Maximum Dynamic Shear Modulus Research Articles

Experimental study on the dynamic strength characteristics of combined heavy metals contaminated soil with nZVI treatment

Nanoscale zero-valent iron (nZVI), a high-performance nanomaterial, can treat heavy metal contaminants and is extensively employed for in-situ treatment of groundwater and contaminated subsoil. However, there are few studies that indicate trends in the dynamic strength parameters of nZVI-treated soils to assess site safety. In this study, three heavy metal contaminants, Zn(II), Pb(II), and Ni(II), were selected to contaminate virgin soil. The heavy-metal-contaminated soil was treated with nZVI at two concentrations (a low dose and high dose of 0.5% and 2%, respectively) of the soil's dry mass. Analyses of particle size distribution revealed a consistent shift towards larger particles upon nZVI treatment, and the percentage of sand gradually increased. Heavy metal contamination decreased the liquid and plastic limits of the virgin soil, while those of the treated soil increased with nZVI content. The dynamic triaxial results showed significantly lower maximum dynamic shear modulus for MS, MS-LdN, and MS-HdN than for NS. The damping ratios of all samples showed an S-shaped trend. Thus, nZVI has the potential to create cemented structures and immobilize heavy metals. However, its effectiveness is significantly modulated by the initial water content of the soil. While the application of nZVI proves beneficial in immobilizing heavy metal contaminants, careful consideration is imperative under dynamic loading conditions.

Shear modulus and damping ratio of granulated rubber-sand mixtures: Influence of relative particle size

Rubber-sand mixtures (RSM) have gained recognition as a valuable, lightweight, and cost-efficient energy-absorbing material with extensive potential application in engineering construction. However, the small-strain dynamic properties and prevailing mechanisms of RSM have not been thoroughly understood. This study conducted a series of resonant column tests on the small-strain dynamic modulus and damping ratio of RSM, considering the effects of particle size ratio (PSR), rubber content (RC), and confining pressure. The results reveal that the dynamic shear modulus of RSM generally decreases with increasing RC and increases with rising confining pressure. For all RC and confining pressure levels, the maximum dynamic shear modulus of RSM reaches the minimum value as the PSR approaches 1.0. In this case, the dynamic shear modulus of RSM decreases most gently with the strain. The addition of rubber consistently augments the damping ratio, whereas the PSR initially diminishes the damping ratio before eventually enhancing it. Simultaneously, as the PSR is nearing 1.0, the damping ratio achieves its lowest point. Furthermore, new empirical equations were developed to quantitatively analyze the dynamic properties of RSM, in which the predicted values of the dynamic shear modulus and the modulus attenuation coefficient show good agreement with the observed values. This work will facilitate the preparation of artificial RSM-cored geotechnical seismic isolation layers tailored to specific engineering requirements.

Experimental study on the effect of different cement content on the improvement of dynamic characteristics of seismic-prone poor soil.

The improvement of sandy soils with poor seismic properties to modify their dynamic characteristics is of great importance in seismic design for engineering sites. In this study, a series of dynamic tests on sandy soils sandy soils with poor seismic conditions were conducted using the GCTS resonant column system to investigate the improvements effects of different cement contents on dynamic characteristic parameters. The research findings are as follows: The cement content has certain influences on the dynamic shear modulus, dynamic shear modulus ratio, the maximum dynamic shear modulus, and the damping ratio of sandy soils with poor seismic properties. Among them, the influence on dynamic shear modulus is limited, while the damping ratio is significantly affected. The addition of cement to seismic-poor sandy soils significantly enhances their dynamic characteristics. The most noticeable improvement is observed when the cement content is 8%. Through curve fitting analysis, a relationship equation is established between the maximum dynamic shear modulus and the cement content, and the relevant parameters are provided. A comparative test between the improved soils and the remolded soils reveals that the addition of cement significantly improves the seismic performance of the poor soils. The recommended values for the range of variation of the dynamic shear modulus ratio and damping ratio are provided, considering the effect of improvement. These research findings provide reference guidelines for seismic design and engineering sites.

Dynamic properties of frozen rubber-reinforced expansive soils under confining pressure

In recent years, waste rubber has been increasingly utilized to enhance the performance of expansive soil foundations. This study aims to investigate the influence of rubber powder on the dynamic characteristics of frozen rubber-reinforced expansive soils (RRES) in permafrost regions. Temperature-controlled dynamic triaxial tests were conducted on RRES samples, varying rubber content, freezing temperatures, and confining pressures. The key findings are as follows: (1) A modified Hardin model with freezing temperature and rubber content as correction factors was established, which was verified to be useful for describing the dynamic stress-strain relationship. (2) Under the confining pressure, the dynamic shear modulus decreases with increasing rubber content. When the rubber content changes from 5% to 10%, the dynamic shear modulus decreases by about 20 MPa; the change becomes less obvious after the content exceeds 20%, and the RRES tends to show the characteristics of rubber. (3) As the rubber content increases, the damping ratio rises and shows the phenomenon of increasing and then decreasing with increasing confining pressure, and reaching a maximum at 0.4 MPa. (4) A prediction model for the maximum dynamic shear modulus with rubber content, freezing temperature and confining pressure is proposed.

Experimental investigation on dynamic shear modulus of undisturbed marine soils in the east coast of China

The dynamic shear modulus G is one of the vital parameters for the dynamic properties of marine soils and is crucial for marine geotechnical engineering design. In order to investigate the G characteristics of various marine soils, a series of resonant column tests were performed on undisturbed marine soils with various depths taken from Bohai Bay, Yangtze River estuary, and Jintang Strait, respectively. In addition, the maximum dynamic shear modulus Gmax and strain-compatible G of the tested marine soils were compared with the marine and terrestrial soils from the published literature. A remarkable finding is that, compared with terrestrial soils, the marine soils in different sea area present the stronger nonlinear behavior with lower shear modulus due to the special depositional environment. With the increasing of H, G in each strain range increase, and the dynamic characteristics of the marine soils gradually transition from nonlinear to linear, the Gmax and reference shear strain γ0 value of marine soils in different sea areas increases linearly with the increasing H, but the Gmax and γ0 growth rate varied with the sea environment and soil type. Based on the quantitative prediction equation of the Gmax and G attenuation relationship (G/Gmax ∼ γ) of various marine soils, a new prediction equation can be also established to predict G value in different depth and strain levels of various marine soils. The proposed equation are validated by independent experimental data of marine and terrestrial soils from the literature. In this regard, the proposed procedure provides a significant advantage in the evaluation of dynamic properties of marine soils in practice.

Study on the Geotechnical Property Changes of Loess after Seismic Landslides—A Case Study of the Subao Loess Landslide in Ningxia, China

This study aims to explore the differences between the loess and landslide deposits, focusing on aspects such as particle distribution, consolidation characteristics, and the dynamic shear modulus. Through a series of experiments, the research reveals the similarities and differences between these two entities, yielding several key findings. Firstly, the process of landsliding disrupts the original structure of the loess, resulting in a reduction in porosity and a densification of the soil. Additionally, the movement and sorting of particles during the landslides cause variations in particle size distribution across different sections of the landslide deposits. Secondly, the landslide process not only alters the soil’s structure but also changes the particle sizes within the loess. Particle wear and sieving results in the transformation of larger particles into smaller ones, leading to a more uniform particle size distribution. This shift in the structure and particle size directly impacts the consolidation characteristics of landslide deposits, resulting in a substantial reduction in the compression coefficient. Despite undergoing consolidation for decades, the middle and lower sections of the landslide deposits still exhibit under-consolidation. Although the differences in the maximum dynamic shear modulus between the loess and landslide deposits at varying depths are relatively minor, differences in the porosity and consolidation characteristics lead to faster decay rates of the dynamic shear modulus for the latter. The study also highlights a reduction in the water sensitivity of the maximum dynamic shear modulus within the landslide deposits. Based on the experimental results, a predictive model is proposed, utilizing the A and m values to estimate the maximum dynamic shear modulus of both the loess and landslide deposits. In conclusion, this research uncovers the impact of landslide processes on the structure and properties of the loess, providing an insightful understanding into the disparities between these two entities.

Experimental Study on Maximum Dynamic Shear Modulus of Yangtze River Overconsolidated Floodplain Soft Soils

This study conducted experimental tests on the undisturbed Nanjing Yangtze River floodplain soft soil using the bender element instrument to determine the maximum dynamic shear modulus of the Yangtze River floodplain overconsolidated soft soil. The Gmax of floodplain soft soil with different overconsolidated ratio OCR, initial effective confining pressure σ3c′, and void ratio e are discussed. The results indicated that Gmax reduced as e rose for given σ3c′ and OCR. In addition, an increase in OCR contributed to a gradual decrease in the decay rate of Gmax, while the Gmax decay rate is insensitive to the change of σ3c′. The void ratio-normalized maximum shear modulus Gmax/F(e) improved with the increase in the stress-normalized initial effective confining pressure σ3c′/Pa, whereas the growth rate gradually drops, and a power relationship is then obtained between Gmax/F(e) and σ3c′/Pa. Based on the regression analysis, a Gmax prediction method is established for reasonably characterizing Yangtze River floodplain soft soils with various over-consolidation states, initial stress conditions, and compactness levels, with a prediction error of less than 10%.

Characteristics of dynamic shear modulus and damping ratio and the structural formula of EPS particles lightweight soil

Dynamic triaxial tests of lightweight soil were conducted to explore the dynamic characteristics of expanded polystyrene (EPS) particle lightweight soil under traffic load. The effects of different mixed ratios, confining pressure, frequency on the backbone curves, dynamic shear modulus, and damping ratio characteristics of lightweight soil were investigated. The maximum dynamic shear modulus formula and maximum damping ratio formula of lightweight soil were established. The results indicated that backbone curves of lightweight soil had typical nonlinear and strain-hardening characteristics. With an increase in dynamic shear strain, the dynamic shear modulus curves appeared as inverse “S-shaped”. The dynamic shear modulus in the initial stage varied under different confining pressures. For γd＞10−4, the attenuation rate of the dynamic shear modulus increased with an increase in the dynamic shear strain, and for γd＞10−2, the relationship curve between the dynamic shear modulus and dynamic shear strain coincided gradually, and the attenuation process then stabilized. Owing to the special structure of lightweight soil, the damping ratio curves were “Bell-shaped” and “S-shaped.” Both the confining pressure and compressive yield stress determined the change trends of the damping ratio curves of the lightweight soil. The specimens were in an over-consolidated state and the mixed soil was in the state of shear dilatancy under dynamic loads when the confining pressure was less than the compressive yield stress, resulting in “Bell-shaped” damping ratio curve. The specimens were in the normal consolidated state and the mixed soil was in the state of shear shrinkage under dynamic loads when the confining pressure was greater than the compressive yield stress, resulting in “S-shaped” damping ratio curves. The calculation methods of the relative structural degree k and generalized void ratio e' of lightweight soil were defined to express the structural damage laws of lightweight soil having different mixed ratios under complex stress conditions using a unified formula. Based on Hardin's empirical formulas, the maximum dynamic shear modulus and maximum damping ratio formulas of lightweight soil were established by introducing the relative structural degree k and generalized void ratio e'. The formulas can quantitatively describe the dynamic responses of the special structure of lightweight soil under complex stress conditions.

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.

Dynamic Characteristics of Post-Cyclic Saturated Loess

Damage to soil structure caused by strong earthquakes is one of the main reasons for post-earthquake geohazard development. To investigate the nonlinear dynamic behaviors of the post-earthquake loess, a pre-shock reconsolidation test was designed to simulate the process of the loess undergoing earthquake and post-earthquake reconsolidation in a natural state. Furthermore, dynamic triaxial tests of the specimens before and after pre-shock action and consolidation stabilization with different over-consolidation ratios (OCR) were conducted to investigate the variety of the dynamic modulus and damping ratio of the saturated loess. The influence of pre-shock and reconsolidation on the dynamic behaviors was determined. Moreover, the mechanism of the changes after pre-shock and consolidation was discussed by combining the microstructure test results of soil samples before and after pre-shock and reconsolidation. The results suggest that the kinetic stiffness of the pre-shock saturated loess decreases significantly under the same consolidation conditions. The growth of the damping ratio-dynamic strain curve increases, and the deformation potential of the loess has a remarkable growth. With an increase in OCR, the dynamic elastic modulus after pre-shock increases continuously; however, the damping ratio decreases significantly. The dynamic stiffness increases and the deformation potential weakens significantly. The strong earthquake leads to the weakening of interparticle cementation, pore penetration, and structural reorganization in the local area, causes connecting of the macropores, and produces microfractures in the soil, which makes a significant decrease in the dynamic shear modulus ratio and an increase in the damping ratio of the loess, leading to the enhancement of soil dynamic nonlinearity and the attenuation of the dynamic strength. Moreover, the compaction effect of reconsolidation on the soil increases the interparticle friction and heals some microfractures, which leads to an increase in soil stiffness. This makes the maximum dynamic shear modulus and the maximum dynamic shear stress amplitude of the post-cyclic saturated loess perform at the same level compared with the natural loess without shock when the OCR equals three. However, the dynamic shear modulus and the damping ratio of the post-cyclic saturated loess are close to the natural loess when the OCR equals two.

Experimental Static and Dynamic Characteristics of Recycled Waste Tire Rubber Particle-Cement-Sand Composite Soil.

To investigate the static and dynamic characteristics of rubber-sand composite soil (RS soil) reinforced with cement, a series of triaxial compression tests and resonant column tests was performed by considering the influence of rubber content (10%, 20%, 30%, 40%, and 50%), cement content (0, 1.5, 2.5, 3.5 and 4.0 g/100 mL), and effective consolidation confining pressure (50, 100, and 150 kPa). Compared with the RS soil, the addition of cement significantly improved the shear strength of a cement-rubber-sand composite soil (RCS soil), based on an undrained shear test. The increase in cement content not only makes the elastic modulus and cohesion of the RCS soil increase but also reduces the internal friction angle of the RCS soil. With the increase in rubber content, the failure of the RCS soil samples changes from strain-softening to hardening, and the prediction equation of the initial elastic modulus of the RCS soil is given herein when the recommended cement content is 3.5 g/100 mL. The effects of rubber content, cement content, and effective confining pressure on the dynamic shear modulus and damping ratio of the RCS soil were studied via the resonant column test. The test results show that the increase in rubber content slows down the modulus attenuation of the RCS soil, but increases its damping ratio. The test results also show that the increase in cement content makes the bonding force between particles greater so that the modulus attenuation of the RCS soil becomes slower and the damping ratio is reduced. At the same time, according to the change rule of the maximum dynamic shear modulus of the RCS soil with the rubber content, when the recommended cement content is 3.5 g/100 mL, an empirical formula and recommended value of the shear modulus Gmax of the RCS soil are proposed.

Comparative Investigation on Small-Strain Stiffness Characteristics of Undisturbed and Compacted Highly Weathered Granites at Various Densities

To investigate the small-strain stiffness characteristics of highly weathered granite (HWG), a resonance column test system was used to conduct resonance column tests on highly weathered granite taken from the Lincang City, Yunnan Province, China. The effects of effective consolidation stress and structural changes is caused by remodeling process and initial dry density on the small-strain stiffness of HWG. Furthermore, the difference between the test data and other geotechnical materials were compared and analyzed. The test results show that the maximum dynamic shear modulus <math xmlns="http://www.w3.org/1998/Math/MathML" id="M1"> <mfenced open="(" close=")"> <mrow> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </mrow> </mfenced> </math> of remodeled highly weathered granite samples is greater than that of undisturbed samples once the effective consolidation stress is smaller than 300 kPa, but the opposite result is observed once the effective consolidation stress exceeds 300 kPa, and the phenomenon was also explained from a microscopic perspective based on the scanning electron microscopy (SEM). The <math xmlns="http://www.w3.org/1998/Math/MathML" id="M2"> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </math> of remodeled highly weathered granite gradually increases with the increase in dry density and effective consolidation stress. At an identical effective consolidation stress, the dynamic shear modulus ratio <math xmlns="http://www.w3.org/1998/Math/MathML" id="M3"> <mfenced open="(" close=")"> <mrow> <mi>G</mi> <mo>/</mo> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </mrow> </mfenced> <mo>−</mo> <mi>γ</mi> </math> curves of remodeled highly weathered granites at different initial dry densities are nearly consistent. Additionally, according to the test data, the mathematical model of <math xmlns="http://www.w3.org/1998/Math/MathML" id="M4"> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </math> for remodeled highly weathered granite considering effective consolidation pressure and initial dry density was established and agrees well with the test results of practical engineering cases. The range of variation in <math xmlns="http://www.w3.org/1998/Math/MathML" id="M5"> <mfenced open="(" close=")"> <mrow> <mi>G</mi> <mo>/</mo> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </mrow> </mfenced> </math> was given by the research results, which were compared with the <math xmlns="http://www.w3.org/1998/Math/MathML" id="M6"> <mfenced open="(" close=")"> <mrow> <mi>G</mi> <mo>/</mo> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </mrow> </mfenced> </math> of weathered granite obtained from the existing research, and the results in this work can provide a valuable reference for analyzing dynamic stability of buildings in the engineering construction of weathered granite sites.

Reduction of dynamic shear modulus of saturated marine sandy silt under complex stress conditions

Investigating the dynamic characteristics of seabed soil under complex vibrations or cyclic loads such as waves and earthquakes is important for analyzing the dynamic response and stability of the foundations of marine geotechnical structures. This paper presents an experimental investigation on the dynamic shear modulus (G) of saturated marine sandy silt subjected to various initial consolidation conditions and cyclic loading patterns. The initial consolidation condition is characterized by the initial effective mean principal stress P 0 ' and the stress ratio of anisotropic consolidation R 0 (= σ 1/σ 3), and the cyclic loading pattern is described quantitatively by the ellipse ratio of elliptical stress path (δ) and the orientation angle of major principal stress of linear stress path (α 0). A remarkable finding is that the maximum dynamic shear modulus G max and G/G max–γz θ curve is affected significantly by the initial consolidation condition (P 0′ or R 0) but is insensitive to changes in the cyclic loading pattern (δ and α 0). G max increases with increasing P 0′ or R 0, and the nonlinearity of the G/G max–γz θ curve decreases with increasing P 0′ or R 0. The control parameters G max and reference torsional shear strain γ r of the modified hyperbolic model usually known as the KZS model are related linearly to the synthesizing initial consolidation state parameters (P 0′/P a)(R 0)0.5 and (P 0′/P a)0.5 R 0, respectively. A wide-strain-range G evaluation method with comprehensive consideration of the initial consolidation condition and the cyclic loading pattern was established, and the applicability of the proposed method was verified.

Experimental investigation of dynamic shear modulus of saturated marine coral sand

Shear modulus is an essential parameter for deformation prediction and site response analysis of geological problems. This paper considers the dynamic shear modulus degradation of saturated marine coral sand containing fine particles from a reef in the Nansha Islands. Resonant-column tests were carried out on specimens of the saturated coral sand with varying non-plastic fines content (FC) and relative density (Dr) subjected to initial effective confining pressure (σ′m). The test results show that the stress exponent n—which reflects the rate of increase of the maximum dynamic shear modulus (Gmax) with increasing σ′m—is a soil-specific constant. A significant finding is that the equivalent skeleton void ratio e*sk has a unique power relationship with the normalised maximum dynamic shear modulus [Gmax/(σ′m/Pa)n]. An improved Hardin model based on binary packing theory is proposed to evaluate Gmax of the coral sand, and its applicability is verified using experimental data for three different sands from the literature. For a given shear strain, dynamic shear modulus G decreases with increasing FC and increases with increasing Dr and σ′m. The curves of the maximum dynamic shear modulus rate (G/Gmax) tend to fall with increasing FC, while Dr and σ′m have little influence on G/Gmax. The fitting parameters A and B of the Davidenkov model are insensitive to σ′m, Dr, and FC and are fixed at 1.08 and 0.42, respectively, for the saturated coral sand. Furthermore, the reference shear strain γ0 in the Davidenkov model—corresponding to the shear strain at G/Gmax = 0.5—can be evaluated uniformly by e*sk regardless of σ′m, Dr, and FC. A unified form of shear-strain-dependent G prediction method is established and provides a significant advantage in evaluating G for marine coral sand in practice.

Mechanical properties and modification mechanism of phosphogypsum stabilized soil

The red clay is widely distributed in Guizhou province, which is characterized by high natural moisture content, difficult compaction and serious shrinkage and crackingin, and phosphogypsum is discharged for 5 million tons every year in Guizhou province. For the sake of effectively reducing the accumulation of phosphogypsum, mixtures were prepared with cement as a curing agent and mass ratios of cement to phosphogypsum of 1:1, 1:2 and 1:3 (low content phosphogypsum group) and phosphogypsum to red clay of 1:1, 1:2 and 1:3 (high content phosphogypsum group). Unconfined compressive strength, expansion, shrinkage and dynamic characteristic tests were conducted to analyze the behavior and mechanical properties of the mixtures. The modification mechanism of the mixtures by phosphogypsum was further explored by XRD (X-ray diffraction) and SEM (scanning electron microscopy). which provided a theoretical basis for the application of phosphogypsum in highway engineering and improved the engineering properties of red clay. The results show that the unconfined compressive strength of the phosphogypsum stabilized soil in the low content phosphogypsum group is greater than that in the high content phosphogypsum group. When cement:phosphogypsum = 1:2.2–1:3, the unconfined compressive strength of the mixture is maximum. When cement:phosphogypsum = 1:3, the maximum dynamic shear modulus of phosphogypsum stabilized soil is the largest. The absolute expansion rate and linear shrinkage rate of phosphogypsum stabilized soil in the low content phosphogypsum group are greater than those in the high content phosphogypsum group. When cement: phosphogypsum = 1:1–1:3, the absolute expansion rate is 6.5–12.3%, and the linear shrinkage rate is 1.3–2%. When red clay:Phosphogypsum = 1:1–1:3, the absolute expansion rate is 0.2–4%, and the linear shrinkage rate is 1–1.5%. The more phosphogypsum content, the smaller the expansion deformation and shrinkage deformation of the mixture. It is suggested that mass ratios of phosphogypsum to red clay is 1:1, and the cement content is 5%. Which can not only make full use of phosphogypsum solid waste, but also improve the engineering properties of red clay.Article Highlights The unconfined compressive strength of the phosphogypsum stabilized soil in the low content phosphogypsum group is greater than that in the high content phosphogypsum group. The absolute expansion rate and linear shrinkage rate of phosphogypsum stabilized soil in the low content phosphogypsum group are greater than those in the high content phosphogypsum group. The strength of phosphogypsum stabilized soil is derived from the comprehensive effect of cement and phosphogypsum. Due to the increment of the phosphogypsum and the decline of proportion of red clay, leading to the decrease in the content of hydrophilic minerals, the expansion deformation and shrinkage deformation characteristics are changed. Considering strength and deformation characteristics, it is recommended that mixtures with 5% cement content, and phosphogypsum to red clay of 1:1 as subgrade filler, which can not only make full use of phosphogypsum solid waste, but also improve the engineering properties of red clay.

The Small Strain Stiffness Properties of Undisturbed Weathered Granite With Different Weathering Degrees

To evaluate the small strain stiffness properties of undisturbed weathered granite, the circular computer numerical control (CNC) abrasive wire sawing technology was applied to weathered granite sample processing and a series of resonance column tests were carried out to study the effects of weathering degree and effective consolidation pressure on dynamic shear modulus of undisturbed weathered granite. The results show that the degree of weathering and effective consolidation pressure have significant effects on the small strain stiffness properties of weathered granite. The samples with lower weathering degrees have higher dynamic shear modulus under the same effective consolidation pressure. The maximum dynamic shear modulus of samples with higher weathering degrees is more sensitive to effective consolidation pressure. Besides, a comparison between the experimental results with the previous results from other researchers indicates that the dynamic shear modulus ratio of weathered granite in the study area exceeds the parameter range obtained from others. According to the experimental results, a mathematical model of the relation between corrected standard penetration test (SPT) N’ value and dynamic shear modulus was established, and besides, the variation range of dynamic shear modulus ratio of weathered granite in the study area was given, which may provide a reference for dynamic stability analysis of engineering in the study area.

Study on Modified Dynamic Constitutive Model for Calcareous Sand considering Particle Breakage

Calcareous sand is special sand widely distributed in the South China Sea, which is characterized by the irregular particle shape, high porosity, easy-breaking, etc. Through a series of dynamic triaxial tests, this paper will study the influence of particle breakage on the dynamic deformation characteristics of calcareous sand and explore a modified dynamic constitutive model considering particle breakage suitable for calcareous sand. The research shows that the dynamic deformation characteristics of calcareous sand can be described by the Hardin-Drnevich model. The maximum dynamic shear modulus and average effective stress of calcareous sand obey Janbu empirical formula, with approximate a linear relationship. Through screening experiment, it is found that there is a linear relationship between particle crushing rate and effective confining pressure. On the basis of Hardin-Drnevich, the dynamic constitutive model of calcareous sand considering the influence of particle breakage is established by introducing relative crushing rate Br and constitutive model parameters. By comparing with the experimental data, it is found that the relative error between the calculated value and the experimental value of the model is no more than 12%, and the average error is no more than 8%, indicating that the modified dynamic constitutive model can better predict the dynamic characteristics of calcareous sand.

Dynamic Characteristics of Coral Sand in the Condition of Particle Breakage

To study the influence of coral sand particle breakage on its dynamic characteristics, taking the South China Sea coral sand as the research object, one-dimensional consolidation test was conducted to prepare different particle breakage degree samples, and then, the GCTS resonant column test was carried out on these samples. The results show that with the degree of coral sand particle breakage increases, the maximum dynamic shear modulus of coral sand first increases and then decreases, and the minimum damping ratio also shows a similar trend. In addition, based on Hardin’s theory of the relative breakage, this study proposes a new modified relative breakage B r ′ for describing particle breakage and establishes a relationship between the maximum dynamic shear modulus and the modified relative breakage B r ′ .

Effect of different fibers on small-strain dynamic properties of microbially induced calcite precipitation–fiber combined reinforced calcareous sand

Microbially induced calcite precipitation (MICP)–fiber combined reinforcement through the addition of fibers during the MICP process is a novel, natural, and green technique for foundation improvement, which can effectively enhance the mechanical properties of cemented soil. However, the small-strain dynamic properties of this method remain unexplored. The effects of different polyester fiber and hemp fiber contents (0%, 0.1%, 0.2%, and 0.4%) on the dynamic properties of the MICP–fiber combined reinforced calcareous sand under small-strain conditions were studied using resonant column tests, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The maximum dynamic shear modulus of the MICP–fiber combined reinforced calcareous sand under small-strain increases with the fiber content; the stiffness degradation rate of the dynamic shear modulus ratio of the test sample increases with the addition of two types of fibers, and the addition of hemp fibers greatly boosts the increase rate of the damping ratio. The SEM results indicate that excessive fibers distributed between the sand particles occupy the nucleation sites of bacteria, hinder the bonding between sand particles, and ultimately affect the dynamic shear modulus parameters of the sample. The AFM results show that the hemp fiber has much greater surface roughness than the polyester fiber. Therefore, the change rate of the damping ratio of the hemp fiber-doped MICP–fiber combined reinforced calcareous sand is much greater than that of the polyester fiber-doped sample. This is the first report on the basic mechanism of the small-strain dynamic properties of the MICP–fiber combined reinforced calcareous sand with different fiber contents and types. Furthermore, it provides a new theoretical basis for related research on improving the dynamic properties of sand thus reinforced.

Factors Affecting Site-Specific Response Analysis

ABSTRACT The engineering purpose of a site-specific response analysis is to estimate the uniform hazard acceleration spectrum on the ground surface for a selected hazard level. One of the mandatory components for site response analyses is one or more representative acceleration time histories that need to be scaled with respect to the calculated seismic hazard level for the selected site. The selection and scaling procedures of earthquake acceleration records play an important role in this approach. The effects and differences in using two different scaling approaches are studied: scaling with respect to ground motion parameters and response spectrum scaling. A set of homogeneous ground motion prediction relationships are developed for peak ground acceleration, peak ground velocity, root-mean-square acceleration, Arias intensity, cumulative absolute velocity, maximum spectral acceleration, response spectrum intensity, and acceleration spectrum intensity based on a uniform set of acceleration records for ground motion parameter scaling. The uncertainties associated with site response analysis are considered as epistemic and aleatory uncertainties in source characteristics, soil profile, and soil properties. Aleatory variability is due to the intrinsic randomness of natural systems; it cannot be reduced with additional data (Passeri et al. 2020), however; its variability may be modeled by probability distribution functions. Thus, one possibility is to determine the probability distribution of the acceleration spectrum calculated on the ground surface for all possible input acceleration records, site profiles, and dynamic soil properties. The variability in the earthquake source and path effects are considered using a large number of acceleration records compatible with the site-dependent earthquake hazard in terms of fault mechanism, magnitude, and distance range recorded on stiff site conditions. Likewise, a large number of soil profiles may be considered to account for the site condition variability. The uncertainties related to dynamic soil properties may be considered as possible variability of maximum dynamic shear modulus in site response analyses. A methodology is proposed to estimate a uniform hazard acceleration spectrum on the ground surface based on the probabilistic assessment of the factors involved in site response analysis. The uniform hazard acceleration spectra obtained from a case study are compared with the spectra calculated by probabilistic models proposed in the literature.