Undrained Triaxial Tests Research Articles

Vertical Response of Stress Transmission Through Sand–Tire Mixture Under Impact

This study evaluates the vertical stress transmission through a sand–tire mixture layer under impact, focusing on this innovative blended material that can impact underground structures such as tunnels or pipelines. By conducting consolidated undrained triaxial tests, the friction angle (φ) of the sand–tire mixture was determined, ranging from 29° for pure tire to 41° for pure sand. The vertical stress factor (α), representing the ratio of response load to applied load, was found to decrease significantly with increased tire content, with a reduction of up to 50% for mixtures containing 20% tire. Additionally, the vertical stress response decreased from 35 kPa for pure sand to as low as 15 kPa for mixtures with a high tire content under a consistent applied load of 65 kPa. This study not only presents a methodological advancement in analyzing sand–tire mixtures under dynamic loads but also suggests a sustainable approach to utilizing waste tire material in civil engineering projects, thereby contributing to environmental conservation and improved material performance in geotechnical applications.

Factors influencing static and cyclic behaviour of polymer-grouted sands

ABSTRACT In this study, thorough laboratory research was conducted in order to increase knowledge of the beneficial effect of water-soluble epoxy resin on the monotonic or cyclic triaxial strength of different sands. Seven sand fractions (with different particle sizes, uniformity coefficients and mineralogical compositions) were injected with solutions of epoxy resin and water, at ratios of 3.0, 2.0 and 1.5. To evaluate the influence of chemical treatment on the static strength behaviour of grouted sands, a series of monotonic triaxial tests on dry specimens and isotropically consolidated undrained (CIU) triaxial tests, were conducted on samples cured for 90 days. CIU cyclic triaxial compression tests were also performed, to assess improvements in the cyclic resistance of treated sands. The experiments showed that this resinous grouting resulted in an appreciable increase in cohesion values, particularly for fine sands and well-graded sands, ranging from 0.15 to 0.66 MPa. Despite the fact that friction angle values were reduced, the overall shear strength increased over a wide range of stresses. Moreover, all grouted sands exhibited a substantial improvement in cyclic properties, with failure occurring at significantly elevated stress levels and after enduring a larger number of loading cycles, compared to their untreated counterparts.

Performance of geocell reinforced rubber sand mixtures under undrained triaxial test

Large quantities of scrap tires are produced by the automobile industry each year, which causes disposal challenges and impacts the environment. However, scrap tires exhibit various properties, including tensile strength, abrasion resistance, durability, thermal conductivity, elasticity, and more. Due to their versatile characteristics, these scrap tires can be utilized as construction materials for various civil engineering works to reduce their negative environmental effects and conserve natural resources. This study aims to understand the shear strength behaviours exhibited by geocell-reinforced mixtures of rubber and sand through the unconsolidated undrained triaxial test. Various parameters, including rubber sizes (425 μm to 12 mm), rubber contents (10% to 40% by volume), confining pressures (50 to 300 kPa), and geocell heights (0.2H to 0.8H, where H is the height of triaxial sample), were systematically examined to understand their impact on shear strength characteristics. The experimental findings reveal that deviatoric stress is enhanced with increasing confining pressure and rubber sizes. The maximum benefits of the rubber-sand mixture were observed at 30% rubber content. Geocell-reinforced rubber sand mixture has a higher shear strength with respect to the unreinforced mixture. Furthermore, the energy absorption capacity of the geocell-reinforced rubber sand mixtures was much better as compared to either the clean sand or rubber-sand mixture. The findings of this research demonstrate that geocellreinforced rubber sand mixtures are suitable for various geotechnical engineering works.

Laboratory assessment of the effect of rice husk, groundnut shells and RHA on the shear, permeability and consolidation of clayey sands

Utilizing waste materials to improve soil properties can result in cost savings and environmental benefits. This study aims to determine the effect of adding agricultural wastes like rice husk ash (RHA), rice husk (RH), and groundnut shells (GS) to clayey sands from Mysore district, India. The study focused on the undrained strength, permeability and volume change behaviour of soils mixed with RHA, RH and GS. The soil samples were mixed with varying amounts of RHA (5%, 10%, 15%, and 20%) and RH-GS (1%, 2%, 3%, 4%, and 5%) and cured for 1, 7, 14 and 21 days. These blended specimens were then used to determine the maximum dry density (MDD), optimum moisture content (OMC) and unconfined compressive strength (UCS). The soil mixture containing 5% RHA and 4% (RH + GS) yielded optimal results in the UCS test. Further tests, including unconsolidated undrained (UU) triaxial, permeability and consolidation tests, were conducted on the parent soil and the soil composite with 5% RHA and 4% (RH + GS). From the undrained test, the strength increased for the soil admixture, with a reduction in the cohesion and an increment in the friction angle, compared to that of the parent soil. The experimental results also showed improvement in the permeability and consolidation characteristics of the blended soil. As RH, GS, and RHA are abundant and considered to be agricultural waste products, using them represents an innovative, sustainable, and cost-effective solution with promising potential for soil improvement.

Undrained shear mechanical behaviors of dense gassy sand

Shallow gas can cause many disasters, and it is reported in many marine engineering constructions. For this, it is imperative to understand the impact of gas on the mechanical behaviors of soil. This study investigated the influence of undrained triaxial compression tests on dense gassy sand commonly encountered in coastal areas. Triaxial tests were performed on specimens with saturations of 100%, 99.8%, 95.9%, and 92.7% under confining pressures of 50 kPa and 200 kPa by a self-developed multi-purpose integrated triaxial apparatus (MITA) for gassy soil. The results are presented in terms of monotonic stress‒strain behavior, volumetric behavior, shear strength, and excess pore water pressure (EPWP). The occurrence of gas bubbles has different effects on loose and dense sands, augmenting the undrained shear strength of loose sand while concurrently diminishing that of dense sand. The deviatoric stress of dense sand increases during shear shrinkage, which is similar to the characteristics of loose sand under the influence of gas bubbles. However, following sand dilation, the effect of gas bubbles on deviatoric stress manifests in an antithetical manner. With elevated gas content, the shear strength of dense sand decreases, accompanied by a deceleration in the development of EPWP and a notable increase in volumetric changes. To this end, a microscopic explanation concerning the deformation and evolution of gas bubbles within sand during the shear process was presented to reveal the macroscopic laws governing the undrained shear attributes of dense gassy sand.

Analysis of Liquefaction in Tailings Deposits by Fem Modeling of Undrained Cyclic Triaxial

In this article, a numerical calibration procedure for undrained cyclic triaxial tests is presented to evaluate the liquefaction potential in sand and silt samples from mining tailings in northern Chile. The numerical modeling of an axisymmetric specimen involved two stages: isotropic consolidation using the Hardening Soil Small (HSS) model and a cycling phase employing the UBC3D-PLM model to simulate the onset of liquefaction using the criterion that the excess pore pressure ratio Ru should exceed 0.8. The results demonstrate that the UBC3D-PLM modeling calibrated with experimental data from cyclic triaxial tests effectively represents the excess pore pressure in both sandy and silty soils from mining tailings. The accuracy of the modeling decreases when a single set of parameters is applied to the same soil at different cyclic stress ratios (CSR), highlighting the need for specific calibrations for each loading.

A Review on Geotechnical Properties of Soil Profile

The geotechnical properties and litho-stratigraphic soil profile of soils in Ikole area of Ekiti State were investigated from the analysis of results of laboratory tests on disturbed and undisturbed soil and water samples obtained from 3 borings. The investigation revealed a subsurface stratification made up of reddish brown granitic clayey sand from existing ground level to a depth of 9m to 12.0m. This is underlain by a layer of mottled, brown, decomposed micaceous sand to a depth of 16.5m - 18m immediately after which are layers of mottled grey, decomposing quartzite sand to about 18.0m to 19.0m depth. This is further underlain by fragments of freshly weathered granitic rock to the termination depth of 19.5m. The consistency limits indicate LL of 44 – 58% and PL of 18 – 26% while the quick undrained triaxial tests indicate undrained cohesion within the range (128.4 - 157) kN/m2 and undrained angle of internal friction (15.0 - 20.0)0. Groundwater was encountered between 6.5m to 7.5m below the existing ground level during the course of soil exploration. The water in the area has pH values of 5.79 to 7.05, the chloride content values range between 12.0mg/l and 16.0mg/l while sulphate content varies from 6.12mg/l to 7.10mg/l.

Investigation of strain-softening behaviours and development of constitutive model of red clays in Guiyang, China

Red clay is widely used in engineering projects; it is characterized by high moisture content, high plasticity, large porosity, high strength and low compressibility. The engineering properties and deformation modelling of red clay in Guiyang differ significantly from those of ordinary soils. Consequently, it is essential to conduct a detailed study of the stress–strain relationship of red clay in order to obtain accurate engineering parameters. Hence, a series of unconsolidated undrained triaxial compression tests (UU) was conducted on red clay in Guiyang under different water contents and confining pressures. The test results show that the stress–strain curve of the clay undergoes three stages: elastic deformation, plastic yielding and stress reduction after failure. After reaching peak deviatoric stress, the deviatoric stress decreases gradually and stabilizes, showing noticeable strain-softening characteristics. The non-linear model from the Nanjing Hydraulic Research Institute (NHRI) was introduced for fitting and obtaining relevant parameters. Then, based on the FLAC 3D platform, numerical simulation was carried out on a standard soil sample. The research results show that the calculated curve from the non-linear model fits the experimental curve quite well, and the numerical test curve also agrees with it. This indicates that the non-linear model from NHRI can effectively reflect the strain-softening behaviour of clay and is highly applicable to Guiyang red clay.

Predicting cyclic liquefaction behavior of saturated granular materials using an updated state evolution model

Liquefaction and dynamic response of granular materials under dynamic loading has been studied intensively in field and laboratory tests. However, theoretical modeling and analytical solutions on liquefaction are still lagging and investigations are mostly restricted to laboratory observations. To investigate undrained liquefaction shear deformation and fluidity of granular material, the updated state evolution model is proposed by introducing an excess pore water pressure ratio parameter. A series of undrained cyclic triaxial tests and DEM simulations are conducted to verify the proposed model. The result indicates that the liquefaction behavior of granular materials can be captured by the updated state evolution model both at constant and varying loading frequency. Furthermore, the state parameter based on the deviatoric strain and excess pore water pressure ratio is determined to quantify assess the fluidity of granular materials. It facilitates the refinement of the discriminative criteria for cyclic liquefaction of granular materials. This parameter increases slowly at the beginning of loading, followed by a rapid and fluctuating rise, and reaches the peak before the initial liquefaction. Another significant finding is that the turning point of the state parameter range from 0.89 to 0.95 in the θ−t/t0 plane and between 0.84 and 0.94 in the θ−ru plane, as affected by the cyclic loading conditions.

Enhanced Water Resistance of TiO2-GO-SMS-Modified Soil Composite for Use as a Repair Material in Earthen Sites.

Most earthen sites are located in open environments eroded by wind and rain, resulting in spalling and cracking caused by shrinkage due to constant water absorption and loss. Together, these issues seriously affect the stability of such sites. Gypsum-lime-modified soil offers relatively strong mechanical properties but poor water resistance. If such soil becomes damp or immersed in water, its strength is significantly reduced, making it unviable for use as a material in the preparation of earthen sites. In this study, we achieved the composite addition of a certain amount of sodium methyl silicate (SMS), titanium dioxide (TiO2), and graphene oxide (GO) into gypsum-lime-modified soil and analyzed the microstructural evolution of the composite-modified soil using characterization methods such as XRD, SEM, and EDS. A comparative study was conducted on changes in the mechanical properties of the composite-modified soil and original soil before and after immersion using water erosion, unconfined compression (UCS), and unconsolidated undrained (UU) triaxial compression tests. These analyses revealed the micro-mechanisms for improving the waterproof performance of the composite-modified soil. The results showed that the addition of SMS, TiO2, and GO did not change the crystal structure or composition of the original soil. In addition, TiO2 and GO were evenly distributed between the modified soil particles, playing a positive role in filling and stabilizing the structure of the modified soil. After being immersed in water for one hour, the original soil experienced structural instability leading to collapse. While the water absorption rate of the composite-modified soil was only 0.84%, its unconfined compressive strength was 4.88 MPa (the strength retention rate before and after immersion was as high as 93.1%), and the shear strength was 614 kPa (the strength retention rate before and after immersion was as high as 96.7%).

Undrained triaxial compression tests on normally consolidated bentonite considering temperature/confining pressure dependency

In the geological repository of high-level radioactive wastes (HLRW), one of the most important issues is the stability of artificial barrier basically using bentonite. However, due to the exist gaps between bentonite block and surround rock mass, the bentonite can swell relatively freely, whose constraining condition is quite different from the normal swelling pressure test. As an extreme case, the bentonite may engage completely into the surrounding ground and become a complete normal consolidated state. Therefore, in order to investigate the thermo-mechanical behavior of saturated bentonite at normally consolidated state, a newly proposed static compaction method for preparing specimen of saturated normally consolidated bentonite was proposed first. Then, a series of undrained triaxial compression tests were conducted under different confining pressure and temperature, by which the thermo-mechanical behavior of bentonite, used as an artificial barrier of geological repository of HLRW, is investigated systematically. The tests results reveal that the specimen prepared by the proposed method is confirmed to have sufficient saturation (> 0.92), meanwhile the prepared specimen is at slightly overconsolidated state that roughly equal to a K0-line consolidation. The deformation of the bentonite in undrained triaxial compression tests changes from plastic to brittle as the temperature increases. Simulation based on a sophisticated constitutive model considering water compressibility at high confining pressure was also discussed. The results are useful for assessing the mechanical behavior of bentonite after hundreds years of geological repository of HLRW.

Seismic resilience assessment of sheet-pile wharves in liquefiable soils using different liquefaction countermeasures

Seismic resilience assessment is essential for maintaining the functionality of sheet-pile wharves in liquefiable soils, preventing significant damages and minimizing losses during earthquakes. This study delves into the seismic resilience of sheet-pile wharves, focusing specifically on the effectiveness of four different liquefaction countermeasure techniques: anchor lengths, cement deep mixing, stone columns, and soil compaction. As such, an advanced two-dimensional (2D) Finite Element (FE) computational framework is established, motivated by a typical large-scale sheet-pile wharf configuration. Within this framework, a recently developed multi-yield surfaces plasticity model is employed, with the modeling parameters calibrated through undrained stress-controlled cyclic triaxial tests and a centrifuge test. Subsequently, the impacts of these liquefaction countermeasures on the seismic resilience of the sheet-pile wharves are systematically investigated. Additionally, the effectiveness of combining longer anchor lengths with the other three mitigation techniques to enhance the seismic resilience of the sheet-pile wharves are examined. It is demonstrated that the synergistic effects of different liquefaction countermeasures can further reduce the liquefaction potential, thereby improving the seismic resilience. Overall, the FE analysis technique and the resulting insights are highly significant for the seismic resilience assessment of equivalent sheet-pile wharves in liquefiable soils, particularly when implementing such liquefaction mitigation countermeasures.

Undrained triaxial tests of underconsolidated overlying sediments of hydrate deposits in the South China Sea

The South China Sea (SCS) is an important repository for natural gas hydrates (NGHs), where some NGH deposits and their overlying sediments (OSs) are in an underconsolidated state. During the exploitation of NGHs, the stability of the OSs of the NGH deposits is one of the key factors in ensuring mining safety. Especially under different consolidation degrees, the mechanical response and stability of the OSs will vary, which directly affects the safety and efficiency of the NGH mining. This research explores the influence of different consolidation degrees on the mechanical properties of the OSs of NGH deposits in the SCS. The strength and pore pressure characteristics were analyzed through undrained triaxial shear tests. The findings indicate that an increase in consolidation degree enhances the strain softening behavior, and an increase in initial effective stress enhance the strain hardening and shear contraction behaviors of the samples. The failure strength, modulus, and maximum excess pore pressure increase with the consolidation degree and initial effective stress, and there is an approximately linear correlation between failure strength and consolidation degree. Therefore, the exploitation of NGHs in the SCS must comprehensively consider the burial depth and consolidation degree of the OSs. The findings of this study will assist in optimizing mining plans and enhancing safety during the exploitation process.

Influence of physical properties and shear rate on static liquefaction of saturated loess

Flow sliding instability of saturated loess slopes is a common geological hazard in loess areas of China. Previous studies have found that the occurrence of flow-slip loess landslides is closely related to static liquefaction and is controlled by physical characteristics and load conditions. In this work, we comprehensively study these influences of physical properties (i.e. initial pore structure, gradation, dry density) and shear rate on the static liquefaction of saturated loess through a series of consolidated undrained triaxial tests, and the effect mechanism of these related factors on the static liquefaction of saturated loess are also discussed. The results present that: (1) The peak deviator stress and the maximum pore pressure of the undisturbed loess are much greater than these of the remodeled one under each level of confining pressure (except 450 kPa). Further, the calculated liquefaction potential index (LPI) of undisturbed loess is much greater, indicating that undisturbed loess is more prone to static liquefaction due to the initial pore structure. (2) The lower the relative clay/silt content ratio of the saturated remodeled loess, the stronger the potential liquefaction ability. With the increase of the relative content of clay from 0.125 to 0.698, the stress-strain curve gradually transitions from strain softening to hardening. (3) The remodeled loess show the steady-state strength tends to continuously increase with the increase of dry density from 1.38 g/cm3 to 1.56 g/cm3, while the LPI increases first and then decreases, and the largest value appears when the dry density reaches to 1.44 g/cm3. The reason is that the value of 1.44 g/cm3 is the normal consolidated condition, which essentially reflects the potential liquefaction change during the transformation from under consolidated to over consolidated state.(4) The effect of shear rate on the stress-strain curve of remolded loess is not significant, but the peak strength and ultimate pore pressure show a trend of increasing and then decreasing with the increase of shear rate. There exists a “critical shear rate “of 0.1 mm/min reflecting the liquefaction of loess is more likely to occur when reaches to this critical value. (5) Based on the comparison of static liquefaction tests, the influencing factors of static liquefaction of saturated loess are: initial pore structure> gradation > dry density > shear rate. This study can provide a systematic evaluation for understanding the influencing factors of static liquefaction capacity of saturated loess (especially remolded one), and also has a reference for explaining the loess flow-sliding failure mechanism under disturbance conditions.

A numerical model for assessing the effect of low clay content on wave-induced seabed liquefaction

In the marine environment, the seabed contains a certain amount of clay. Experimental studies show that the liquefaction susceptibility of the sandy seabed increases as clay content (CC) rises to a certain threshold, beyond which further increases in CC reduce liquefaction susceptibility. However, numerical models that describe the effect of CC on seabed liquefaction are very limited. This study proposed a dynamic poro-elasto-plastic finite element method model for analyzing liquefaction in the sandy seabed with CC below the threshold. Based on a series of undrained triaxial compression tests on sand-clay mixtures from existing literature, a unified constitutive framework was demonstrated to be effective for describing the liquefaction behavior of sand with low CC using one set of model parameters. Existing wave flume model tests validated the effectiveness of the proposed seabed model in describing the effect of low CC on excess pore water pressure (EPWP). Numerical results confirmed that adding a small amount of clay to the seabed increased the soil contraction and thus its liquefaction susceptibility. Wave-induced liquefaction was limited to a certain depth of the seabed, and the liquefaction depth was significantly affected by the CC. Adding a low content of clay the sandy seabed significantly increased both horizontal and vertical displacements under wave action, potentially leading to the instability of the seabed. This study provides a new method for accurately assessing the wave-induced stability of marine structures built on the sandy seabed containing certain amounts of clay.

Utilising the Ipzo parameter for more reliable estimates of undrained shear strength directly from CPTU data in saturated natural clay-like soils

Ramsey and Tho illustrated the ability of the Ipzo parameter to estimate plasticity index in a wide range of saturated natural soils and highlighted the potential of the Ipzo parameter for improving the reliability of estimations of other soil properties affected by plasticity index. In this note, an improved method is proposed for estimating undrained shear strength in clay-like soils using CPTU data, where clay-like is defined as Ipzo ≥ 12%. The improved method is validated using a geographically and geologically diverse “Nkt1-database” comprising 54 anisotropically consolidated undrained triaxial compression tests, with complementary CPTU measurements from 36 geological units at 18 globally distributed marine sites.

Thermo-mechanical response of sand-silt mixtures

The thermo-mechanical response under undrained conditions is crucial in evaluating the mechanical behaviors of sand-silt mixtures. A series of consolidated undrained triaxial shear tests were conducted to investigate the mechanical response of sand-silt mixtures with different fines contents, temperatures, and initial mean effective stresses. The results showed that the volume shrinkage was observed in all specimens during heating. The amplitudes of volume shrinkage were dependent on the fines content and initial mean effective stress. Moreover, the fines content and temperature significantly influence the peak strength, flow behavior, stress ratio at the undrained instability state, and collapsibility index. Furthermore, a unified critical state line has been established in the compression plane for both clean sand and binary mixture under different temperatures and fines contents. It is reliable and suitable to use the equivalent skeleton void ratio to illustrate the thermo-mechanical response of sand-silt mixtures under undrained conditions.

Nonlinear seismic response analysis of liquefiable sites based on effective stress method

In this study, the one-dimensional nonlinear Matasovic model was extended to the two- and three- dimensional stress space by replacing the shear strain with the generalized shear strain. The extended Matasovic model was subsequently combined with Dobry’s excess pore water pressure generation model, and the reliability of the proposed loosely coupled effective stress analysis model was verified through undrained cyclic triaxial tests and a one-dimensional site response analysis. Finally, this method was applied to an engineering site in China to evaluate the nonlinear seismic response of liquefiable sites. The results show that the proposed effective stress analysis method can capture the dynamic behavior of the soil and the generation of pore water pressure during strong shaking. Moreover, there are differences between the proposed effective stress analysis method and the total stress analysis method for liquefiable sites, which indicates the need for careful selection in practical applications.

Enhancing sand liquefaction resistance through microbial-induced partial saturation: An experimental study

The liquefaction potential of saturated sand can be significantly reduced by inducing partial saturation in the soil. Conventional soil liquefaction mitigation methods, namely soil densification, drainage, cementing, and groundwater lowering, pose environmental concerns and are challenging to apply to pre-existing structures. However, the microbially induced partial saturation (MIPS) method is emerging as a novel and eco-friendly approach to mitigate liquefaction. The MIPS method involves microbial denitrification, which produces nitrogen gas and results in a desaturating effect in the saturated soil. The current study conducted a series of stress-controlled undrained cyclic triaxial tests on saturated sandy soil and microbially-desaturated sandy soil under different relative densities and loading conditions. In addition, the study systematically analyzed the effects of temperature and pH on bacterial activity and the denitrification process. Batch experiments were conducted to establish a relationship between the initial nitrate concentration in the bacterial media and the resulting desaturation.Comprehensive analyses of cyclic resistance curves were performed to gain a thorough understanding. Additionally, the study conducts detailed analyses of the accumulation of excess pore pressure and the resulting axial strains and deformation patterns in both treated and untreated sand. This study demonstrates that the MIPS treatment considerably enhances the liquefaction resistance of treated sand.

Experimental research on shear strength characteristics of cement-stabilized dredged silty clay reinforced with alginate fiber

In order to avoid uneven dispersion or agglomeration of traditional fibers after mechanical mixing, alginate fibers as natural fibers were selected in this study to reinforce the cement-stabilized dredged silty clay, forming alginate fiber-reinforced cement-stabilized dredged silty clay. The shear strength of cement-stabilized dredged silty clay reinforced with alginate fibers with the same cement content (9 % by wet weight) and cured for 7 and 28 days was investigated. Consolidated undrained (CU) triaxial compression tests were carried out on reinforced soil samples with varying fiber lengths (3 mm, 6 mm, and 9 mm) and fiber contents (0 %, 0.3 %, 0.6 %, and 0.9 % by weight of wet soil) to assess the shear strength characteristics. The results showed that, on average, the shear strength increased by 18.30 % and 18.56 % with the increasing content and length of alginate fibers, respectively. The variation in deviator stress and axial strain exhibited a shift from strain-softening to strain-hardening with increased confining pressure, alginate fiber content, and length. Hence, a double exponential curve model with different fiber content and length in three confined pressures was proposed, and the correlation coefficient of the fitting results was above 0.90. The secant modulus E50 increased and subsequently decreased with the length of fibers, with the largest secant modulus E50 observed for 6 mm fiber length. The strength parameters (cohesion c and internal friction angle φ) exhibited contrasting responses to variations in alginate fiber length and content. The cohesion of the fiber-reinforced soil specimens increased by 29.0 % and 13.1 %, respectively, for increased fiber content and length. Nevertheless, the angle of internal friction remained relatively unchanged. The findings of this study can serve as a reference guide for related engineering projects.