dissipation of osmotic suction gradients may induce osmotic swelling and consolidation strains. This paper examines the osmotic swelling and consolidation behaviour of compacted clays exposed to salinization and desalinization cycles at consolidation pressure of 200 kPa in oedometer assemblies. During salinization cycle, sodium ions of reservoir fluid replaced the divalent exchangeable cations. The osmotic swelling strain developed during first desalinization cycle was 29-fold higher than matric suction induced swelling strain of the compacted specimen. Further, the diffusion controlled osmotic swelling strain was 100-fold slower than matric suction-driven swelling process. After establishment of ion-exchange equilibrium, saturated saline specimens develop reversible osmotic swelling strains on exposure to desalinization cycles. Likewise the saturated desalinated specimen develops reversible osmotic consolidation strains on exposure to cycles of salinization. Variations in compaction dry density has a bearing on the osmotic swelling and consolidation strains, while, compaction water content had no bearing on the osmotic volumetric strains. 相似文献
10.
Kai Li Hossein Nowamooz Cyrille Chazallon Bernard Migault 《Geomechanics and Geoengineering》2018,13(2):77-87
Unsaturated expansive soils subjected to wetting and drying cycles result in huge differential settlements of structures built on these materials. The existed models for these materials present large number of parameters that lead to time-consuming procedure to characterise their mechanical behaviour during wetting–drying cycles. In this context, Zarka shakedown theory previously applied to the mechanical loading of granular materials has been used for expansive soils subjected to suction cycles. The parameters of this shakedown-based model were calibrated for two different expansive soils. The comparisons between the experimental results and the calculations for the different tests, demonstrate the capacity of Zarka shakedown theory to simulate the mechanical behaviour of unsaturated expansive soils. 相似文献
11.
This paper presents a three‐dimensional elastoplastic constitutive model for predicting the hydraulic and mechanical behaviour of unsaturated soils. It is based on experimental results obtained from a series of controlled‐suction triaxial tests on unsaturated compacted clay with different initial densities. Hydraulic hysteresis in the water‐retention behaviour is modelled as an elastoplastic process, with the elastic part modelled by a series of scanning curves and the elastoplastic part modelled by the main drying and wetting curves. The effect of void ratio on the water‐retention behaviour is studied using data obtained from controlled‐suction wetting–drying cyclic tests on unsaturated compacted clay with different initial densities. The effect of the degree of saturation on the stress–strain‐strength behaviour and the effect of void ratio on the water‐retention behaviour are considered in the model, as is the effect of suction on the hydraulic and mechanical behaviour. The initial density dependency of the compacted soil behaviour is modelled by experimental relationships between the initial density and the corresponding yield stress and, thereby, between the initial density and the normal compression line. The model is generalized to three‐dimensional stress states by assuming that the shapes of the failure and yield surfaces in the deviatoric stress plane are given by the Matsuoka–Nakai criterion. Model predictions of the stress–strain and water‐retention behaviour are compared with those obtained from triaxial tests with different initial densities under isotropic compression, triaxial compression and triaxial extension, with or without variation in suction. The comparisons indicate that the model accurately predicts the hydraulic and mechanical behaviour of unsaturated compacted soils with different initial densities using the same material constant. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
12.
An advanced understanding of the strain accumulation phenomenon in granular soils subjected to low amplitude cyclic loading with relatively high frequency is needed to enhance the ability to predict the settlement of granular soils induced by vibrations. In the current study, the discrete element method is used to study this phenomenon. A loose and a medium dense sample composed of a relatively large number of spheres are considered. A series of stress controlled cyclic triaxial tests with different excitation amplitudes and frequencies is performed on these samples at different static stress states. The response of these samples at the macroscopic and microscopic scales is analyzed. The sample density, the cyclic stress amplitude and the static stress state importantly affect strain accumulation. However, the cyclic excitation frequency has a small effect on strain accumulation. At the microscopic scale, frictional sliding occurring at a few contacts continuously dissipates energy and the fraction of these contacts varies periodically during cyclic loading. The coordination number of these samples increases slightly as strain accumulates. However, the anisotropy remains almost constant during low amplitude cyclic excitation. A qualitatively good agreement between numerical and experimental results is found. 相似文献
13.
Effect of suction on the mechanical behaviour of iron ore rock 总被引：1，自引：0，他引：1
The effect of suction on the behaviour of iron ore has been studied from both physical and mechanical points of view. The porosity and the suction phenomena have been analysed using different experimental techniques. Uniaxial compressive tests on partially saturated samples have shown that the suction is responsible for strength and cohesion improvement. Considering the theory of partially saturated porous soils of Coussy and Dangla (Mécanique des sols non saturés (2002 edn). Hermès Science: 2002; 390), we have proposed a constitutive law for partially saturated iron ore. The real increase in the apparent cohesion due to the capillary attraction forces is overestimated if the yield function is written in terms of effective stresses. The effect of the capillary cohesion has been modelled with a function in the expression of the apparent cohesion of the yield function. The effect of suction on the mechanical behaviour has been represented in the effective stresses space and in the total stresses space like the Alonso model (Géotechnique 1990; 40 :405–430). Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
14.
Snehasis Tripathy Kanakapura S. Subba Rao 《Geotechnical and Geological Engineering》2009,27(1):89-103
Laboratory cyclic swell–shrink tests were carried out on compacted expansive soil specimens to study in detail the effect
of changes in shrinkage pattern on the swell–shrink behaviour of compacted expansive soils. Compacted soil specimens were
allowed to swell and either shrank fully or partially shrank to several predetermined heights in each cycle. The tests were
carried out at a surcharge pressure of 50 kPa. The test results revealed that shrinkage of compacted saturated soil specimens
to predetermined height in each shrinkage cycle provides similar conditions as that of the controlled suction tests with an
increasing number of swell–shrink cycles. The water content of soil specimens and hence soil suction was found to remain nearly
constant for each pattern of shrinkage. For soil specimens equilibrated to a given swell–shrink pattern, suction at the end
of shrinkage cycles was changed from a higher suction to a lower suction, and also from a lower to a higher suction. The experimental
results showed that there may be an immediate equilibrium state attained by the soil in terms of swell–shrink potential if
suction at the shrinkage cycles was less than the past suction; otherwise, the equilibrium state was accompanied by fatigue
of swelling. The volumetric deformation of the soil specimen subjected greater shrinkage was found to be much larger than
the corresponding vertical deformation. The compressibility index of microstructure, κm, was determined for several shrinkage patterns. It is shown that κm is heavily influenced by suction at the end of shrinkage cycles. 相似文献
15.
Alberto Burghignoli Salvatore Miliziano Fabio M. Soccodato 《Geotechnical and Geological Engineering》2010,28(6):815-833
This paper describes the main findings of a laboratory study on the mechanical behaviour of cemented geologically normally
consolidated lacustrine clayey soils from two sites, Bacinetto (BA) and Avezzano (AZ), in the Fucino basin (Italy). One-dimensional
and triaxial compression tests were carried out in order to investigate the effects of the presence and of the progressive
degradation of the interparticle cementation bonds. The two tested soils showed quite different physical and mechanical properties,
the more apparent ones being plasticity and yield stress values. The experimental results allowed the gross yield curves and the critical state conditions to be identified for both soils (BA clay and AZ silt). A number of typical
features generally exhibited by cemented soils were clearly apparent: yield stresses greater than the in situ stress states,
both soils being geologically normally consolidated; high values of compressibility index after yielding, which gradually
reduce with increasingly applied stresses; strength reductions associated with a globally contractive behaviour. A convenient
normalisation of the experimental results, in which the critical state conditions are assumed as a reference state, allowed
the effects of cementation bonds and of their progressive degradation to be highlighted. In particular, BA samples were found
to be characterised by different structures related to different degrees of cementation. Furthermore, despite the larger values of the yielding stresses exhibited by AZ silt, stronger effects of
cementation are apparent in BA soil. Experimental results seem to indicate that at high values of the applied stress and strain
paths, when bonds are largely damaged, the structures of the natural and parent reconstituted BA soil continue to be different. 相似文献
16.
Cheng Wei Chen Ren-peng Hong Peng-yun Cui Yu-jun Pereira Jean-Michel 《Acta Geotechnica》2020,15(10):2741-2755
In thermal-related engineering such as thermal energy structures and nuclear waste disposal, it is essential to well understand volume change and excess pore water pressure buildup of soils under thermal cycles. However, most existing thermo-mechanical models can merely simulate one heating–cooling cycle and fail in capturing accumulation phenomenon due to multiple thermal cycles. In this study, a two-surface elasto-plastic model considering thermal cyclic behavior is proposed. This model is based on the bounding surface plasticity and progressive plasticity by introducing two yield surfaces and two loading yield limits. A dependency law is proposed by linking two loading yield limits with a thermal accumulation parameter nc, allowing the thermal cyclic behavior to be taken into account. Parameter nc controls the evolution rate of the inner loading yield limit approaching the loading yield limit following a thermal loading path. By extending the thermo-hydro-mechanical equations into the elastic–plastic state, the excess pore water pressure buildup of soil due to thermal cycles is also accounted. Then, thermal cycle tests on four fine-grained soils (natural Boom clay, Geneva clay, Bonny silt, and reconstituted Pontida clay) under different OCRs and stresses are simulated and compared. The results show that the proposed model can well describe both strain accumulation phenomenon and excess pore water pressure buildup of fine-grained soils under the effect of thermal cycles.
相似文献17.
多次干湿循环后土-水特征曲线的模拟 总被引：3，自引：0，他引：3
目前对于土体的干湿循环过程中变形、强度变化规律研究较多,而对经过多次干湿循环后土-水特征曲线的试验研究较少。由于吸力平衡需要时间太长,对干湿循环过程中土-水特征曲线的研究也多限于单次的干湿循环试验。但考虑到实际岩土工程中气候条件的多变性和自然环境的复杂性,一般土体均要经历多次干湿循环,因此,对多次干湿循环后的土-水特性曲线研究显得非常重要。结合已有的试验数据总结脱湿曲线与吸湿曲线随着干湿循环次数的变化规律,通过引入一个与干湿循环次数有关的函数,提出能预测多次干湿循环后土-水特征曲线的方法。本方法仅需土-水特征曲线的首次干湿循环脱湿与吸湿曲线和塑性指数,就可以预测多次干湿循环后的土-水特征曲线。 相似文献
18.
It is well known that the specimen preparation method and the resulting sand fabric significantly affect sand behaviour and sand liquefaction resistance. In this study, a simple experimental method namely tensiometric method is presented for evaluation of the effect of the samples reconstituting methods on microstructure and the pore-access size distribution of sands. Specimens were prepared using dry funnel pluviation (DFP) and wet deposition (WD) at two densities Dr = 40% (loose state) and Dr = 80% (dense state). The water-retention curve of a sand specimen is evaluated using a technique similar to the hanging column method by application of a step-by-step variation of suction and measure of the corresponding changes in water content. The pore-access size distribution is then evaluated from the water-retention curve. In this experimental study the effects of the mode of deposition and the uniformity coefficient on the pore-access size distribution are investigated. It was found that the specimen generated by the WD method contained a higher percentage of pore size, contrary to the specimen prepared by the DFP which contained a limited percentage of pore size, causing a great influence on the mechanical behaviour of the specimens. 相似文献
19.
20.
Expansive soils exhibit large volume changes when their water content changes. Alternate heave and settlement due to seasonal
climatic variations result in distress and damage in civil infrastructure systems. This research focuses on the understanding
of swelling and shrinkage phenomenon in the surface layer of expansive soils. Undisturbed field samples were used to capture
the effect of in situ conditions (geologically induced fissuring and environmentally caused saturation) on volume change properties of Regina clay.
Based on laboratory investigations, the swelling potential and swelling pressure of the native clay at S = 82% were found to be 1.5% and 3.5 kPa, respectively. The swell-shrink path during progressive soil drying followed an S-shaped curve comprising of an initial low structural shrinkage followed by a sharp decline during normal shrinkage and then
by a low decrease during residual shrinkage. The soil microstructure correlated well with the observed volume change behaviour
as well as with the consistency limits. The presence of fissures in field samples at various degrees of saturation confirmed
that the investigated deposit is at an equilibrium condition with respect to the swell-shrink phenomenon. The swelling properties
at any initial saturation state were estimated using the free swelling test and the swell-shrink test data in conjunction.
The swelling potential increased 12 times (from 2 to 24%) and the swelling pressure increased by two orders of magnitude (from
27 to 2500 kPa) with a change in the degree of saturation from 80% (at the plastic limit) to 60% (at the shrinkage limit). 相似文献