The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique natu...The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique nature of this soil type.In this study,a series of unconfined compression tests were carried out on unsaturated CWG soil in an underground engineering site,and the effects of varying the environmental variables on the main undrained mechanical properties were analyzed.Based on the experimental results,a novel constitutive model was then established using the damage mechanics theory and the undetermined coefficient method.The results demonstrate that the curves of remolded CWG specimens with different moisture contents and dry densities exhibited diverse characteristics,including brittleness,significant softening,and ductility.As a typical indicator,the unconfined compression strength of soil specimens initially increased with an increase in moisture content and then decreased.Meanwhile,an optimal moisture content of approximately 10.5%could be observed,while a critical moisture content value of 13.0%was identified,beyond which the strength of the specimen decreases sharply.Moreover,the deformation and fracture of CWG specimens were predominantly caused by shear failure,and the ultimate failure modes were primarily influenced by moisture content rather than dry density.Furthermore,by comparing several similar models and the experimental data,the proposed model could accurately replicate the undrained mechanical characteristics of unsaturated CWG soil,and quantitatively describe the key mechanical indexes.These findings offer a valuable reference point for understanding the underlying mechanisms,anticipating potential risks,and implementing effective control measures in similar underground engineering projects.展开更多
Clay deposits typically exhibit significant degrees of heterogeneity and anisotropy in their strength and stiffness properties.Such non-monotonic responses can significantly impact the stability analysis and design of...Clay deposits typically exhibit significant degrees of heterogeneity and anisotropy in their strength and stiffness properties.Such non-monotonic responses can significantly impact the stability analysis and design of overlying shallow foundations.In this study,the undrained bearing capacity of shallow foundations resting on inhomogeneous and anisotropic clay layers subjected to oblique-eccentric combined loading is investigated through a comprehensive series of finite element limit analysis(FELA)based on the well-established lower-bound theorem and second-order cone programming(SOCP).The heterogeneity of normally consolidated(NC)clays is simulated by adopting a well-known general model of undrained shear strength increasing linearly with depth.In contrast,for overconsolidated(OC)clays,the variation of undrained shear strength with depth is considered to follow a bilinear trend.Furthermore,the inherent anisotropy is accounted for by adopting different values of undrained shear strength along different directions within the soil medium,employing an iterative-based algorithm.The results of numerical simulations are utilized to investigate the influences of natural soil heterogeneity and inherent anisotropy on the ultimate bearing capacity,failure envelope,and failure mechanism of shallow foundations subjected to the various combinations of vertical-horizontal(V-H)and vertical-moment(V-M)loads.展开更多
Shallow gas can cause many disasters,and it is reported in many marine engineering constructions.For this,it is imperative to understand the impact of gas on the mechanical behaviors of soil.This study investigated th...Shallow gas can cause many disasters,and it is reported in many marine engineering constructions.For this,it is imperative to understand the impact of gas on the mechanical behaviors of soil.This study investigated the influence of undrained triaxial compression tests on dense gassy sand commonly encountered in coastal areas.Triaxial tests were performed on specimens with saturations of 100%,99.8%,95.9%,and 92.7% under confining pressures of 50 kPa and 200 kPa by a self-developed multipurpose integrated triaxial apparatus(MITA)for gassy soil.The results are presented in terms of monotonic stress‒strain behavior,volumetric behavior,shear strength,and excess pore water pressure(EPWP).The occurrence of gas bubbles has different effects on loose and dense sands,augmenting the undrained shear strength of loose sand while concurrently diminishing that of dense sand.The deviatoric stress of dense sand increases during shear shrinkage,which is similar to the characteristics of loose sand under the influence of gas bubbles.However,following sand dilation,the effect of gas bubbles on deviatoric stress manifests in an antithetical manner.With elevated gas content,the shear strength of dense sand decreases,accompanied by a deceleration in the development of EPWP and a notable increase in volumetric changes.To this end,a microscopic explanation concerning the deformation and evolution of gas bubbles within sand during the shear process was presented to reveal the macroscopic laws governing the undrained shear attributes of dense gassy sand.展开更多
This opinion article discusses the original research work of Yünkül et al.(the Authors)published in the Journal of Mountain Science 21(9):3108–3122.Employing non-linear regression,fuzzy logic and artificial...This opinion article discusses the original research work of Yünkül et al.(the Authors)published in the Journal of Mountain Science 21(9):3108–3122.Employing non-linear regression,fuzzy logic and artificial neural network modeling techniques,the Authors interrogated a large database assembled from the existing research literature to assess the performance of twelve equation rules in predicting the undrained shear strength(s_(u))mobilized for remolded fine-grained soils at different values of liquidity index(I_(L))and water content ratio.Based on their analyses,the Authors proposed a simple and reportedly reliable correlation(i.e.,Eq.9 in their paper)for predicting s_(u) over the I_(L) range of 0.15 to 3.00.This article describes various shortcomings in the Authors’assembled database(including potentially anomalous data and covering an excessively wide I_(L) range in relation to routine geotechnical and transportation engineering applications)and their proposed s_(u)=f(I_(L))correlation.Contrary to the Authors’assertions,their proposed correlation is not reliable for fine-grained soils with consistencies in the general firm to stiff range(i.e.,for 0.15<I_(L)<0.40),increasingly overestimating s_(u) for reducing I_(L),and eventually predicting s_(u)→+∞for I_(L)→0.15+(while producing mathematically undefined s_(u) for I_(L)<0.15),thus rendering their correlation unconservative and potentially leading to unsafe geotechnical designs.Exponential or regular-power type s_(u)=f(I_(L))models are more s_(u)itable when developing correlations that are applicable over the full plastic range(of 0<I_(L)<1),thereby providing reasonably conservative s_(u) predictions for use in the preliminary design for routine geotechnical engineering applications.展开更多
Conventional empirical equations for estimating undrained shear strength(s_(u))from piezocone penetration test(CPTu)data,without incorporating soil physical properties,often lack the accuracy and robustness required f...Conventional empirical equations for estimating undrained shear strength(s_(u))from piezocone penetration test(CPTu)data,without incorporating soil physical properties,often lack the accuracy and robustness required for geotechnical site investigations.This study introduces a hybrid virus colony search(VCS)algorithm that integrates the standard VCS algorithm with a mutation-based search mechanism to develop high-performance XGBoost learning models to address this limitation.A dataset of 372 seismic CPTu and corresponding soil physical properties data from 26 geotechnical projects in Jiangs_(u)Province,China,was collected for model development.Comparative evaluations demonstrate that the proposed hybrid VCS-XGBoost model exhibits s_(u)perior performance compared to standard meta-heuristic algorithm-based XGBoost models.The res_(u)lts highlight that the consideration of soil physical properties significantly improves the predictive accuracy of s_(u),emphasizing the importance of considering additional soil information beyond CPTu data for accurate s_(u)estimation.展开更多
Biostimulation has been proven to be an available approach for microbially induced calcium carbonate precipitation(MICP).However,biostimulation may not be as effective as bioaugmentation in some unfavorable situations...Biostimulation has been proven to be an available approach for microbially induced calcium carbonate precipitation(MICP).However,biostimulation may not be as effective as bioaugmentation in some unfavorable situations.In this study,the feasibility of biochar-assisted MICP for improving the shear strength of calcareous sand is investigated.The optimization of cementation solution for biostimulated MICP is first determined through a series of unconfined compressive tests.The shear characteristics of biocemented calcareous sand,enhanced by biochar and treated through biostimulation,are then assessed using consolidated undrained(CU)shear triaxial tests.To characterize the shear strength of biocemented sand under low effective normal stress,both Mohr-Coulomb failure envelopes and nonlinear failure envelopes were employed.Meanwhile,the current study also compared and analyzed two distinct stress states:maximum principal stress ratio(σ'_(1)/σ'_(3)max)and Skempton’s pore pressure parameter A=0,to identify an appropriate failure criterion for determination of the shear strength parameters.Furthermore,the microscopic features and post-failure characteristics of biochar-assisted calcareous sand were examined and discussed.The findings indicate that biochar can contribute to an increase in cementation content by serving as additional nucleation sites.The study may provide valuable insights into the potential of biochar-assisted MICP for enhancing the biostimulation approach.展开更多
When tunnelling through low-permeability saturated ground,the pore pressure decreases in the vicinity of the cavity.In certain instances of deep tunnels crossing weak rocks,the pore pressure may even become negative.A...When tunnelling through low-permeability saturated ground,the pore pressure decreases in the vicinity of the cavity.In certain instances of deep tunnels crossing weak rocks,the pore pressure may even become negative.All existing analytical solutions for the undrained ground response curve(GRC)in the literature assume that the ground fully retains its saturation,in which case the development of negative pore pressures has a stabilising effect e it results in increased effective stresses,and thus shearing resistance,which in turn leads to reduced deformations and plastification.In practice,however,negative pore pressures can induce partial or complete ground desaturation,which may even invalidate the premise of undrained conditions and lead to considerably increased deformations and plastification.In such cases,existing solutions are unsafe for design.The present paper aims to address this shortcoming,by presenting a novel analytical solution for the undrained GRC which incorporates the effect of the excavation-induced desaturation.The solution is derived under the assumption that the ground desaturates completely and immediately under negative pore pressures,which provides the upper bound of deformations and plastification for cases of partial desaturation.The rock is considered to be a linear elastic,brittle-plastic material,obeying a non-associated Mohr-Coulomb(MC)yield criterion.Nevertheless,the solution is also applicable to perfectly plastic rocks via a simple modification of the input parameters.Although the solution is in general semi-analytical,simple closed-form expressions are obtained in the special case of non-dilatant rocks.These expressions are also applicable to rocks exhibiting limited dilatancy,which is usually the case.An application example,based on the planned deep geological repository for radioactive waste in Switzerland,demonstrates the significant practical value and usefulness of the novel solution and underscores its necessity in cases where existing solutions that disregard desaturation are rendered thoroughly unsafe for design.展开更多
Transparent sand is a special material to realize visualization of concealed work in geotechnical engineering. To investigate the dynamic characteristics of transparent sand, a series of undrained cyclic simple shear ...Transparent sand is a special material to realize visualization of concealed work in geotechnical engineering. To investigate the dynamic characteristics of transparent sand, a series of undrained cyclic simple shear tests were conducted on the saturated transparent sand composed of fused quartz and refractive index-matched oil mixture. The results reveal that an increase in the initial shear stress ratio significantly affects the shape of the hysteresis loop, particularly resulting in more pronounced asymmetrical accumulation. Factors such as lower relative density, higher cyclic stress ratios and higher initial shear stress ratio have been shown to accelerate cyclic deformation, cyclic pore water pressure and stiffness degradation. The cyclic liquefaction resistance curves decrease as the initial shear stress ratio increases or as relative density decreases. Booker model and power law function model were applied to predict the pore water pressure for transparent sand. Both models yielded excellent fits for their respective condition, indicating a similar dynamic liquefaction pattern to that of natural sands. Finally, transparent sand displays similar dynamic characteristics in terms of cyclic liquefaction resistance and Kα correction factor. These comparisons indicate that transparent sand can serve as an effective means to mimic many natural sands in dynamic model tests.展开更多
Machine learning(ML)models are widely used for predicting undrained shear strength(USS),but interpretability has been a limitation in various studies.Therefore,this study introduced shapley additive explanations(SHAP)...Machine learning(ML)models are widely used for predicting undrained shear strength(USS),but interpretability has been a limitation in various studies.Therefore,this study introduced shapley additive explanations(SHAP)to clarify the contribution of each input feature in USS prediction.Three ML models,artificial neural network(ANN),extreme gradient boosting(XGBoost),and random forest(RF),were employed,with accuracy evaluated using mean squared error,mean absolute error,and coefficient of determination(R^(2)).The RF achieved the highest performance with an R^(2) of 0.82.SHAP analysis identified pre-consolidation stress as a key contributor to USS prediction.SHAP dependence plots reveal that the ANN captures smoother,linear feature-output relationships,while the RF handles complex,non-linear interactions more effectively.This suggests a non-linear relationship between USS and input features,with RF outperforming ANN.These findings highlight SHAP’s role in enhancing interpretability and promoting transparency and reliability in ML predictions for geotechnical applications.展开更多
Foam plays a crucial role in conditioning the mechanical properties of coarse-grained soil during earth pressure balance shield tunneling.Experimental findings have shown that an appropriate foam injection ratio impro...Foam plays a crucial role in conditioning the mechanical properties of coarse-grained soil during earth pressure balance shield tunneling.Experimental findings have shown that an appropriate foam injection ratio improves the workability and compressibility of conditioned soil,while reducing its shear strength under undrained conditions.Understanding how foam operates in soil pores is essential for interpreting these phenomena.This study utilized a theoretical two-dimensional(2D)model to analyze the effects of gas saturation,gas-liquid interface,and gas dissolution on the undrained mechanical properties of foamconditioned soil.Based on these analyses,a constitutive equation was developed,using the transition void ratio,compression index and contact coefficient as key parameters to describe the relationships among vertical stress σ_(v),void ratio e_(c),and shear strengthτ.The undrained mechanical properties calculated by the 2D model align well with experimental observations,indicating that while foam enhances the bonding force between soil particles,both excessive and insufficient gas saturation,along with larger contact angles,notably undermine this enhancement,resulting in unsuitable workability.A gas saturation of 0.5-0.8 is recommended for soil conditioning.Under typical chamber pressures,the effects of gas-liquid interface and gas dissolution on compressibility and shear strength are negligible.The constitutive equation demonstrates excellent agreement with experimental data,and can well predict the variations in σ_(v)-e_(c)-τ.This study contributes to understanding the role of foam in soil pores,and the developed constitutive equation serves as a valuable reference for describing the undrained mechanical behavior of foam-conditioned coarse-grained soil.展开更多
The microbial-induced calcite precipitation(MICP)technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils.However,the efficiency of MICP-treated s...The microbial-induced calcite precipitation(MICP)technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils.However,the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions.Furthermore,the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented.Moreover,the effect of wetting-drying(WD)cycles on the cyclic characteristics of MICP-treated sand is not readily available,which may contribute to the limited adoption of MICP treatment in field applications.In this study,strain-controlled consolidated undrained(CU)cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains:Sporosarcina pasteurii and Bacillus subtilis.The treatment durations of 7 d and 14 d were considered,with an interval of 12 h between treatments.The cyclic characteristics,such as the shear modulus and damping ratio,of the MICP-treated sand with the different bacterial strains have been estimated and compared.Furthermore,the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5–15 cycles and aging of samples up to three months.The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand,considering the influence of different bacterial strains,treatment duration,and WD cycles.展开更多
This study aims to predict the undrained shear strength of remolded soil samples using non-linear regression analyses,fuzzy logic,and artificial neural network modeling.A total of 1306 undrained shear strength results...This study aims to predict the undrained shear strength of remolded soil samples using non-linear regression analyses,fuzzy logic,and artificial neural network modeling.A total of 1306 undrained shear strength results from 230 different remolded soil test settings reported in 21 publications were collected,utilizing six different measurement devices.Although water content,plastic limit,and liquid limit were used as input parameters for fuzzy logic and artificial neural network modeling,liquidity index or water content ratio was considered as an input parameter for non-linear regression analyses.In non-linear regression analyses,12 different regression equations were derived for the prediction of undrained shear strength of remolded soil.Feed-Forward backpropagation and the TANSIG transfer function were used for artificial neural network modeling,while the Mamdani inference system was preferred with trapezoidal and triangular membership functions for fuzzy logic modeling.The experimental results of 914 tests were used for training of the artificial neural network models,196 for validation and 196 for testing.It was observed that the accuracy of the artificial neural network and fuzzy logic modeling was higher than that of the non-linear regression analyses.Furthermore,a simple and reliable regression equation was proposed for assessments of undrained shear strength values with higher coefficients of determination.展开更多
In order to obtain the reasonable undrained shear strength Su for geotechnical analyses of bridge foundations in Yangtze River floodplain clayey soils, a site-specific study is conducted using the imported piezocone p...In order to obtain the reasonable undrained shear strength Su for geotechnical analyses of bridge foundations in Yangtze River floodplain clayey soils, a site-specific study is conducted using the imported piezocone penetration test （CPTu） with dissipation phases at the Fourth Nanjing Yangtze River Bridge construction sites. Taking the values of Su from laboratory tests as references, several existing Su-predicted methods based on CPTu are compared and evaluated. To verify the presented cone factor Nk, additional test sites are selected and examined. The results show that the values of cone factors such as Nkt, Nke, and Nau, depend on the shear test mode and disturbance. Generally, the values of Nke show more scattering than those of Nkt and N△u. For the stratified and layered sediments of the Yangtze River floodplain, it is recommended using the net cone resistance qT to estimate Su and the preliminary cone factor values Nkt are from 7 to 16, with an average of 11. It is also confirmed that the CPTu test, as a new technique in site characterization, can present reasonable parameters for bridge foundations.展开更多
The undrained shear strength of shallow strata is a critical parameter for safety design in deep-water operations.In situ piezocone penetration tests(CPTU) and laboratory experiments are performed at Site W18-19 in th...The undrained shear strength of shallow strata is a critical parameter for safety design in deep-water operations.In situ piezocone penetration tests(CPTU) and laboratory experiments are performed at Site W18-19 in the Shenhu area, northern South China Sea, where China's first marine hydrate exploitation operation is due to be located. The validation of the undrained shear strength prediction model based on CPTU parameters. Different laboratory tests, including pocket penetrometer, torvane, miniature vane and unconsolidated undrained triaxial tests, are employed to solve empirical cone coefficients by statistical and mathematical methods. Finally, an optimized model is proposed to describe the longitudinal distribution of undrained shear strength in calcareous clay strata in the Shenhu area. Research results reveal that average empirical cone coefficients based on total cone resistance, effective resistance, and excess-pore pressure are 13.8, 4.2 and 14.4, respectively. The undrained shear strength prediction model shows a good fit with the laboratory results only within specific intervals based on their compaction degree and gas-bearing conditions. The optimized prediction model in piecewise function format can be used to describe the longitudinal distribution of the undrained shear strength for calcareous clay within all depth intervals from the mud-line to the upper boundary of hydrate-bearing sediments(HBS). The optimized prediction result indicates that the effective cone resistance model is suitable for very soft to firm calcareous clays,the excess-pore pressure model can depict the undrained shear strength for firm to very stiff but gas-free clays,while the total cone resistance model is advantageous for evaluating the undrained shear strength for very stiff and gassy clays. The optimized model in piecewise function format can considerably improve the adaptability of empirical models for calcareous clay in the Shenhu area. These results are significant for safety evaluations of proposed hydrate exploitation projects.展开更多
Extensive data of undrained shear strength for various remolded soils are compiled to normalize the remolded undrained strength. Remolded soils have a wide spectrum of liquid limits ranging from 25% to 412%. It is fou...Extensive data of undrained shear strength for various remolded soils are compiled to normalize the remolded undrained strength. Remolded soils have a wide spectrum of liquid limits ranging from 25% to 412%. It is found that the remolded undrained strength is a function of water content and liquid limit. Furthermore, a simple index designated as normalized water content w * is introduced for normalizing remolded undrained strength for various soils. The normalized water content w * is the ratio of water content to liquid limit. The relationship between the remolded undrained strength and the normalized water content can be expressed by a simple equation. The new simple equation is not only valuable theoretically for helping in assessing the in situ mechanical behavior, but also useful to ocean engineering practice.展开更多
A parametric study of undrained stability of a spherical cavity in clays is investigated by finite elementlimit analysis with an axisymmetric condition. Influences of cover depth ratio of cavity and dimensionlessoverb...A parametric study of undrained stability of a spherical cavity in clays is investigated by finite elementlimit analysis with an axisymmetric condition. Influences of cover depth ratio of cavity and dimensionlessoverburden factor on predicted failure mechanisms and dimensionless load factor are examined.It is found that a previously recommended and up-to-date lower bound solution to the problem wassignificantly inaccurate for practice use. Thus, an accurate approximate solution to the problem is proposedfrom nonlinear regression analysis of the computed average bound solutions. New cavity stabilityfactors for the soil cohesion and soil unit weight are proposed. New findings are revealed for the threedimensionaleffect of the cavity shape on these factors between the axisymmetric and plane strainconditions, and their applications to the undrained stability evaluation of cavity problems in practice aredescribed.展开更多
Accurate assessment of undrained shear strength(USS)for soft sensitive clays is a great concern in geotechnical engineering practice.This study applies novel data-driven extreme gradient boosting(XGBoost)and random fo...Accurate assessment of undrained shear strength(USS)for soft sensitive clays is a great concern in geotechnical engineering practice.This study applies novel data-driven extreme gradient boosting(XGBoost)and random forest(RF)ensemble learning methods for capturing the relationships between the USS and various basic soil parameters.Based on the soil data sets from TC304 database,a general approach is developed to predict the USS of soft clays using the two machine learning methods above,where five feature variables including the preconsolidation stress(PS),vertical effective stress(VES),liquid limit(LL),plastic limit(PL)and natural water content(W)are adopted.To reduce the dependence on the rule of thumb and inefficient brute-force search,the Bayesian optimization method is applied to determine the appropriate model hyper-parameters of both XGBoost and RF.The developed models are comprehensively compared with three comparison machine learning methods and two transformation models with respect to predictive accuracy and robustness under 5-fold cross-validation(CV).It is shown that XGBoost-based and RF-based methods outperform these approaches.Besides,the XGBoostbased model provides feature importance ranks,which makes it a promising tool in the prediction of geotechnical parameters and enhances the interpretability of model.展开更多
The undrained shear strength （su） of fine-grained soils that can be measured in situ and in laboratory isone of the key geotechnical parameters. The unconfined compression test （UCT） is widely used in laboratoryto...The undrained shear strength （su） of fine-grained soils that can be measured in situ and in laboratory isone of the key geotechnical parameters. The unconfined compression test （UCT） is widely used in laboratoryto measure this parameter due to its simplicity; however, it is severely affected by sampledisturbance. The vane shear test （VST） technique that is less sensitive to sample disturbance involves acorrection factor against the soil plasticity, commonly known as the Bjerrum＇s correction factor, m. Thisstudy aims to reevaluate the Bjerrum＇s correction factor in consideration of a different approach and arelatively new method of testing. Atterberg limits test, miniature VST, and reverse extrusion test （RET）were conducted on 120 remolded samples. The effect of soil plasticity on undrained shear strength wasexamined using the liquidity index instead of Bjerrum＇s correction factor. In comparison with the resultobatined using the Bjerrum＇s correction factor, the undrained shear strength was better representedwhen su values were correlated with the liquidity index. The results were validated by the RET, whichwas proven to take into account soil plasticity with a reliable degree of accuracy. This study also showsthat the RET has strong promise as a new tool for testing undrained shear strength of fine-grained soils.展开更多
Consolidated-isotropically undrained triaxial compression （CIUC） tests were performed on the reconstituted deep clay from a mine in East China. It was consolidated to maximum stresses in the range of 0.3-2.6 MPa. Th...Consolidated-isotropically undrained triaxial compression （CIUC） tests were performed on the reconstituted deep clay from a mine in East China. It was consolidated to maximum stresses in the range of 0.3-2.6 MPa. The test results show that the stress-strain-strength properties of the clay during undrained shear are significantly stress-dependent. In particular, in the case of high consolidation pressure, the post-peak drop in strength on stress-strain curves and shear plane in soil specimens are more evident, the peak stress ratio and the axial strain at which this ratio was reached are smaller, and the relationship between pore pressure and axial strain is also significantly different from that for the case of low consolidation pressure. The environmental scanning electron microscope observations and micro analysis lead to an understanding of the physical mechanisms underlying the above stress-dependent mechanical behavior. In addition, the CIUC behaviors of the studied clay are discussed in the context of critical state soil mechanics.展开更多
Rapid advances in deep-sea mining engineering have created an urgent need for the accurate evaluation of the undrained strength of marine soils,especially surface soils.Significant achievements have been made using fu...Rapid advances in deep-sea mining engineering have created an urgent need for the accurate evaluation of the undrained strength of marine soils,especially surface soils.Significant achievements have been made using full-flow penetration penetrometers to evaluate marine soil strength in the deep penetration;however,a method considering the effect of ambient water on the surface penetration needs to be established urgently.In this study,penetrometers with multiple probes were developed and used to conduct centrifuge experiments on South China Sea soil and kaolin clay.First,the forces on the probes throughout the penetration process were systematically analyzed and quantified.Second,the spatial influence zone was determined by capturing the resistance changes and sample crack development,and the penetration depth for a sample to reach a stable failure mode was given.Third,the vane shear strength was used to invert the penetration resistance factor of the ball and determine the range of the penetration resistance factor values.Furthermore,a methodology to determine the penetration resistance factors for surface marine soils was established.Finally,the effect of the water cavity above various probes in the surface penetration was used to formulate an internal mechanism for variations in the penetration resistance factor.展开更多
基金Project(42202318)supported by the National Natural Science Foundation of ChinaProject(252300421199)supported by the Natural Science Foundation of Henan Province,ChinaProject(2024JJ6219)supported by the Hunan Provincial Natural Science Foundation of China。
文摘The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique nature of this soil type.In this study,a series of unconfined compression tests were carried out on unsaturated CWG soil in an underground engineering site,and the effects of varying the environmental variables on the main undrained mechanical properties were analyzed.Based on the experimental results,a novel constitutive model was then established using the damage mechanics theory and the undetermined coefficient method.The results demonstrate that the curves of remolded CWG specimens with different moisture contents and dry densities exhibited diverse characteristics,including brittleness,significant softening,and ductility.As a typical indicator,the unconfined compression strength of soil specimens initially increased with an increase in moisture content and then decreased.Meanwhile,an optimal moisture content of approximately 10.5%could be observed,while a critical moisture content value of 13.0%was identified,beyond which the strength of the specimen decreases sharply.Moreover,the deformation and fracture of CWG specimens were predominantly caused by shear failure,and the ultimate failure modes were primarily influenced by moisture content rather than dry density.Furthermore,by comparing several similar models and the experimental data,the proposed model could accurately replicate the undrained mechanical characteristics of unsaturated CWG soil,and quantitatively describe the key mechanical indexes.These findings offer a valuable reference point for understanding the underlying mechanisms,anticipating potential risks,and implementing effective control measures in similar underground engineering projects.
文摘Clay deposits typically exhibit significant degrees of heterogeneity and anisotropy in their strength and stiffness properties.Such non-monotonic responses can significantly impact the stability analysis and design of overlying shallow foundations.In this study,the undrained bearing capacity of shallow foundations resting on inhomogeneous and anisotropic clay layers subjected to oblique-eccentric combined loading is investigated through a comprehensive series of finite element limit analysis(FELA)based on the well-established lower-bound theorem and second-order cone programming(SOCP).The heterogeneity of normally consolidated(NC)clays is simulated by adopting a well-known general model of undrained shear strength increasing linearly with depth.In contrast,for overconsolidated(OC)clays,the variation of undrained shear strength with depth is considered to follow a bilinear trend.Furthermore,the inherent anisotropy is accounted for by adopting different values of undrained shear strength along different directions within the soil medium,employing an iterative-based algorithm.The results of numerical simulations are utilized to investigate the influences of natural soil heterogeneity and inherent anisotropy on the ultimate bearing capacity,failure envelope,and failure mechanism of shallow foundations subjected to the various combinations of vertical-horizontal(V-H)and vertical-moment(V-M)loads.
基金the National Natural Science Foundation of China(Grant No.52127815)the Hubei Provincial Natural Science Foundation of China(Grant No.2023AFA078).
文摘Shallow gas can cause many disasters,and it is reported in many marine engineering constructions.For this,it is imperative to understand the impact of gas on the mechanical behaviors of soil.This study investigated the influence of undrained triaxial compression tests on dense gassy sand commonly encountered in coastal areas.Triaxial tests were performed on specimens with saturations of 100%,99.8%,95.9%,and 92.7% under confining pressures of 50 kPa and 200 kPa by a self-developed multipurpose integrated triaxial apparatus(MITA)for gassy soil.The results are presented in terms of monotonic stress‒strain behavior,volumetric behavior,shear strength,and excess pore water pressure(EPWP).The occurrence of gas bubbles has different effects on loose and dense sands,augmenting the undrained shear strength of loose sand while concurrently diminishing that of dense sand.The deviatoric stress of dense sand increases during shear shrinkage,which is similar to the characteristics of loose sand under the influence of gas bubbles.However,following sand dilation,the effect of gas bubbles on deviatoric stress manifests in an antithetical manner.With elevated gas content,the shear strength of dense sand decreases,accompanied by a deceleration in the development of EPWP and a notable increase in volumetric changes.To this end,a microscopic explanation concerning the deformation and evolution of gas bubbles within sand during the shear process was presented to reveal the macroscopic laws governing the undrained shear attributes of dense gassy sand.
文摘This opinion article discusses the original research work of Yünkül et al.(the Authors)published in the Journal of Mountain Science 21(9):3108–3122.Employing non-linear regression,fuzzy logic and artificial neural network modeling techniques,the Authors interrogated a large database assembled from the existing research literature to assess the performance of twelve equation rules in predicting the undrained shear strength(s_(u))mobilized for remolded fine-grained soils at different values of liquidity index(I_(L))and water content ratio.Based on their analyses,the Authors proposed a simple and reportedly reliable correlation(i.e.,Eq.9 in their paper)for predicting s_(u) over the I_(L) range of 0.15 to 3.00.This article describes various shortcomings in the Authors’assembled database(including potentially anomalous data and covering an excessively wide I_(L) range in relation to routine geotechnical and transportation engineering applications)and their proposed s_(u)=f(I_(L))correlation.Contrary to the Authors’assertions,their proposed correlation is not reliable for fine-grained soils with consistencies in the general firm to stiff range(i.e.,for 0.15<I_(L)<0.40),increasingly overestimating s_(u) for reducing I_(L),and eventually predicting s_(u)→+∞for I_(L)→0.15+(while producing mathematically undefined s_(u) for I_(L)<0.15),thus rendering their correlation unconservative and potentially leading to unsafe geotechnical designs.Exponential or regular-power type s_(u)=f(I_(L))models are more s_(u)itable when developing correlations that are applicable over the full plastic range(of 0<I_(L)<1),thereby providing reasonably conservative s_(u) predictions for use in the preliminary design for routine geotechnical engineering applications.
基金funded by the National Science Fund for Distinguished Young Scholars(Grant No.42225206)the National Key R&D Program of China(Grant No.2020YFC1807200)the National Natural Science Foundation of China(Grant No.42072299).
文摘Conventional empirical equations for estimating undrained shear strength(s_(u))from piezocone penetration test(CPTu)data,without incorporating soil physical properties,often lack the accuracy and robustness required for geotechnical site investigations.This study introduces a hybrid virus colony search(VCS)algorithm that integrates the standard VCS algorithm with a mutation-based search mechanism to develop high-performance XGBoost learning models to address this limitation.A dataset of 372 seismic CPTu and corresponding soil physical properties data from 26 geotechnical projects in Jiangs_(u)Province,China,was collected for model development.Comparative evaluations demonstrate that the proposed hybrid VCS-XGBoost model exhibits s_(u)perior performance compared to standard meta-heuristic algorithm-based XGBoost models.The res_(u)lts highlight that the consideration of soil physical properties significantly improves the predictive accuracy of s_(u),emphasizing the importance of considering additional soil information beyond CPTu data for accurate s_(u)estimation.
基金financially supported by the Natural Science Foundation of China(Grant Nos.42377166 and 42007246)Key R&D Program Social Development Project of Jiangsu Province(Grant No.BE2023800)the National Key R&D Program of China(Grant No.2023YFC3709600).
文摘Biostimulation has been proven to be an available approach for microbially induced calcium carbonate precipitation(MICP).However,biostimulation may not be as effective as bioaugmentation in some unfavorable situations.In this study,the feasibility of biochar-assisted MICP for improving the shear strength of calcareous sand is investigated.The optimization of cementation solution for biostimulated MICP is first determined through a series of unconfined compressive tests.The shear characteristics of biocemented calcareous sand,enhanced by biochar and treated through biostimulation,are then assessed using consolidated undrained(CU)shear triaxial tests.To characterize the shear strength of biocemented sand under low effective normal stress,both Mohr-Coulomb failure envelopes and nonlinear failure envelopes were employed.Meanwhile,the current study also compared and analyzed two distinct stress states:maximum principal stress ratio(σ'_(1)/σ'_(3)max)and Skempton’s pore pressure parameter A=0,to identify an appropriate failure criterion for determination of the shear strength parameters.Furthermore,the microscopic features and post-failure characteristics of biochar-assisted calcareous sand were examined and discussed.The findings indicate that biochar can contribute to an increase in cementation content by serving as additional nucleation sites.The study may provide valuable insights into the potential of biochar-assisted MICP for enhancing the biostimulation approach.
文摘When tunnelling through low-permeability saturated ground,the pore pressure decreases in the vicinity of the cavity.In certain instances of deep tunnels crossing weak rocks,the pore pressure may even become negative.All existing analytical solutions for the undrained ground response curve(GRC)in the literature assume that the ground fully retains its saturation,in which case the development of negative pore pressures has a stabilising effect e it results in increased effective stresses,and thus shearing resistance,which in turn leads to reduced deformations and plastification.In practice,however,negative pore pressures can induce partial or complete ground desaturation,which may even invalidate the premise of undrained conditions and lead to considerably increased deformations and plastification.In such cases,existing solutions are unsafe for design.The present paper aims to address this shortcoming,by presenting a novel analytical solution for the undrained GRC which incorporates the effect of the excavation-induced desaturation.The solution is derived under the assumption that the ground desaturates completely and immediately under negative pore pressures,which provides the upper bound of deformations and plastification for cases of partial desaturation.The rock is considered to be a linear elastic,brittle-plastic material,obeying a non-associated Mohr-Coulomb(MC)yield criterion.Nevertheless,the solution is also applicable to perfectly plastic rocks via a simple modification of the input parameters.Although the solution is in general semi-analytical,simple closed-form expressions are obtained in the special case of non-dilatant rocks.These expressions are also applicable to rocks exhibiting limited dilatancy,which is usually the case.An application example,based on the planned deep geological repository for radioactive waste in Switzerland,demonstrates the significant practical value and usefulness of the novel solution and underscores its necessity in cases where existing solutions that disregard desaturation are rendered thoroughly unsafe for design.
基金Project(U2268213) supported by the National Natural Science Foundation of ChinaProject(2024YFHZ0121) supported by the Sichuan Science and Technology Program,China。
文摘Transparent sand is a special material to realize visualization of concealed work in geotechnical engineering. To investigate the dynamic characteristics of transparent sand, a series of undrained cyclic simple shear tests were conducted on the saturated transparent sand composed of fused quartz and refractive index-matched oil mixture. The results reveal that an increase in the initial shear stress ratio significantly affects the shape of the hysteresis loop, particularly resulting in more pronounced asymmetrical accumulation. Factors such as lower relative density, higher cyclic stress ratios and higher initial shear stress ratio have been shown to accelerate cyclic deformation, cyclic pore water pressure and stiffness degradation. The cyclic liquefaction resistance curves decrease as the initial shear stress ratio increases or as relative density decreases. Booker model and power law function model were applied to predict the pore water pressure for transparent sand. Both models yielded excellent fits for their respective condition, indicating a similar dynamic liquefaction pattern to that of natural sands. Finally, transparent sand displays similar dynamic characteristics in terms of cyclic liquefaction resistance and Kα correction factor. These comparisons indicate that transparent sand can serve as an effective means to mimic many natural sands in dynamic model tests.
基金Ho Chi Minh City University of Technology (HCMUT), VNU-HCM for supporting this study
文摘Machine learning(ML)models are widely used for predicting undrained shear strength(USS),but interpretability has been a limitation in various studies.Therefore,this study introduced shapley additive explanations(SHAP)to clarify the contribution of each input feature in USS prediction.Three ML models,artificial neural network(ANN),extreme gradient boosting(XGBoost),and random forest(RF),were employed,with accuracy evaluated using mean squared error,mean absolute error,and coefficient of determination(R^(2)).The RF achieved the highest performance with an R^(2) of 0.82.SHAP analysis identified pre-consolidation stress as a key contributor to USS prediction.SHAP dependence plots reveal that the ANN captures smoother,linear feature-output relationships,while the RF handles complex,non-linear interactions more effectively.This suggests a non-linear relationship between USS and input features,with RF outperforming ANN.These findings highlight SHAP’s role in enhancing interpretability and promoting transparency and reliability in ML predictions for geotechnical applications.
基金financial support from the National Natural Science Foundation of China(Grant No.51979144)the State Key Laboratory of Hydroscience and Engineering(Grant No.SKLHSE-2024-B-02).
文摘Foam plays a crucial role in conditioning the mechanical properties of coarse-grained soil during earth pressure balance shield tunneling.Experimental findings have shown that an appropriate foam injection ratio improves the workability and compressibility of conditioned soil,while reducing its shear strength under undrained conditions.Understanding how foam operates in soil pores is essential for interpreting these phenomena.This study utilized a theoretical two-dimensional(2D)model to analyze the effects of gas saturation,gas-liquid interface,and gas dissolution on the undrained mechanical properties of foamconditioned soil.Based on these analyses,a constitutive equation was developed,using the transition void ratio,compression index and contact coefficient as key parameters to describe the relationships among vertical stress σ_(v),void ratio e_(c),and shear strengthτ.The undrained mechanical properties calculated by the 2D model align well with experimental observations,indicating that while foam enhances the bonding force between soil particles,both excessive and insufficient gas saturation,along with larger contact angles,notably undermine this enhancement,resulting in unsuitable workability.A gas saturation of 0.5-0.8 is recommended for soil conditioning.Under typical chamber pressures,the effects of gas-liquid interface and gas dissolution on compressibility and shear strength are negligible.The constitutive equation demonstrates excellent agreement with experimental data,and can well predict the variations in σ_(v)-e_(c)-τ.This study contributes to understanding the role of foam in soil pores,and the developed constitutive equation serves as a valuable reference for describing the undrained mechanical behavior of foam-conditioned coarse-grained soil.
基金the financial support provided by the Ministry of Education(MoE),Government of IndiaThe second author acknowledges Coal India Limited for providing financial assistance for the research(Project No.CIL/R&D/01/73/2021).
文摘The microbial-induced calcite precipitation(MICP)technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils.However,the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions.Furthermore,the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented.Moreover,the effect of wetting-drying(WD)cycles on the cyclic characteristics of MICP-treated sand is not readily available,which may contribute to the limited adoption of MICP treatment in field applications.In this study,strain-controlled consolidated undrained(CU)cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains:Sporosarcina pasteurii and Bacillus subtilis.The treatment durations of 7 d and 14 d were considered,with an interval of 12 h between treatments.The cyclic characteristics,such as the shear modulus and damping ratio,of the MICP-treated sand with the different bacterial strains have been estimated and compared.Furthermore,the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5–15 cycles and aging of samples up to three months.The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand,considering the influence of different bacterial strains,treatment duration,and WD cycles.
文摘This study aims to predict the undrained shear strength of remolded soil samples using non-linear regression analyses,fuzzy logic,and artificial neural network modeling.A total of 1306 undrained shear strength results from 230 different remolded soil test settings reported in 21 publications were collected,utilizing six different measurement devices.Although water content,plastic limit,and liquid limit were used as input parameters for fuzzy logic and artificial neural network modeling,liquidity index or water content ratio was considered as an input parameter for non-linear regression analyses.In non-linear regression analyses,12 different regression equations were derived for the prediction of undrained shear strength of remolded soil.Feed-Forward backpropagation and the TANSIG transfer function were used for artificial neural network modeling,while the Mamdani inference system was preferred with trapezoidal and triangular membership functions for fuzzy logic modeling.The experimental results of 914 tests were used for training of the artificial neural network models,196 for validation and 196 for testing.It was observed that the accuracy of the artificial neural network and fuzzy logic modeling was higher than that of the non-linear regression analyses.Furthermore,a simple and reliable regression equation was proposed for assessments of undrained shear strength values with higher coefficients of determination.
基金The National Natural Science Foundation of China(No.40702047)
文摘In order to obtain the reasonable undrained shear strength Su for geotechnical analyses of bridge foundations in Yangtze River floodplain clayey soils, a site-specific study is conducted using the imported piezocone penetration test （CPTu） with dissipation phases at the Fourth Nanjing Yangtze River Bridge construction sites. Taking the values of Su from laboratory tests as references, several existing Su-predicted methods based on CPTu are compared and evaluated. To verify the presented cone factor Nk, additional test sites are selected and examined. The results show that the values of cone factors such as Nkt, Nke, and Nau, depend on the shear test mode and disturbance. Generally, the values of Nke show more scattering than those of Nkt and N△u. For the stratified and layered sediments of the Yangtze River floodplain, it is recommended using the net cone resistance qT to estimate Su and the preliminary cone factor values Nkt are from 7 to 16, with an average of 11. It is also confirmed that the CPTu test, as a new technique in site characterization, can present reasonable parameters for bridge foundations.
基金The National Natural Science Foundation of China under contract No.41606078the Taishan Scholar Special Experts Project under contract No.ts201712079+1 种基金the National Key Research and Development Plan under contract No.2017YFC0307600the Open Fund of Qingdao National Laboratory for Marine Science and Technology of China under contract Nos QNLM2016ORP0203 and QNLM2016ORP0207
文摘The undrained shear strength of shallow strata is a critical parameter for safety design in deep-water operations.In situ piezocone penetration tests(CPTU) and laboratory experiments are performed at Site W18-19 in the Shenhu area, northern South China Sea, where China's first marine hydrate exploitation operation is due to be located. The validation of the undrained shear strength prediction model based on CPTU parameters. Different laboratory tests, including pocket penetrometer, torvane, miniature vane and unconsolidated undrained triaxial tests, are employed to solve empirical cone coefficients by statistical and mathematical methods. Finally, an optimized model is proposed to describe the longitudinal distribution of undrained shear strength in calcareous clay strata in the Shenhu area. Research results reveal that average empirical cone coefficients based on total cone resistance, effective resistance, and excess-pore pressure are 13.8, 4.2 and 14.4, respectively. The undrained shear strength prediction model shows a good fit with the laboratory results only within specific intervals based on their compaction degree and gas-bearing conditions. The optimized prediction model in piecewise function format can be used to describe the longitudinal distribution of the undrained shear strength for calcareous clay within all depth intervals from the mud-line to the upper boundary of hydrate-bearing sediments(HBS). The optimized prediction result indicates that the effective cone resistance model is suitable for very soft to firm calcareous clays,the excess-pore pressure model can depict the undrained shear strength for firm to very stiff but gas-free clays,while the total cone resistance model is advantageous for evaluating the undrained shear strength for very stiff and gassy clays. The optimized model in piecewise function format can considerably improve the adaptability of empirical models for calcareous clay in the Shenhu area. These results are significant for safety evaluations of proposed hydrate exploitation projects.
基金ThisresearchprojectwasfinanciallysupportedbytheMinistryofScienceandTechnology Japan (DomesticResearchFellowship 1999 2 0 0 1) .
文摘Extensive data of undrained shear strength for various remolded soils are compiled to normalize the remolded undrained strength. Remolded soils have a wide spectrum of liquid limits ranging from 25% to 412%. It is found that the remolded undrained strength is a function of water content and liquid limit. Furthermore, a simple index designated as normalized water content w * is introduced for normalizing remolded undrained strength for various soils. The normalized water content w * is the ratio of water content to liquid limit. The relationship between the remolded undrained strength and the normalized water content can be expressed by a simple equation. The new simple equation is not only valuable theoretically for helping in assessing the in situ mechanical behavior, but also useful to ocean engineering practice.
文摘A parametric study of undrained stability of a spherical cavity in clays is investigated by finite elementlimit analysis with an axisymmetric condition. Influences of cover depth ratio of cavity and dimensionlessoverburden factor on predicted failure mechanisms and dimensionless load factor are examined.It is found that a previously recommended and up-to-date lower bound solution to the problem wassignificantly inaccurate for practice use. Thus, an accurate approximate solution to the problem is proposedfrom nonlinear regression analysis of the computed average bound solutions. New cavity stabilityfactors for the soil cohesion and soil unit weight are proposed. New findings are revealed for the threedimensionaleffect of the cavity shape on these factors between the axisymmetric and plane strainconditions, and their applications to the undrained stability evaluation of cavity problems in practice aredescribed.
基金financial support from High-end Foreign Expert Introduction program(No.G20190022002)Chongqing Construction Science and Technology Plan Project(2019-0045)as well as Chongqing Engineering Research Center of Disaster Prevention&Control for Banks and Structures in Three Gorges Reservoir Area(Nos.SXAPGC18ZD01 and SXAPGC18YB03)。
文摘Accurate assessment of undrained shear strength(USS)for soft sensitive clays is a great concern in geotechnical engineering practice.This study applies novel data-driven extreme gradient boosting(XGBoost)and random forest(RF)ensemble learning methods for capturing the relationships between the USS and various basic soil parameters.Based on the soil data sets from TC304 database,a general approach is developed to predict the USS of soft clays using the two machine learning methods above,where five feature variables including the preconsolidation stress(PS),vertical effective stress(VES),liquid limit(LL),plastic limit(PL)and natural water content(W)are adopted.To reduce the dependence on the rule of thumb and inefficient brute-force search,the Bayesian optimization method is applied to determine the appropriate model hyper-parameters of both XGBoost and RF.The developed models are comprehensively compared with three comparison machine learning methods and two transformation models with respect to predictive accuracy and robustness under 5-fold cross-validation(CV).It is shown that XGBoost-based and RF-based methods outperform these approaches.Besides,the XGBoostbased model provides feature importance ranks,which makes it a promising tool in the prediction of geotechnical parameters and enhances the interpretability of model.
文摘The undrained shear strength （su） of fine-grained soils that can be measured in situ and in laboratory isone of the key geotechnical parameters. The unconfined compression test （UCT） is widely used in laboratoryto measure this parameter due to its simplicity; however, it is severely affected by sampledisturbance. The vane shear test （VST） technique that is less sensitive to sample disturbance involves acorrection factor against the soil plasticity, commonly known as the Bjerrum＇s correction factor, m. Thisstudy aims to reevaluate the Bjerrum＇s correction factor in consideration of a different approach and arelatively new method of testing. Atterberg limits test, miniature VST, and reverse extrusion test （RET）were conducted on 120 remolded samples. The effect of soil plasticity on undrained shear strength wasexamined using the liquidity index instead of Bjerrum＇s correction factor. In comparison with the resultobatined using the Bjerrum＇s correction factor, the undrained shear strength was better representedwhen su values were correlated with the liquidity index. The results were validated by the RET, whichwas proven to take into account soil plasticity with a reliable degree of accuracy. This study also showsthat the RET has strong promise as a new tool for testing undrained shear strength of fine-grained soils.
基金the National Natural Science Foundation of China，the Ministry of Science and Technology of China
文摘Consolidated-isotropically undrained triaxial compression （CIUC） tests were performed on the reconstituted deep clay from a mine in East China. It was consolidated to maximum stresses in the range of 0.3-2.6 MPa. The test results show that the stress-strain-strength properties of the clay during undrained shear are significantly stress-dependent. In particular, in the case of high consolidation pressure, the post-peak drop in strength on stress-strain curves and shear plane in soil specimens are more evident, the peak stress ratio and the axial strain at which this ratio was reached are smaller, and the relationship between pore pressure and axial strain is also significantly different from that for the case of low consolidation pressure. The environmental scanning electron microscope observations and micro analysis lead to an understanding of the physical mechanisms underlying the above stress-dependent mechanical behavior. In addition, the CIUC behaviors of the studied clay are discussed in the context of critical state soil mechanics.
基金partially supported by the National Key Research and Development Program of China(No.2018YFC0309200)the National Natural Science Foundation of China(No.51879036)+1 种基金the LiaoNing Revitalization Talents Program(No.XLYC2002036)the Fundamental Research Funds for the Central Universities of Dalian University of Technology。
文摘Rapid advances in deep-sea mining engineering have created an urgent need for the accurate evaluation of the undrained strength of marine soils,especially surface soils.Significant achievements have been made using full-flow penetration penetrometers to evaluate marine soil strength in the deep penetration;however,a method considering the effect of ambient water on the surface penetration needs to be established urgently.In this study,penetrometers with multiple probes were developed and used to conduct centrifuge experiments on South China Sea soil and kaolin clay.First,the forces on the probes throughout the penetration process were systematically analyzed and quantified.Second,the spatial influence zone was determined by capturing the resistance changes and sample crack development,and the penetration depth for a sample to reach a stable failure mode was given.Third,the vane shear strength was used to invert the penetration resistance factor of the ball and determine the range of the penetration resistance factor values.Furthermore,a methodology to determine the penetration resistance factors for surface marine soils was established.Finally,the effect of the water cavity above various probes in the surface penetration was used to formulate an internal mechanism for variations in the penetration resistance factor.
