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
This study aims to numerically and experimentally investigate the response of a medium strength rock material under unconfined compression loading up to failure. The unconfined compressive strength(UCS) is one of the ...This study aims to numerically and experimentally investigate the response of a medium strength rock material under unconfined compression loading up to failure. The unconfined compressive strength(UCS) is one of the most important parameters in characterising rock material behaviour. Hence the UCS is crucial in understanding the failure mechanism of fractured rocks. An effective approach to determine the UCS and to investigate the behaviours of rock materials under unconfined compression is essential in the majority of research fields of rock mechanics. The experimental configuration for the unconfined compression test, suggested by the protocols of the ASTM standard, has some limitations which affect the accuracy in determination of the real UCS. Among several alternative configurations proposed, the Mogi’s configuration seems to be the most appropriate one. Therefore, the ASTM and Mogi’s configurations were used to perform the tests on a medium strength rock material, i.e. Pietra Serena sandstone. The results using two configurations were discussed in terms of the differences. The tests were also replicated in LSDYNA using a finite element method(FEM) coupled smooth particle hydrodynamics(SPH) technique.This technique is employed in this study due to its capabilities to cope with large deformation issues related to the rocks. An advanced material model, called the Karagozian and Case Concrete(KCC) model,is implemented in the numerical simulations. The KCC model consists of three independent fixed failure surfaces and it can consider the damage accumulation based on the current state of stress among these failure surfaces. An equation-of-state(EOS) is used in conjunction with KCC material model for decoupling the volumetric and deviatoric responses. The numerical and experimental results were finally compared with the focus on the stress-strain diagram and the failure patterns. The comparison shows that the numerical results are in good agreement with the experimental results.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 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 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
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
Discrete element method(DEM)-based numerical models in the YADE environment are used to simulate the constitutive response of uncemented and bio-cemented sands to investigate the influence of boundary conditions,loadi...Discrete element method(DEM)-based numerical models in the YADE environment are used to simulate the constitutive response of uncemented and bio-cemented sands to investigate the influence of boundary conditions,loading and testing conditions,and material types.Both the classical DEM model and the pore scale finite volume(PFV)-coupled DEM model are used to simulate the response of saturated uncemented and lightly cemented sands with a rigid wall boundary under both drained and undrained triaxial compression.A DEM model with flexible boundaries created using particle facet(PFacet)elements is used to simulate undrained triaxial compression of moderately cemented sands,including the influence of confining stress.The PFacet-based model is used to predict the transition from barreling failure to shear banding when the confining stress or the cementation degree increases.The classical DEM model with cohesive bonds of uniform strength is also used to successfully simulate the uniaxial compression response of a sand with an extremely high degree of cementation.Finally,this paper presents a particle-packing model consisting of multiple solid phases for cemented sands based on the understanding that not all particle types will have the same cohesive properties.This multiple solidphase model is a refinement of the classical DEM model that represents the particle physics more realistically,especially for heterogeneous systems.A preliminary parametric study is carried out considering varying cohesive properties and volume fractions for the different solid phases.展开更多
This study tested the electrical conductivity and pressure sensitivity of lime⁃improved silty sand reinforced with Carbon Fiber Powder(CFP)as the conductive medium.The influence of CFP dosage,moisture content and curi...This study tested the electrical conductivity and pressure sensitivity of lime⁃improved silty sand reinforced with Carbon Fiber Powder(CFP)as the conductive medium.The influence of CFP dosage,moisture content and curing duration on the unconfined compressive strength,initial resistivity and pressure sensitivity of the improved soil was systematically analysed.The results showed that the unconfined compressive strength varied non⁃monotonically with increasing CFP dosage,reaching a peak at a dosage of 1.6%.Furthermore,the initial resistivity showed slight variations under different moisture conditions but eventually converged towards the conductive percolation threshold at a dosage of 2.4%.It is worth noting that CFP reinforced lime⁃improved silty sand(CRLS)exhibit a clear dynamic synchronization of strain with stress and resistivity rate of variation.The pressure sensitivity was optimized with CFP dosages ranging from 1.6%to 2.0%.Both insufficient and excessive dosages had a negative impact on pressure sensitivity.It is important to consider the weakening effect of high moisture content on the pressure sensitivity of the specimens in practical applications.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
This study aimed to address the challenges of solid waste utilization,cost reduction,and carbon reduction in the treatment of deep-dredged soil at Xuwei Port in Lianyungang city of China.Past research in this area was...This study aimed to address the challenges of solid waste utilization,cost reduction,and carbon reduction in the treatment of deep-dredged soil at Xuwei Port in Lianyungang city of China.Past research in this area was limited.Therefore,a curing agent made from powdered shells was used to solidify the dredged soil in situ.We employed laboratory orthogonal tests to investigate the physical and mechanical properties of the powdered shell-based curing agent.Data was collected by conducting experiments to assess the role of powdered shells in the curing process and to determine the optimal ratios of powdered shells to solidified soil for different purposes.The development of strength in solidified soil was studied in both seawater and pure water conditions.The study revealed that the strength of the solidified soil was influenced by the substitution rate of powdered shells and their interaction with cement.Higher cement content had a positive effect on strength.For high-strength solidified soil,the recommended ratio of wet soil:cement:lime:powdered shells were 100:16:4:4,while for low-strength solidified soil,the recommended ratio was 100:5.4:2.4:0.6.Seawater,under appropriate conditions,improved short-term strength by promoting the formation of expansive ettringite minerals that contributed to cementation and precipitation.These findings suggest that the combination of cement and powdered shells is synergistic,positively affecting the strength of solidified soil.The recommended ratios provide practical guidance for achieving desired strength levels while considering factors such as cost and carbon emissions.The role of seawater in enhancing short-term strength through crystal formation is noteworthy and can be advantageous for certain applications.In conclusion,this research demonstrates the potential of using a powdered shell-based curing agent for solidifying dredged soil in an environmentally friendly and cost-effective manner.The recommended ratios for different strength requirements offer valuable insights for practical applications in the field of soil treatment,contributing to sustainable and efficient solutions for soil management.展开更多
Although soil exhibits excellent mechanical performance,the microstructural changes of biopolymer within soil due to dehydration and rehydration are rarely explored.This study aims to explore xanthan gum soil microstr...Although soil exhibits excellent mechanical performance,the microstructural changes of biopolymer within soil due to dehydration and rehydration are rarely explored.This study aims to explore xanthan gum soil microstructure and strength behavior under different dehydration and rehydration degrees using nuclear magnetic resonance(NMR)and unconfined compressive strength tests.The results showed that the proportion of large-volume biopolymer gel within the sample decreased from 91.91%to 38.28%during dehydration,but increased to 90.44%upon rehydration when sample moisture returned to its original level.The NMR images revealed that biopolymer gel evaporated from outside during the dehydration process,causing the dehydrated biopolymer to shrink and form a high-strength glass,which directly enhanced the soil's macroscopic mechanical properties.Upon rehydration,the biopolymer reabsorbed moisture and gradually expanded,leading to weakened connections between soil particles and a decrease in strength.Therefore,even when the moisture content of soil remained constant during the dehydration and rehydration processes,their unconfined compressive strength(UCS)and failure patterns exhibited significant differences.Both the UCS and NMR signal of biopolymer-treated soil decreased after the first dehydration and rehydration cycle,stabilizing gradually after subsequent cycles.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
Enzyme induced carbonate precipitation(EICP)is a promising technique in the field of biocementation due to its efficiency and controllability.Although many studies have proved its reliability in different environment,...Enzyme induced carbonate precipitation(EICP)is a promising technique in the field of biocementation due to its efficiency and controllability.Although many studies have proved its reliability in different environment,little attention has been paid to the influence of humic substances on the EICP.Humic substances cover most of the surface soil across the world land with vegetation,which varies according to the density of vegetation and climate.To understand the compatibility of this technique to distinct problematic soils,it is important to figure out how humic substances could affect the carbonate precipitation process induced by urease enzyme.Therefore,this study aims to investigate the effects of humic acid(HA),one type of humic substance,on the soil solidification through EICP.For this purpose,HA was added to natural soil with varying addition amounts(0%,1%,2%,4%,8%,16%)in soil column solidification tests.The results found that the cementation effectiveness was enhanced by a small amount of HA addition(<4%),while an addition up to 8%greatly inhibited the formation of calcium carbonate.At the same time,soil samples were buffered by HA in a weak acidic condition,thus preventing the emission of undesirable by-product ammonia in the ureolysis process.Therefore,this study makes a contribution to research on enzymatic biocementation by demonstrating the effects of HA on the cementation effectiveness of EICP technique.展开更多
Regulating reservoirs with clay slopes are prone to severe erosion caused by wind-wave actions and water-level fluctuations.Conventional bank protection methods often rely on rigid structures,which can adversely affec...Regulating reservoirs with clay slopes are prone to severe erosion caused by wind-wave actions and water-level fluctuations.Conventional bank protection methods often rely on rigid structures,which can adversely affect ecosystems.This study explores the use of microbially induced carbonate precipitation(MICP)for soil stabilization to enhance the erosion resistance of clay slopes and support plant growth.Through unconfined compressive strength(UCS)tests and seed germination trials,an optimal MICP treatment formula was identified.Using calcium acetate as the calcium source,with a cementation solution concentration of 0.5 mol/L and a reagent dosage of 23%,the UCS increased by 235.3%(from 20.5 to 68.7 kPa).Euphrasia pectinate Ten and Sesbania cannabina were found to be suitable plant species for MICP-treated soil,achieving germination rates of 45%and 30%,respectively.Disintegration and wave erosion tests demonstrated that the disintegration rate of MICP-treated specimens decreased from 23.1%to 0%,and the erosion mass rate decreased from 1.5%to 0.2%.Field tests further validated the effectiveness of MICP,with treated slopes exhibiting no erosion and demonstrating penetration and shear strengths of 47.9 kPa and 114.5 kPa,respectively—2.5 and 3.2 times higher than those of untreated slopes.The MICP process facilitates calcium carbonate deposition,reduces pore space,and enhances interparticle bonding.Calcium carbonate crystals derived from calcium acetate exhibited stronger adhesion than those formed from calcium chloride.Filamentous organic matter was closely adhered between soil particles,further enhancing the ductility and resistance to hydraulic erosion.Additionally,acetate ions reduce MICP toxicity to plants and enhance microbial activity and nutrient cycling,creating more favorable conditions for plant growth.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
The treatment of contaminated soil is a crucial issue in geotechnical and environmental engineering.This study proposes to incorporate appropriate polypropylene fibers and cements as an effective method to treat heavy...The treatment of contaminated soil is a crucial issue in geotechnical and environmental engineering.This study proposes to incorporate appropriate polypropylene fibers and cements as an effective method to treat heavy metal contaminated soil(HMCS).The objective of this paper is to investigate the effects of fiber content,fiber length,cement content,curing time,heavy metal types and concentration on the mechanical properties of soils.To this end,a series of direct shear test,unconfined compression strength(UCS)test,dry-wet cycle and freeze-thaw cycle test are performed.The results confirm that the appropriate reinforcement of polypropylene fibers and cement is an effective way to recycle HMCS as substitutable fillers in roadbed,which exhibits benefits in environment and economy development.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This study aims to numerically and experimentally investigate the response of a medium strength rock material under unconfined compression loading up to failure. The unconfined compressive strength(UCS) is one of the most important parameters in characterising rock material behaviour. Hence the UCS is crucial in understanding the failure mechanism of fractured rocks. An effective approach to determine the UCS and to investigate the behaviours of rock materials under unconfined compression is essential in the majority of research fields of rock mechanics. The experimental configuration for the unconfined compression test, suggested by the protocols of the ASTM standard, has some limitations which affect the accuracy in determination of the real UCS. Among several alternative configurations proposed, the Mogi’s configuration seems to be the most appropriate one. Therefore, the ASTM and Mogi’s configurations were used to perform the tests on a medium strength rock material, i.e. Pietra Serena sandstone. The results using two configurations were discussed in terms of the differences. The tests were also replicated in LSDYNA using a finite element method(FEM) coupled smooth particle hydrodynamics(SPH) technique.This technique is employed in this study due to its capabilities to cope with large deformation issues related to the rocks. An advanced material model, called the Karagozian and Case Concrete(KCC) model,is implemented in the numerical simulations. The KCC model consists of three independent fixed failure surfaces and it can consider the damage accumulation based on the current state of stress among these failure surfaces. An equation-of-state(EOS) is used in conjunction with KCC material model for decoupling the volumetric and deviatoric responses. The numerical and experimental results were finally compared with the focus on the stress-strain diagram and the failure patterns. The comparison shows that the numerical results are in good agreement with the experimental results.
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.
基金support for this study from National Science Foundation(NSF)under the Engineering Research Centers(ERC)program,grant EEC-1449501.
文摘Discrete element method(DEM)-based numerical models in the YADE environment are used to simulate the constitutive response of uncemented and bio-cemented sands to investigate the influence of boundary conditions,loading and testing conditions,and material types.Both the classical DEM model and the pore scale finite volume(PFV)-coupled DEM model are used to simulate the response of saturated uncemented and lightly cemented sands with a rigid wall boundary under both drained and undrained triaxial compression.A DEM model with flexible boundaries created using particle facet(PFacet)elements is used to simulate undrained triaxial compression of moderately cemented sands,including the influence of confining stress.The PFacet-based model is used to predict the transition from barreling failure to shear banding when the confining stress or the cementation degree increases.The classical DEM model with cohesive bonds of uniform strength is also used to successfully simulate the uniaxial compression response of a sand with an extremely high degree of cementation.Finally,this paper presents a particle-packing model consisting of multiple solid phases for cemented sands based on the understanding that not all particle types will have the same cohesive properties.This multiple solidphase model is a refinement of the classical DEM model that represents the particle physics more realistically,especially for heterogeneous systems.A preliminary parametric study is carried out considering varying cohesive properties and volume fractions for the different solid phases.
基金Sponsored by Jilin Provincial Department of Education Scientific Research Project(Grant Nos.JJKH20190875KJ,JJKH20230348KJ).
文摘This study tested the electrical conductivity and pressure sensitivity of lime⁃improved silty sand reinforced with Carbon Fiber Powder(CFP)as the conductive medium.The influence of CFP dosage,moisture content and curing duration on the unconfined compressive strength,initial resistivity and pressure sensitivity of the improved soil was systematically analysed.The results showed that the unconfined compressive strength varied non⁃monotonically with increasing CFP dosage,reaching a peak at a dosage of 1.6%.Furthermore,the initial resistivity showed slight variations under different moisture conditions but eventually converged towards the conductive percolation threshold at a dosage of 2.4%.It is worth noting that CFP reinforced lime⁃improved silty sand(CRLS)exhibit a clear dynamic synchronization of strain with stress and resistivity rate of variation.The pressure sensitivity was optimized with CFP dosages ranging from 1.6%to 2.0%.Both insufficient and excessive dosages had a negative impact on pressure sensitivity.It is important to consider the weakening effect of high moisture content on the pressure sensitivity of the specimens in practical applications.
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Funded by the Science and Technology Project of Jiangsu Provincial Transportation Department(No.2022Y13)。
文摘This study aimed to address the challenges of solid waste utilization,cost reduction,and carbon reduction in the treatment of deep-dredged soil at Xuwei Port in Lianyungang city of China.Past research in this area was limited.Therefore,a curing agent made from powdered shells was used to solidify the dredged soil in situ.We employed laboratory orthogonal tests to investigate the physical and mechanical properties of the powdered shell-based curing agent.Data was collected by conducting experiments to assess the role of powdered shells in the curing process and to determine the optimal ratios of powdered shells to solidified soil for different purposes.The development of strength in solidified soil was studied in both seawater and pure water conditions.The study revealed that the strength of the solidified soil was influenced by the substitution rate of powdered shells and their interaction with cement.Higher cement content had a positive effect on strength.For high-strength solidified soil,the recommended ratio of wet soil:cement:lime:powdered shells were 100:16:4:4,while for low-strength solidified soil,the recommended ratio was 100:5.4:2.4:0.6.Seawater,under appropriate conditions,improved short-term strength by promoting the formation of expansive ettringite minerals that contributed to cementation and precipitation.These findings suggest that the combination of cement and powdered shells is synergistic,positively affecting the strength of solidified soil.The recommended ratios provide practical guidance for achieving desired strength levels while considering factors such as cost and carbon emissions.The role of seawater in enhancing short-term strength through crystal formation is noteworthy and can be advantageous for certain applications.In conclusion,this research demonstrates the potential of using a powdered shell-based curing agent for solidifying dredged soil in an environmentally friendly and cost-effective manner.The recommended ratios for different strength requirements offer valuable insights for practical applications in the field of soil treatment,contributing to sustainable and efficient solutions for soil management.
基金supported by the National Natural Science Foundation of China(Grant No.42102324)the Natural Science Foundation of Hubei Province of China(Grant No.2024AFB686)Open Fund of Badong National Observation and Research Station of Geohazards(Grant No.BNORSG-202102).
文摘Although soil exhibits excellent mechanical performance,the microstructural changes of biopolymer within soil due to dehydration and rehydration are rarely explored.This study aims to explore xanthan gum soil microstructure and strength behavior under different dehydration and rehydration degrees using nuclear magnetic resonance(NMR)and unconfined compressive strength tests.The results showed that the proportion of large-volume biopolymer gel within the sample decreased from 91.91%to 38.28%during dehydration,but increased to 90.44%upon rehydration when sample moisture returned to its original level.The NMR images revealed that biopolymer gel evaporated from outside during the dehydration process,causing the dehydrated biopolymer to shrink and form a high-strength glass,which directly enhanced the soil's macroscopic mechanical properties.Upon rehydration,the biopolymer reabsorbed moisture and gradually expanded,leading to weakened connections between soil particles and a decrease in strength.Therefore,even when the moisture content of soil remained constant during the dehydration and rehydration processes,their unconfined compressive strength(UCS)and failure patterns exhibited significant differences.Both the UCS and NMR signal of biopolymer-treated soil decreased after the first dehydration and rehydration cycle,stabilizing gradually after subsequent cycles.
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JST SPRING,Grant Number JPMJSP2119Japan Society for the Promotion of Science(JSPS)KAKENHI Grant Number JP22H01581。
文摘Enzyme induced carbonate precipitation(EICP)is a promising technique in the field of biocementation due to its efficiency and controllability.Although many studies have proved its reliability in different environment,little attention has been paid to the influence of humic substances on the EICP.Humic substances cover most of the surface soil across the world land with vegetation,which varies according to the density of vegetation and climate.To understand the compatibility of this technique to distinct problematic soils,it is important to figure out how humic substances could affect the carbonate precipitation process induced by urease enzyme.Therefore,this study aims to investigate the effects of humic acid(HA),one type of humic substance,on the soil solidification through EICP.For this purpose,HA was added to natural soil with varying addition amounts(0%,1%,2%,4%,8%,16%)in soil column solidification tests.The results found that the cementation effectiveness was enhanced by a small amount of HA addition(<4%),while an addition up to 8%greatly inhibited the formation of calcium carbonate.At the same time,soil samples were buffered by HA in a weak acidic condition,thus preventing the emission of undesirable by-product ammonia in the ureolysis process.Therefore,this study makes a contribution to research on enzymatic biocementation by demonstrating the effects of HA on the cementation effectiveness of EICP technique.
基金Science and Technology Project of Anhui Provincial Group Limited for Yangtze-to-Huaihe Water Diversion,Grant/Award Number:YJJH-ZT-ZX-20221130515Natural Science Foundation of Hebei Province,Grant/Award Number:E2024210095National Natural Science Foundation of China,Grant/Award Number:52308365。
文摘Regulating reservoirs with clay slopes are prone to severe erosion caused by wind-wave actions and water-level fluctuations.Conventional bank protection methods often rely on rigid structures,which can adversely affect ecosystems.This study explores the use of microbially induced carbonate precipitation(MICP)for soil stabilization to enhance the erosion resistance of clay slopes and support plant growth.Through unconfined compressive strength(UCS)tests and seed germination trials,an optimal MICP treatment formula was identified.Using calcium acetate as the calcium source,with a cementation solution concentration of 0.5 mol/L and a reagent dosage of 23%,the UCS increased by 235.3%(from 20.5 to 68.7 kPa).Euphrasia pectinate Ten and Sesbania cannabina were found to be suitable plant species for MICP-treated soil,achieving germination rates of 45%and 30%,respectively.Disintegration and wave erosion tests demonstrated that the disintegration rate of MICP-treated specimens decreased from 23.1%to 0%,and the erosion mass rate decreased from 1.5%to 0.2%.Field tests further validated the effectiveness of MICP,with treated slopes exhibiting no erosion and demonstrating penetration and shear strengths of 47.9 kPa and 114.5 kPa,respectively—2.5 and 3.2 times higher than those of untreated slopes.The MICP process facilitates calcium carbonate deposition,reduces pore space,and enhances interparticle bonding.Calcium carbonate crystals derived from calcium acetate exhibited stronger adhesion than those formed from calcium chloride.Filamentous organic matter was closely adhered between soil particles,further enhancing the ductility and resistance to hydraulic erosion.Additionally,acetate ions reduce MICP toxicity to plants and enhance microbial activity and nutrient cycling,creating more favorable conditions for plant growth.
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.
基金Projects(51778386,51708377,51608059)supported by the National Natural Science Foundation of ChinaProject(BK20170339)supported by Natural Science Foundation of Jiangsu Province,China+2 种基金Project(17KJB560008)supported by Natural Science Fund for Colleges and Universities in Jiangsu Province,ChinaProjects(KFJ170106,KFJ180105)supported by Open Fund of National Engineering Laboratory of Highway Maintenance Technology(Changsha University of Science&Technology),ChinaProjects(2016ZD18,2017ZD002)supported by Jiangsu Provincial Department of Housing,Urban-Rural Development,China。
文摘The treatment of contaminated soil is a crucial issue in geotechnical and environmental engineering.This study proposes to incorporate appropriate polypropylene fibers and cements as an effective method to treat heavy metal contaminated soil(HMCS).The objective of this paper is to investigate the effects of fiber content,fiber length,cement content,curing time,heavy metal types and concentration on the mechanical properties of soils.To this end,a series of direct shear test,unconfined compression strength(UCS)test,dry-wet cycle and freeze-thaw cycle test are performed.The results confirm that the appropriate reinforcement of polypropylene fibers and cement is an effective way to recycle HMCS as substitutable fillers in roadbed,which exhibits benefits in environment and economy development.
