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The composition of high rockfill dam materials is complex, and the mechanical parameters are uncertain and correlated in unknown ways due to the influences of the environment and construction, leading to complex deformation mechanisms in the dam–foundation system. Statistical characteristics of material parameters are the basis for deformation and stress analysis of high core rockfill dams, and using an inaccurate distribution model may result in erroneous analysis results. Furthermore, empirically evaluated distribution types of parameters are susceptible to the influence of small sample sizes, which are common in the statistics of geotechnical engineering. Therefore, proposing a multi-dimensional joint distribution model for parameters based on small-sample data is of great importance. This study determined the interval estimation values of Duncan–Chang E-B model parameters—such as the mean value and coefficient of variation for the core wall, rockfill, and overburden materials—using parameter statistical analysis, bootstrap sampling methods, and Akaike information criterion (AIC) optimization. Additionally, the marginal distribution types of each parameter were identified. Subsequently, a multi-dimensional joint distribution model for Duncan–Chang model parameters was constructed based on the multi-dimensional nonlinear correlation analysis of parameters and the Copula function theory. The application results for the PB dam demonstrate that joint sampling can effectively reflect the inherent correlation laws of material parameters, and that the results for stress and deformation are reasonable, leading to a sound evaluation of the cracking risk in the core wall of high core rockfill dams. [ABSTRACT FROM AUTHOR]

The dynamic compaction method has been widely adopted in foundation treatment to densify the soil fillers. However, for the complexity of the impact behavior and soil mechanical properties, the theoretical research of dynamic compaction lags behind its practice for complex soil properties and stress paths. This paper presents a theoretical model applied to describe soil column plastic deformation under impact load. The relationship among stress increment, strain increment, and plastic wave velocity was derived from the aspect of propagation characteristics of stress waves in soil first. Combined with the Duncan-Chang Model, a one-dimensional theoretical model was established then. A numerical model was developed further to check the performance of the model. It showed that the deformation at the end of the soil column was mushroom-shaped. Both the axial and lateral deformation increased with the impact velocity. While some particles located at the side of the soil column end may splash under repeated impact. The theoretical deformations of the soil column were consistent with the experimental results both in the direction of axial and lateral. [ABSTRACT FROM AUTHOR]

Accurate evaluation of the mechanical response of hydrate-bearing reservoirs is a prerequisite for safe and efficient exploitation of natural gas hydrate resources. Therefore, it is necessary to develop a suitable constitutive model and to determine reasonable model parameters for hydrate-bearing sediments (HBSs) during exploitation. In this study, based on the strain-hardening behavior of clayey sand reservoirs published in the previous study, Duncan–Chang model was used as the basic model to establish constitutive models for HBSs during exploitation. The model parameters, initial elastic modulus and ultimate deviatoric stress, were determined by modifying existing formulas and establishing empirical formulas. Four nonlinear elastic constitutive models were proposed by combining the model parameters determined by different methods. Multi-stage and single-stage triaxial test data were used to verify the applicability of the model and determine the optimal model suitable for the sediments under study. [ABSTRACT FROM AUTHOR]

When conducting tunnel construction in sandy gravel strata, disturbance to the sandy gravel soil is inevitable, resulting in alterations to the properties of the surrounding rock. This paper investigates the relationship between the relative density (Dr) and shear strength parameters under different disturbance states through the implementation of indoor triaxial tests. Utilizing Dr as a disturbance parameter, a unified disturbance function that reflects the weakening and strengthening of sandy gravel soil is proposed. Furthermore, a revised constitutive model based on this unified disturbance function is established for the first time. The study results indicated that the results calculated by traditional models, which do not take into account disturbance effects, deviate from the experimental results by more than 20%. However, the error rate of the results computed by the modified model can be reduced to within 8%. The new model establishes a dynamic relationship between relative compactness and shear strength parameters of sand and pebble soils, which can take into account both the effects of negative and positive perturbations. The results can more accurately characterise the strength and deformation properties of the surrounding rock under the influence of construction disturbances in sand and pebble ground tunnels. [ABSTRACT FROM AUTHOR]

This paper aims to establish a model that can reasonably reflect the mechanical properties of coal containing gas under different water content and confining pressure conditions. Firstly, the stress-strain characteristics of coal containing gas under different water content and confining pressure conditions are analyzed based on triaxial tests. Afterwards, this paper obtains the Duncan-Chang model parameters by combining the Duncan-Chang model and Janbu formula. Moreover, it establishes the fitting formulas of initial elastic modulus failure stress and various influencing factors, and conducts an improved Duncan-Chang model to characterize the deformation law of coal containing gas under different stress levels. Finally, this paper verifies the improved model and evaluate the accuracy of the mode. The results show that the increase of water content is an important reason for the dynamic change of coal model parameters of coal containing gas. The prediction curve of the improved model is in good agreement with the actual test curve, and the improved model can accurately reflect the stress-strain characteristics of coal containing gas under different confining pressures and water contents.

When conducting tunnel construction in sandy gravel strata, disturbance to the sandy gravel soil is inevitable, resulting in alterations to the properties of the surrounding rock. This paper investigates the relationship between the relative density (Dr) and shear strength parameters under different disturbance states through the implementation of indoor triaxial tests. Utilizing Dr as a disturbance parameter, a unified disturbance function that reflects the weakening and strengthening of sandy gravel soil is proposed. Furthermore, a revised constitutive model based on this unified disturbance function is established for the first time. The study results indicated that the results calculated by traditional models, which do not take into account disturbance effects, deviate from the experimental results by more than 20%. However, the error rate of the results computed by the modified model can be reduced to within 8%. The new model establishes a dynamic relationship between relative compactness and shear strength parameters of sand and pebble soils, which can take into account both the effects of negative and positive perturbations. The results can more accurately characterise the strength and deformation properties of the surrounding rock under the influence of construction disturbances in sand and pebble ground tunnels.

The composition of high rockfill dam materials is complex, and the mechanical parameters are uncertain and correlated in unknown ways due to the influences of the environment and construction, leading to complex deformation mechanisms in the dam–foundation system. Statistical characteristics of material parameters are the basis for deformation and stress analysis of high core rockfill dams, and using an inaccurate distribution model may result in erroneous analysis results. Furthermore, empirically evaluated distribution types of parameters are susceptible to the influence of small sample sizes, which are common in the statistics of geotechnical engineering. Therefore, proposing a multi-dimensional joint distribution model for parameters based on small-sample data is of great importance. This study determined the interval estimation values of Duncan–Chang E-B model parameters—such as the mean value and coefficient of variation for the core wall, rockfill, and overburden materials—using parameter statistical analysis, bootstrap sampling methods, and Akaike information criterion (AIC) optimization. Additionally, the marginal distribution types of each parameter were identified. Subsequently, a multi-dimensional joint distribution model for Duncan–Chang model parameters was constructed based on the multi-dimensional nonlinear correlation analysis of parameters and the Copula function theory. The application results for the PB dam demonstrate that joint sampling can effectively reflect the inherent correlation laws of material parameters, and that the results for stress and deformation are reasonable, leading to a sound evaluation of the cracking risk in the core wall of high core rockfill dams.

The shear strength characteristics and weakening effect of soils under freeze–thaw (FT) cycling are the key problems that should be solved to ensure the integrity of infrastructure construction in seasonally frozen soil areas. Thus far, however, the research on the mechanism of strength deterioration resulting from microstructural changes induced by FT cycles remains insufficiently comprehensive. To investigate the deterioration characteristics of the shear strength of seasonally frozen soils in FT cycles, a series of laboratory experiments were conducted using compacted silty clay subjected to a maximum of five closed-system FT cycles. The stress–strain curve, secant module, shear strength, and microscopic structure were measured for specimens before and after the FT cycles. The stress–strain curves of the unfrozen and thawed specimens demonstrated a strain-hardening behavior, indicating an increase in resistance to deformation. Moreover, the shear strength and secant modulus of the unfrozen specimen surpassed those of the thawed specimen significantly. As the number of FT cycles increased, there was a gradual decline observed in the strength, stiffness, cohesive properties, and internal friction angle of the thawed specimen. The nuclear magnetic resonance technique was employed to interpret the experimental findings. It was demonstrated that the micro-pores undergo continuous enlargement and transformation into medium-sized and large-sized pores, leading to FT deterioration. Based on the experimental results, a modified Duncan–Chang model was developed to simulate the mechanical behavior of compacted silty clay while considering the influence of FT cycles. [ABSTRACT FROM AUTHOR]

The mechanical properties of soil rock mixture (S-RM) are complex, especially the strength deterioration after encountering water, which readily leads to engineering instability. A series of large triaxial tests of S-RM with different water contents under various confining pressures were performed, the mechanical properties of S-RM were explored from a macroscopic perspective. The constitutive model of S-RM – an extended Duncan-Chang (DC) model considering water content – was developed. The results show that: (a) the stress-strain curves of S-RM are strain hardening type, the peak strength decreases non-linearly with the increase of water content, the higher the water content of sample, the more significant the bulging phenomenon and the more numerous and extensive the surface cracks; (b) the cohesion c and internal friction angle φ of S-RM both decrease approximately linearly with the increase of water content, and the secant modulus decreases significantly with the increase of water content, the reason of which can be attributed to the porosity and compression characteristics of S-RM; (c) the extended DC model can be used to describe the mechanical behavior of S-RM affected by water under triaxial test conditions. The material constant K, failure ratio Rf, c, and φ are all related to water content ω, while material constant n is independent, only ω, n, maximum principal stress σ1, and minimum principal stress σ3 are needed to determine the tangent modulus of the DC model of S-RM. The results can provide an experimental basis and mechanical understanding applicable to engineering practice in an S-RM formation.

Copyright of Geology & Exploration is the property of Geology & Exploration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Ground Improvement is the property of Journal of Ground Improvement Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Engineering construction in cold regions cannot be separated from permafrost research. This study aimed to determine the mechanical properties and changing laws of artificially frozen clay through triaxial tests. Two models have been established: a physical model based on the tradi-tional phenomenological constitutive theory and a deep learning model based on the data-driven constitutive theory, taking into account the softening phenomenon. The accuracy and applica-bility of the models were verified, followed by a comparative analysis. The results of the analysis are as follows. The Duncan-Chang model can describe the characteristics of the hardening-type deviatoric stress-strain curve, but it cannot describe the characteristics of the softening-type de-viatoric stress-strain curve. The Modified Duncan-Chang (MDC) model fails to accurately de-scribe the characteristics of a smooth deviatoric stress-strain curve. The Strain-Damage Modified Duncan-Chang (SD-MDC) model exhibits a good fit in both the ascending and descending seg-ments of the curve, but it lacks effectiveness in the convergence segment of the S-shaped sof-tening curve. For this reason, this paper has chosen the arctangent function to establish a Strain-Damage Modified arctangent constitutive model (SD-MAM). This model accurately re-flects the stress evolution process of different types of frozen soils. Additionally, the Informer time series prediction algorithm was utilized to develop the Informer permafrost deviatoric stress prediction model which achieved an R2 value above 99%. In comparison to the SD-MAM model, the Informer model demonstrates higher precision, does not rely on assumptions, is cost-effective, and has a wide range of applications. However, it lacks physical meaning, and interpretability, and requires further discussion regarding the reliability of the results. This study offers valuable insights into the development and application of constitutive models for frozen soils.

To study the modification effect of nano-clay and nano-SiO2 on cement-reinforced coastal soft soil, the effects of the nano-SiO2 and nano-clay on the mechanical properties of cement soil were studied through unconfined compressive and unconsolidated undrained shear tests, and the Duncan–Chang model was used to fit the test results. Results show that adding nano-clay and nano-SiO2 to cement soil improved its compressive and shear strength. The compressive strength and shear strength increased by 18–57% and 3–32%, respectively, with the increase in nano-clay content in a content range of 0–10%. Additionally, nano-clay can enhance the ductility of cement soil. Moreover, nano-clay and nano-SiO2 improve the shear strength by increasing the internal friction angle by 1°–2° and cohesion of 9–25%, and the cement-stabilized coastal soft soil enhanced by nano-SiO2 and nano-clay conforms to the Duncan–Chang model well. [ABSTRACT FROM AUTHOR]

In order to reflect the whole deformation process of unsaturated foundation soil, the consolidated drained triaxial compression test is carried out on the unsaturated soil of a foundation project. It is found that the partial stress-strain curve of unsaturated soil is similar to hyperbola, and the matrix suction has an obvious influence on the mechanical behavior of soil. The greater the matrix suction, the higher the partial stress of soil. According to the deformation characteristics and engineering characteristics of unsaturated soil, the Duncan-Chang hyperbolic model is selected as the basic model, and the statistical damage theory is introduced. Assuming that the micro element strength of unsaturated soil obeys the Weibull probability density distribution, the Duncan-Chang statistical damage model is established. By establishing the relationship between the initial tangent modulus and matrix suction, a new Duncan-Chang statistical damage model of the unsaturated soil considering matrix suction is established. The parameter analysis method is given, and the empirical expression of the Weibull distribution parameters is obtained, which is used to modify the model. The damage accumulation law of unsaturated soil under different matrix suction conditions is analyzed, and the partial stress-strain test curve of unsaturated soil is compared with the traditional Duncan-Chang model, which proves the feasibility and rationality of the model. The research results provide a certain reference for the study of mechanical properties and identification simulation of unsaturated soil.

In this study, the stress-strain relationships of clayey soil were estimated by Duncan-Chang model, and the mathematical relationships between model parameters and freeze-thaw cycles were explained. By examining the correlations between the experimental study and the model outputs, it was determined to what extent the model was able to predict the stress-strain relationships of clay soils under freeze-thaw cycles. As a result, the relationship between the numbers of the freeze-thaw cycle and Duncan-Chang model parameters was revealed by using different curve fitting functions. Gray correlation analysis showed that the freeze-thaw effect on the model parameters cannot be ignored. By creating model parameters in the tangent deformation modulus of the Duncan-Chang model, the variation of stress-strain curves under freeze-thaw cycles was obtained with high correlations for unconsolidatedundrained soils. [ABSTRACT FROM AUTHOR]

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The clays of the Zhanjiang Formation in the coastal area of Beibu Gulf of China are thixotropic, and the existing constitutive relationship models relevant for clay are incapable of accurately simulating their stress–strain relationships. It is vital to study the changes of mechanical properties of Zhanjiang Formation clay that occur during thixotropy, and to establish a constitutive model considering thixotropy. The varying measures of its shear strength, cohesion, internal friction angle, and initial tangential modulus during thixotropy were investigated by means of triaxial consolidation and drainage tests. Furthermore, the quantitative relationships between the clay's cohesion, internal friction angle, and initial tangential modulus of the clay and time were examined. This relationship was introduced into the Duncan–Chang model, and a Duncan–Chang model considering the thixotropy of clay was developed. The established model was used to make predictions to assume the validation of the experimental data, and numerical simulations were then carried out. All of the results from the model's prediction, numerical simulation and experimental measurements were compared against each other in order to verify the reasonableness of the model we had utilized. The results positively demonstrated that: (1) the shear strength, cohesion, angle of internal friction, and initial tangent modulus of the clay gradually increases with longer curing times, and eventually it will stabilize; and (2) compared with the Duncan–Chang model not considering thixotropy, the established thixotropic model is better able to reflect the influence of clay thixotropy on the clay stress–strain relationship, as its mean relative error is smaller. The results of this study provide references for calculating strength and deformation of the clay thixotropy. Further, it also provides references for bearing load calculations of pile foundations in thixotropic clay strata when subjected to long-term loading conditions. [ABSTRACT FROM AUTHOR]

Interests appear in investigating methane-hydrate-bearing sands (MHBS) to address engineering problems, such as foundation instability of man-made permafrost facilities, wellbore instability and sanding during production. Mechanical behavior of MHBS is critical issue to analyze geomechanical hazards. In this paper, MHBS is synthesized in laboratory and triaxial compressive tests are carried out to capture mechanical response. A discrete element method (DEM) model is developed to examine mechanical responses of MHBS by considering real MHBS-based microstructure and particles contact. To describe nonlinear mechanical behavior, Duncan–Chang model is embedded into DEM model and verified with experimental results. Triaxial drained and undrained numerical tests are carried out to investigate effects of hydrate saturation, confining stress, heterogeneity and grading properties on mechanical behavior of pore-filling hydrate sediment. Experimental and numerical results indicate that (1) triaxial compression strength increases with confining stress and hydrate saturation; (2) stress–strain curve becomes smooth at a higher hydrate saturation thanks to the stability enhancement of MHBS structure; (3) heterogeneous distribution of hydrates leads to local instability with non-bonded hydrate particles; (4) grading properties (uniformity coefficient and mean particle diameter) non-apparent influence on compressive strength and dilatancy due to particles re-distribution; and (5) MHBS presents mechanical behavior of brittleness or plasticity in undrained tests rather than strain softening in drained tests. Except for Duncan–Chang model parameters fitting in this work, more experimental and numerical researches are expected to improve the performance in predicting post-failure behavior. [ABSTRACT FROM AUTHOR]

The Duncan-Chang nonlinear elastic model is widely used to calculate the stress-strain relationship of coarse-grained soils in water conservancy projects such as cofferdam construction and earth-rock dams. However, the Duncan-Chang model has relatively many parameters, and the calculation results often cannot fully reflect the dilatancy characteristics of the soil. In order to solve the above shortcomings, a more simplified stress-strain expression was proposed based on the Duncan-Zhang model. Based on the Shen Zhujiang model, the quadratic parabolic was used to describe the strain, while the model parameter form was improved to establish a volume ratio expression reflecting the relationship between soil volume strain and axial strain. Finally, the improved model was validated by using the test results of coarse-grained soil and cohesive soil. The results show that the theoretical calculation results are in good agreement with the experimental results, and the improved model can better reflect the characteristics of soil volume strain and the stress-strain relationship, which provides a reference for the calculation of the soil stress-strain relationship in practical engineering. [ABSTRACT FROM AUTHOR]

Both indoor conventional test and three-dimensional numerical simulation on triaxial compressive properties of sandy pebble soil have been conducted. The results obtained from indoor compressive test on sandy pebble soil with different relative densities show that its strength-deformation property is strongly affected by its relative compactness. In addition, the modified Duncan-Chang model that is used to reflect the contribution of disturbance to the strength-deformation properties of sandy pebble soil is presented by establishing the relationship among such parameters as initial tangent modulus Ei, peak strength (σ1-σ3)f as well as relative compaction Dr. The comparison of the predicted results between the modified Duncan-Chang model and traditional one shows that the results obtained from the modified model are consistent with the ones obtained from indoor test when disturbance degree D approaches zero; the stress value obtained by using Duncan-Chang model is larger than that by modified model when sand pebble soil is subject to positive disturbance; the stress value obtained by using traditional Duncan-Chang model is smaller than that obtained from the modified model when sandy pebble soil is subject to negative disturbance. It is found that the modified Duncan-Chang model can be used to describe the strength-deformation property of sandy pebble soil more accurate than traditional Duncan-Chang model at disturbed state. The former provides theoretical support for the design and construction of metro station and tunnel, pile foundation, foundation pit, and other subterranean projects in sandy pebble soil stratum, and also provides theoretical ideas for the study on constitutive model of sandy pebble soil subject to triaxial compression. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To study the modification effect of nano-clay and nano-SiO2 on cement-reinforced coastal soft soil, the effects of the nano-SiO2 and nano-clay on the mechanical properties of cement soil were studied through unconfined compressive and unconsolidated undrained shear tests, and the Duncan–Chang model was used to fit the test results. Results show that adding nano-clay and nano-SiO2 to cement soil improved its compressive and shear strength. The compressive strength and shear strength increased by 18–57% and 3–32%, respectively, with the increase in nano-clay content in a content range of 0–10%. Additionally, nano-clay can enhance the ductility of cement soil. Moreover, nano-clay and nano-SiO2 improve the shear strength by increasing the internal friction angle by 1°–2° and cohesion of 9–25%, and the cement-stabilized coastal soft soil enhanced by nano-SiO2 and nano-clay conforms to the Duncan–Chang model well.

Compared with other natural fibers, coir fiber has good strength characteristics and long-term anti-biodegradation ability. At present, most studies on randomly distributed coir fiber-reinforced soil have focused on cohesionless soil or granular soil. In this paper, the influence of randomly distributed coir fiber on the deviatoric stress and shear strength index of red clay with different fiber content was assessed by a consolidated undrained (CU) triaxial compression test. Since the hyperbolic variational character of the stress–strain relation of the samples conformed to the hyperbolic hypothesis of the Duncan–Chang model of nonlinear elastic model, the Duncan–Chang model was used to fit it, and the influences of fiber content and confining pressure on the parameters of the Duncan–Chang model were studied. The fiber content was determined by testing to be 0%, 0.2%, 0.25%, 0.3%, 0.35% and 0.4% of the dry soil mass. It has been found that coir fiber distributed in a random radial manner can significantly increase the deviatoric stress of red clay, and thus can be effectively used in the case of soil and fiber mixing. The cohesion of the red clay first increases and then decreases with the increase in fiber content, with an optimum content of 0.3%. The internal friction angle changes little with increasing fiber content.

This study was the first to examine the mechanical behavior of sediment-bearing methane hydrates (SBMHs) with hydrate abundance up to 80%. The experiment results showed that the stress–strain curves of the SBMH specimens were characterized by the elastic–plastic deformation or plastic–elastic–plastic deformation of the specimens, prominent strain softening, and a rounded head-like trailing peak shape with no obvious stress cusps. Increasing the hydrate content and pore pressure, and reducing the temperature significantly enhanced the peak strength and initial tangent modulus of the specimens, but led to a decline in the peak strain. New correlation equations for initial tangent modulus, peak strength, and peak strain depending on hydrate abundance, pore pressure, and temperature were developed. A modified hyperbolic constitutive model was proposed by introducing a correction term to the Duncan–Chang model that reflects the degree of specimen softening and considering the effects of the hydrate abundance, temperature, and pore pressure. The modified model satisfactorily revealed the strain-softening characteristics of the SBMHs and accurately reproduced the peak strength and strain of all experimental specimens, effectively characterizing the contributions of the hydrate content, pore pressure, and temperature to the stress–strain behaviors of the specimens. • Mechanical properties of high-abundance methane hydrates are investigated. • The effects of hydrate abundance, temperature, and pore pressure are considered. • Changing patterns for the elastic modulus, peak strength and strain are revealed. • Stress-strain curves exhibit strain softening behavior and a rounded peak strength. • A nonlinear constitutive model considering the strain softening effect is proposed. [ABSTRACT FROM AUTHOR]

To study the mechanical properties of Y-shaped polypropylene fiber-reinforced subgrade fill, the strength characteristics of fiber-reinforced soil with different fiber contents, fiber lengths, and confining pressures were investigated through triaxial compression tests. The test results showed that fiber reinforcement significantly improved the strength and cohesion of the subgrade fill but had a limited impact on the internal friction angle. The fiber-reinforced soil specimens exhibited a failure pattern of bulging deformation, showing plastic failure characteristics. As the fiber content and length increased, the strength of the fiber-reinforced soil increased and then decreased. The optimal fiber content was 0.2%, and the optimal fiber length was between 12 and 18 mm in all test conditions. The strength of the fiber-reinforced soil increased with increasing confining pressure. An empirical model for predicting the failure strength of fiber-reinforced soil was established by analyzing the relationships between the failure strength of the fiber-reinforced soil and the fiber content, fiber length, and confining pressure. The stress-strain relationship of the fiber-reinforced soil exhibited strain-hardening characteristics and could be approximated by a hyperbolic curve. The Duncan-Chang model could be used to describe the stress-strain relationship of this fiber-reinforced soil. A calculation method to determine the model parameters (initial tangent modulus and ultimate deviator stress) was proposed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Henan University of Technology Natural Science Edition is the property of Henan University of Technology Journal Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Parameter selection is always a critical issue for the numerical modeling of many geotechnical problems. In this work, an idea of non-parameterized numerical analysis is demonstrated by incorporating tri-axial data as the input into the distinct lattice spring model (DLSM). An automatic parameter acquisition procedure is developed to determine the parameters of a modified Duncan–Chang (DC) model which is implemented in the DLSM through the further development of an incremental DLSM and a fabric stress calculation scheme. These newly developed algorithms are verified against available numerical results and experimental counterparts. Then, the discrete feature of the DC-DLSM is explored and discussed through the numerical modeling of large-scale tri-axial tests and a fracturing test. Finally, a real rockfill dam project is analyzed by using the DC-DLSM with the available tri-axial data as the input, and a reasonable fitting is obtained, which shows the possibility for the numerical modeling of the DLSM with no parameter selection burden. [ABSTRACT FROM AUTHOR]

In seasonally frozen areas, physical and mechanical soil properties change dynamically under the effect of the freeze-thaw cycles (FTCs), which is a problem that cannot be ignored in geotechnical engineering. In order to study the effect of the FTC on the strength and the mechanism of deformation and failure of saline soil, this paper took Nong'an saline soil as the research object. In total, 105 groups of remolded samples with different salt contents (S) after FTCs were examined in unconsolidated-undrained tests. On the basis of the experiment results, the influence of FTCs on the mechanical properties of Nong'an saline soil was analyzed. The failure principal stress difference (σ1 − σ3)f and cohesion (c) were both decreased with FTC. This occurred especially rapidly after the first cycle and became stable between 30 and 60 cycles. The internal friction angle φ increased at first and then decreased. According to experimental data, a modified Duncan-Chang model was established. Compared with the experiment results, this model was reasonable to simulate the stress-strain relationship of Nong'an saline soil. Furthermore, the empirical formulas of Duncan-Chang model parameters were obtained by regression analysis. This provides a theoretical basis for saline–soil foundation and subgrade engineering in seasonal frozen areas. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mechanical properties of coarse-grained high embankment fillers are key factors that affect embankment stability. A large-scale triaxial shear tester is used to carry out consolidated drained and undrained shear tests on high embankment fillers. The mechanical properties and the stability of the high embankment in the filling process and operational period are analyzed under the background of a high rockfill embankment project (50.6 m filling height) located in the Qinba Mountain Area. Stress-strain characteristics and strength characteristics of fillers are analyzed and pore pressure coefficient was introduced to analyze filler deformation characteristics. The effects of grain breakage on filler strength and deformation are also discussed and the applicability of Duncan-Chang Model verified. Test results indicate the sample experience strain softening phenomenon under high confining pressure. Grain breakage index Âr is used to analyze the filler grain breakage features and the causes for this phenomenon are expounded. The degree of grain breakage increases significantly with confining pressure. Changes in the peak and critical-state friction angles of the fillers are related closely to grain breakage process. Under serious grain breakage, the friction angles decline significantly with grain breakage index. In the end, the applicability of Duncan-Chang model is analyzed on the test basis; neither the E~ì nor the E~B model can describe the deformation characteristics of coarse-grained embankment fillers very well. The results obtained in this study can provide a reference for the deformation characteristics of coarse-grained high embankment fillers and embankment stability analysis. [ABSTRACT FROM AUTHOR]

To study the mechanical properties of Y-shaped polypropylene fiber-reinforced subgrade fill, the strength characteristics of fiber-reinforced soil with different fiber contents, fiber lengths, and confining pressures were investigated through triaxial compression tests. The test results showed that fiber reinforcement significantly improved the strength and cohesion of the subgrade fill but had a limited impact on the internal friction angle. The fiber-reinforced soil specimens exhibited a failure pattern of bulging deformation, showing plastic failure characteristics. As the fiber content and length increased, the strength of the fiber-reinforced soil increased and then decreased. The optimal fiber content was 0.2%, and the optimal fiber length was between 12 and 18 mm in all test conditions. The strength of the fiber-reinforced soil increased with increasing confining pressure. An empirical model for predicting the failure strength of fiber-reinforced soil was established by analyzing the relationships between the failure strength of the fiber-reinforced soil and the fiber content, fiber length, and confining pressure. The stress-strain relationship of the fiber-reinforced soil exhibited strain-hardening characteristics and could be approximated by a hyperbolic curve. The Duncan-Chang model could be used to describe the stress-strain relationship of this fiber-reinforced soil. A calculation method to determine the model parameters (initial tangent modulus and ultimate deviator stress) was proposed.

In seasonally frozen areas, physical and mechanical soil properties change dynamically under the effect of the freeze-thaw cycles (FTCs), which is a problem that cannot be ignored in geotechnical engineering. In order to study the effect of the FTC on the strength and the mechanism of deformation and failure of saline soil, this paper took Nong’an saline soil as the research object. In total, 105 groups of remolded samples with different salt contents (S) after FTCs were examined in unconsolidated-undrained tests. On the basis of the experiment results, the influence of FTCs on the mechanical properties of Nong’an saline soil was analyzed. The failure principal stress difference (σ1 − σ3)f and cohesion (c) were both decreased with FTC. This occurred especially rapidly after the first cycle and became stable between 30 and 60 cycles. The internal friction angle φ increased at first and then decreased. According to experimental data, a modified Duncan-Chang model was established. Compared with the experiment results, this model was reasonable to simulate the stress-strain relationship of Nong’an saline soil. Furthermore, the empirical formulas of Duncan-Chang model parameters were obtained by regression analysis. This provides a theoretical basis for saline−soil foundation and subgrade engineering in seasonal frozen areas.

A constitutive model for marine sediments containing natural gas hydrate is essential for the simulation of the geomechanical response to gas extraction from a gas-hydrate reservoir. In this study, the triaxial compressive properties of artificial methane-hydrate-bearing sediment samples reported in an earlier work were analyzed to examine the applicability of a nonlinear elastic constitutive model based on the Duncan-Chang model. The presented model considered the dependences of the mechanical properties on methane hydrate saturation and effective confining pressure. Some parameters were decided depending on the type of sand forming a specimen. The behaviors of lateral strain versus axial strain were also formulated as a function of effective confining pressure. The constitutive model presented in this study will provide a basis for an elastic analysis of the geomechanical behaviors of the gas-hydrate reservoir in the future study, although it is currently available to a limited extent.

Based on CU triaxial tests on basalt fibre-reinforced silt (BFRS), a shear strength and stress-strain relationship analysis was conducted under various cell pressures, fibre mixing ratios and fibre lengths. It was found that basalt fibre can effectively increase the shear strength of BFRS and that the improvement is mainly in the cohesion but slightly in the angle of internal friction. The model equation between the shear strength parameters and two-fibre factor is built, and the best mixing scheme is demonstrated. The curves of the stress-strain relationship exhibit a softening character under low cell pressure and a hardening feature under high cell pressure, and there is a demarcation point of approximately 50-100 kPa between softening and hardening in this study. A softening formulation was adopted to describe the softening curves under low cell pressure, and the Duncan-Chang model was used for the hardening curves under high cell pressure. Combining the two models mentioned above, the stress-strain relationship of BFRS can be effectively depicted. [ABSTRACT FROM AUTHOR]

To reveal the influence of material composition on mechanical properties of light-weight soil, stress-strain -volumetric strain characteristics and Poisson's ratio of mixed soil were researched by consolidated drained shear tests. The results show that light-weight soil is a kind of structural soil, so its mechanical properties are affected by mixed ratio and confining pressure, and mixed soil possesses structural yield stress. When confining pressure is less than the structural yield stress, strain softening occurs; when confining pressure is more than the structural yield stress, strain hardening is observed. There are two kinds of volume change behavior: shear contraction and shear dilatancy. Shear dilatancy usually leads to strain softening, but there isn't an assured causal relationship between them. Poisson's ratio of mixed soil is a variational state parameter with the change of stress state, it decreases with increased confining pressure, and it increases with increased stress level. When axial strain is near 5%, Poisson’ ratio is gradually close to a steady value. The main range of Poisson's ratio is 0.25∼0.50 when confining pressure changes from 50 to 300 kPa. When unconfined compressive strength of mixed soil is less than 328 kPa, its stress-strain-volumetric strain characteristics can be predicted very well by Duncan-Chang model (E-B model). However, when the range of unconfined compressive strength is [328 kPa, 566 kPa], the model can't predict stress-strain characteristics accurately when confining pressure is under 200 kPa, and it also can't predict the strong shear dilatancy phenomenon of mixed soil under low confining pressure. [ABSTRACT FROM PUBLISHER]

Records show that research leading to the successful introduction of integral-type structures such as continuous beams and frames actually began in the 1930s. Simple stub-type abutments have been found to perform well and are recommended for widespread use. The purpose of this analysis was to consider the behavior of the superstructure and substructure/backfill soil when they are subjected to thermally induced lateral movement and vertically imposed load at deck level. With the Oasys Safe finite-element analysis programs, finite-element models were developed to represent a typical stub-type integral abutment bridge configuration and backfill/foundation soil profile. It was found that the behavior of the superstructure of an integral bridge was predominantly influenced by the loading magnitude, irrespective of backfill soil properties. The results suggest that when designing the superstructure, the design requirements to resist the imposed loading may be sufficient to accommodate any effects attributable to the thermal load. [ABSTRACT FROM AUTHOR]

A constitutive model for marine sediments containing natural gas hydrate is essential for the simulation of the geomechanical response to gas extraction from a gas-hydrate reservoir. In this study, the triaxial compressive properties of artificial methane-hydrate-bearing sediment samples reported in an earlier work were analyzed to examine the applicability of a nonlinear elastic constitutive model based on the Duncan-Chang model. The presented model considered the dependences of the mechanical properties on methane hydrate saturation and effective confining pressure. Some parameters were decided depending on the type of sand forming a specimen. The behaviors of lateral strain versus axial strain were also formulated as a function of effective confining pressure. The constitutive model presented in this study will provide a basis for an elastic analysis of the geomechanical behaviors of the gas-hydrate reservoir in the future study, although it is currently available to a limited extent. [ABSTRACT FROM AUTHOR]

Abstract: Based on the Duncan-Chang hyperbolic nonlinear elastic material model, this paper carried out the stress and strain numerical analysis of a clay core rock-fill dam, which is a certain building reservoir dam in Yunnan province. By loading on each layer step by step and with the static nonlinear finite element simulation of deposition, it obtained the results of the stress and deformation of the clay core rock-fill dam. The calculation showed that the great difference in deformation modulus causes non-smooth variations in deformation, stress and strain between the transition area and the rock-debris fill. From the analysis it can be seen that the present design of the dam is reasonable since no any abnormal stresses and deformations occurred in the dam. Moreover, this also indicated a feasible and provided a valuable evident for the optimization of cross-section zones in a project. [Copyright &y& Elsevier]

Interval analysis is a new uncertainty analysis method for engineering structures. In this paper, a new sensitivity analysis method is presented by introducing interval analysis which can expand applications of the interval analysis method. The interval analysis process of sensitivity factor matrix of soil parameters is given. A method of parameter intervals and decision-making target intervals is given according to the interval analysis method. With FEM, secondary developments are done for Marc and the Duncan-Chang nonlinear elastic model. Mutual transfer between FORTRAN and Marc is implemented. With practial examples, rationality and feasibility are validated. Comparison is made with some published results. [ABSTRACT FROM AUTHOR]

Abstract: Finite element method (FEM) have been widely used for the calculation of settlement of embankment on soft soils in the last decade. However, due to the complexity of construction, spatial inhomogeneity of soils, as well as sensitivity of numerical results to the variation of soil parameters, large discrepancy typically exists between numerical outputs and field observations. This paper presents a novel method, combining FEM and an improved back-propagation (BP) neural network, for correction of soil parameters in numerical prediction of embankment settlement. Duncan–Chang hyperbolic soil model is adopted with the sensitivity of eight constitutive parameters numerically investigated. The soil parameters with large sensitivity are identified, and together with the representative settlements, are used for the training of the improved BP neural network which, once established, generates correction factors of soil parameters for subsequent more accurate FEM forward predictions. It is demonstrated that the proposed numerical back-analysis framework is very efficient in practical engineering applications to calculate highway settlement. [Copyright &y& Elsevier]