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Bentonite pellets are recognized as good buffer/backfill materials for sealing technological voids in high-level radioactive waste (HLW) repository. Compared to that of a traditional compacted bentonite block, one of the most important particularities of this material is the initially discrete pellets and the inevitable heterogeneous porosity formed, leading to a distinctive water retention behaviour. In this paper, water retention and mercury intrusion porosimetry (MIP) tests were conducted on pellet mixture (constant volume), single pellet (free swelling) and compacted block (constant volume) of GMZ bentonite, water retention properties and pore structure evolutions of the specimens were comparatively investigated. Results show that the water retention properties of the three specimens are almost similar to each other in the high suction range (> 10 MPa), while the water retention capacity of pellet mixture is lower than those of the compacted block and single pellet in the low suction range (< 10 MPa). Based on the capillary water retention theory (the Young–Laplace equation), a new concept ‘saturated void ratio’ that was positively related to water content and dependent on pore size distribution of the specimen was defined. Then, according to the product of saturated void ratio and water density in saturated void, differences of water retention properties for the three specimens at low suctions were explained. Meanwhile, MIP tests indicate that as suction decreases, the micro- and macrovoid ratios of pellet mixture and compacted block decrease as the mesovoid ratio increases, while all the void ratios of single pellets increase. This could be explained that upon wetting, water is successively adsorbed into the inter-layer, inter-particle and inter-pellet voids, leading to the subdivision of particles and swelling of aggregates and pellets. Under constant volume condition, aggregates and pellets tend to swell and fill into the inter-aggregates or inter-pellets voids. While under free swelling condition, the particles and aggregates in a single pellet tend to swell outward rather than squeezing into the inter-aggregate voids, leading to the expansion of the pores and even formation of cracks. Results including the effects of initial conditions (initial dry density and fabric) and constraint conditions (constant volume or free swelling) on the water retention capacity and pore structure evolution reached in this work are of great importance in designing of engineering barrier systems for the HLW repository.

The minimum and maximum void ratios (emin and emax, respectively) of soils are intrinsic soil properties related to their particle size distribution (PSD) and particle shape. Different attempts have been made to predict these reference void ratios for cohesionless soils through the involved particle morphology. However, these predictive models do not handle flaky and elongated particles. Besides, these kinds of models just consider the particle shape throughout a two-dimensional analysis. In this current study, experimental work has been carried out on particles with five different geological and morphological properties and nine different gradations. The particle shape effect involves glass beads, rounded, angular, flaky, and elongated particles to expand both the range of particle sphericity and roundness. A wide range of particle sizes, including uniformly distributed, widely distributed, and upward concave graded soils were chosen. Particle sphericity and roundness were measured by micro CT images and image processing. Furthermore, a comprehensive database was gathered based on past experimental results from the literature. This database was used to derive the predictive equations for determining emin,emax, and the void ratio range (emax-emin), considering sphericity, roundness, and uniformity coefficient. The developed new formulas show good agreement with the current and past experimental results.

Compressibility of granular materials depends on its initial density and is significantly affected by particle breakage, especially at high stress levels. In this study, a simple compression model for granular soils is proposed by incorporating a new equivalent concept. The initial density effect on the curvature of compression line is captured by a novel equivalent void ratio, which features a state variable for describing the evolution of grain crushing and corresponding yielding behavior. An Equivalent Compression Curve (ECC) is further established by directly implementing the equivalent void ratio into a reference compression curve. Validation has been done by comparing the simulated curves with the test data from available literature. It reveals a good linear relationship between the state variable and breakage index. Moreover, the ECC can well normalize the compression behavior of granular soils with a wide range of initial densities and stress levels. The simplified version of ECC includes only three parameters which are consistent with the reference model. The proposed model provides a basis for establishing versatile and rigorous hardening law that can be readily used in conjunction with the general elasto-plasticity theory.

Soil-water characteristic curve (SWCC) and shrinkage curve are essential information required for analyzing the behaviors and properties of unsaturated soils. This study proposes a new method for simultaneous measurement of SWCC and shrinkage curve of a “single” soil specimen. The validation of the method was carried out using kaolin specimens prepared at low levels of consolidation pressures. The changes in void ratio, gravimetric water content, and soil suction of the specimen under continuous or discrete drying procedures were measured using the vernier caliper, the balance, and the osmotic tensiometer, respectively. The results show that the shrinkage curves of all specimens are almost the same regardless of their different initial gravimetric water contents and initial void ratios. However, the obtained gravimetric water content SWCC (SWCC- ) in the lower suction range was related to the initial gravimetric water content of the specimen. In contrast, the degree of saturation SWCC (SWCC- ) of all specimens were almost the same and the air-entry values of different specimens were shown to be quite close. The results indicate that continuous drying procedures would not cause obvious differences in the measured SWCC as well as shrinkage curve compared with the discrete drying procedures. The relationship between the void ratio and soil suction of the specimens shows that the void ratio has a rapid decrease in the lower suction range and reaches the minimum value when the soil suction is about 300 kPa. The proposed method would shorten the time for obtaining the properties of unsaturated soils and would benefit the related analyses.

This study investigates the strength and permeability properties of pervious concrete-containing coal bottom ash (CBA) aggregates. Two pervious concrete mixtures were fabricated with different aggregate size distributions. One mixture contained CBA aggregates with a single-type distribution and the other mixture contained CBA aggregates with a hybrid-type distribution. The test parameters of the CBA pervious concrete included the water/cement (W/C) ratio and compaction level to investigate their effects on the properties. W/C ratios of 0.25, 0.30, and 0.35 were considered for the mixture, and compaction levels of 0.5, 1.5, and 3.0 MPa were applied to fabricate the pervious specimen. The increase in the W/C ratio reduced the strength by approximately 20% to 30% of the CBA pervious concrete. The increase in the compaction level reduced the permeability by approximately four to five times but significantly increased the strength of the CBA pervious concrete. The test results indicate that the use of single-type CBA or hybrid CBA aggregates with different size distributions affected the properties of the pervious concrete. The strength of specimens, including hybrid CBA aggregates, was 30% to 45% greater than that of the specimens containing single-type CBA aggregates. Meanwhile, the use of hybrid CBA aggregates reduced the permeability of the CBA pervious concrete by approximately 20% to 35%. Finally, relationships between the strength properties, permeability characteristics and total void ratios of the CBA pervious concrete specimens are suggested based on the test results.

The tensile strength of unsaturated soils is a fundamental property in various geotechnical designs. Reliable estimation of the tensile strength of unsaturated soils, in particular fine-grained soils, is required in both theoretical research and engineering practice. Although several tensile strength models have been proposed in the literature, an overestimation may occur over a wide suction range, when applying them in the modelling of tensile strength of fine-grained soils. In this paper, the tensile strength of an unsaturated lean clay has been measured over a wide range of void ratio and water content by employing the Brazilian tensile strength test. A critical degree of saturation can be observed for specimens with different void ratios, at which the soil tensile strength reaches the peak. In addition, a predictive tensile strength model considering the effect of initial void ratio has been subsequently proposed for both coarse-grained and fine-grained unsaturated soils based on the interaction mechanisms between the adsorptive and capillary soil water. Finally, the proposed model has been demonstrated to be capable of modelling the tensile strength characteristic curve of various soil types ranging from clean sands to silty and clayey soils.

Because surface texture is nearly the sole indicator of pavement functional properties and highly correlated with critical operational characteristics of roadways like traffic noise and safety, the change in pavement surface texture because of traffic loadings and environment has to be evaluated routinely. There are numerous direct or indirect evaluation techniques in the market. However, most of these methods have some limitations like requiring lane closure or being expensive. In this study, a 2D image processing method was established to estimate the surface mean texture depth (MTD) of chip sealed pavements. We produced chip sealed pavement samples in the laboratory with different aggregate type, shape, and size ranging between 2 and 19 mm to cover wide range of live conditions. Two well-known conventional test methods, Sand Patch (SP) and Hydrotimer (HT), were used to determine MTDs of chip seal samples. Subsequently numerous photos were taken on surface of the samples with a camera for 2-D image processing that was done based on surface void ratio (SVR) approach. With the image processing, SVR of all samples were determined. At the point of whether there is a relationship or not, correlation analysis was made between the MTDs obtained with SP and HT and the data obtained by SVR approach with the artificial neural network method. The results show that the proposed SVR approach construed on 2D image processing method can be a reliable alternative to evaluate the surface texture of pavements.

The published literature has revealed conflicting results regarding the effect of low plastic fines fraction (Ip ≤ 5.0%) on the mechanical behavior of sandy soils. For this reason, the use of different sample initial structures as (initial relative density approach, global void ratio index approach, etc.) could explain these different mechanical responses of granular materials. Thus, it is necessary to evaluate the quantitative aspect of the low plastic fines effects on the undrained monotonic response of sand-silt mixtures using the global void ratio approach. To achieve this goal, an experimental testing program through controlled monotonic triaxial tests was carried out on reconstituted saturated Chlef sand containing from 0 to 50% silt with an interval of 10% at three global void ratios (e = 0.64, 0.66 and 0.68) and subjected to constant confining pressure (σ'3 = 100 kPa). The different samples were reconstituted using two different preparation techniques: DFP and MT. The obtained results show that the low plastic fines content appears as a very relevant parameter in the characterization of the mechanical response of sand-silt mixture samples reconstituted at constant global void ratios, where the steady state shear strength and instability shear strength decreased with the increase in low plastic fines content up to the limiting fines contents (Fc = 40% and Fc = 10%) considering both studied initial structures (Dry funnel pluviation and Moist tamping), respectively. Beyond these thresholds fines contents, a reverse trend was observed for all parameters under study. Moreover, the test results indicate that the brittleness index, flow potential (Vf), friction index, equivalent void ratio (e*) and equivalent relative density (Dr*) could be considered as reliable parameters in the prediction of the mechanical behavior of the silty sand soils under study.

Maximum and minimum void ratios (emax and emin) of granular soils are commonly used as indicators of many engineering properties. However, few methods, apart from laboratory tests, are available to provide a rapid estimation of both emax and emin. In this study, we present a theoretical model to map the densest and the loosest packing configurations of granular soils onto the void space. A corresponding numerical procedure that can predict both emax and emin of granular soils with arbitrary grain size distributions is proposed. The capacity of the proposed method is evaluated by predicting the maximum and minimum void ratios of medium to fine mixed graded sands with different contents of fines. The influence of the grain size distribution, characterized quantitatively by uniformity parameter and the fractal dimension, on emax and emin is discussed using the proposed method. Moreover, application of this method in understanding the controlling mechanism for the void ratio change during grain crushing is presented.

The permeability coefficient of saturated clay plays a crucial role in practical engineering applications. In this paper, based on the fractal geometry theory and combined with the relationship between the flowing water volume and non-flowing water volume in saturated clay, the theoretical formulas for the effective pore specific surface area and the effective void ratio of saturated clay are established. Based on the capillary seepage channel model of saturated clay, combined with Poiseuille’s law and the concept of equivalent hydraulic radius, the theoretical formula for the permeability coefficient of saturated clay is established. Finally, the physical parameters of the remolded clay samples are measured and substituted into the modified Kozeny–Carman equation and the equivalent capillary seepage equation of saturated clay before and after the modification. Through the comparative analysis of the above theoretical values and the measured values of indoor seepage tests, it is found that the saturated clay seepage equation established in this paper is more suitable for dense saturated clay with relatively small pores. It has the characteristics of higher calculation accuracy and easier acquisition of basic parameters. The research results provide important references for practical engineering and the study of saturated clay seepage theory, and have broad prospects for practical engineering applications.