Triaxial Apparatus Research Articles

Experimental Study of Influence of Freeze–Thaw Cycles on the Dynamic Properties of Weathered Sand-Amended Expansive Soils

Expanded soils are widely distributed in Xinjiang, China, so roadbeds will inevitably pass through the areas of the expansive soil during road construction. While Xinjiang belongs to the seasonal frozen region, subjected to a freeze–thaw cycle, mud pumping is likely to occur in the subgrade under dynamical load. To study the dynamic properties of expansive soil for a range of freezing–thawing cycles and weathered sand contents, a series of dynamic triaxial tests were performed using a medium-scale true triaxial apparatus equipped with the cyclic loading device. And the maximum dynamic elastic modulus (Edmax) and ultimate dynamic stress amplitude (σdmax) were quantitatively analyzed by the modified Hardin–Drnevich three-parameter model, on which the expression of the damage degree under the joint action of both was established. The results indicate that the dynamic performance of expansive soil is greatly affected by freezing–thawing. Under the same weathered sand content, the maximum dynamic elastic modulus and the maximum dynamic stress amplitude of soil are inversely related to the number of freezing–thawing cycles. And, those two parameters tend to be stable after the sixth freeze–thaw cycle. Under the same number of freeze–thaw cycles, the maximum dynamic elastic modulus and the maximum dynamic stress amplitude firstly decrease and then increase with the increase in the weathered sand content. The critical dosage of weathered sand is 10%, and the strength of the improved soil reached the minimum value under this context. The damage degree model that integrates the effects of freeze–thaw cycles and the weathered sand can better predict the damage degree of soil.

Cyclic stress–strain characteristics of red clay treated with permeable water-soluble polyurethane

Red clay, a globally distributed type of chemical weathering soil, is commonly utilized as a road base in road infrastructure. However, due to its susceptibility to water and vibrations, it is prone to settlement and formation of potholes during operation, consequently leading to damage in the pavement structure. This paper employs a dynamic triaxial apparatus to simulate realistic traffic loads and investigates the dynamic properties of red clays treated with permeable water-soluble polyurethane (PSP). Additionally, a series of microscopic tests are conducted to elucidate the microstructural mechanisms of using PSP for improving red clay, as well as the microscopic deformation mechanisms of the PSP-treated red clay (PSP clay) under cyclic loading. The results provide detailed insights into the influence of soil moisture content and PSP content on key parameters, including the resilient modulus, damping ratio, permanent deformation, and strength of PSP clay after repeated loading. Moreover, the overall performance of PSP clay is evaluated under varying loading amplitudes and confining pressures. These results are complemented and interpreted in conjunction with the findings from the microscopic tests. The findings reveal that the inclusion of PSP improves the strength of the soil skeleton by enveloping and interlocking with the clay particles. Furthermore, it is observed that the engineering properties of high-moisture-content red clay soils can be significantly improved with low levels of PSP. Under specific conditions, repeated loading further compact the PSP clays, thereby enhancing their mechanical properties. The experimental findings presented in this study are of utmost importance for the improvement and application of red clays through the utilization of rapid solutions, such as PSP.

Experimental Investigation on Shear Behavior of Partially Saturated Silty Soil under Constant Water Content and Constant Void Ratio Conditions

Abstract Matric suction is a crucial parameter that affects how unsaturated soils behave in terms of shear strength. Understanding it is essential for solving geotechnical problems like the stability of unsaturated soil slopes, foundations, embankments, and retaining walls. To investigate the shear behavior in unsaturated soil, a double cell triaxial test apparatus is used in the current research to carry out a series of triaxial compression tests under constant water content and constant void ratio conditions. Samples of silty soil, named DL-clay, were prepared with three different degrees of compaction: 80 %, 83 %, and 86 %, and water contents of 20 % (optimum water content) and 25 %. The soil samples were consolidated isotropically under net confining pressures of 300 kPa and 500 kPa before being sheared with constant volume. In another series of tests, water was infiltrated into the sample at 0 kPa deviatoric stress before the start of shearing with constant volume. Some specimens were also sheared with constant confining pressure for comparison purposes. From the test results, it is ascertained that maintaining a constant volume, i.e., constant void ratio during shearing, gives contour-like trajectories that can aid in defining the state boundary surface of unsaturated soil. It was also observed that within the axial strain range of 0–2 %, there was unusual behavior of a temporary sudden dip in the axial stress, which was more perceivable for samples having a high value of initial matric suction.

A 3D image-based method to measure soil stiffness in triaxial tests

This paper describes a new simple and inexpensive method for accurately measuring the three-dimensional deformation of soil specimens during triaxial tests. The method incorporates a cost-effective image capture system that can be applied to any triaxial apparatus as well as an automated post-image analysis approach for processing the images acquired during triaxial tests. Image capture is performed using multiple low-cost Raspberry Pi cameras and accessories placed outside the triaxial chamber. The system employs particle image velocimetry, camera calibration and stereophotogrammetry to determine the spatial variation in axial and radial sample strains as samples are loaded. It is demonstrated that axial and radial displacements can be measured with an accuracy of 1–2 μm, respectively, and it is verified by comparison with data from triaxial tests on sand samples that the full nonlinear stiffness–strain degradation of soil samples from fully elastic conditions can be determined without the need for any additional sensors.

Undrained cyclic loading behavior of stiff Eocene-to-Jurassic plastic, high-OCR clays

Assessing foundation response to cyclic loading is vital when designing transport infrastructure, such as road pavements and rail tracks, as well as offshore, port, and tall tower structures. While detailed guidance is available on characterizing many soil types’ cyclic behavior, relatively few studies have been reported on stiff, geologically aged, plastic clays. This paper addresses this gap in knowledge by reporting cyclic loading experiments on three natural stiff UK clays that were deposited and buried between the Jurassic Age and Eocene Epoch before geological unloading to their currently heavily over-consolidated states. High-quality samples taken at relatively shallow depths were reconsolidated to nominally in situ K0 stresses in triaxial and hollow cylinder apparatus before imposing cyclic loading. The completely stable, metastable, or unstable outcomes invoked by different levels of undrained cyclic loading are interpreted within a kinematic yielding framework that is compatible with monotonic control experiments’ outcomes. The cyclic limits marking the onset of significant changes in permanent strain accumulation, pore pressure development, and stress–strain hysteresis demonstrate that the weathered Gault clay offers the lowest cyclic resistance. The experiments show that energy considerations provide a promising way of evaluating undrained pore pressure generation and stiffness degradation. They also provide a basis for developing cyclic constitutive models and analysis procedures for cyclic foundation design in stiff, high-OCR, plastic clay strata.

Experimental and Numerical Simulation Study on Mechanical Properties of Shallow Slope Root-soil Composite in Qinghai Area

Natural disasters such as landslides often occur in Qinghai under the double deterioration of earthquake and freeze-thaw cycles, ecological slope protection is an effective way to prevent and control this type of disaster. In this paper, the mechanical properties of root-soil composites are investigated experimentally using triaxial apparatus and dynamic single shear (DSS) apparatus, and based on the discrete element method, a contact model more suitable for reinforced soil materials is proposed to study the dynamic properties of root-soil composites under cyclic shear from a fine viewpoint. Based on the results of the study, the following conclusions were drawn: 1) The presence of roots under the action of freeze-thaw cycles increases the strength properties of the soil. At the same number of freeze-thaw cycles, the shear strength and cyclic resistance of the root-soil composites are higher than those of the loess. And the strength of the root-soil composites decreases with the increase of the number of freeze-thaw cycles and then flattens out; 2) The proposed contact model can better simulate the softening effect of reinforced loess material under cyclic shear, which is more suitable for simulating the mechanical behavior of loess and laying the foundation for further study of reinforced loess material from a fine viewpoint.; 3) The presence of the root system will improve the stability of the slope soil, and the root system will have a positive effect on the shear strength of the soil when the moisture content is within a certain range. The presence of the root system also increases the cyclic resistance of the soil. Under the same cyclic shear stress conditions, the number of damage cycles of the root-soil composites is higher than that of the loess, the cumulative shear strain is less than that of the loess. However, the root system no longer exerts positive effects under saturated conditions. The research results can provide some guidance for the construction of ecological slopes in loess areas, and provide a new way to investigate the dynamic properties of root-soil composites from a fine viewpoint.

Grain size distribution does not affect the residual shear strength of granular materials: An experimental proof.

Granular materials are used in several fields and in a wide variety of processes. An important feature of these materials is the diversity of grain sizes, commonly referred to as polydispersity. When granular materials are sheared, they exhibit a predominant small elastic range. Then, the material yields, with or without a peak shear strength depending on the initial density. Finally, the material reaches a stationary state, in which it deforms at a constant shear stress, which can be linked to the residual friction angle ϕ_{r}. However, the role of polydispersity on the shear strength of granular materials is still a matter of debate. In particular, a series of investigations have proved, using numerical simulations, that ϕ_{r} is independent of polydispersity. This counterintuitive observation remains elusive to experimentalists, and especially for some technical communities that use ϕ_{r} as a design parameter (e.g., the soil mechanics community). In this Letter, we studied experimentally the effects of polydispersity on ϕ_{r}. In order to do so, we built samples of ceramic beads and then sheared these samples in a triaxial apparatus. We varied polydispersity, building monodisperse, bidisperse, and polydisperse granular samples; this allowed us to study the effects of grain size, size span, and grain size distribution on ϕ_{r}. We find that ϕ_{r} is indeed independent of polydispersity, confirming the previous findings achieved through numerical simulations. Our work fairly closes the gap of knowledge between experiments and simulations.

Analysis of Electrical Resistivity Characteristics and Damage Evolution of Soil-Rock Mixture under Triaxial Shear.

Construction of engineering structures in geomaterials with soil-rock mixture (S-RM) is often a challenging task for engineers. When analyzing the stability of the engineering structures, the mechanical properties of S-RM often receive the most attention. To study the mechanical damage evolution characteristics of S-RM under triaxial loading conditions, a modified triaxial apparatus was used to conduct shear test on S-RM, and the change of electrical resistivity was measured simultaneously. The stress-strain-electrical resistivity curve and stress-strain characteristics under different confining pressures were obtained and analyzed. Based on the electrical resistivity, a mechanical damage model was established and verified to analyze the damage evolution regularities of S-RM during shearing. The results show that the electrical resistivity of S-RM decreases with increasing axial strain and that the differences in decrease rates correspond to the different deformation stages of the samples. With the increase in loading confining pressure, the stress-strain curve characteristics change from a slight strain softening to a strong strain hardening. Additionally, an increase in rock content and confining pressure can enhance the bearing capacity of S-RM. Moreover, the derived damage evolution model based on electrical resistivity can accurately characterize the mechanical behavior of S-RM under triaxial shear. Based on the damage variable D, it is found that the damage evolution process of S-RM can be divided into a non-damage stage, a rapid damage stage and a stable damage stage. Furthermore, the structure enhancement factor, which is a model modification parameter for the effect of rock content difference, can accurately predict the stress-strain curves of S-RMs with different rock contents. This study sets the stage for an electrical-resistivity-based monitoring method for studying the evolution of internal damage in S-RM.

Evaluation of shear strength parameters of sustainable utilization of scrap tires derived geo-materials for civil engineering applications

The devastation caused by the illegal dumping and burning of tires has been staggering. In civil engineering, using tires engineering properties has become a major concern. For this investigation, the research used locally sourced tire chips and sand. Using tire chips sand as an alternative backfill material requires less pressure and has more improved properties than traditional backfill. Four specimens were utilized in this experiment: pure sand and sand mixtures containing 20%, 30%, and 40% tire chips, respectively. Both the Direct Shear and Triaxial Apparatus, two of the most important geotechnical tools, were used to compare and evaluate the shear properties of soil and sand tire chips. 50, 100, and 150 kPa Confining pressure and normal stress have been utilized to maintain a consistent stress level. Direct shear apparatus had a circular shape with an area of 16.62 cm2 and Triaxial shear apparatus had a height of 7.2 cm and a diameter of 3.2 cm. The stress-strain behavior of both apparatuses under ordinary loading and deviatoric stress was reported. The angles of internal friction (Φ′) and cohesion (c′) were measured for both equipment and specimens with and without tire chips, and the failure planes for direct shear and triaxial tests were reported. In both the direct and triaxial shear tests, 30% of the tire chips sand exhibit the best results, respectively. The addition of tire chips may significantly improve the toughness of the soil.

Cross-anisotropic stiffness characteristics of a compacted lateritic clay from very small to large strains

Lateritic clay is widely distributed in tropical and subtropic regions, with distinct engineering properties from other clays. Its stiffness properties, which are often anisotropic and crucial for analysing the serviceability limit state of earthen structures, have not been well understood. This study investigated the cross-anisotropic stiffness of compacted lateritic clay through comprehensive isotropic compression and consolidated drained and undrained shear tests. Both vertically and horizontally cut specimens were tested using triaxial apparatus equipped with bender elements and local strain measurements. The results show that compared with other clays, the lateritic clay shows a weaker dependency of shear modulus to confining pressure, a higher shear modulus at the same confining pressure, and a higher degradation rate of stiffness with strain. The lateritic clay behaves like granular material due to its large-size aggregated microstructure and 42% sand content. The widely used correlations between stiffness parameters and plasticity index seem unsuitable for it. Furthermore, the elastic shear modulus in the vertical direction is slightly higher than that in the horizontal direction, and the anisotropy evolves during shearing. A complete set of cross-anisotropic stiffness parameters for both effective and total stress analysis were determined. They are useful for developing constitutive models and analysing earth structures' serviceability involving lateritic soils.

The oedometric EOS of equal strength and different mix compositions concrete specimens

The uniaxial compressive strength of concrete is commonly used to characterize concrete properties. The three-dimensional behavior of concrete structures is modelled by the hydrostatic and deviatoric relationships. These relationships are assigned to a given concrete according to its uniaxial compressive strength. Based on high velocity penetration test results at targets with identical concrete strength, that were prepared from different mix designs, the authors conjectured that the slab behavior is not governed by the uniaxial compressive strength but by the concrete composition.This paper presents an experimental investigation of concrete specimens of equal uniaxial compressive strength, that are made from different mix compositions, aiming at examining the equation of state (EOS) and its relationship to the uniaxial compressive strength and to several mix components, in attempt to validate the above conjecture.A set of specimens was prepared characterized by equal uniaxial compressive strength (fc = 56 MPa) measured on 100 mm sided cubes. Several specimen groups were tested, each of them made from a different composition. The mix variables were the weight of water (and the corresponding weight of cement), the aggregates weight and the maximum aggregate size. The specimens were tested in a special triaxial apparatus, to high load-levels (up to 5000 kN), at a quasi-static rate of ∼ 5 kN/sec. Test results show a wide scatter of the EOS curves, depending on the different mix parameters. These results refute the commonly assumed correlation between the uniaxial compression strength and the EOS and validates the conjecture that the EOS depends on the specific concrete mix composition.

A rigid true triaxial apparatus for analyses of deformation and failure features of deep weak rock under excavation stress paths

The squeezing scenario in deep weak rock tunnels can hinder underground construction. However, due to the limitations of test technologies at hand, the real excavation stress path cannot be mimicked in the laboratory. Thus, the large deformation mechanism of deep weak rocks still remains unclear. For this, a true triaxial apparatus (TTA) to investigate the mechanical responses of deep weak rock under excavation stress paths in field and reveal the squeezing mechanism of deep tunnels is assembled and developed at Northeastern University, China. The apparatus can perform instantaneous unloading in σ3 direction based on electromagnetism technology. In addition, uniform loading and deformation measurements can be carried out based on the proposed linked interlocking clamp and antifriction device, even if the sample has a strong dilatation deformation performance. Next, a bore trepanning is designed to capture noiseless acoustic emission (AE) signals for deep weak rock at a low threshold. Finally, two tests were are conducted using this instrument to preliminarily understand the failure and deformation features of deep weak rock based on fractured marble. The results show that the complete stress–strain curves of fractured marble have the characteristics of low strengths and large deformations, and the larger deformation and the more serious failure occur when the fractured marble enters the post-peak state after excavation. The results show that the developed apparatus is likely to be applicable for deep weak rock engineering. © 2022 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The Generalized Mohr-Coulomb Failure Criterion

With the construction of supertall buildings such as high earth dams, the linear envelope of the Mohr-Coulomb (M-C) failure criterion fitted to lower confined pressure would significantly underestimate the loading capacity of foundations, causing a huge increase in the amount of earthwork. Given that the M-C criterion has dominated in the stability analysis of geotechnical structures, it is proposed in this study that the M-C criterion remain invariant in form but the cohesion c and the frictional factor f be related to the coefficient of intermediate principal stress b, called the Generalized Mohr-Coulomb (GMC) criterion. In other words, c and f are both functions of b, written as c(b) and f(b). In the simplest way, the GMC criterion for soils, a true three-dimensional failure criterion, can be established by using a piece of conventional triaxial apparatus. The GMC has a non-smooth strength surface like its conventional version. However, we prove from true triaxial tests and the characteristic theory of stress tensors that the failure surfaces in the stress space should be non-smooth per se for b = 0 or 1. Comparisons with other prominent failure criteria indicate that the GMC fits the test data best.

A new apparatus for investigating gas transport property in geomaterials with ultralow permeability

The gas flow in geological materials with ultra-low permeability can vary dramatically, i. e., from almost no measurable quantity of gas before breakthrough to a massive gas flux at breakthrough. It is a great challenge to realize the whole process measurement of gas transport in saturated geomaterials with ultra-low permeability. In this work, a newly designed temperature-controlled triaxial apparatus was developed. In which, a water-to-gas-exchanger was designed for precise injection of gas at a constant pressure or constant injection rate, due to that water is less compressible and much more difficult to leak through the seal of a regulator. Meanwhile, eddy current sensors and displacement transducer with high resolutions were utilized to accurately measure the specimen deformation at different locations in a non-contact way to explore the mechanism of gas entry and breakthrough. In addition, a gas flow detection device that contains four gas flowmeters with different measurement ranges and can automatically switch between these flowmeters was developed to monitor the gas outflow of the whole process. To validate the performance of the developed apparatus, systematic gas injection tests on Gaomiaozi (GMZ) bentonite were conducted, during which the helium gas was injected in a constant rate. Real-time data on inlet gas pressure, gas outflow rate, stress state (both isotropic and axial stresses) and volume deformation (both axially and radially) were monitored. Results show that the developed apparatus could successfully capture the gas entry and the subsequent breakthrough points of the compacted bentonite with ultralow permeability. For compacted bentonite with high saturation, capillary flow, dilatant flow and interfacial leakage could co-exist during the gas transport process and the dominated mechanism was closely related to the gas injection pressure.

Development and Application of Triaxial Apparatus for Soil with High Bearing Pressure by Computed Tomography

Abstract In order to study the macro and micro-mechanical properties of a soil sample under high pressure, we improved the traditional triaxial apparatus with high-bearing pressure for soil by combining it with the computed tomography (CT) system. The new apparatus overcomes the existing limits of low bearing pressure in the traditional triaxial apparatus and the small sample size in the micro-CT triaxial apparatus, keeping all the functions of the traditional triaxial apparatus. It can attain dynamic, quantitative, and noninvasive scanning of the internal structure of soil samples during the testing process. Moreover, the pressure chamber is made of high-strength and lightweight aircraft aluminum materials, allowing high X-ray penetration while ensuring that the scanned image is clear under high pressure. Consolidated undrained and drained triaxial tests are conducted by the apparatus on coral sand. The results show that the stress–strain curve is reasonable, the CT image is clear, and the particle breakage in the real-time loading process can be analyzed through image processing in single grading. As a result, the apparatus can be used to study the micro-mechanism of the internal structure of soil aiming at explaining its macro-mechanical behavior.

A new high-pressure high-temperature deformation apparatus to study the brittle to ductile transition in rocks

Understanding the micro-mechanisms underlying the localized–ductile transition (LDT) as well as the brittle–plastic transition (BPT) has become crucial for our wider understanding of crustal processes and seismicity. Given how difficult in situ observations of these transitions are to perform, laboratory experiments might be our only way to investigate the processes active under these conditions (high T and high P). Here, we present Triaxial AppaRatus for GEoThermal energy, a new gas-based triaxial apparatus located at EPFL in Switzerland that was specifically designed to operate under conditions where both the LDT and BPT can occur in geomaterials. We show that the machine is capable of deforming rock samples at confining pressures of up to 400 MPa, temperatures of up to 800 °C, and pore pressures (liquid or gas) of up to 300 MPa while keeping the temperature gradient along samples of 40 mm in length and 20 mm in diameter minimal (less than 30 at 700 °C). Most importantly, the maximum load is 1000 kN (stresses as high as 2.2 GPa on 24 mm samples and 3 GPa on 20 mm samples), allowing for the deformation of very competent rock samples. Moreover, during deformation, the pair of syringe pore pressure pumps allow for continuous permeability or dilatancy recording. We benchmarked our machine against existing data in the literature and show that it accurately and precisely records stress, strain, permeability, pressure, and temperature.

Thermal Effects on Shear Characteristics of Unbound Granular Materials under Drained Conditions

In this study, the thermally induced changes in the shear characteristics of unbound granular materials (UGMs) were investigated. A series of drained shear tests were conducted using a large-scale triaxial apparatus under controlled temperatures. The thermal dependence of the peak strength, critical strength, internal friction angle, and dilatancy of UGMs were investigated under different temperatures, initial mean effective stresses, and relative compaction. Dense UGMs tended to expand during heating and slightly contract during cooling. In the heating and cooling process, a nonlinear relationship was observed between thermal deformation and temperature. Thermal deformation was attributed to the deformation, movement, and rotation of soil particles and closely related to the initial mean effective stress and relative compaction. A thermal softening effect was observed during the shear test, and the peak strength decreased with increasing temperature. However, negligible thermal effects were observed relative to residual strength. The effect of temperature on the shear characteristics of UGMs was primarily related to the thermal expansion of pores in the soil skeleton. The relationship between peak strength and initial thermal volumetric strain was found to be exponential. Considering the thermal effect, a normalized semi-empirical model of the parabolic Hvorslev envelope for dense UGMs was proposed to supply guidelines for road base design.

Permanent Deformation and Its Unified Model of Coal Gangue Subgrade Filler under Traffic Cyclic Loading

Using coal gangue as subgrade filler can not only solve the environmental problems of coal mine waste accumulation but also decrease the subgrade cost, which has important theoretical and practical significance. A series of cyclic triaxial tests was carried out using the large-scale dynamic and static triaxial apparatus (LSDSTA) to investigate the permanent deformation (ε) of coal gangue subgrade filler (CGSF) under cyclic loading. Experimental grading was designed by using the fractal model grading equation (FMGE), and then well-grading limits of CGSF were captured. The relationship curve between ε and the numbers of cyclic loading (N) can be divided into three stages, i.e., the rapid growth phase, the deceleration growth phase, and the approaching stability phase. N = 1000 can be used as the criterion for reaching the stable stage of CGSF. The effect of confining pressure (σ3′) on ε is related to the level of σ3′. The effect of σ3′ on ε is significant when σ3′ is smaller, whereas the influence of σ3′ on ε is smaller when σ3′ is larger. Furthermore, the influence of grading (Df) on ε of coal gangue samples is significant. With the increase of Df, ε first increases and then decreases, reflecting that there is an obvious optimal grading for coal gangue samples under cyclic loading. Moreover, the effect of compaction degree (Dc) on ε of CGSF depends on the level of Dc. ε is hardly affected when Dc is smaller, whereas increasing Dc has a significant effect on restraining ε when Dc is bigger. In addition, according to the analysis of the permanent deformation curve for CGSF, the unified calculation model of permanent deformation for CGSF under cyclic loading is established. Compared with the existing permanent deformation models, the proposed model in this paper can better describe the permanent deformation of CGSF under cyclic loading. Finally, the model parameters are analyzed, and the model is verified.

Effect of stress-induced anisotropy on shear modulus response of compacted coal ash under small-strain dynamic loading conditions

Un-utilized coal ash is commonly used as fill material for the construction of highway and railway embankment, which experiences different anisotropic stress conditions under different types of loading conditions. This study investigated the shear modulus of compacted coal ash under different anisotropic stress conditions simulating highway and railway embankment stress states. The small-strain shear modulus was obtained by performing the bender element tests under consolidation and shearing stages of consolidated undrained (CU) triaxial testing. The effect of different consolidation stress paths on the small-strain shear modulus of coal ash was evaluated using experimental data obtained from a bender element system affiliated with a stress-path controlled advanced triaxial setup. The small-strain shear modulus of coal ash at different ranges of mean effective stresses (at the end of consolidation) was also determined under various anisotropic stress conditions. The measured shear modulus (Gmax) of compacted coal ash under small-strain dynamic loading conditions was determined to be the function of mean effective stresses and deviatoric stress. At the later stage of shearing, the shear modulus was observed to attain a constant value subjected to large strain levels.

Biocementation as a Pro-Ecological Method of Stabilizing Construction Subsoil

The principle of sustainable development imposes an obligation on societies to manage natural resources rationally and to care for the quality of the environment, by, among other things, reducing CO2 emissions. Alternative ways of stabilising building substrates by increasing their shear strength (cu) are increasingly being sought. This paper presents how microorganisms can influence cu and thus the load-bearing capacity of building substrates. Tests were performed in a triaxial compression apparatus in three variants. The first variant of testing was carried out on cemented soil samples, which were cemented in situ. The next two series of tests were performed on reconstructed samples, i.e., natural soil and soil inoculated with a solution of Sporosarcina pasteurii bacteria. The results obtained show that carbonate cementation increases the shear strength of the soil; in addition, this biomineralization-induced cementation gives higher cu results than natural carbonate cementation.