Thixotropic Strength Research Articles

Experimental study on the thixotropic strength of the marine soft clay from the Yangtze River estuary

Soft clay in the offshore area of the Yangtze River estuary has been investigated considering its basic physical properties. Forty-five unconfined compressive strength tests were conducted on the remolded marine soft clay to investigate the impacts of curing time T, water content w, plasticity index IP, and clay particle content ρc on the thixotropic static shear strength ratio As of the marine soft clay from the Yangtze River estuary. Results show that the stress–strain curves were primarily strain hardening and strain softening curve types. Unconfined compressive strength qu increased with an increase in T. All specimens with different basic physical properties were capable of thixotropic strength recovery. When T = 0–28 days, As increased rapidly, while for T > 28 days, As of most specimens increased slightly or tended to stabilize. The impacts of w, IP and ρc on As do not follow a consistent pattern, but there is a strong correlation between As and w/wL (wL is the liquid-limit water content). For w/wL < 0.75, As increased with increasing w/wL, whereas for w/wL ≥0.75, As decreased with increasing w/wL. We proposed a simple and widely applicable power function prediction model for the As of the soft clay from the Yangtze River estuary.

Rheological behavior of high-pour-point oil: Insights into viscosity–temperature prediction and viscoelastic-yielding transition

The rheological characteristics of high-pour-point (high-PPT) oil are crucial for its economical and safe production and transportation. However, current research on the viscosity–temperature prediction and viscoelastic-yielding transition of high-PPT oil is insufficient. The Arrhenius formula faces challenges in accurately depicting the viscosity–temperature relationship, and there is a lack of a quantitative description of the viscoelastic-yielding transition behavior in gelled high-PPT oil. This study addresses these gaps through a series of rheological experiments. The results reveal that the viscosity–temperature relationship of high-PPT oil can be classified into three regions, each associated with a sequentially increasing activation energy Ea. Introducing two characteristic parameters, T0 and n, yields a modified Arrhenius formula with an extended range of applicability. Thixotropy and gelation process experiments demonstrate an exponential increase in thixotropic strength with a decreasing temperature below the wax appearance temperature, while an optimum cooling rate maximizes the gelation degree of high-PPT oil. A brittleness index BI was defined to quantitatively describe the fracture mode of gelled crude. Critical characteristic strains and BI exhibit a decrease with an increase in the reciprocal of the average free degree 1/wfree, where the diminishing trend of BI follows a robust power-law form. This comprehensive investigation contributes valuable insights into the rheological behavior of high-PPT oil, offering a foundation for more accurate modeling and control strategies in its production and transportation.

An analysis of thixotropic micropore variation and its mechanism in loess

The relationship between the thixotropic mechanism and the macroscopic thixotropic strength can be clarified by analyzing the changes in microstructure and pores in the loess thixotropic process. This approach is of significant importance for calculating the strength of compacted loess foundations. In the present study, a representative sample prepared from Xi’an loess was analyzed and eight resting ages were set. The micropore characteristics of the remolded loess and undisturbed loess at different resting ages were obtained using electron microscope observation and nuclear magnetic resonance testing. The results indicate that the thixotropy in the prepared loess samples is significant. It is also found that as the resting age grew, newly formed cements in the remolded loess continuously accumulated and filled in the microcracks between the aggregates. Consequently, the contact area of aggregates increased, thereby decreasing the width and length of the microcracks. The proportion of cementation pore and small microcracks gradually increased, while the proportion of large microcracks gradually decreased, indicating that thixotropy increased the cohesive force and friction force of soil structure at the mesoscale. This phenomenon also explains the increase of thixotropic strength at the macroscopic scale. The mesoscopic mechanism of loess thixotropic strength recovery is that the connection between soil particles is re-established after the break of the clay particle–water–charge system. Moreover, the elastic potential energy of soil particles generated by compression promoted the polymerization of clay particles dispersed in a pore water solution to produce flocculating aggregates during resting dissipation. The continuous consumption of clay particles expanded the processing time and flocs and continuously decreased the strength growth rate.

An investigation on the thixotropic parameters and mechanical properties of loess

The analysis of thixotropic mechanical properties of loess has a significant influence on the calculation of the strength of compacted loess foundation. In order to distinguish the consolidation growth strength of loess from the thixotropic strength, a resting thixotropic instrument is developed. The proposed device is capable of maintaining a constant volume pressure. To attain the goals, after selecting the representative Xi’an loess, the samples were pressed by the resting thixotropic instrument under constant volume pressure. Eight resting ages were also set. Moreover, the thixotropic mechanical properties of loess soil were studied at 6 months resting ages through uniaxial compression without lateral limit and triaxial CU test. The thixotropic triaxial shear strength ratio Jt, thixotropic triaxial shear strength recovery ratio Kt and thixotropic cohesion recovery ratio Lt were defined, the mechanical properties of which were investigated under different stress states. The obtained results demonstrated the obvious thixotropy of Xi’an loess, the strength of which was found to increase with an increase in the resting age. This is while, an increase in the resting age was observed to decrease the its growth rate. Moreover, the unconfined thixotropic strength was found to increase by 1.75 times after resting for 160d, which corroborates the influence of thixotropic strength in designing the foundation bearing capacity of loess. Furthermore, the recovery ratio of unconfined thixotropic strength and the growth ratio of eccentric stress strength were found to be 0.187 and 0.115, respectively. In addition, the thixotropic triaxial shear strength ratio Jt, the recovery ratio of thixotropic triaxial shear strength ratio Kt, and the recovery ratio of thixotropic cohesion ratio Lt were observed to be 0.15, 0.527, and 0.5, respectively. The obtained results suggest the resting age of 40 days to be used as the inflection point for the recovery of thixotropic strength such as uniaxial compressive strength, peak deviator stress, shear strength and cohesion of loess. Despite the insignificant variation range of the friction Angle in the resting process, the contribution ratio of friction force in increasing the shear strength was also found to be much greater than that of the cohesion.

DYNAMIC STRENGTH PARAMETRS OF CLAY SOILS AND METHODS FOR THEIR DETERMINATION

Correct determination of strength properties is always relevant for the prediction of soil mechanical behavior. This issue in a static formulation of the problem is widely discussed in technical literature. However, the determination of strength properties under dynamic loading remains debatable. This paper discusses a new methodological approach developed to determine the parameters of dynamic shear strength of saturated samples of model clay soils based on a combined analysis of static and dynamic triaxial testing data. It is demonstrated that, other conditions being equal, the value of the angle of internal friction of clay soil samples with predominantly a coagulative structure is the same under static and dynamic conditions; however, cohesion decreases under dynamic loading and this effect is attributed to the thixotropic strength loss in such a soil.

Discussion of “Experimental Study of the Thixotropic Strength Recovery and Microstructural Evolution of Marine Clays”

Discussion of “Experimental Study of the Thixotropic Strength Recovery and Microstructural Evolution of Marine Clays”

Closure to “Experimental Study of the Thixotropic Strength Recovery and Microstructural Evolution of Marine Clays”

Closure to “Experimental Study of the Thixotropic Strength Recovery and Microstructural Evolution of Marine Clays”

Geotechnical Characterization of Laponite as Transparent Clay Surrogate

Abstract The use of so-called “transparent soils” as proxy geotechnical materials has allowed for the nonintrusive observation of a variety of models representing different engineered systems. Laponite is one such soft clay surrogate that has seen increased usage in recent years. However, this material has yet to be subjected to a thorough characterization and quantification of its physical and mechanical properties. The study presented herein followed a systematic approach toward the characterization of Laponite RD colloids from a geotechnical perspective across a wide range of mixes and additive dosages. Rheology tests were conducted to study the variation in apparent viscosity with time and after remixing. These tests identified two sources/types of strength gain: a reversible thixotropic strength gain and an irreversible particle aggregation strength gain. Different mixtures tested in a one-dimensional consolidation oedometer showed that mixes with laponite colloid contents as high as 21 % could be achieved from mixes with an initial colloid content of 11 % by mass. Finally, results from vane shear tests showed that the undrained shear strength increased with: (1) increasing laponite colloid content, (2) decreasing additive dosage, (3) aging time, and (4) increasing temperature. The base geotechnical characteristics and mechanical properties of the clay surrogate as provided in this study are expected to facilitate proper interpretation of the behavior of this surrogate material in geotechnical physical models involving transparent clays.

Experimental Study of the Thixotropic Strength Recovery and Microstructural Evolution of Marine Clays

Experimental Study of the Thixotropic Strength Recovery and Microstructural Evolution of Marine Clays

Effect of a novel semi-solid middle-layer structure formed during twin-roll casting on the mechanical properties of AA6022 alloy

During a twin-roll casting (TRC) process with low-rolling force and near-liquidus melt treatment, a novel semi-solid middle structure is produced. The formation of this structure and its influence on the alloy mechanical properties were investigated using polarized light microscopy, electron backscattered diffraction, scanning electron microscopy, and transmission electron microscopy. The middle structure was generated by rolling a semi-solid melt with high thixotropic strength. The size of its sedimentary grains strongly affected the thixotropic strength by influencing the grain boundary density, which promoted different grain movements in the rolling process. The large grains slid along each other, whereas the small grains were deformed, inhibiting their macrosegregation. Compared with the conventional TRC structure, the semi-solid middle layer containing small sedimentary grains increased the slab elongation from 17.5% to 25.4% without reducing the tensile strength; however, the slab with large sedimentary grains exhibited low plasticity. The effect of the middle structure on the alloy mechanical properties is elucidated in terms of dislocation density, grain size, texture type, and resistance to crack propagation. The obtained results can help develop new approaches to designing TRC slab structures with desired characteristics.

Thixotropy of soft clay: A review

Thixotropy of soil is, after softening by remoulding, a process of time-dependent return to a harder state under constant water content and constant volume conditions. This paper presents a critical review of previous investigations on the thixotropy of soft clay. Thixotropic behavior is primarily a structural effect accompanied by the spontaneous dissipation of excess internal energy, and some microstructural observations provide a deeper insight into its mechanism. Mathematical theories and models to simulate thixotropic strength recovery of soil are introduced. Different test methods to evaluate the thixotropic behavior of soil are summarized. Correlations between the thixotropic behavior of soil and some basic indexes, such as water content, Atterberg limits, mineralogy, activity and salt concentration, are described. Some remarks on future improvement for thixotropy of soil are also provided based on the results of up-to-date research.

Strength Recovery Model of Clay during Thixotropy

Thixotropy is a hot topic in the field of rheology of dispersed systems. Many researchers have proposed different models and hypotheses to explain the thixotropy of clay. In this paper, the strength recovery model of Zhanjiang Formation clay in the process of thixotropy is studied. Firstly, through unconfined compressive strength test, the influence of soil sensitivity, moisture content, and density on the strength growth of remolded soil was studied. The results show great influence of sensitivity, moisture content, and density on the thixotropic strength of the Zhanjiang Formation clay: the higher the sensitivity and the density, the stronger the thixotropy of soil; the higher the moisture content, the weaker the thixotropy of soil. Based on the test results, a strength recovery model of Zhanjiang Formation clay in the process of thixotropy was established. The model was verified by the validation test data and the data obtained from the existing literature. The results suggest that the model prediction is in good agreement with the verification test data and data from existing literature, which proves the confidence of the model in predicting the degree of strength recovery in the process of thixotropy of Zhanjiang Formation clay. The model provides basis for stability calculation of surrounding soil after construction disturbance of underground structures in this stratum.

Experimental Investigation on the Strength and Deformation Aspects of Thixotropic Aging in Reconstituted Clays

This study is aimed at comprehending the effect of thixotropic aging on strength and deformation response of natural clays reconstituted in the laboratory. Three clays have been collected and samples were prepared at a moisture content of corresponding liquid limits. Prepared soil specimens were subjected to a thixotropic aging (constant moisture, constant volume and constant temperature conditions) period of 7, 14, 21, 28, 35 and 42 days. Unconfined compressive strength and direct shear tests were performed to assess thixotropic strength recovery. Thereafter, one-dimensional consolidation tests were conducted on the thixotropically aged samples to assess the compressibility characteristics. Interpretation of the responses from unconfined compression test, direct shear test coupled with Scanning Electron Microscopy imaging analyses suggest that thixotropic strength recovery is dependent on activity, percentage of clay fraction, and initial grain structure. Thixotropic strength ratio obtained from unconfined compression test and direct shear test are noticed to be different, although the trend is similar. Interpretation of 1-D consolidation test data suggest that as the thixotropic aging period increased, samples tend to provide higher yield stress compared to the unaged samples. All the void ratio-effective vertical stress responses for the clays at different thixotropic aging periods tend to converge at a same void ratio at a consolidation stress of > 1000 kPa, indicating no effect of thixotropic structuration at high consolidation stresses. In addition, it was observed that thixotropically active clays swell more than the inactive clays during the thixotropic aging period. In addition, a proportional relationship between thixotropic strength ratio and plasticity index was also noticed.

Determination of the Sensitivity and Thixotropic Effects of Clay Soil for Selected Sites in Diwaniya City - Iraq

This paper is conducted to determine the sensitivity and thixotropic effects of clay soil for selected sites in Diwaniya city which are: (Dawr Aldubbat, Al-Zawra square, 14 Ramadan square, Al'iiskan Alaqadim and Military square). The main aim of this investigation is to study the sensitivity and thixotropy of clay soil, and determination and classification of soils to (Insensitive), (slightly to very sensitive) and (slightly to extra quick)) relying on special test methods in sensitivity and thixotropic phenomena. The experimental tests that were done including geotechnical, chemical and mineralogical tests to natural soils and special tests were for the identification and classification of sensitivity of soils. The results of sensitivity of soils test displayed low to medium for all the types of the soils in the study area. The results of the thixotropic strength ratio test showed a small increase in thixotropic strength ratio values with time. The results of Atterberg limits test indicated that increasing the proportion of the clay causes an increase in the plasticity index of the soil. While the results of the liquidity index varied from 0.24 to 0.70, which reflects the low sensitivity of the clay soil in the study area.

Rheological behaviour of partially solidified A356 alloy: Experimental study and constitutive modelling

Rheological behaviour of the mushy zone is dependent on the microstructure and related to parameters such as temperature, shear rate and shear strain/time. However, constitutive modelling of the rheological behaviour is difficult due to the diversity of the parameters. This study focuses on the influence of the microstructure and the above parameters on the rheological behaviour of partially solidified A356 alloy and establishing a constitutive model accordingly. During solidification, the evolution of α-Al phase leads to the changes of the apparent viscosity of mushy zone. Steady-state viscosity and peak viscosity measured by rotational rheometry reveal the thixotropy of the mushy zone. The thixotropic strength is found to increase with increasing shear rate and decreasing temperature. The peak viscosity, as well as the steady-state viscosity, is found to obey a power law model and is modelled using the power law model with the coupling of temperature and shear rate. Furthermore, a constitutive model with temperature, shear rate, shear tress and shear strain/time as parameters which describes the rheological behaviour of the mushy zone of partially solidified A356 alloy accurately and completely is established. Comparing with previously reported experimental results, the FEM simulation employing the constitutive model works well in enabling visualization of the viscoelastic filling process of A356 alloy in mushy zone. The constitutive model provides a solution for characterizing the forming behaviour of other mushy zone/semi-solid aluminium alloys with corresponding rheological parameters.

Thixotropic aging and its effect on 1-D compression behavior of soft reconstituted clays

Abstract The present study investigates the moisture content at which the thixotropic effect is maximum, as well as the effect of such aging on compression. For this research, samples were prepared at moisture contents ranging from 0.55–1.25 times their corresponding liquid limits, and fall cone and vane shear tests were administered to determine the shear strength. Oedometer tests were performed on both thixotropically aged and unaged samples to observe the effects of thixotropic aging on 1-D compression characteristics. It was observed that the maximum thixotropic strength was obtained at a moisture content close to 0.75 times the corresponding liquid limit for all samples, and thixotropic strength recovery was negligible at a moisture content of 0.55 times the corresponding liquid limit. Vane shear strength was found to be lower than fall cone strength, and an increase in the rate of strain resulted in lower estimation of thixotropic strength recovery. The thixotropic strength ratio was observed to be dependent on the plasticity index and activity of the clay sample. Of all of the clays examined, the thixotropically aged sample provided the highest yield stress. The study suggests that in situations where the effective vertical stress is less than 100 kPa, the settlement calculation, using the conventional effective stress principle, needs to be rigorously revised. A scheme for considering both strength and compressibility behavior in design practice is also provided.

Dewatering Behaviour of a Uranium Ore Slurry Containing Clays

The main objective of this paper was to investigate the dewatering behaviour of a clayey uranium ore slurry. The slurry (containing 28% clay size) exhibited moderate water adsorption (w l = 83% and w p = 30%). Primarily composed of muscovite (46%) and quartz (30%), the clay minerals included illite (8%), chlorite (5%) and kaolinite (2%) alongside a CEC of 41 (cmol(+)/kg) with Ca2+ and Mg2+ as the dominant cations. Likewise, the high EC (17,600 μS/cm) and ionic strength (1.15 mol/L) indicated a flocculated microstructure due to the presence of SO4 2− (22,600 mg/L) and Mg2+ (1340 mg/L) in the slurry water. Settling included sedimentation and consolidation at low initial solids condition (25–35%) whereas only consolidation was observed at high initial solids contents (40–50%). The average k reduced from 1.2 × 10−6 m/s (initial s = 25%) to 5.3 × 10−8 m/s (initial s = 50%) along with a void ratio reduction from 7.4 to 2.6. Due to thixotropic strength, volume compressibility during consolidation showed apparent pre-consolidation at low effective stress (0.3–2 kPa) with a reduction in void ratio from 2.6 to 2.5. The e s was found to be 2.46 at σ′ = 2 kPa and was followed by a steeper slope with the void ratio reducing to 2.1 at σ′ = 31 kPa. Likewise, the hydraulic conductivity during consolidation decreased from 2.6 × 10−9 m/s (at e = 2.6) to 2.0 × 10−10 m/s (at e = 2.1).

Determination of consolidation behaviour of clay slurries

The main objective of this study was to determine the consolidation behaviour of clay slurries. A fine-grained clay with high consistency limits (wL=180%, wP=120%) was investigated using conventional oedometer and bench-top centrifuge tests. Results indicated that the slurry had an apparent preconsolidation (due to initial conditions, electrochemical interactions, tortuous drainage, and thixotropic strength) from e=5.7 to e=5.5 followed by virgin compression. Likewise, the low hydraulic conductivity (10−10–10−12m/s) was due to low porosity (small pore throats) and high tortuosity (long flow paths). Unlike consolidation of soils, the cv and mv decreased with increasing σ′ but increased with increasing e and k. The data from the two tests correlated well in the range of σ′=10–65kPa, e=5.5–3.86, k=1.7×10−10–5×10−11m/s, Fc=1–40MN. New equations were developed to correlate the consolidation parameters (e, σ′, k) with Fc. The deviation of k beyond 40MN (e=4.65) was due to deviation from the initial straight line portion of the settlement curve in the centrifuge test.

Rheological properties of aqueous solution of new exopolysaccharide secreted by a deep-sea mesophilic bacterium

The rheological properties, such as shear flow behavior, thixotropy and viscoelasticity, of aqueous solution of a new type of exopolysaccharide (SM-A87 EPS) secreted by a deep-sea mesophilic bacterium were investigated using shear flow and dynamic rheological measurements. For the SM-A87 EPS solutions, the overlapping concentration C * and crossover concentration C ** were confirmed to be 0.95 g/L and 4.99 g/L respectively by the concentration-dependences of rheological parameters, such as equilibrium viscosity, thixotropic strength, static and dynamic stress, critical shear rate, and storage modulus in the linear viscoelastic region besides the zero-shear viscosity of solutions. At concentrations higher than C *, the solutions exhibited a static stress, a dominant elastic behavior and a stronger absolute positive thixotropic strength. Otherwise, at concentrations lower than C *, no static stress, a dominant viscous behavior and a weaker absolute positive thixotropic strength were exhibited. The SM-A87 EPS solutions may be used as enhanced oil recovery system.

Thixotropic Strength and Thixotropic Criteria in Semi-Solid Processing

Thixotropy is essential to semi-solid processing, and because of it the semi-solid material is characterized by ‘shear shinning’. Here, thixotropic strength and thixotropic criteria in semi-solid processing are put forward based on related theories and experiments, and thixotropic mechanism and its influencing factors are also investigated. The results are as follows: 1) the term of thixotropic strength means that with constant shear rate at semi-solid temperature, the semi-solid body begins to flow when the shear stress reach a certain value. This value of shear stress is defined as the thixotropic strength; 2) Thixotropic behavior happens with ‘shear thinning’ because of the deagglomeration of solid particles, while ‘shear thickening’ happens because of the agglomeration at the same time. With increasing shear time, the shear stress increases first and then decreases rapidly to reach a stable value. 3) There are three important factors that influence ‘thixotropic strength’: temperature (hence solid content), initial microstructure (including size, shape factor and uniformity of solid particles) and shear rate.