Types Of Geomaterials Research Articles

Site observations of weathered granitic soils subjected to cementation and partial drainage using SCPTU

Because of the cementation inherited from the parent rock, weathered granitic soil is usually susceptible to disturbance, which poses considerable challenges for laboratory characterization. The cone penetration test with pore pressure measurements has long been known for its reliability in site investigations and stratigraphic profiling. However, although extensive piezocone test results and experience are available for sedimentary soil, similar advances are yet to be made for weathered granitic soil. Moreover, the experience from sedimentary soil may not be directly applicable to weathered profiles because of the essentially different natures of the two types of geomaterials. This study performs seismic piezocone tests in a weathered granitic profile comprising residual granitic soil, completely weathered granite, and highly weathered granite. Pore pressure is measured at both the cone mid-face and the shoulder, and the effects of penetrometer size and penetration rate are considered. A series of updated soil behavior type charts is proposed to interpret the test results, thereby allowing the effect of weathering to be evaluated. This paper offers an important extension to the sparse data on the in situ responses of weathered materials.

Unified description of different soils based on the superloading and subloading concepts

Geotechnical engineering often involves different types of geomaterials, such as sandy soil and clayey soil. Existing studies have confirmed that these soils have some common features, i.e. their mechanical behaviors depend not only on the inherent characteristics but also on their initial states. To describe the main mechanical behaviors of different soils within a simple and reasonable constitutive framework is of great significance for the numerical analysis on geotechnical engineering. This paper first introduces a model based on the concepts of superloading and subloading, which considers the “state dependence” (effects of overconsolidation and structure) of soil and only adds two material parameters compared with the Cam-Clay model. Secondly, conventional triaxial tests are systematically carried out on four types of soils (i.e. sand, silty clay, clay, and intermediate soil) with different initial void ratios, and the mechanical similarities and differences of these soils are discussed uniformly. After that, six material parameters of these soils are uniformly determined based on the concepts of superloading and subloading, and then used in constitutive calculations to verify the feasibility. The calculated results show a good agreement with test data, indicating that the model based on the concepts of superloading and subloading has great potential for describing the general mechanical behaviors of different soils within a unified framework. This work is expected to be applied to constitutive selection and parameter determination in the geotechnical numerical analysis of complex soil profiles.

Porosity-based representative elementary volume for geomaterials and its fractal theory-based approximate criterion

<p indent=0mm>The representative volume element (RVE) and/or the representative elementary volume (REV) and their existence and determination are a basic scientific issue in the research field of size effect. The similarities and differences between the RVE and REV are analyzed from the fields of composite micromechanics and geotechnical engineering. A three-level classification of the REV research on geomaterials is then proposed based on these fields, especially REV research in geotechnical engineering. The pore size distribution and the corresponding fractal dimension are introduced and selected as the constrained parameters for describing the complex pore structure of geomaterials. Accordingly, an approximate criterion is first presented via theoretical deduction and comparison with previous research results, through which the size of a P-REV of mesoscale porous geomaterials can be determined using their pore size distributions (i.e., the edge length of the cubic P-REV is approximately equal to five times of the maximum pore diameter). Finally, some statistical methods, such as low-order probability functions, are utilized to validate the performance of the proposed criterion. The verification results using two types of geomaterials, namely, sandstone and foamed concrete, reveal that both are in a reasonable agreement, indicating that the P-REV determined according to this approximate criterion can provide representative statistical results and find a balance between characterization accuracy and calculation efficiency.

Effects of Biostabilization on Engineering Properties of Geomaterials

Biostabilization is a newly proposed method to improve the strength and durability of geomaterials, and it can serve as an alternative to chemical and mechanical stabilization. The objectives of this study are to perform biostabilization treatments for selected roadway construction geomaterials and to evaluate the biostabilization effects on engineering properties of the geomaterials. Three types of geomaterials were selected, and two of them were compacted soil from unpaved road surface. Bacillus pasteurii, the biostabilization bacterium, was used to induce mineral precipitates within the geomaterial pore spaces, where the biostabilization effects were performed. Two types of liquid incubation media, containing NH4Cl or (NH4)2 SO4, were applied for bacteria culturing. Unconfined compression, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) measurements were conducted to evaluate the biostabilization results. From unconfined compression, sample strength performance was improved by the biostabilization treatments; the benefits of biostabilization were pronounced by a relatively long culturing time and an oven-dry procedure; the liquid culturing medium containing NH4Cl performed better than the medium containing (NH4)2 SO4. After biostabilization, SEM photographs provided direct evidence for the precipitates induced by bacteria within the geomaterial pore space. The precipitates either connected the adjoined particles or partially covered the particle surface, which increased the surface roughness. EDS and XRD results indicated that calcite, dolomite, and albite were the major precipitates produced during biostabilization treatments. In conclusion, biostabilization ameliorated the microstructures of the geomaterials and improved their strength. Future research topics should include the applications of biostabilization for in situ road construction.

Experimental study of thermomechanical effects in water-saturated limestones during their deformation

Stability control of elements of stone constructions of various structures is a prerequisite for their safe operation. The use of modern methods of non-destructive diagnostics of the stress-strain state of such constructions is an effective, and in many cases the only way to control it. Studies of thermal radiation accompanying the processes of solid bodies deformation allowed to justify and develop a method that allows to obtain non-contact information about changes in the stress-strain state in various types of geomaterials, including limestones. However, studies of the water saturation influence of rocks on the thermal radiation parameters recorded in this way are currently superficial. Taking into account the water saturation degree of rocks is necessary when monitoring the mechanical condition of stone structures that are in direct contact with water. The main purpose of this work is to study the dependences of changes in the intensity of thermal radiation from the surface of limestone samples with different humidity under conditions of uniaxial compression. The obtained results showed the expected significant decrease in the mechanical properties (uniaxial compressive strength and elastic modulus) of water-saturated samples in comparison with dry ones. At the same time, a significant increase in the intensity of thermal radiation of limestone samples subjected to compression with an increase in their water saturation was recorded, which makes it necessary to take into account the revealed regularity when identifying changes in the stress state of stone structures established according to non-contact IR diagnostics in real conditions.

Effect of landfill leachate on the hydromechanical behavior of bentonite-geomaterials mixture

The paper presents an experimental study on the compressibility, conductivity hydraulic (ksat) shear strength, unconfined compressive strength, and unconfined tensile strength and chemical characteristics of compacted bentonite- geomaterials mixtures for use as landfill bottom liners. To complete each experiment, MSW landfill leachate was used to determine the stress of strength under the effect of pollution on the mineralogy of the optimal mixture (the least permeable mixture). All three materials used in this study, including bentonite and two types of geomaterials (tuff and calcareous sand (crushed sand)) were obtained in the Laghouat, South Algeria, region. First, a study of the geotechnical properties of all selected materials and mixtures (under the effect of leachate) was carried out. A mineralogical survey was also conducted on these three materials to better understand the experimental results obtained. Measurements of the pH and EC of leachate-contaminated mixtures indicated a decrease in pH values and an increase in EC values. Interaction results of these mixtures with the MSW landfill leachate indicated that it reduces the compressibility behaviour, decrease the saturated hydraulic conductivity and increase the compressive strength and tensile strength. As for shear strength, an increase was observed in shear strength with an increase in calcareous sand content. The shear strength of the previously contaminated optimal mixture is shown an increase in the cohesion and a decrease in the friction angle. This observation was demonstrated by the Fang and Hirst (1973) method (Modified Mohr-Coulomb failure criterion). Finally, a consolidated drained study of the optimal mixture was carried out using a triaxial test. Results showed that the optimal mixture behavior is normally consolidated, and the internal friction angle value has attained 35°. It can be summarized that the 10% bentonite – 20% calcareous sand – 70% tuff mixture (named: B10CS20T70) meets the design requirements for landfill bottom liners.

Effect of water content on hydraulic properties of bentonite–geomaterials mixture

This article examines the effect of water content on hydraulic properties of bentonite–geomaterials mixture. The relationship between the initial water content, matric suction and hydraulic conductivity (saturated and unsaturated) and the soil–water characteristic curve were controlled established during a laboratory test. Three materials were used during this study: bentonite and two types of geomaterials . First, the mixture of 10% bentonite–20% calcareous sand–70% tuff was selected on the basis of the minimum saturated hydraulic conductivity (k sat) . The results showed that the effect of the initial variation in water content from 12.35% to 16.35% does not make a difference in the k sat values; the values are between 10−8 and 10−11 m/s. Then, the effect of the initial water content on the soil–water characteristic curve was studied using suction control methods. The soil–water characteristic curves showed that the air entry value (AEV) increases with decreasing initial water content The unsaturated hydraulic conductivity (k w) study with different initial water content was measured with an original vapour equilibrium technique (VET). The results showed that the k w varied between 3 × 10−17 and 4 × 10−15 m/s in all cases of initial water . In addition, the Van Genuchten hydraulic conductivity model is compared to the experimental results. . Finally, the effect of the initial water content on the saturated and unsaturated hydraulic conductivity of this mixture is not apparent for the much lower (Sr > 80%, k = k sat) and very high suction values, respectively.

Developing a unified nonlinear strength (UNS) criterion for geomaterials

There is a need for a unified strength criterion, which is a variable suitable for describing the different strength properties of different types of geomaterials. In this study, a unified nonlinear strength (UNS) criterion is proposed based on the Lade-Duncan criterion for the sake of versatility to capture the complex strength behaviors of geomaterials under three-dimensional (3D) stress paths. The strength curves in this theory are a series of continuous and smooth conical loci that covers wide ranges of the meridian and octahedral planes to describe the nonlinear strength behaviors of soils. The strength curves are located between von Mises and Lade-Duncan strength curves in the deviatoric plane in the principal stress space. Verifications between the proposed criterion and experimental data from triaxial tests found in the literature show that this new criterion is able to reasonably reflect the three-dimensional (3D) strength properties and strength nonlinearity of a variety of geomaterials.

Localised failure mechanism as the basis for constitutive modelling of geomaterials

Localised failure of geomaterials in the form of cracks or shear bands always requires special attention in constitutive modelling of solids and structures. This is because the validity of classical constitutive models based on continuum mechanics is questionable once localised inelastic deformation has occurred. In such cases, due to the fact that the macro inelastic responses are mainly governed by the deformation and microstructural changes inside the localisation zone, internal variables, representing these microstructural changes, should be defined inside this zone. In this paper, the localised failure mechanism is identified and employed as an intrinsic characteristic upon which a constitutive model is based on at the first place, instead of being dealt with after developing the model using various regularisation techniques. As a result, inelastic responses of the model are correctly associated with the localisation bands, and not smeared out over the whole volume element as in classical continuum constitutive models. It is shown that this inbuilt localisation mechanism in a constitutive model can naturally capture important features of the material and possess intrinsic regularisation effects while minimising the use of additional phenomenological treatments, and also possessing intrinsic regularisation effects. The development of the proposed model is based on an additional kinematic enhancement to account for high gradient of deformation across the localisation band. This enrichment allows the introduction of an additional constitutive relationship for the localisation band, which is represented in the form of a cohesive-frictional model describing traction-displacement jump relationship across two sides of the localisation band. The model, formulated within a thermodynamically consistent approach, possesses constitutive responses of the bulk material and two localisation bands connected through internal equilibrium conditions. Its key characteristics are demonstrated and validated against experimental data from different types of geomaterials under different loading conditions at both material and structural levels.

Detection of thermal response of geomaterials: a critical appraisal

Heat sensors and thermal probes have been employed to determine the thermal properties (viz. thermal flux, thermal conductivity, thermal resistivity and volumetric heat capacity/specific heat) of geomaterials (viz. soils and rocks) in both laboratory and in situ conditions. However, the applicability of these methods for different types of geomaterials and the influence of the inherent properties of the sensors on the obtained results are still a matter of concern. Hence, it becomes essential to review conventional and state-of-the-art methods that can be used to determine these properties of geomaterials along with their advantages and limitations. In addition to this study, a review of different sensors and probes and the influence of various specific characteristics of geomaterials (viz. morphology, mineralogy, pore structure, microbial aspect, organic content and material heterogeneity) on their thermal response is discussed. It is highlighted that the mineralogy and pore structure of geomaterials have a significant influence on their thermal response.

Development of a New Nonlinear Unified Strength Theory for Geomaterials Based on the Characteristic Stress Concept

AbstractThere is a need for a unified strength criterion, which is a variable suitable for describing the different strength properties of different types of geomaterials. There have been efforts to develop unified strength criteria; however, they are usually based on a mechanistic approach with adjustable failure planes and complex expressions. This study presents an alternative mechanistic approach to developing a simple unified strength theory by an adjustable characteristic stress. The characteristic stress is unique for a certain geomaterial. The frictional rule is used to explain the failure mechanism of geomaterials, and by defining the shear strength as a proportion function of normal stress acting on the failure plane, a new nonlinear unified strength theory is developed, which is similar to the Drucker-Prager strength theory. The strength curves of this theory are a series of continuous and smooth conical loci, which are located between Drucker-Prager and Matsuoka-Nakai strength curves in the de...

GIS-based variability of building materials towards the Île-de-France cuesta (Paris Basin, France): inventory, distribution, uses and relationship with the environment

Abstract The Pays rémois in the eastern Paris Basin is an administrative area of 1394 km 2 ; in the surroundings of Reims (France). Two main geological substrata are separated by the Île-de-France cuesta: the Tertiary substratum in the western part is composed of various types of geomaterials (clay, sandstone, limestone, burrstone), whereas the substratum in the eastern part is composed only of Cretaceous Chalk. A field survey in each commune of the Pays rémois identified 26 building materials documented in a Geographic Information System database (GIS-database) that includes information about them (lithology, petrographical and petrophysical data, weathering) and the corresponding buildings (e.g. town, georeferenced data, building type, position on the façade). The spatial analysis of the building materials’ distribution (Standard Deviational Ellipse) with GIS identifies their uses and the criteria established for the selection of the materials: availability, efficiency, workability and durability. Some lithologies were preferred for particular buildings or selected for their efficiency in specific positions. The study also defines the relation between the stones’ origin (local and non-local stones) and their application. This database is useful to establish stone replacement strategies in the Pays rémois .

Development of radial strains in hollow cylinders of rock subjected to radial compression

Localised failure of geomaterials in the form of cracks or shear bands always requires special attention in constitutive modelling of solids and structures. This is because the validity of classical constitutive models based on continuum mechanics is questionable once localised inelastic deformation has occurred. In such cases, due to the fact that the macro inelastic responses are mainly governed by the deformation and microstructural changes inside the localisation zone, internal variables, representing these microstructural changes, should be defined inside this zone. In this paper, the localised failure mechanism is identified and employed as an intrinsic characteristic upon which a constitutive model is based on at the first place, instead of being dealt with after developing the model using various regularisation techniques. As a result, inelastic responses of the model are correctly associated with the localisation bands, and not smeared out over the whole volume element as in classical continuum constitutive models. It is shown that this inbuilt localisation mechanism in a constitutive model can naturally capture important features of the material and possess intrinsic regularisation effects while minimising the use of additional phenomenological treatments, and also possessing intrinsic regularisation effects. The development of the proposed model is based on an additional kinematic enhancement to account for high gradient of deformation across the localisation band. This enrichment allows the introduction of an additional constitutive relationship for the localisation band, which is represented in the form of a cohesive-frictional model describing traction-displacement jump relationship across two sides of the localisation band. The model, formulated within a thermodynamically consistent approach, possesses constitutive responses of the bulk material and two localisation bands connected through internal equilibrium conditions. Its key characteristics are demonstrated and validated against experimental data from different types of geomaterials under different loading conditions at both material and structural levels.

Small- and High-Strain Measurements of In Situ Soil Properties Using the Seismic Cone Penetrometer

Seismic cone penetration tests provide an economical and expedient means of assessing small-strain properties (low-amplitude shear modulus, GMAX) and large-strain behavior (shear strength, τmax) of soil deposits from a single sounding. That measurements are taken at complete opposite ends of the strain spectrum permits development of the entire stress-strain-strength representation of soil layers with depth. A modified hyperbola is shown to be appropriate in a modulus degradation scheme for application to static monotonic loading of soils. Also, a global correlation of mass density (ρ) with shear wave velocity (Vs) for all types of geomaterials is presented, which facilitates the calculation of GMAX = ρVs2.