Dynamic Triaxial Test System Research Articles

The Liquefaction Behavior of Leachate-Contaminated of Sand under Cyclic Loads

Uncontrolled solid waste affects the stress-strain behavior of the sand as well as causes an environmental problem. In this research, the effect of leachate on the dynamic behavior of sand has been studied and the results were compared with clean sand with different saturation degrees. The modified split molds at 50 mm diameter and 100 mm height were used to prepare the leachate-contaminated sand. Both contaminated and clean sand samples were prepared by dry pluviation method. After preparation, the sand samples in the modified mold were put in the leachate wastewater to keep for different cure times. Then they were installed on the dynamic triaxial test system at 0.1 Hz and the same cyclic stress ratio. During the saturation process to prevent the structure of contaminated sands from being disturbed, samples were not passed through CO2 and distilled water. Stress-controlled cyclic tests were conducted at on both clean and contaminated sand consolidated at 100 kPa isotropically. After consolidation phase the measured B values varied between 0.45-0.93. Results show that leachate-contaminated sands are more liquefiable depending on cure time at the same saturation value and saturated clean sand samples and partially saturated leachatecontaminated sand samples show similar liquefaction behavior under the same cyclic ratio.

Experimental investigation of the dynamic mechanical properties of concrete under different strain rates and cyclic loading

To investigate the effects of strain rate and cyclic loading on the mechanical parameters of concrete compressive strength, residual strain, peak strain and elastic modulus, a series of cyclic loading tests over concrete were conducted by setting different numbers of cycles, magnitude factors, and cycle frequencies/periods based on the FST-1000 alpine geotechnical dynamic and static triaxial test system. The quantitative relationships between the mechanical parameters of concrete and the parameters of cyclic loading as well as the strain rate were also proposed. The results show that as the strain rate increases, the concrete compressive strength and elastic modulus increase linearly, while the residual strength and peak strain show a decreasing trend. Under cyclic loading, the compressive strength was quadratically related to each cyclic loading parameter, and the elastic modulus was quadratically related to the cyclic number and magnitude factor. The trend of the concrete compressive strength rate sensitivity undergoes a change at the specific thresholds of 0.145 for the magnitude factor and 1.93 Hz for the frequency. The minimum value of the peak strain rate sensitivity corresponds to the specific thresholds of 6023 for the number of cycles, 0.14 for the magnitude factor, and 1.38 Hz for the frequency thresholds, respectively. Additionally, the enhancement of the elastic modulus rate sensitivity occurs when the number of cycles exceeds 918 or when the magnitude factor surpasses 0.33. The results can provide a theoretical basis for the design of concrete structures and seismic engineering.

Dynamic behaviour of oyster shell powder-modified expansive soil under cyclic loading

This paper systematically studies the dynamic mechanical properties of oyster shell powder (OSP)-modified expansive soil under simulated train loads. A GDS dynamic triaxial test system was used in the study. The axial cumulative strain development and hysteresis curve characteristics of expansive soil with different oyster shell powder particle sizes (dosp=0–0.075 mm, 0.075–0.15 mm, 0.15–0.25 mm, 0.25–0.5 mm, 0.5–1.0 mm, 1.0–2.0 mm), dosages (Fosp=0 %, 3 %, 6 %, 9 %) and cyclic stress ratios (CSR=0.1, 0.15, 0.2, 0.25, 0.275, 0.3) were studied. The results show that when dosp< 0.5 mm, the axial cumulative strain, damping ratio and dynamic resilient modulus of the modified soil are significantly improved with increasing oyster shell powder content; when Fosp= 9 % and dosp< 0.5 mm, the dynamic performance of the modified soil is similar. When Fosp= 9% and dosp= 0.25–0.5 mm, compared with plain soil, the axial cumulative strain decreases by 37.3 %, the damping ratio decreases by 39 %, and the dynamic elastic modulus increases by 29.9 % after 200,000 cycles. When dosp> 0.5 mm, the performance of each dynamic performance index of the modified soil deteriorates compared with that of the plain soil, and the deterioration effect is more significant with increasing oyster shell powder content and particle size. When oyster shell powder-modified soil is used as a subgrade filler for a ballasted track railway with a design speed below 200 km/h, it is recommended to control the content of oyster shell powder as Fosp= 9 % and the particle size of oyster shell powder as dosp= 0.25–0.5 mm. At this time, from the perspective of controlling the postconstruction settlement of the railway subgrade, the cyclic stress ratio CSR should be controlled below 0.2.

Experimental Study on Dynamic Characteristics of Saturated Soft Clay with Sand Interlayer under Unidirectional and Bidirectional Vibration

The marine and alluvial plains along the southeastern coast of China are widely distributed in sandy formations, including smaller sand lenses and interlayers. The interlayers of sand have a significant impact on the mechanical properties of soft clay. In this paper, a large number of undrained unidirectional and bidirectional cyclic loading tests for soft clay with sand interlayers were carried out by a dynamic triaxial test system. Test results show that, under unidirectional and bidirectional cyclic vibration, the area of the hysteresis loop decreases and the slope of the connecting line at both ends of the hysteresis loop increases with the increasing of frequency. For the same vibration frequency, the area of the bidirectional vibration hysteresis loop and the slope of the connecting line at both ends are smaller than that of the unidirectional cyclic vibration. Under the same dynamic stress ratio, cumulative axial deformation caused by unidirectional and bidirectional vibration increases with the increasing frequency. Under unidirectional vibration, dynamic elastic modulus decreases at first, and then increases with the increasing frequency. For the same frequency, dynamic elastic modulus of the sample increases with the increase in cycles. Due to the effect of radial cyclic stress, the curves of dynamic elastic modulus and damping ratio with frequency under bidirectional vibration are opposite to those under unidirectional vibration.

Effect of temperature on the dynamic parameters of silty clay in a seasonally frozen region

The effect of temperature on the dynamic parameters of silty clay in a seasonally frozen region was assessed using a GDS dynamic triaxial test system. The strength parameters, dynamic elastic modulus, damping ratio, and other dynamic parameters of the soil samples were analyzed under different temperature conditions. The results demonstrated that the shear strength parameters (internal friction angle and cohesion) of the silty clay under a dynamic load increased significantly with decreasing temperature, and the internal friction angle increased sharply below 0 °C. The dynamic elastic modulus increased as the temperature decreased and changed significantly in the ice-water phase change region. The slope of the dynamic stress–strain curve of the soil sample increased significantly with decreasing temperature. As the temperature decreased, the damping ratio reduced, and the ability of the soil to absorb seismic waves declines. The research results provide new data and information to guide construction projects in seasonally frozen region.

Study on Characteristics of Acoustic Emission b Value of Coal Rock with Outburst-Proneness under Coupled Static and Dynamic Loads

In this paper, a rock dynamic and static triaxial mechanical test system is adopted to conduct triaxial compression failure acoustic emission test on coal rock with outburst-proneness. The purpose is to study the evolution law of the acoustic emission (AE) b value of coal rock under static and dynamic load of varying frequencies. The test results show that the dynamic load disturbance will accelerate the instability failure process of coal rock, that the average stress level/ultimate strain of coal rock decline/rises correspondingly with the increasing dynamic load frequency. Moreover, the overall AE b value after dynamic load disturbance is relatively low, and the higher the dynamic load frequency, the larger the decrease in the b value. In addition, as the dynamic load frequency increases, the AE ringing count and AE energy show a trend of first increasing and then decreasing, and they are negatively correlated with the evolution characteristics of the acoustic emission b value. Furthermore, the change rule of AE b value is closely related to the instability and failure process of coal rock. A second-stage of the overall b value of acoustic emission shows a “cliff jumping type” decrease dip angle or “fault cliff type” decrease dip angle indicates the imminent failure of coal rock, which can be used as an evaluation index for real-time monitoring of dynamic disasters of coal rock with outburst-proneness.

Experimental Study on Dynamic Shear Modulus and Damping Ratio of Loess Considering Disturbance

Loess is a special kind of Quaternary sediment. The sub-stable skeleton formed by fine grains and salt crystals makes the loess with great risk of catastrophic changes under dynamic action. In order to study the influence of the natural structure of loess on its dynamic properties, the test was conducted on the loess at the near-fault site of the Lishan piedmont fault to analyze the influence of soil structure disturbance on the dynamic properties of loess. The test adopts dynamic triaxial test system. The results show that the soil structure disturbance has a large effect on the dynamic shear modulus of the loess, while it has little effect on the damping ratio. Under low confining pressure, the maximum dynamic shear modulus of original loess is smaller than that of remodeled loess. Under the high confining pressure, the original loess is larger than the remodeled loess. When the confining pressure is 400 kPa, the maximum dynamic shear modulus of the original loess is 93.28 MPa, which is 53.8% larger than that of the remodeled loess. When the dynamic strain reaches 0.15%, the difference between the damping ratio of the remodeled loess and the original loess is less than 0.04, and it can concluded that the soil structure disturbance has little effect on the loess in the Lishan piedmont fault.

Post-cyclic Loading Relationship Effects to the Shear Stress and Cyclic Shear Strain of Peat Soil

Peats originate from plants and denote the various stages in the humification process. This condition renders the peat extremely soft and can be considered problematic soil. Thus, this study is conducted to examine and comprehend the particularities of peat engineering behaviour in respect to the relationship effects to the shear stress and cyclic shear strain of peat soil various characteristics to establish suitable correlation. This study carried out by using triaxial testing described by geotechnical test standards BS-1377: Part 8: 1990. Methods of Testing Soils for Civil Engineering Purposes: Shear Strength Tests (Effective Stress) that required for consolidated undrained and consist of five main stages: saturation, consolidation, static, dynamic, and post-cyclic loading using the GDS Enterprise Level Dynamic Triaxial Testing System (ELDYN). The parameters of shear strength were obtained in the peak deviator stress at a maximum of 20% of axial strain by using an undisturbed sample with an effective pressure imposed of 25, 50, and 100 kPa. In this study, all specimens are subjected to cyclic loading up to 100 cycles based on a one-way loading system with strain-controlled conditions. Based on the analysis conveyed, the post-cyclic shear stress decreased compared to its initial value of about 65.56 kPa (PNpt-100 kPa) in static and decreased to 14.9616 kPa in post-cyclic (PNpt-25 kPa-1 Hz). The principal stress ratio (σ'1/σ'3) shows the maximum values of this ratio that are located in the narrow zone of 1.61 to 1.12. Doi: 10.28991/CEJ-2022-08-12-08 Full Text: PDF

Study on Dynamic Performance of Standard Sand Based on KTL Dynamic Triaxial Apparatus

The determination of dynamic properties is of great scientific significance to the constitutive modeling and parameter determination of large deformation for sand liquefaction. For Fujian standard sand, a new high-precision KTL bidirectional dynamic triaxial test system was used to carry out liquefaction tests under equal consolidation and different equal amplitude cyclic stresses. The dynamic characteristics of Fujian standard sand, such as dynamic stress and dynamic strain test results, pore water pressure model, effective stress path, and stress-strain relationship curve, were studied. The main results are as follows: the whole vibration process of the sample could be basically divided into four stages: the greater the dynamic stress is, the easier the sample is to liquefy. With the increasing vibration times, the samples under different dynamic stress amplitudes meet the qualitative analysis of the first three stages of liquefaction; that is, the pore water pressure increases rapidly at the beginning of vibration, and the growth is stable in the middle stage. When the effective pore water pressure increases to 60 kPa, it begins to increase sharply and finally reaches the effective confining pressure, and then, the soil sample liquefies. The axial strain begins to accumulate in the compression direction and gradually increases. After liquefaction, the strain accumulates in the tensile direction in equal amplitude. During the whole vibration process, the axial strain of the sample can develop greatly in the tensile and compressive direction. Under the action of different cyclic stresses, the stress path of the soil sample tends to zero, and the rate of effective stress state varies greatly, indicating that the dynamic stress has a great influence on the dynamic liquefaction process of Fujian standard sand. In the dynamic triaxial test of standard sand, the difference in dynamic stress amplitude will lead to great changes in the stress-strain relationship curve. But it has little effect on the analysis of liquefaction dynamic characteristics of sand.

Experimental study of the dynamic characteristics of Songhua River silt with fine grains under freeze-thaw cycles using asymmetric hysteresis

The contact and bonding of soil particles are affected by the fine particle content of silty sand and the freeze-thaw cycle effects in the seasonal frozen zone, which are reflected as the dynamic characteristics of silty sand from the macroscopic point of view. The dynamic stress, dynamic shear modulus, dynamic shear modulus ratio, and damping ratio of Songhua River silt with different contents of fine soil particle (less than 0.075 mm) after repeated freeze-thaw cycles were studied respectively using a low-temperature dynamic triaxial test system and were compared with those of quartz sand. In order to approach the real test results, a piecewise equation was used to solve for the dynamic parameters. The results show that repeated freeze-thaw cycles have a great influence on reducing the dynamic stress, the dynamic shear modulus, and the dynamic shear modulus ratio, while they increase the damping ratio. For a given fine particle content and number of freeze-thaw cycles, the dynamic stress, dynamic shear modulus, and damping ratio of the Songhua River silt with fine particles are larger than those of quartz sand when the dynamic strain reaches 0.2%, and the difference gradually decreases as the number of freeze-thaw cycles increases. The dynamic shear modulus of the Songhua River silt with fine grains decreases more slowly with increasing dynamic strain than that of quartz sand. Therefore, a normalized empirical model was established to describe the relationship between the dynamic shear modulus ratio, the damping ratio, and the dynamic strain. This model is suitable for Songhua River silt with different fine particle contents and numbers of freeze-thaw cycles, and it provides good prediction results. Furthermore, the evolution of the model parameters with the experimental conditions was analyzed, and the limit value of the fine particle content was determined to be 10%. After repeated freezing and thawing, the influence of the fine particle content on parameters a and c weakened. The regression relationship between the model parameters and the test conditions can be described by a binary quadratic equation. It is suggested that the soil parameters should be used for the dynamic response analysis of Songhua River silt with fine grains after five freeze-thaw cycles.

EXPERIMENTAL STUDY ON THE DYNAMIC SHEAR MODULUS AND DAMPING RATIO OF SATURATED SAND UNDER CYCLIC LOADING

Initial shear stress is inevitable in actual engineering slopes, subgrades and foundations, and soils exhibit different dynamic characteristics under the influence of initial shear stress. Using a dynamic triaxial test system, this study explores the dynamic shear modulus and damping ratio of saturated sand from Wenchuan, investigates the effects of the initial shear stress and vibration frequencies on the dynamic shear modulus and damping ratio of saturated sand and proposes a normalised dynamic shear modulus formula that considers the initial shear stress and vibration frequency. Results show a threshold dynamic shear strain of the saturated sand. When the dynamic shear strain is below this threshold, the dynamic shear modulus significantly increases with the initial shear stress and vibration frequency. Otherwise, the influence of the initial shear stress and vibration frequency gradually decreases and eventually stabilises. The initial shear stress significantly affects the normalised dynamic shear modulus/strain curves where a larger initial shear stress corresponds to a higher curve. Meanwhile, the vibration frequency only exerts a slight influence. The curves under different frequencies are generally within the same band and fall near the Seed upper envelope. The initial shear stress also has a significant influence on the damping ratio where a larger initial shear stress corresponds to a smaller damping ratio. On the basis of the experimental results, a normalised dynamic shear modulus/shear strain formula that considers the influence of the initial shear stress and vibration frequency is established. Fitting results indicate that this formula shows good agreement with the test data.

A Novel Local Temperature-Controlled Apparatus for Thermal Effect on Dynamic Properties of Soft Clay

Abstract To investigate the thermal effect on soft clay, a novel local temperature-controlled device is presented based on an advanced dynamic triaxial testing system. Then, a calibration study is carried out to verify the robustness and effectiveness of the designed temperature-controlled apparatus. Preliminary tests show that the developed apparatus can achieve temperature uniformity with a temperature control ranging from −16°C to 80°C with an accuracy of 0.1°C and temperature uniformity. In addition, the heating and cooling speeds are in the range of 0°C∼1.117°C/min and −0.533°C∼0°C/min, respectively. Finally, the temperature-controlled apparatus is employed to investigate the axial cumulative plastic strain and cumulative pore pressure of soft clay through cyclic triaxial tests from low temperatures to high temperatures. A negative relationship is found between the axial plastic strain and temperature. Similarly, the temperature shows a significant effect on the cumulative excess pore water pressure mainly when N &amp;gt; 3,000, and a negative relationship between Rus and the temperature is also found.

Uniaxial stress relaxation behavior of marble after cyclic disturbance loads

It is known that time-dependent rheological deformation of rocks is influenced by cyclic disturbance loads. However, the stress relaxation behavior after cyclic disturbance is still poorly understood. To study such effects, a dynamic disturbance electrohydraulic servo triaxial test system was developed. A series of disturbance relaxation tests with different disturbance numbers and amplitudes were carried out on marble at several strain levels. The influence of cyclic disturbance parameters on the relaxation magnitude, relaxation rate, and peak stress was analyzed. Relaxation magnitude and relaxation rate after cyclic disturbance loads are larger than those of conventional relaxation. In addition, sensitivity analysis reveals that the relaxation magnitude is more sensitive to the disturbance amplitude. Damage variables defined by the plastic strain method can well reflect the evolution law of relaxation damage under different disturbance conditions. It is believed that the damage model constructed by Harris function can better describe the relaxation damage evolution law at various strain levels.

Experimental study on the dynamic properties of lime-solidified soft soil under cyclic loading

The dynamic properties of lime-solidified soft soil affect the safety and function of buildings. In this study, lime was used to solidify soft soil from the Binhai New District of Tianjin, China. A dynamic triaxial testing system was used to measure the dynamic stress-strain curves of solidified soft soil samples for different lime mixing ratios and confining pressures. The relationship between the dynamic strength and the static strength, the influence of the lime mixing ratio on the dynamic strength, and the variation of the dynamic shear modulus G and the damping ratio λ were analyzed. The results show that under static and dynamic loads, the internal friction angles of the lime-solidified soft soil are almost the same and range between 21.72° and 24.42°. Different cohesion values are obtained under static and dynamic loads, and these two values increase and approach each other with increasing lime mixing ratios. G and λ depend on the shear strain, the lime mixing ratio, and the confining pressure. These results serve as a reference for the formulation of a solidification scheme for soft soil.

An apparatus for measuring water content of unsaturated soil based on the van der Pauw principle

Understanding water migration in soil specimens under triaxial test conditions is of great significance for investigating the mechanism of distress in railway subgrades. However, the water content distribution along the specimen height is difficult to determine with current equipment. Motivated by such limitations, we developed an apparatus relying on the van der Pauw principle, to measure the water content based on the specimen’s electrical properties. Additionally, a series of exploratory tests on unsaturated soil specimens were conducted to evaluate the performance of this apparatus. To verify the practicability of the apparatus, a water-supply dynamic triaxial test was also carried out with an unsaturated dynamic triaxial test system (GDS). The results indicate that this apparatus is stable, as the measurement accuracy is not influenced by the electrode position or the soil geometry or dimensions. In a narrow triaxial pressure chamber, this apparatus can be used to determine the distribution of water content in unsaturated specimens nondestructively and consecutively during a triaxial test. The maximum error obtained from the apparatus when measuring the gravimetric water content was 0.7%. The soil resistivity calculation function was obtained considering the dry density and gravimetric water content with high correlation and precision. This apparatus has broad applications for investigating the mechanism of water migration within some geotechnical materials.

Experimental Study on Strength Characteristics of Frozen Sands

The MTS-Landmark 370.10 dynamic and static triaxial test system is used to carry out low temperature conventional triaxial tests at a temperature of -10 ° C and the confining pressures of 0.5MPa, 1MPa, 2MPa, 6MPa, and 8MPa to study the strength characteristics of frozen sands. The test results show that under different confining pressures, the stress-strain curves of frozen sand are strain soften. With the increasing confining pressures, the degree decreases gradually, and the strength has a non-linear characteristic. Based on the envelope theorem, a non-linear strength criterion is proposed in this paper. Compared with the test results, the strength criterion can well describe the non-linear relationship between the strength of frozen sand and confining pressure.

Dynamic Elastic Modulus and Damping Ratio of Unsaturated Red Clay

Dynamic modulus of elasticity and damping ratio are two important parameters of dynamic properties of soil. These two parameters were extensively studied in the laboratory. However, there has been little research on these two parameters of the unsaturated red clay which is located in the southwest of Hunan, China. With the rapid development of high-speed railway in China, it is urgent to identify the dynamic properties of the unsaturated red clay to provide reference for the civil engineering industry. In this paper, DDS-70, an electromagnetic type dynamic tri-axial testing system, was used to study the effects of water content, dry density, confining pressure, over-consolidation ratio and loading frequency on dynamic elastic modulus and damping ratio of unsaturated red clay. The result shows that within the phase of small strain the influences of water content, dry density, confining pressure, over-consolidation ratio and loading frequency on dynamic modulus of elasticity are obvious. Dynamic modulus of elasticity increases with the increase of dry density, confining pressure and over-consolidation ratio under the same strain, whereas dynamic modulus of elasticity decreases with the increase of water content and loading frequency. Moreover, the effects of these factors on damping ratio are also significant during the phase of small strain. With the increase of strain, damping ratio increases with the decrease of dry density, confining pressure and over-consolidation ratio under the same dynamic strain. There is no clear relationship between damping ratio and loading frequency. It is concluded that the influence of above factors on the dynamic modulus of elasticity and damping ratio is significant.

Experimental Study on Anisotropy of Intact Loess under Cyclic Loading

In order to investigate the effects of anisotropy of undisturbed loess on failure strength, dynamic shear modulus and damping ratio under cyclic loading, the dynamic characteristics of undisturbed loess in HaiDong area of Qinghai Province were studied by using the British GDS two-way dynamic triaxial test system. The results show that under the action of equal strain control cyclic load, as the number of cycles increases, the deformation of the sample gradually accumulates, the amplitude of dynamic strain decreases gradually, and the dynamic shear stress decreases. With the increase of dynamic shearing, the strain increases slowly and the strain hardening phenomenon appears. Different sampling angles have an important influence on the failure strength and dynamic shear modulus of undisturbed loess.

Study on dynamic stress-strain response law of frozen saline soil

The subgrade saline soil in a certain area of western Qinghai province was studied, based on the British GDS dynamic triaxial test system, the dynamic triaxial test under laboratory test was carried out to study variation dynamic stress-strain and dynamic shear modulus under the different temperature, frequency and confining pressure. The test results show that the dynamic stress-strain relationship is significantly affected by temperature change under cyclic dynamic load, followed by frequency and confining pressure. Under the same strain amplitude, the lower the temperature, the larger the dynamic shear modulus. When frequency and confining pressure increase, dynamic shear modulus also increases. Whereas, the influence of confining pressure on the dynamic shear modulus is more obvious, and the backbone curve development trend is steeper. Both maximum dynamic shear modulus and final shear stress amplitude increase with the frequency increases when temperature and confining pressure remain unchanged. Meantime, the maximum dynamic shear modulus curve is a convex shape, and the final shear stress amplitude curve is a convex shape at positive temperature,while which a concave shape at negative temperature. At constant frequency and confining pressure, the maximum dynamic shear modulus and final shear stress amplitude increase with the decrease of temperature. Curves of change trend are slower above 0°C, and steeper below 0°C.

Experimental Study on Dynamic Elastic Modulus and Critical Dynamic Stress of Cinder-Improved Soil Subgrade

The dynamic elasticity modulus and critical dynamic stress of improved soil under different confining pressures and frequencies are investigated by using GDS dynamic triaxial test system to examine the dynamic characteristics of cinder-improved soil as subgrade under medium and low confining pressure. The attenuation model of the dynamic elastic modulus was established to analyze the influence of different confining pressures and loading frequencies on the dynamic modulus. A fuzzy linear regression model based on structural element method was used according to the uncertainty of critical dynamic stress. Results show that the dynamic elastic modulus of soil decreases exponentially with the increase of loading times. The attenuation model can reflect the influence of frequency and confining pressure on the dynamic modulus of elasticity. The critical dynamic stress of soil is negatively correlated with the frequency of loading and is positively correlated with the confining pressure. The fuzzy linear regression model based on the structural element method can reflect the relationship between the critical dynamic stress and the frequency and confining pressure.