This study aims to quantify the influence of the amount of cement and chloride salt on the unconfined compression strength （UCS） of Lianyungang marine clay. The clays with various sodium chloride salt concentrations...This study aims to quantify the influence of the amount of cement and chloride salt on the unconfined compression strength （UCS） of Lianyungang marine clay. The clays with various sodium chloride salt concentrations were prepared artificially and stabilized by ordinary Portland cement with various contents. A series of UCS tests of cement stabilized clay specimen after 28 d curing were carried out. The results indicate that the increase of salt concentration results in the decrease in the UCS of cement-treated soil. The negative effect of salt concentration on the strength of cement stabilized clay directly relates to the cement content and salt concentration. The porosity-salt concentration/cement content ratio is a fundamental parameter for assessing the UCS of cement-treated salt-rich clay. An empirical prediction model of UCS is also proposed to take into account the effect of salt concentration. The findings of this study can be referenced for the stabilization improvement of chloride slat- rich soft clay.展开更多
Quantitatively correcting the unconfined compressive strength for sample disturbance is an important research project in the practice of ocean engineering and geotechnical engineering. In this study, the specimens of ...Quantitatively correcting the unconfined compressive strength for sample disturbance is an important research project in the practice of ocean engineering and geotechnical engineering. In this study, the specimens of undisturbed natural marine clay obtained from the same depth at the same site were deliberately disturbed to different levels. Then, the specimens with different extents of sample disturbance were trimmed for both oedometer tests and unconfined compression tests. The degree of sample disturbance SD is obtained from the oedometer test data. The relationship between the unconfined compressive strength q u and SD is studied for investigating the effect of sample disturbance on q u. It is found that the value of q u decreases linearly with the increase in SD. Then, a simple method of correcting q u for sample disturbance is proposed. Its validity is also verified through analysis of the existing published data.展开更多
Understanding the strength characteristics and deformation behaviour of the tunnel surrounding rock in a fault zone is significant for tunnel stability evaluation.In this study,a series of unconfined compression tests...Understanding the strength characteristics and deformation behaviour of the tunnel surrounding rock in a fault zone is significant for tunnel stability evaluation.In this study,a series of unconfined compression tests were conducted to investigate the mechanical characteristics and failure behaviour of completely weathered granite(CWG)from a fault zone,considering with height-diameter(h/d)ratio,dry densities(ρd)and moisture contents(ω).Based on the experimental results,a regression mathematical model of unconfined compressive strength(UCS)for CWG was developed using the Multiple Nonlinear Regression method(MNLR).The research results indicated that the UCS of the specimen with a h/d ratio of 0.6 decreased with the increase ofω.When the h/d ratio increased to 1.0,the UCS increasedωwith up to 10.5%and then decreased.Increasingρd is conducive to the improvement of the UCS at anyω.The deformation and rupture process as well as final failure modes of the specimen are controlled by h/d ratio,ρd andω,and the h/d ratio is the dominant factor affecting the final failure mode,followed byωandρd.The specimens with different h/d ratio exhibited completely different fracture mode,i.e.,typical splitting failure(h/d=0.6)and shear failure(h/d=1.0).By comparing the experimental results,this regression model for predicting UCS is accurate and reliable,and the h/d ratio is the dominant factor affecting the UCS of CWG,followed byρd and thenω.These findings provide important references for maintenance of the tunnel crossing other fault fractured zones,especially at low confining pressure or unconfined condition.展开更多
To explore an environmentally friendly improvement measure for red clay,the function and mechanism of xanthan gum biopolymer and polypropylene fibers on the strength properties of red clay were investigated by unconfi...To explore an environmentally friendly improvement measure for red clay,the function and mechanism of xanthan gum biopolymer and polypropylene fibers on the strength properties of red clay were investigated by unconfined compressive strength and scanning electron microscopy tests.The test results demonstrated that the contents and curing ages of xanthan gum had significant influences on the unconfined compressive strength of red clay.Compared with untreated soil,1.5%xanthan gum content was the optimal ratio in which the strength increment was between 41.52 kPa and 64.73 kPa.On the other hand,the strength of xanthan gum-treated red clay increased,whereas the ductility decreased with the increase in curing ages,indicating that the xanthan gum-treated red clay started to gradually consolidate after 3 days of curing and stiffness significantly improved between 7 and 28 days of curing.The results also showed that the synergistic consolidation effects of the xanthan gum–polypropylene fibers could not only effectively enhance the strength of red clay but also reduce the brittle failure phenomenon.The strengths of soil treated with 2.0%xanthan gum-polypropylene fibers were 1.9–2.41 and 1.12–1.47 times than that of red clay and 1.5%xanthan gum-treated clay,respectively.The results of study provide the related methods and experiences for the field of ecological soil treatment.展开更多
In the seasonal permafrost region with loess distribution,the influence of freeze-thaw cycles on the engineering performance of reinforced loess must be paid attention to.Many studies have shown that the use of fiber ...In the seasonal permafrost region with loess distribution,the influence of freeze-thaw cycles on the engineering performance of reinforced loess must be paid attention to.Many studies have shown that the use of fiber materials can improve the engineering performance of soil and its ability to resist freeze-thaw cycles.At the same time,as eco-environmental protection has become the focus,which has been paid more and more attention to,it has become a trend to find new environmentally friendly improved materials that can replace traditional chemical additives.The purpose of this paper uses new environmental-friendly improved materials to reinforce the engineering performance of loess,improve the ability of loess to resist freeze-thaw cycles,and reduce the negative impact on the ecological environment.To reinforce the engineering performance of loess and improve its ability to resist freeze-thaw cycles,lignin fiber is used as a reinforcing material.Through a series of laboratory tests,the unconfined compressive strength(UCS)of lignin fiber-reinforced loess under different freeze-thaw cycles was studied.The effects of lignin fiber content and freeze-thaw cycles on the strength and deformation modulus of loess were analyzed.Combined with the microstructure features,the change mechanism of lignin fiber-reinforced loess strength under freeze-thaw cycles was discussed.The results show that lignin fiber can improve the UCS of loess under freeze-thaw cycles,but the strengthening effect no longer increases with the increase of fiber content.When the fiber content is less than 1%,the UCS growth rate of loess is the fastest under freeze-thaw cycles.And the UCS of loess with 1%fiber content is the most stable under freeze-thaw cycles.The freeze-thaw cycles increase the deformation modulus of loess with 1%fiber content,and its ability to resist deformation is obviously better than loess with 1.5%,2%and 3%fiber content.The fiber content over 1%will weaken the strengthening effect of lignin fiber-reinforced loess,and the optimum fiber content of lignin fiber-reinforced loess under freeze-thaw cycles is 1%.展开更多
In order to investigate the effect o f some factors on the unconfined compressive strength(UCS)for composite soil stabilizer-stabilized gravel soil(CSSSGS),the orthogonal test is adopted to set up the experimental sch...In order to investigate the effect o f some factors on the unconfined compressive strength(UCS)for composite soil stabilizer-stabilized gravel soil(CSSSGS),the orthogonal test is adopted to set up the experimental scheme.Three levels o f each factor armconsidered to obtain the change laws o f UCS,in which the binder dosages are8%,10%,and12%;the curing times ae7,14and21d;the gradation nae0.3,0.35and0.4;and the degrees of compaction are95%,97%,and99%.The range analysis clearly indicates that the influence degree o f the four factors on UCS is in such an order:dosage,age,gradation,and degree o f compaction.The variance analysis shows that only the composite soil stabilizer dosage can significantly affect UCS.In road construction,the examination o f composite soil stabilizer dosage and base-course maintenance should be given much more attention to obtain satisfactory base-course strength,compared w ith gradation floating and the change of degree o f compaction.展开更多
Three types of activators such as sodium hydroxide,calcium oxide and triethanolamine(TEA)are used to establish different activation environments to address the problems associated with the process of activating fly as...Three types of activators such as sodium hydroxide,calcium oxide and triethanolamine(TEA)are used to establish different activation environments to address the problems associated with the process of activating fly ash paste.We conducted mechanical tests and numerical simulations to understand the evolution of microstructure,and used environmental scanning electron microscopy(ESEM)and energy dispersive spectroscopy(EDS)techniques to analyze the microenvironments of the samples.The mechanical properties of fly ash paste under different activation conditions and the changes in the microstructure and composition were investigated.The results revealed that under conditions of low NaOH content(1%-3%),the strength of the sample increased significantly.When the content exceeded 4%,the rate of increase in strength decreased.Based on the results,the optimal NaOH content was identified,which was about 4%.A good activation effect,especially for short-term activation(3-7 d),was achieved using TEA under high doping conditions.The activation effect was poor for long-term strength after 28 days.The CaO content did not significantly affect the degree of activation achieved.The maximum effect was exerted when the content of CaO was 2%.The virtual cement and concrete testing laboratory(VCCTL)was used to simulate the hydration process,and the results revealed that the use of the three types of activators accelerated the formation of Ca(OH)_(2) in the system.The activators also corroded the surface of the fly ash particles,resulting in a pozzolanic reaction.The active substances in fly ash were released efficiently,and hydration was realized.The pores were filled with hydration products,and the microstructure changed to form a new frame of paste filling that helped improve the strength of fly ash paste.展开更多
Ternary geopolymers incorporating multiple solid wastes such as steel slag(SS),fly ash(FA),and granulated blast furnace slag(GBFS)are considered environmentally friendly and exhibit enhanced performance.However,the me...Ternary geopolymers incorporating multiple solid wastes such as steel slag(SS),fly ash(FA),and granulated blast furnace slag(GBFS)are considered environmentally friendly and exhibit enhanced performance.However,the mechanisms governing strength development and the design of optimal mixtures are not fully understood due to the complexity of their components.This study presents the development of four machine learning mod-els-Artificial Neural Network(ANN),Support Vector Regression(SVR),Extremely Randomized Tree(ERT),and Gradient Boosting Regression(GBR)-for predicting the unconfined compressive strength(UCS)of ternary geopolymers.The models were trained using a dataset comprising 120 mixtures derived from laboratory tests.Shapley Additive Explanations analysis was employed to interpret the machine learning models and elucidate the influence of different components on the properties of ternary geopolymers.The results indicate that ANN ex-hibits the highest predictive accuracy for UCS(R=0.949).Furthermore,the UCS of ternary geopolymers is most sensitive to the content of GBFS.This study provides valuable insights for optimizing the mix proportions in ternary blended geopolymer mixtures.展开更多
Geotechnical engineering usually produces drillholes in the ground for investigation and construction.Drilling is a rock-breaking process by applying normal(thrust)and shear(torque)force from the drill bit to the rock...Geotechnical engineering usually produces drillholes in the ground for investigation and construction.Drilling is a rock-breaking process by applying normal(thrust)and shear(torque)force from the drill bit to the rock below the bit.These rock-breaking data can be obtained by digital monitoring and recording the drilling parameters through an instrumented drilling machine.However,there is no mature and standard method to determine rock strength properties(such as unconfined compressive strength,UCS,or tensile strength)from real-time monitored drilling parameter(such as thrust force,torque,rotation speed,drilling speed and specific energy).This paper presents a complete procedure to accurately determine each drilling parameter.More importantly,the specific energy develops nonlinearly with change of the thrust force,which is related to the UCS and tensile strength of the rock.This finding provides an insight into determining the UCS and tensile strength of the rock based on real-time monitored drilling parameters.In addition,novel test setups are demonstrated to determine the thrust force and torque from hydraulics pressures and rotation speeds.These setups can significantly reduce the sophisticated instrumentation cost for drilling monitoring studies.Three type rocks including granite,limestone and sandstone are used for the testing.The findings from this study provide supporting theories to upgrade drilling monitoring technique to a standard geotechnical testing method.展开更多
Microbially induced carbonate precipitation(MICP)is an eco-friendly soil improvement technique.However,this method still has some drawbacks,such as low conversion efficiency of CaCO_(3) crystallization,insufficient st...Microbially induced carbonate precipitation(MICP)is an eco-friendly soil improvement technique.However,this method still has some drawbacks,such as low conversion efficiency of CaCO_(3) crystallization,insufficient strength for certain applications,and requiring multiple treatments.Previous studies have re-ported that sticky rice can regulate CaCO_(3) crystals(i.e.,chemical CaCO_(3))in the sticky rice-lime mortar,showing potential for improving the bio-cementation.Therefore,this study explored the possibility of using sticky rice to enhance the biocementation effect.Tests were carried out to assess the strength and perme-ability of bio-cemented sand with the inclusion of sticky rice.The results indicated that sticky rice may regulate the type and size of bio-CaCO_(3) crystals,and the use of an appropriate amount of sticky rice as additive could increase the strength of sand columns by regulating CaCO_(3) crystallization.Polyhedral calcites may be more favourable for the increasing strength than some vaterites with a hollow spherical structure.The combination of MICP and sticky rice can significantly decrease the coefficient of permeability to a value that was much lower than that by using sticky rice and MICP alone.Bio-CaCO_(3) immobilized the sticky rice on one end on sand particles,and the reticulated structure of sticky rice divided large pores into small pores,which may be the important cause of the decrease in permeability coefficient.Finally,this study proposed that the MICP with the sticky rice as an additive may enhance the MICP effect and prevent the surface erosion of coarse-grained sand slopes.展开更多
The improvement of question soils with cement shows great technical, economic and environmental advantages. And interest in introducing electrical resistivity measurement to assess the quality of cement treated soils ...The improvement of question soils with cement shows great technical, economic and environmental advantages. And interest in introducing electrical resistivity measurement to assess the quality of cement treated soils has increased markedly recently due to its economical, non-destructive, and relatively non-invasive advantages. This work aims to quantify the effect of cement content （aw）, porosity （nt）, and curing time（T） on the electrical resistivity （p） and unconfined compression strength （UCS） of cement treated soil. A series of electrical resistivity tests and UCS tests of cement treated soil specimen after various curing periods were carried out. A modified Archie empirical law was proposed taking into account the effect of cement content and curing period on the electrical resistivity of cement treated soil. The results show that nt/（aw·T） and nt/（aw·T^1/2） ratio are appropriate parameters to assess electrical resistivity and UCS of cement treated soil, respectively. Finally, the relationship between UCS and electrical resistivity was also established.展开更多
Dry jet mixing (DJM) for soft soil stabilization has been widely used since 1980s. The quality and strength of stabilized columns are fundamental parameters to evaluate the stabilization work. This paper presents the ...Dry jet mixing (DJM) for soft soil stabilization has been widely used since 1980s. The quality and strength of stabilized columns are fundamental parameters to evaluate the stabilization work. This paper presents the standard penetration test (SPT) method and its test results on cement columns. It is shown that SPT is an effective and simple method for inspecting and evaluating cement columns. The strength characteristics along the length of the column, a good correction between SPT blow count and the unconfined compressive strength are achieved.展开更多
In order to simulate and study the erosion effect process such as the changes of corrosive depth and unconfined compression strength of cemented soil sample in earlier period from 0 day to 60 days, a series of tests i...In order to simulate and study the erosion effect process such as the changes of corrosive depth and unconfined compression strength of cemented soil sample in earlier period from 0 day to 60 days, a series of tests including unconfined compressive tests, measuring the blocks＇ sizes, and taking photos, are conducted on the cemented soil blocks which were cured in different concentrations of H2SO4 solutions. The results of tests show that the corrosive depth is increasing and the unconfined compression strength is decreasing with the increase of H2SO4 solution concentration at the same erosion time, and the corrosive degree is increasing with the corrosive time. In the earlier state, the corrosive effect is serious, but the effect becomes slow in the later state in the same concentrated H2SO4 solution. After take statistics the date, a coefficient a is put forward to predict the reduction of the compressive strength of cemented soil in various concentration of H2SO4 solution, which could be used in practical design.展开更多
A series of unconfined compression tests(UCTs) were conducted to investigate the effects of content of reactive magnesia(Mg O) and carbonation time on the engineering properties including apparent characteristics, str...A series of unconfined compression tests(UCTs) were conducted to investigate the effects of content of reactive magnesia(Mg O) and carbonation time on the engineering properties including apparent characteristics, stress-strain relation, and deformation and strength characteristics of reactive Mg O treated silt soils. The soils treated with reactive Mg O at various contents were subjected to accelerated carbonation for different periods of time and later, UCTs were performed on them. The results demonstrate that the reactive Mg O content and carbonation time have remarkable influences on the aforementioned engineering properties of the soils. It is found that with the increase in reactive Mg O content, the unconfined compressive strength(qu) increases at a given carbonation time(<10 h), whereas the water content and amounts of crack of the soils decrease. A threshold content of reactive Mg O exists at approximately 25% and a critical carbonation time exists at about 10 h for the development of qu. A simple yet practical strength-prediction model, by taking into account two variables of reactive Mg O content and carbonation time, is proposed to estimate qu of carbonated reactive Mg O treated soils. A comparison of the predicated values of qu with the measured ones indicates that the proposed model has satisfactory accuracy.展开更多
Nowadays,using biopolymer as a ground improvement method has become very popular.However,since biopolymers are organic and degradable,their long-term effect is not fully known.In this study,the effects of biopolymers ...Nowadays,using biopolymer as a ground improvement method has become very popular.However,since biopolymers are organic and degradable,their long-term effect is not fully known.In this study,the effects of biopolymers on the mechanical behavior of kaolin clay were investigated through a comprehensive program of experiments.Two types of biopolymer,i.e.xanthan gum and guar gum were chosen to investigate the effect of biopolymer type.For this purpose,specimens were prepared using standard Proctor energy at four different water contents(25%,30%35%and 40%)with 0.5%,1%,1.5%and 2%biopolymer inclusions.The specimens were cured for 1 d,7 d,28 d and 90 d.Moreover,some of the specimens were kept in the curing room for 3 years to observe the long-term effect of the biopolymers.At the end of the curing periods,the specimens were subjected to unconfined compression test,and scanning electron microscopy(SEM)analysis was performed to observe the mechanism of strength improvement.The results revealed that the unconfined compressive strength(UCS)of the specimens treated with biopolymers increased in all biopolymer inclusion levels and water contents up to a 90-d curing period.For specimens containing xanthan gum,the maximum strength increase was observed at 25%water content and 2%xanthan gum with 90-d curing.The strength increased 5.23 times induced by xanthan gum addition when compared to the pure clay.Moreover,the increase in strength reached 8.53 times in specimens treated with guar gum.Besides,increasing water content caused more ductile behavior,thus increasing the axial deformation.展开更多
To reduce the difficulty of obtaining the unconfined compressive strength(UCS) value of fiber-reinforced cemented paste backfill(CPB) and analyze the comprehensive impact of conventional and fiber variables on the com...To reduce the difficulty of obtaining the unconfined compressive strength(UCS) value of fiber-reinforced cemented paste backfill(CPB) and analyze the comprehensive impact of conventional and fiber variables on the compressive property, a new artificial intelligence model was proposed by combining a newly invented meta-heuristics algorithm(salp swarm algorithm, SSA) and extreme learning machine(ELM) technology. Aiming to test the reliability of that model, 720 UCS tests with different cement-to-tailing mass ratio, solid mass concentration, fiber content, fiber length, and curing time were carried out, and a strength evaluation database was collected. The obtained results show that the optimized SSA-ELM model can accurately predict the uniaxial compressive strength of the fiber-reinforced CPB, and the model performance of SSA-ELM model is better than ANN, SVR and ELM models. Variable sensitivity analysis indicates that fiber content and fiber length have a significant effect on the UCS of fiber-reinforced CPB.展开更多
To explore the stabilization effect of stabilizing agent GX07 on treating organic soil and the influence of organic matter on the strength development of stabilized soil,artificial organic soil with various organic ma...To explore the stabilization effect of stabilizing agent GX07 on treating organic soil and the influence of organic matter on the strength development of stabilized soil,artificial organic soil with various organic matter content was obtained by adding different amounts of fulvic acid into non-organic clay,and then liquid-plastic limit tests were carried out on the artificial organic soil.Meanwhile,unconfined compressive strength(UCS) tests were performed on cement-only soil and composite stabilized soil,respectively.The test results indicate that the plastic limit of soil samples increases linearly,and the liquid limit increases exponentially as the organic matter content increases.The strength of stabilized soil is well correlated with the organic matter content,cement content,stabilizing agent content and curing time.When the organic matter content is 6%,as the cement content varies in the range of 10%-20%,the strength of cement-only soil increases from 88.5 to 280.8 kPa.Once 12.6% GX07 is added into the mix,the strength of stabilized soil is 4.93 times compared with that of cement-only soil.GX07 can obviously improve the strength of cemented-soil and has a good economic applicability.A strength model is proposed to predict strength development.展开更多
Despite the fact that mixing uniformity(i.e.the consistency of binder distribution)significantly influence the quality of ground improvement during in situ soil mixing projects,its quantitative evaluation was rarely c...Despite the fact that mixing uniformity(i.e.the consistency of binder distribution)significantly influence the quality of ground improvement during in situ soil mixing projects,its quantitative evaluation was rarely concerned due to the difficulty of measurement from an engineering perspective.A methodology was proposed to quantitatively evaluate the mixing uniformity of stabilized soil using handheld Xfluorescence spectrometry(XRF),which is helpful to elucidate the significance of mixing uniformity on strength.In other words,the calcium content was monitored to ascertain the distribution of cement within the matrix,and a quantitative index was subsequently established.It was observed that an increase in mixing uniformity resulted in a transition in the behavior of the stabilized clay from a plastic to a brittle failure mode,and from a localized failure to a global shear failure under unconfined compression.Subsequent observation of the destruction process revealed that cracks were more readily formed in the low cement zones and then bypass the high cement zones.Furthermore,the effect of mixing uniformity on strength is likely to be amplified with prolonged curing periods.The enhancement of uniformity would increase the volume of the high binder zones,thereby enhancing the overall highstrength performance.The proposed methodology is capable of characterizing the discreteness between the tracked element's measured and theoretical contents,thusing avoiding the uncertainty associated with other indirect indicators.The convenience of the portable handheld XRF apparatus was confirmed,as it can be readily deployed in situ or ex situ to track calcium content within the stabilized mass after borehole sampling.展开更多
This paper presents an investigation on strength of cement deep mixing （CDM） mixture. Four typical works of offshore or land-based projects are introduced. With samples from these projects and laboratory tests, stat...This paper presents an investigation on strength of cement deep mixing （CDM） mixture. Four typical works of offshore or land-based projects are introduced. With samples from these projects and laboratory tests, statistical analysis is made on the increment law of the strength of cement-soil mixture with different amount of cement, and strengths under different working conditions are compared. It is found that the amount of cement in the cement-soil mixture is closely related to the unconfined compressive strength of the mixture. At the age of 90 d,the unconfined compressive strength of the cement-soil mixture increased by 0.054 MPa—0.124 MPa with each cement increasing 10 kg/m3 in the cement-soil mixture, averagely increased by 0.085 MPa, while that at the age of 120 d increased by 1100 in comparison.The quality of the cement-soil mixture should be comprehensively evaluated in accordance with the trimmed average of strength, coefficient of variation and rock quality designation （RQD） indicators of sampling ratio.展开更多
Construction on soft soil is one of the most challenging situations faced by geotechnical engineers. The heterogeneous and complex nature of soil, especially those containing organic clay, often makes it impossible fo...Construction on soft soil is one of the most challenging situations faced by geotechnical engineers. The heterogeneous and complex nature of soil, especially those containing organic clay, often makes it impossible for the construction specification to be addressed properly. Generally, clay exhibits low strength, high compressibility, and strength reduction when subjected to mechanical disturbance. This means that construction on clay soil is vulnerable to bearing capacity failure induced by low inherent shear strength. All these properties can be improved by the effective stabilization of soil. This study analyzed the effectiveness of incorporating salt-lime mixtures at various dosages in improving the strength increment of the soil. The results indicate that among different combinations of salt and lime, the best performance in terms of strength increase was achieved by adding 10% NaCl with 3% lime in the soil. The outcome of this study focuses on enhancing the ultimate strength of soil and its implementation in the field of foundation engineering.展开更多
基金The Natural Science Foundation of Jiangsu Province(No.BK2011618)the National Key Technology R&D Program of China during the12th Five-Year Plan Period(No.2012BAJ01B02)
文摘This study aims to quantify the influence of the amount of cement and chloride salt on the unconfined compression strength （UCS） of Lianyungang marine clay. The clays with various sodium chloride salt concentrations were prepared artificially and stabilized by ordinary Portland cement with various contents. A series of UCS tests of cement stabilized clay specimen after 28 d curing were carried out. The results indicate that the increase of salt concentration results in the decrease in the UCS of cement-treated soil. The negative effect of salt concentration on the strength of cement stabilized clay directly relates to the cement content and salt concentration. The porosity-salt concentration/cement content ratio is a fundamental parameter for assessing the UCS of cement-treated salt-rich clay. An empirical prediction model of UCS is also proposed to take into account the effect of salt concentration. The findings of this study can be referenced for the stabilization improvement of chloride slat- rich soft clay.
文摘Quantitatively correcting the unconfined compressive strength for sample disturbance is an important research project in the practice of ocean engineering and geotechnical engineering. In this study, the specimens of undisturbed natural marine clay obtained from the same depth at the same site were deliberately disturbed to different levels. Then, the specimens with different extents of sample disturbance were trimmed for both oedometer tests and unconfined compression tests. The degree of sample disturbance SD is obtained from the oedometer test data. The relationship between the unconfined compressive strength q u and SD is studied for investigating the effect of sample disturbance on q u. It is found that the value of q u decreases linearly with the increase in SD. Then, a simple method of correcting q u for sample disturbance is proposed. Its validity is also verified through analysis of the existing published data.
基金supported by the National Natural Science Foundation of China,NSFC(No.42202318).
文摘Understanding the strength characteristics and deformation behaviour of the tunnel surrounding rock in a fault zone is significant for tunnel stability evaluation.In this study,a series of unconfined compression tests were conducted to investigate the mechanical characteristics and failure behaviour of completely weathered granite(CWG)from a fault zone,considering with height-diameter(h/d)ratio,dry densities(ρd)and moisture contents(ω).Based on the experimental results,a regression mathematical model of unconfined compressive strength(UCS)for CWG was developed using the Multiple Nonlinear Regression method(MNLR).The research results indicated that the UCS of the specimen with a h/d ratio of 0.6 decreased with the increase ofω.When the h/d ratio increased to 1.0,the UCS increasedωwith up to 10.5%and then decreased.Increasingρd is conducive to the improvement of the UCS at anyω.The deformation and rupture process as well as final failure modes of the specimen are controlled by h/d ratio,ρd andω,and the h/d ratio is the dominant factor affecting the final failure mode,followed byωandρd.The specimens with different h/d ratio exhibited completely different fracture mode,i.e.,typical splitting failure(h/d=0.6)and shear failure(h/d=1.0).By comparing the experimental results,this regression model for predicting UCS is accurate and reliable,and the h/d ratio is the dominant factor affecting the UCS of CWG,followed byρd and thenω.These findings provide important references for maintenance of the tunnel crossing other fault fractured zones,especially at low confining pressure or unconfined condition.
基金This study was supported by the State Key Laboratory Project of China(Grant No.KF2020-12)the Yunnan Education Department Project of China(Grant Nos.2020Y0175 and 2020J0240).
文摘To explore an environmentally friendly improvement measure for red clay,the function and mechanism of xanthan gum biopolymer and polypropylene fibers on the strength properties of red clay were investigated by unconfined compressive strength and scanning electron microscopy tests.The test results demonstrated that the contents and curing ages of xanthan gum had significant influences on the unconfined compressive strength of red clay.Compared with untreated soil,1.5%xanthan gum content was the optimal ratio in which the strength increment was between 41.52 kPa and 64.73 kPa.On the other hand,the strength of xanthan gum-treated red clay increased,whereas the ductility decreased with the increase in curing ages,indicating that the xanthan gum-treated red clay started to gradually consolidate after 3 days of curing and stiffness significantly improved between 7 and 28 days of curing.The results also showed that the synergistic consolidation effects of the xanthan gum–polypropylene fibers could not only effectively enhance the strength of red clay but also reduce the brittle failure phenomenon.The strengths of soil treated with 2.0%xanthan gum-polypropylene fibers were 1.9–2.41 and 1.12–1.47 times than that of red clay and 1.5%xanthan gum-treated clay,respectively.The results of study provide the related methods and experiences for the field of ecological soil treatment.
基金This study was supported in part by the Earthquake Science and Technology Development Fund,Gansu Earthquake Agency(Grant Nos.2021M7,2019Q08)the Construction Project of Scientific Research team of Seismological Bureau of Gansu Province(Grant No.2020TD-01-01)the National Natural Science Foundation of China(Grant No.51778590).
文摘In the seasonal permafrost region with loess distribution,the influence of freeze-thaw cycles on the engineering performance of reinforced loess must be paid attention to.Many studies have shown that the use of fiber materials can improve the engineering performance of soil and its ability to resist freeze-thaw cycles.At the same time,as eco-environmental protection has become the focus,which has been paid more and more attention to,it has become a trend to find new environmentally friendly improved materials that can replace traditional chemical additives.The purpose of this paper uses new environmental-friendly improved materials to reinforce the engineering performance of loess,improve the ability of loess to resist freeze-thaw cycles,and reduce the negative impact on the ecological environment.To reinforce the engineering performance of loess and improve its ability to resist freeze-thaw cycles,lignin fiber is used as a reinforcing material.Through a series of laboratory tests,the unconfined compressive strength(UCS)of lignin fiber-reinforced loess under different freeze-thaw cycles was studied.The effects of lignin fiber content and freeze-thaw cycles on the strength and deformation modulus of loess were analyzed.Combined with the microstructure features,the change mechanism of lignin fiber-reinforced loess strength under freeze-thaw cycles was discussed.The results show that lignin fiber can improve the UCS of loess under freeze-thaw cycles,but the strengthening effect no longer increases with the increase of fiber content.When the fiber content is less than 1%,the UCS growth rate of loess is the fastest under freeze-thaw cycles.And the UCS of loess with 1%fiber content is the most stable under freeze-thaw cycles.The freeze-thaw cycles increase the deformation modulus of loess with 1%fiber content,and its ability to resist deformation is obviously better than loess with 1.5%,2%and 3%fiber content.The fiber content over 1%will weaken the strengthening effect of lignin fiber-reinforced loess,and the optimum fiber content of lignin fiber-reinforced loess under freeze-thaw cycles is 1%.
基金The National Natural Science Foundation of China(No.51108081)
文摘In order to investigate the effect o f some factors on the unconfined compressive strength(UCS)for composite soil stabilizer-stabilized gravel soil(CSSSGS),the orthogonal test is adopted to set up the experimental scheme.Three levels o f each factor armconsidered to obtain the change laws o f UCS,in which the binder dosages are8%,10%,and12%;the curing times ae7,14and21d;the gradation nae0.3,0.35and0.4;and the degrees of compaction are95%,97%,and99%.The range analysis clearly indicates that the influence degree o f the four factors on UCS is in such an order:dosage,age,gradation,and degree o f compaction.The variance analysis shows that only the composite soil stabilizer dosage can significantly affect UCS.In road construction,the examination o f composite soil stabilizer dosage and base-course maintenance should be given much more attention to obtain satisfactory base-course strength,compared w ith gradation floating and the change of degree o f compaction.
基金Supported by Yunnan Major Scientific and Technological Projects(No.202403AA080001)National Natural Science Foundation of China(No.52074137)Yunnan Fundamental Research Projects(No.202201AT070151)。
文摘Three types of activators such as sodium hydroxide,calcium oxide and triethanolamine(TEA)are used to establish different activation environments to address the problems associated with the process of activating fly ash paste.We conducted mechanical tests and numerical simulations to understand the evolution of microstructure,and used environmental scanning electron microscopy(ESEM)and energy dispersive spectroscopy(EDS)techniques to analyze the microenvironments of the samples.The mechanical properties of fly ash paste under different activation conditions and the changes in the microstructure and composition were investigated.The results revealed that under conditions of low NaOH content(1%-3%),the strength of the sample increased significantly.When the content exceeded 4%,the rate of increase in strength decreased.Based on the results,the optimal NaOH content was identified,which was about 4%.A good activation effect,especially for short-term activation(3-7 d),was achieved using TEA under high doping conditions.The activation effect was poor for long-term strength after 28 days.The CaO content did not significantly affect the degree of activation achieved.The maximum effect was exerted when the content of CaO was 2%.The virtual cement and concrete testing laboratory(VCCTL)was used to simulate the hydration process,and the results revealed that the use of the three types of activators accelerated the formation of Ca(OH)_(2) in the system.The activators also corroded the surface of the fly ash particles,resulting in a pozzolanic reaction.The active substances in fly ash were released efficiently,and hydration was realized.The pores were filled with hydration products,and the microstructure changed to form a new frame of paste filling that helped improve the strength of fly ash paste.
基金support provided by the Natural Science Foundation of China(Grant No.52208240)S&T Program of Hebei(Grant No.E2022202051,236Z3809G)+1 种基金Education Department of Hebei Province(Grant No.:C20220311)Hebei University of Technology(Grant No.:24/424132021).
文摘Ternary geopolymers incorporating multiple solid wastes such as steel slag(SS),fly ash(FA),and granulated blast furnace slag(GBFS)are considered environmentally friendly and exhibit enhanced performance.However,the mechanisms governing strength development and the design of optimal mixtures are not fully understood due to the complexity of their components.This study presents the development of four machine learning mod-els-Artificial Neural Network(ANN),Support Vector Regression(SVR),Extremely Randomized Tree(ERT),and Gradient Boosting Regression(GBR)-for predicting the unconfined compressive strength(UCS)of ternary geopolymers.The models were trained using a dataset comprising 120 mixtures derived from laboratory tests.Shapley Additive Explanations analysis was employed to interpret the machine learning models and elucidate the influence of different components on the properties of ternary geopolymers.The results indicate that ANN ex-hibits the highest predictive accuracy for UCS(R=0.949).Furthermore,the UCS of ternary geopolymers is most sensitive to the content of GBFS.This study provides valuable insights for optimizing the mix proportions in ternary blended geopolymer mixtures.
基金supported by the National Natural Science Foundation of China(Grant Nos.42272338,41902275)the Sichuan Transportation Science and Technology Program(Grant No.2018-ZL-02).
文摘Geotechnical engineering usually produces drillholes in the ground for investigation and construction.Drilling is a rock-breaking process by applying normal(thrust)and shear(torque)force from the drill bit to the rock below the bit.These rock-breaking data can be obtained by digital monitoring and recording the drilling parameters through an instrumented drilling machine.However,there is no mature and standard method to determine rock strength properties(such as unconfined compressive strength,UCS,or tensile strength)from real-time monitored drilling parameter(such as thrust force,torque,rotation speed,drilling speed and specific energy).This paper presents a complete procedure to accurately determine each drilling parameter.More importantly,the specific energy develops nonlinearly with change of the thrust force,which is related to the UCS and tensile strength of the rock.This finding provides an insight into determining the UCS and tensile strength of the rock based on real-time monitored drilling parameters.In addition,novel test setups are demonstrated to determine the thrust force and torque from hydraulics pressures and rotation speeds.These setups can significantly reduce the sophisticated instrumentation cost for drilling monitoring studies.Three type rocks including granite,limestone and sandstone are used for the testing.The findings from this study provide supporting theories to upgrade drilling monitoring technique to a standard geotechnical testing method.
基金supported by the State Scholarship Fund from the China Scholarship Council(CSC)No.202006180076.
文摘Microbially induced carbonate precipitation(MICP)is an eco-friendly soil improvement technique.However,this method still has some drawbacks,such as low conversion efficiency of CaCO_(3) crystallization,insufficient strength for certain applications,and requiring multiple treatments.Previous studies have re-ported that sticky rice can regulate CaCO_(3) crystals(i.e.,chemical CaCO_(3))in the sticky rice-lime mortar,showing potential for improving the bio-cementation.Therefore,this study explored the possibility of using sticky rice to enhance the biocementation effect.Tests were carried out to assess the strength and perme-ability of bio-cemented sand with the inclusion of sticky rice.The results indicated that sticky rice may regulate the type and size of bio-CaCO_(3) crystals,and the use of an appropriate amount of sticky rice as additive could increase the strength of sand columns by regulating CaCO_(3) crystallization.Polyhedral calcites may be more favourable for the increasing strength than some vaterites with a hollow spherical structure.The combination of MICP and sticky rice can significantly decrease the coefficient of permeability to a value that was much lower than that by using sticky rice and MICP alone.Bio-CaCO_(3) immobilized the sticky rice on one end on sand particles,and the reticulated structure of sticky rice divided large pores into small pores,which may be the important cause of the decrease in permeability coefficient.Finally,this study proposed that the MICP with the sticky rice as an additive may enhance the MICP effect and prevent the surface erosion of coarse-grained sand slopes.
基金Project(BK2011618) supported by the Natural Science Foundation of Jiangsu Province, ChinaProject(51108288) supported by the National Natural Science Foundation of China
文摘The improvement of question soils with cement shows great technical, economic and environmental advantages. And interest in introducing electrical resistivity measurement to assess the quality of cement treated soils has increased markedly recently due to its economical, non-destructive, and relatively non-invasive advantages. This work aims to quantify the effect of cement content （aw）, porosity （nt）, and curing time（T） on the electrical resistivity （p） and unconfined compression strength （UCS） of cement treated soil. A series of electrical resistivity tests and UCS tests of cement treated soil specimen after various curing periods were carried out. A modified Archie empirical law was proposed taking into account the effect of cement content and curing period on the electrical resistivity of cement treated soil. The results show that nt/（aw·T） and nt/（aw·T^1/2） ratio are appropriate parameters to assess electrical resistivity and UCS of cement treated soil, respectively. Finally, the relationship between UCS and electrical resistivity was also established.
文摘Dry jet mixing (DJM) for soft soil stabilization has been widely used since 1980s. The quality and strength of stabilized columns are fundamental parameters to evaluate the stabilization work. This paper presents the standard penetration test (SPT) method and its test results on cement columns. It is shown that SPT is an effective and simple method for inspecting and evaluating cement columns. The strength characteristics along the length of the column, a good correction between SPT blow count and the unconfined compressive strength are achieved.
文摘In order to simulate and study the erosion effect process such as the changes of corrosive depth and unconfined compression strength of cemented soil sample in earlier period from 0 day to 60 days, a series of tests including unconfined compressive tests, measuring the blocks＇ sizes, and taking photos, are conducted on the cemented soil blocks which were cured in different concentrations of H2SO4 solutions. The results of tests show that the corrosive depth is increasing and the unconfined compression strength is decreasing with the increase of H2SO4 solution concentration at the same erosion time, and the corrosive degree is increasing with the corrosive time. In the earlier state, the corrosive effect is serious, but the effect becomes slow in the later state in the same concentrated H2SO4 solution. After take statistics the date, a coefficient a is put forward to predict the reduction of the compressive strength of cemented soil in various concentration of H2SO4 solution, which could be used in practical design.
基金Projects(41330641,51279032,51278100)supported by(Major Program of)the National Natural Science Foundation of ChinaProject(41330641)supported by National Technology Support Program during the Twelfth Five-Year Plan of China+1 种基金Project(KYLX_0147)supported by Graduate Student Scientific Research Innovation Program of Jiangsu Province,ChinaProject(BK2012022)supported by the Natural Science Foundation of Jiangsu Province,China
文摘A series of unconfined compression tests(UCTs) were conducted to investigate the effects of content of reactive magnesia(Mg O) and carbonation time on the engineering properties including apparent characteristics, stress-strain relation, and deformation and strength characteristics of reactive Mg O treated silt soils. The soils treated with reactive Mg O at various contents were subjected to accelerated carbonation for different periods of time and later, UCTs were performed on them. The results demonstrate that the reactive Mg O content and carbonation time have remarkable influences on the aforementioned engineering properties of the soils. It is found that with the increase in reactive Mg O content, the unconfined compressive strength(qu) increases at a given carbonation time(<10 h), whereas the water content and amounts of crack of the soils decrease. A threshold content of reactive Mg O exists at approximately 25% and a critical carbonation time exists at about 10 h for the development of qu. A simple yet practical strength-prediction model, by taking into account two variables of reactive Mg O content and carbonation time, is proposed to estimate qu of carbonated reactive Mg O treated soils. A comparison of the predicated values of qu with the measured ones indicates that the proposed model has satisfactory accuracy.
基金the context of the research project“Investigation of strength properties of xanthan treated kaolin clay”(Grant No.16MUH013)funded within Research Projects program of Ege University,Turkey.
文摘Nowadays,using biopolymer as a ground improvement method has become very popular.However,since biopolymers are organic and degradable,their long-term effect is not fully known.In this study,the effects of biopolymers on the mechanical behavior of kaolin clay were investigated through a comprehensive program of experiments.Two types of biopolymer,i.e.xanthan gum and guar gum were chosen to investigate the effect of biopolymer type.For this purpose,specimens were prepared using standard Proctor energy at four different water contents(25%,30%35%and 40%)with 0.5%,1%,1.5%and 2%biopolymer inclusions.The specimens were cured for 1 d,7 d,28 d and 90 d.Moreover,some of the specimens were kept in the curing room for 3 years to observe the long-term effect of the biopolymers.At the end of the curing periods,the specimens were subjected to unconfined compression test,and scanning electron microscopy(SEM)analysis was performed to observe the mechanism of strength improvement.The results revealed that the unconfined compressive strength(UCS)of the specimens treated with biopolymers increased in all biopolymer inclusion levels and water contents up to a 90-d curing period.For specimens containing xanthan gum,the maximum strength increase was observed at 25%water content and 2%xanthan gum with 90-d curing.The strength increased 5.23 times induced by xanthan gum addition when compared to the pure clay.Moreover,the increase in strength reached 8.53 times in specimens treated with guar gum.Besides,increasing water content caused more ductile behavior,thus increasing the axial deformation.
基金financial supports from the National Natural Science Foundation of China (51874350,41807259)the National Key Research and Development Program of China (2017YFC0602902)+1 种基金the Fundamental Research Funds for the Central Universities of Central South University of China (2018zzts217)the Innovation-Driven Project of Central South University of China (2020CX040)。
文摘To reduce the difficulty of obtaining the unconfined compressive strength(UCS) value of fiber-reinforced cemented paste backfill(CPB) and analyze the comprehensive impact of conventional and fiber variables on the compressive property, a new artificial intelligence model was proposed by combining a newly invented meta-heuristics algorithm(salp swarm algorithm, SSA) and extreme learning machine(ELM) technology. Aiming to test the reliability of that model, 720 UCS tests with different cement-to-tailing mass ratio, solid mass concentration, fiber content, fiber length, and curing time were carried out, and a strength evaluation database was collected. The obtained results show that the optimized SSA-ELM model can accurately predict the uniaxial compressive strength of the fiber-reinforced CPB, and the model performance of SSA-ELM model is better than ANN, SVR and ELM models. Variable sensitivity analysis indicates that fiber content and fiber length have a significant effect on the UCS of fiber-reinforced CPB.
基金Project(50678158) supported by the National Natural Science Foundation of China
文摘To explore the stabilization effect of stabilizing agent GX07 on treating organic soil and the influence of organic matter on the strength development of stabilized soil,artificial organic soil with various organic matter content was obtained by adding different amounts of fulvic acid into non-organic clay,and then liquid-plastic limit tests were carried out on the artificial organic soil.Meanwhile,unconfined compressive strength(UCS) tests were performed on cement-only soil and composite stabilized soil,respectively.The test results indicate that the plastic limit of soil samples increases linearly,and the liquid limit increases exponentially as the organic matter content increases.The strength of stabilized soil is well correlated with the organic matter content,cement content,stabilizing agent content and curing time.When the organic matter content is 6%,as the cement content varies in the range of 10%-20%,the strength of cement-only soil increases from 88.5 to 280.8 kPa.Once 12.6% GX07 is added into the mix,the strength of stabilized soil is 4.93 times compared with that of cement-only soil.GX07 can obviously improve the strength of cemented-soil and has a good economic applicability.A strength model is proposed to predict strength development.
基金supported by the National Key R&D Program of China(Grant No.2019YFC1806004)the National Natural Science Foundation of China(Grant Nos.42272322 and 51878159).
文摘Despite the fact that mixing uniformity(i.e.the consistency of binder distribution)significantly influence the quality of ground improvement during in situ soil mixing projects,its quantitative evaluation was rarely concerned due to the difficulty of measurement from an engineering perspective.A methodology was proposed to quantitatively evaluate the mixing uniformity of stabilized soil using handheld Xfluorescence spectrometry(XRF),which is helpful to elucidate the significance of mixing uniformity on strength.In other words,the calcium content was monitored to ascertain the distribution of cement within the matrix,and a quantitative index was subsequently established.It was observed that an increase in mixing uniformity resulted in a transition in the behavior of the stabilized clay from a plastic to a brittle failure mode,and from a localized failure to a global shear failure under unconfined compression.Subsequent observation of the destruction process revealed that cracks were more readily formed in the low cement zones and then bypass the high cement zones.Furthermore,the effect of mixing uniformity on strength is likely to be amplified with prolonged curing periods.The enhancement of uniformity would increase the volume of the high binder zones,thereby enhancing the overall highstrength performance.The proposed methodology is capable of characterizing the discreteness between the tracked element's measured and theoretical contents,thusing avoiding the uncertainty associated with other indirect indicators.The convenience of the portable handheld XRF apparatus was confirmed,as it can be readily deployed in situ or ex situ to track calcium content within the stabilized mass after borehole sampling.
文摘This paper presents an investigation on strength of cement deep mixing （CDM） mixture. Four typical works of offshore or land-based projects are introduced. With samples from these projects and laboratory tests, statistical analysis is made on the increment law of the strength of cement-soil mixture with different amount of cement, and strengths under different working conditions are compared. It is found that the amount of cement in the cement-soil mixture is closely related to the unconfined compressive strength of the mixture. At the age of 90 d,the unconfined compressive strength of the cement-soil mixture increased by 0.054 MPa—0.124 MPa with each cement increasing 10 kg/m3 in the cement-soil mixture, averagely increased by 0.085 MPa, while that at the age of 120 d increased by 1100 in comparison.The quality of the cement-soil mixture should be comprehensively evaluated in accordance with the trimmed average of strength, coefficient of variation and rock quality designation （RQD） indicators of sampling ratio.
文摘Construction on soft soil is one of the most challenging situations faced by geotechnical engineers. The heterogeneous and complex nature of soil, especially those containing organic clay, often makes it impossible for the construction specification to be addressed properly. Generally, clay exhibits low strength, high compressibility, and strength reduction when subjected to mechanical disturbance. This means that construction on clay soil is vulnerable to bearing capacity failure induced by low inherent shear strength. All these properties can be improved by the effective stabilization of soil. This study analyzed the effectiveness of incorporating salt-lime mixtures at various dosages in improving the strength increment of the soil. The results indicate that among different combinations of salt and lime, the best performance in terms of strength increase was achieved by adding 10% NaCl with 3% lime in the soil. The outcome of this study focuses on enhancing the ultimate strength of soil and its implementation in the field of foundation engineering.
