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
This study aims to improve the unconfined compressive strength of soils using additives as well as by predicting the strength behavior of stabilized soils using two artificial-intelligence-based models.The soils used ...This study aims to improve the unconfined compressive strength of soils using additives as well as by predicting the strength behavior of stabilized soils using two artificial-intelligence-based models.The soils used in this study are stabilized using various combinations of cement,lime,and rice husk ash.To predict the results of unconfined compressive strength tests conducted on soils,a comprehensive laboratory dataset comprising 137 soil specimens treated with different combinations of cement,lime,and rice husk ash is used.Two artificial-intelligence-based models including artificial neural networks and support vector machines are used comparatively to predict the strength characteristics of soils treated with cement,lime,and rice husk ash under different conditions.The suggested models predicted the unconfined compressive strength of soils accurately and can be introduced as reliable predictive models in geotechnical engineering.This study demonstrates the better performance of support vector machines in predicting the strength of the investigated soils compared with artificial neural networks.The type of kernel function used in support vector machine models contributed positively to the performance of the proposed models.Moreover,based on sensitivity analysis results,it is discovered that cement and lime contents impose more prominent effects on the unconfined compressive strength values of the investigated soils compared with the other parameters.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
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
This study examines the effect of nanosilica(NS)additive to improve the mechanical properties of clay,clayey sand,and sand.The engineering properties of the soils were investigated through Atterberg limits,compaction,...This study examines the effect of nanosilica(NS)additive to improve the mechanical properties of clay,clayey sand,and sand.The engineering properties of the soils were investigated through Atterberg limits,compaction,unconfined compression,ultrasonic pulse velocity(UPV),freeze-thaw,and direct shear tests.The NS content varied from 0%to 0.7%and cement content was 5%and 10%by the dry weight of the soil.The curing period varied from 7 d to 150 d.The consistency,compaction,and strength properties of the soils were affected by the presence of NS and cement.The optimum NS contents in clay specimens with 5%and 10%cement were 0.5%and 0.7%,respectively.It was 0.7%in sand specimens with both cement ratios,as well as 0.3%and 0.7%in clayey sand specimens with 5%and 10%cement,respectively.In terms of freeze-thaw resistance,clayey sand specimens containing 0.5%NS and 10%cement had the minimum strength loss.Exponential relationships existed between the ultrasonic pulse velocity(UPV)and the unconfined compressive strength(UCS)of soil specimens having the same curing period.The shear strength parameters of the soils also improved with the addition of NS.Scanning electron microscope(SEM)images demonstrated that cement and NS contributed to the improvement of the soils by producing a denser and more uniform structure.It was concluded that the minor addition of NS could potentially improve the geomechanical properties of the soils.展开更多
Carbonate rocks are extensively used in civil infrastructure and play a critical role in geoenergy geoengineering,either as hydrocarbon reservoirs or potential repositories for CO_(2)geological storage.Carbonate genes...Carbonate rocks are extensively used in civil infrastructure and play a critical role in geoenergy geoengineering,either as hydrocarbon reservoirs or potential repositories for CO_(2)geological storage.Carbonate genesis and diagenetic overprint determine the properties of carbonate rocks.This study combines recent data gathered from Madison Limestone and an extensive dataset compiled from published sources to analyze the hydraulic and mechanical properties of limestone carbonate rocks.Physical models and data analyses recognize the inherently granular genesis of carbonate rocks and explain the strong dependency of physical properties on porosity.The asymptotically-correct power model in terms of(1-Ф/Ф*)a is a good approximation to global trends of unconfined stiffness E and unconfined compressive strength UCS,cohesive intercept in Mohr-Coulomb failure envelopes,and the brittle-toductile transition stress.This power model is the analytical solution for the mechanical properties of percolating granular structures.We adopted a limiting granular porosityФ*=0.5 for all models,which was consistent with the loosest packing of monosize spheres.The fitted power model has exponent(α=2)in agreement with percolation theory and highlights the sensitivity of mechanical properties to porosity.Data and models confirm a porosity-independent ratio between unconfined stiffness and strength,and the ratio follows a log-normal distribution with mean(E/UCS)≈300.The high angle of internal shear strength measured for carbonate rocks reflects delayed contact failure with increased confinement,and it is not sensitive to porosity.Permeability spans more than six orders of magnitude.Grain size controls pore size and determines the reference permeability k^(*)at the limiting porosityФ*=0.5.For a given grain size from fine to coarse-grained dominant carbonates,permeability is very sensitive to changes in porosity,suggesting preferential changes in the internal pore network during compaction.展开更多
The mechanical performances and water retention characteristics of clays,stabilised by partial substitution of cement with by-products and inclusion of a nanotechnology-based additive called RoadCem(RC),are studied in...The mechanical performances and water retention characteristics of clays,stabilised by partial substitution of cement with by-products and inclusion of a nanotechnology-based additive called RoadCem(RC),are studied in this research.The unconfined compression tests and one-dimensional oedometer swelling were performed after 7 d of curing to understand the influence of addition of 1%of RC material in the stabilised soils with the cement partially replaced by 49%,59%and 69%of ground granulated blast furnace slag(GBBS)or pulverised fuel ash(PFA).The moisture retention capacity of the stabilised clays was also explored using the soil-water retention curve(SWRC)from the measured suctions.Results confirmed an obvious effect of the use of RC with the obtained strength and swell properties of the stabilised clays suitable for road application at 50%replacement of cement.This outcome is associated with the in-depth and penetrating hydration of the cementitious materials by the RC and water which results in the production of needle-like matrix with interlocking filaments e a phenomenon referred to as the‘wrapping’effect.On the other hand,the SWRC used to describe the water holding capacity and corresponding swell mechanism of clays stabilised by a proportion of RC showed a satisfactory response.The moisture retention of the RC-modified clays was initially higher but reduced subsequently as the saturation level increased with decreasing suction.This phenomenon confirmed that clays stabilised by including the RC are water-proof in nature,thus ensuring reduced porosity and suction even at reduced water content.Overall,the stabilised clays with the combination of cement,GGBS and RC showed a better performance compared to those with the PFA included.展开更多
This paper presents an experimental study and micro-mechanism discussion on gypsum role in the mechanical improvements of cement-based stabilized clay(CBSC).A soft marine clay at two initial water contents(i.e.50%and ...This paper presents an experimental study and micro-mechanism discussion on gypsum role in the mechanical improvements of cement-based stabilized clay(CBSC).A soft marine clay at two initial water contents(i.e.50%and 70%)was treated by reconstituted cementitious binders with varying gypsum to clinker(G/C)ratios and added metakaolin to facilitate the formation of ettringite,followed by the measurements of final water contents,dry densities and strengths in accordance with ASTM standards as well as microstructure by mercury intrusion porosimetry(MIP)and scanning electron microscopy(SEM).Results reveal that the gypsum fraction has a significant influence on the index and mechanical properties of the CBSC,and there exists a threshold of the G/C ratio,which is 10%and 15%for clays with 50%and 70%initial water contents,respectively.Beyond which adding excessive gypsum cannot improve the strength further,eliminating the beneficial role.At these thresholds of the G/C ratio,the unconfined compressive strength(UCS)values for clays with 50%and 70%initial water contents are 1.74 MPa and 1.53 MPa at 60 d of curing,respectively.Microstructure characterization shows that,besides the common cementation-induced strengthening,newly formed ettringite also acts as significant pore infills,and the associated remarkable volumetric expansion is responsible,and may be the primary factor,for the beneficial strength gain due to the added gypsum.Moreover,pore-filling ettringite also leads to the conversion of relatively large inter-aggregate to smaller intra-aggregate pores,thereby causing a more homogeneous matrix or solid skeleton with higher strength.Overall,added gypsum plays a vital beneficial role in the strength development of the CBSC,especially for very soft clays.展开更多
A phosphogypsum-based subgrade stabilizer(PBSS)was formulated using industrial by-product phosphogypsum(PG),mixed with slag and calcium-silicon-rich active material(GSR).The active powder(AP)was used to modify PBSS,an...A phosphogypsum-based subgrade stabilizer(PBSS)was formulated using industrial by-product phosphogypsum(PG),mixed with slag and calcium-silicon-rich active material(GSR).The active powder(AP)was used to modify PBSS,and PBSS-AP was obtained.PBSS and PBSS-AP were each mixed with 10%silty soil,and cement and lime(CAL:5%lime+2%cement)were used as the traditional material for comparative experiments.Samples were cured under standard conditions,and tested for unconfined compressive strength(UCS),water stability,volume expansion,and leachate,to explore the stabilization effect of the three solidified materials on silty soil.The results showed that the comprehensive performance of sility soil mixed with 12%PBSS-AP was the best.The CaO,SiO_(2)and Al_(2)O_(3)provided by PG,Slag and GSR will react with water to form a stable C-S-H gel,which is conducive to stabilizing the soil.Field application results showed that the compaction exceeded 95%,the deflection was 144.9 mm,and UCS was 2.5 MPa after 28 days.These findings indicated that PBSS-AP is an effective stabilizer for subgrade soils.展开更多
Micaceous soils are common in many tropical countries and regions,and in some locations with moderate climate.The soils are spongy and unstable when loaded and are not considered suitable as construction material in e...Micaceous soils are common in many tropical countries and regions,and in some locations with moderate climate.The soils are spongy and unstable when loaded and are not considered suitable as construction material in earth structures.To resolve the issue,this work examined performance of micaceous soil reinforced with a combination of jute fibers,hydrated lime or slag-lime.A total of 28 sample sets were prepared at various dosages.Unconfined compression tests were conducted on the samples cured for 7 d and 28 d,respectively.The test results suggested that the unconfined compressive strength(UCS)and material stiffness were increased with the inclusion of up to 1%fiber and decreased if additional fibers were used.The ductility was improved consistently with up to 1.5%fiber content.The inclusions of fibers combined with hydrated lime or slag-lime further enhanced strength and stiffness of micaceous soil,and the improvement depended on the dosages used.For the dosages examined,jute fibers outweighed lime and slag in gaining ductility,and the optimal fiber content was 1%where strength and ductility were considered.展开更多
Recycled powder(RP)is produced as a by-product during the process of recycling construction and demolition(C&D)wastes,presenting a low additional value.Using RP-based solidifying material can not only improve its ...Recycled powder(RP)is produced as a by-product during the process of recycling construction and demolition(C&D)wastes,presenting a low additional value.Using RP-based solidifying material can not only improve its utilization efficiency,but also reduce the cost of commercial solidifying materials.To date,this is the best solidifying material utilized to dispose the original waterworks sludge(OWS)with high moisture contents(60%),and the product could be used to fabricate non-fired bricks.This has become a new environment-friendly technology of“using waste to treat waste”.In this paper,the influence of different particle sizes and dosages of RP on the prepared solidifying material was studied.Besides,unconfined compression strength(UCS),volume stability,chemical composition,and heat of hydration,pore structure of the solidifying material were characterized.Then,non-fired bricks were prepared by using the solidifying material,recycled aggregate,and original waterworks sludge.The UCS and softing coefficient(SC)of the non-fired bricks were evaluated.As a result,the 28-day UCS of the solidifying material with optimal(M30)was 35.40 MPa,which could reach 84.37%of Portland cement(PC).The addition of RP increased the volume stability of the solidifying material.The addition of a large amount of RP reduced the heat flux and cumulative heat release of the solidifying material,while its porosity increased.The UCS of non-fired brick(NF20)in 28 days was 15.19 MPa and the SC after 28 days was 78.35%.In conclusion,the preparation of solidifying material using RP could be a promising approach and has a great potential in disposal of original waterworks sludge.展开更多
Lime-fly ash stabilized loess has a poor early strength,which results in a later traffic opening time when it is used as road-base materials.Consideration of the significant early strength characteristics of sulphate ...Lime-fly ash stabilized loess has a poor early strength,which results in a later traffic opening time when it is used as road-base materials.Consideration of the significant early strength characteristics of sulphate aluminum cement(SAC),it is always added into the lime-fly ash mixtures to improve the early strength of stabilized loess.However,there is a scarcity of research on the mechanical behavior of lime-fly ash-SAC stabilized loess and there is a lack of quantitative evaluation of loess stabilized with binder materials.This research explored the effects of the amount of binder materials,curing time and porosity on the unconfined compressive strength(UCS),splitting tensile strength(STS),cohesion(c)and friction angle(φ)of lime-fly ash-SAC stabilized loess by a series of unconfined compressive tests(UCT)and splitting tensile tests(STT).The results indicate that an increase in curing time and a decrease in porosity lead to a continuous increase in the UCS and STS for lime-fly ash-SAC stabilized loess.The addition of SAC has a prominent enhancement in the early strength of lime-fly ash-SAC stabilized loess.When the curing time,porosity,and binder content were constant,the UCS and STS increase with increasing SAC content;For a stabilized loess with 30%binder content and 5%SAC content after 1 day of curing,the UCS was greater than 0.7 MPa,which meets the requirement of opening traffic,so lime-fly ash-SAC stabilized loess could be used as an excellent maintenance material for road-base;In accordance with the analysis of testing data,empirical relationships between the UCS and STS of lime-fly-SAC stabilized loess and key effect factors(binder materials content,curing time and porosity)were developed,which can provide references for reasonably selecting the amount of binder materials,compaction degree and curing period to meet the required strength of practical engineering.Finally,based on the Mohr-Coulomb theory and the above empirical relationships,a simpler method for calculating the c andφof stabilized loess was proposed,with which,the shear strength parameters can be determined only by UCT or STT.展开更多
With the industrialisation,industrial byproducts are produced in large quantities and create nuisance to natural habitats.The disposal of these wastes like fly ash,marble powder,construction and demolition(C&D)was...With the industrialisation,industrial byproducts are produced in large quantities and create nuisance to natural habitats.The disposal of these wastes like fly ash,marble powder,construction and demolition(C&D)waste,brick powder,agricultural wastes etc.has become the potential threat to the ecosystem and need some real solutions.The direct disposal of such wastes into open land or water bodies causes circumambient pollution.One of the potential solutions is to utilise these wastes in the construction industry on large scale as subgrade rehab or additive to cement based materials.In the present study,the compaction and strength characteristics of stabilised soil have been studied by using various waste materials i.e.lime,cement,plastic waste,industrial waste,fibre,mushroom waste,wet olive pomace etc.and reviewed.The addition of additives improved the engineering properties of soil significantly.展开更多
In order to simulate and study the mechanism of cement stabilized soils polluted by different contents of magnesium sulfate(MS), a series of tests were conducted on the cemented soil samples, including unconfined comp...In order to simulate and study the mechanism of cement stabilized soils polluted by different contents of magnesium sulfate(MS), a series of tests were conducted on the cemented soil samples, including unconfined compression strength(UCS) tests of blocks, X-ray diffraction(XRD) phase analysis of powder samples, microstructure by scanning electronic microscopy(SEM),element composition by energy dispersive spectrometry(EDS), and pore distribution analysis by Image Processed Plus 6.0(IPP 6.0)software. The UCS test results show that UCS of cemented soils reaches the peak value when the MS content is 4.5 g/kg. While, the UCS for Sample MS4 having the MS content of 18.0 g/kg is the lowest among all tested samples. Based on the EDS analysis results,Sample MS4 has the greater contents for the three elements, oxygen(O), magnesium(Mg) and sulfur(S), than Sample MS1. From the XRD phase analysis, C-A-S-H(3Ca O·Al2O3·3Ca SO4·32H2O and 3Ca O·Al2O3·Ca SO4·18H2O), M-A-H(Mg O·Al2O3·H2O), M-S-H(Mg O·Si O2·H2O), Mg(OH)2 and Ca SO4 phase diffraction peaks are obviously intense due to the chemical action associated with the MS. The pore distribution analysis shows that the hydrated products change the distribution of cemented soil pores and the pores with average diameter(AD) of 2-50 μm play a key role in terms of the whole structure of cemented soil. The microscopic structure of the cemented soil with MS exhibits the intertwined and embedded characteristics between the cement and granular soils from the SEM images of cemented soils. The microstructure analysis shows that the magnesium sulfate acts as the additive, which is beneficial to the soil strength when the MS content is low(i.e., Sample MS2). However, higher MS amount involving a chemical action makes samples crystallize and expand, which is adverse to the UCS of cemented soils(i.e., Sample MS4).展开更多
Micaceous soil is a problematic soil due to its low strength and poor ductility.In this context,the performances of micaceous soils were improved by applying a combination of granulated blast furnace slag,fiber and po...Micaceous soil is a problematic soil due to its low strength and poor ductility.In this context,the performances of micaceous soils were improved by applying a combination of granulated blast furnace slag,fiber and polymer additive.The dosages examined included 0%e30%mica,3%e15%slag and 0.25%e1.25%fiber by weight,and 0.1e0.5 g/L polymer additive.Most of the combinations were found to increase the material strength and ductility,yet to be optimized.To refine the dosage,response surface method was used to conduct experimental design and develop predictive models for material strength.The developed models formulate the material strength as a nonlinear function of dosages and,by interrogating it,can optimize additive contents in terms of target requirements.The models were verified through trials and can be used to determine dosages to upscale micaceous soils to field conditions.展开更多
Because of the high cost of cultivating urease-producing bacteria(UPB),this paper proposes soybean-urease-induced carbonate precipitation(SUICP)as a novel biocement for treatment of nickel contaminants and cementation...Because of the high cost of cultivating urease-producing bacteria(UPB),this paper proposes soybean-urease-induced carbonate precipitation(SUICP)as a novel biocement for treatment of nickel contaminants and cementation of sandy soil.We found the optimal soaking time and soybean-powder content to be 30 min and 130 g/L,respectively,based on a standard of 5 U of urease activity.The most efficient removal of nickel ions is obtained with an ideal mass ratio of urea to nickel ions to soybean-powder filtrate(SPF)of 1:2.4:20.The removal efficiency of nickel ions can reach 89.42%when treating 1 L of nickel-ion solution(1200 mg/L with the optimal mass ratio).In incinerated bottom ash(IBA),the removal efficiency of nickel ions is 99.33%with the optimal mass ratio.In biocemented sandy soil,the average unconfined compressive strength(UCS)of sand blocks cemented with soybean urease-based biocement can reach 118.89 kPa when the cementation level is 3.Currently,the average content of CaCO_(3)in sand blocks is 2.52%.As a result,the SUICP process can be applied to remove heavy metal ions in wastewater or solid waste and improve the mechanical properties of soft soil foundations.展开更多
A series of tests were carried out on sulfate rich,high-plasticity clay and poorly-graded natural sand to study the effectiveness of a methylene diphenyl diisocyanate based liquid polymer soil stabilizer in improving ...A series of tests were carried out on sulfate rich,high-plasticity clay and poorly-graded natural sand to study the effectiveness of a methylene diphenyl diisocyanate based liquid polymer soil stabilizer in improving the unconfined compressive strength(UCS) of freshly stabilized soils and aged sand specimens.The aged specimens were prepared by exposing the specimens to ultraviolet radiation,freeze-thaw,and wet-dry weathering.The polymer soil stabilizer also mitigated the swelling of the expansive clay.For clay,the observations indicated that the sequence of adding water and liquid polymer had great influence on the gained UCS of stabilized specimens.However,this was shown to be of little importance for sand.Furthermore,sand samples showed incremental gains in UCS when they were submerged in water.This increase was significant for up to 4 days of soaking in water after 4 days of ambient air curing.Conversely,the clay samples lost a large fraction of their UCS when soaked in water;however,their remaining strength was still considerable.The stabilized specimens showed acceptable endurance under weathering action,although sample yellowing due to ultraviolet radiation was evident on the surface of the specimens.Except for moisture susceptibility of the clay specimens,the results of this study suggested the liquid stabilizer could be successfully utilized to provide acceptable strength,durability and mitigated swelling.展开更多
Facial support in slurry shield tunneling is provided by slurry pressure to balance the external earth and water pressure.Hydraulic fracturing may occur and cause a significant decrease in the support pressure if the ...Facial support in slurry shield tunneling is provided by slurry pressure to balance the external earth and water pressure.Hydraulic fracturing may occur and cause a significant decrease in the support pressure if the slurry pressure exceeds the threshold of the soil or rock material,resulting in a serious face collapse accident.Preventing the occurrence of hydraulic fracturing in a slurry shield requires investigating the effects of related influencing factors on the hydraulic fracturing pressure and fracture pattern.In this study,a hydraulic fracturing apparatus was developed to test the slurry-induced fracturing of cohesive soil.The effects of different sample parameters and loading conditions,including types of holes,unconfined compressive strength,slurry viscosity,and axial and circumferential loads,on the fracturing pressure and fracture dip were examined.The results indicate that the fracture dip is mainly affected by the deviator stress.The fracturing pressure increases linearly with the increase in the circumferential pressure,but it is almost independent of the axial pressure.The unconfined compressive strength of soil can reflect its ability to resist fracturing failure.The fracturing pressure increases with an increase in the unconfined compressive strength as well as the slurry viscosity.Based on the test results,an empirical approach was proposed to estimate the fracturing pressure of the soil.展开更多
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 authors of this paper would like to acknowledge the support provided(No.981861)by Golestan University.
文摘This study aims to improve the unconfined compressive strength of soils using additives as well as by predicting the strength behavior of stabilized soils using two artificial-intelligence-based models.The soils used in this study are stabilized using various combinations of cement,lime,and rice husk ash.To predict the results of unconfined compressive strength tests conducted on soils,a comprehensive laboratory dataset comprising 137 soil specimens treated with different combinations of cement,lime,and rice husk ash is used.Two artificial-intelligence-based models including artificial neural networks and support vector machines are used comparatively to predict the strength characteristics of soils treated with cement,lime,and rice husk ash under different conditions.The suggested models predicted the unconfined compressive strength of soils accurately and can be introduced as reliable predictive models in geotechnical engineering.This study demonstrates the better performance of support vector machines in predicting the strength of the investigated soils compared with artificial neural networks.The type of kernel function used in support vector machine models contributed positively to the performance of the proposed models.Moreover,based on sensitivity analysis results,it is discovered that cement and lime contents impose more prominent effects on the unconfined compressive strength values of the investigated soils compared with the other parameters.
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.
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The authors thank to Ege University Central Research Test and Analysis Laboratory Application and Research Center(EGE-MATAL)for SEM images.
文摘This study examines the effect of nanosilica(NS)additive to improve the mechanical properties of clay,clayey sand,and sand.The engineering properties of the soils were investigated through Atterberg limits,compaction,unconfined compression,ultrasonic pulse velocity(UPV),freeze-thaw,and direct shear tests.The NS content varied from 0%to 0.7%and cement content was 5%and 10%by the dry weight of the soil.The curing period varied from 7 d to 150 d.The consistency,compaction,and strength properties of the soils were affected by the presence of NS and cement.The optimum NS contents in clay specimens with 5%and 10%cement were 0.5%and 0.7%,respectively.It was 0.7%in sand specimens with both cement ratios,as well as 0.3%and 0.7%in clayey sand specimens with 5%and 10%cement,respectively.In terms of freeze-thaw resistance,clayey sand specimens containing 0.5%NS and 10%cement had the minimum strength loss.Exponential relationships existed between the ultrasonic pulse velocity(UPV)and the unconfined compressive strength(UCS)of soil specimens having the same curing period.The shear strength parameters of the soils also improved with the addition of NS.Scanning electron microscope(SEM)images demonstrated that cement and NS contributed to the improvement of the soils by producing a denser and more uniform structure.It was concluded that the minor addition of NS could potentially improve the geomechanical properties of the soils.
基金This research was supported by the KAUST Endowment at King Abdullah University of Science and Technology,Saudi Arabia.We thank Gabrielle.E.Abelskamp in Energy GeoEngineering Laboratory at King Abdullah University of Science and Technology for editing the manuscript.
文摘Carbonate rocks are extensively used in civil infrastructure and play a critical role in geoenergy geoengineering,either as hydrocarbon reservoirs or potential repositories for CO_(2)geological storage.Carbonate genesis and diagenetic overprint determine the properties of carbonate rocks.This study combines recent data gathered from Madison Limestone and an extensive dataset compiled from published sources to analyze the hydraulic and mechanical properties of limestone carbonate rocks.Physical models and data analyses recognize the inherently granular genesis of carbonate rocks and explain the strong dependency of physical properties on porosity.The asymptotically-correct power model in terms of(1-Ф/Ф*)a is a good approximation to global trends of unconfined stiffness E and unconfined compressive strength UCS,cohesive intercept in Mohr-Coulomb failure envelopes,and the brittle-toductile transition stress.This power model is the analytical solution for the mechanical properties of percolating granular structures.We adopted a limiting granular porosityФ*=0.5 for all models,which was consistent with the loosest packing of monosize spheres.The fitted power model has exponent(α=2)in agreement with percolation theory and highlights the sensitivity of mechanical properties to porosity.Data and models confirm a porosity-independent ratio between unconfined stiffness and strength,and the ratio follows a log-normal distribution with mean(E/UCS)≈300.The high angle of internal shear strength measured for carbonate rocks reflects delayed contact failure with increased confinement,and it is not sensitive to porosity.Permeability spans more than six orders of magnitude.Grain size controls pore size and determines the reference permeability k^(*)at the limiting porosityФ*=0.5.For a given grain size from fine to coarse-grained dominant carbonates,permeability is very sensitive to changes in porosity,suggesting preferential changes in the internal pore network during compaction.
文摘The mechanical performances and water retention characteristics of clays,stabilised by partial substitution of cement with by-products and inclusion of a nanotechnology-based additive called RoadCem(RC),are studied in this research.The unconfined compression tests and one-dimensional oedometer swelling were performed after 7 d of curing to understand the influence of addition of 1%of RC material in the stabilised soils with the cement partially replaced by 49%,59%and 69%of ground granulated blast furnace slag(GBBS)or pulverised fuel ash(PFA).The moisture retention capacity of the stabilised clays was also explored using the soil-water retention curve(SWRC)from the measured suctions.Results confirmed an obvious effect of the use of RC with the obtained strength and swell properties of the stabilised clays suitable for road application at 50%replacement of cement.This outcome is associated with the in-depth and penetrating hydration of the cementitious materials by the RC and water which results in the production of needle-like matrix with interlocking filaments e a phenomenon referred to as the‘wrapping’effect.On the other hand,the SWRC used to describe the water holding capacity and corresponding swell mechanism of clays stabilised by a proportion of RC showed a satisfactory response.The moisture retention of the RC-modified clays was initially higher but reduced subsequently as the saturation level increased with decreasing suction.This phenomenon confirmed that clays stabilised by including the RC are water-proof in nature,thus ensuring reduced porosity and suction even at reduced water content.Overall,the stabilised clays with the combination of cement,GGBS and RC showed a better performance compared to those with the PFA included.
基金supported by the National Key R&D Program of China (Grant No. 2019YFC1806004)National Natural Science Foundation of China (Grant Nos. 51878159 and 41572280)
文摘This paper presents an experimental study and micro-mechanism discussion on gypsum role in the mechanical improvements of cement-based stabilized clay(CBSC).A soft marine clay at two initial water contents(i.e.50%and 70%)was treated by reconstituted cementitious binders with varying gypsum to clinker(G/C)ratios and added metakaolin to facilitate the formation of ettringite,followed by the measurements of final water contents,dry densities and strengths in accordance with ASTM standards as well as microstructure by mercury intrusion porosimetry(MIP)and scanning electron microscopy(SEM).Results reveal that the gypsum fraction has a significant influence on the index and mechanical properties of the CBSC,and there exists a threshold of the G/C ratio,which is 10%and 15%for clays with 50%and 70%initial water contents,respectively.Beyond which adding excessive gypsum cannot improve the strength further,eliminating the beneficial role.At these thresholds of the G/C ratio,the unconfined compressive strength(UCS)values for clays with 50%and 70%initial water contents are 1.74 MPa and 1.53 MPa at 60 d of curing,respectively.Microstructure characterization shows that,besides the common cementation-induced strengthening,newly formed ettringite also acts as significant pore infills,and the associated remarkable volumetric expansion is responsible,and may be the primary factor,for the beneficial strength gain due to the added gypsum.Moreover,pore-filling ettringite also leads to the conversion of relatively large inter-aggregate to smaller intra-aggregate pores,thereby causing a more homogeneous matrix or solid skeleton with higher strength.Overall,added gypsum plays a vital beneficial role in the strength development of the CBSC,especially for very soft clays.
基金the Jiangsu Provincial Science and Technology Department’s Social Development-Major Science and Technology Demonstration Project(Grant No.BE2018697)the Jiangsu Provincial Science and Technology Department Social Development Project(Grant No.BE2017704)the Scientific Research Project of the Suqian Municipal Transportation Bureau.
文摘A phosphogypsum-based subgrade stabilizer(PBSS)was formulated using industrial by-product phosphogypsum(PG),mixed with slag and calcium-silicon-rich active material(GSR).The active powder(AP)was used to modify PBSS,and PBSS-AP was obtained.PBSS and PBSS-AP were each mixed with 10%silty soil,and cement and lime(CAL:5%lime+2%cement)were used as the traditional material for comparative experiments.Samples were cured under standard conditions,and tested for unconfined compressive strength(UCS),water stability,volume expansion,and leachate,to explore the stabilization effect of the three solidified materials on silty soil.The results showed that the comprehensive performance of sility soil mixed with 12%PBSS-AP was the best.The CaO,SiO_(2)and Al_(2)O_(3)provided by PG,Slag and GSR will react with water to form a stable C-S-H gel,which is conducive to stabilizing the soil.Field application results showed that the compaction exceeded 95%,the deflection was 144.9 mm,and UCS was 2.5 MPa after 28 days.These findings indicated that PBSS-AP is an effective stabilizer for subgrade soils.
基金the Australian Government Research Training Program Scholarship and University of Adelaide Scholarship.
文摘Micaceous soils are common in many tropical countries and regions,and in some locations with moderate climate.The soils are spongy and unstable when loaded and are not considered suitable as construction material in earth structures.To resolve the issue,this work examined performance of micaceous soil reinforced with a combination of jute fibers,hydrated lime or slag-lime.A total of 28 sample sets were prepared at various dosages.Unconfined compression tests were conducted on the samples cured for 7 d and 28 d,respectively.The test results suggested that the unconfined compressive strength(UCS)and material stiffness were increased with the inclusion of up to 1%fiber and decreased if additional fibers were used.The ductility was improved consistently with up to 1.5%fiber content.The inclusions of fibers combined with hydrated lime or slag-lime further enhanced strength and stiffness of micaceous soil,and the improvement depended on the dosages used.For the dosages examined,jute fibers outweighed lime and slag in gaining ductility,and the optimal fiber content was 1%where strength and ductility were considered.
基金This work was supported by the Jiangsu Provincial Science and Technology Department’s Social Development-Major Science and Technology Demonstration Project(Grant No.BE2018697)the Demonstration Engineering Technology Research Center of Suqian Science and Technology Bureau(Grant No.M201912)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘Recycled powder(RP)is produced as a by-product during the process of recycling construction and demolition(C&D)wastes,presenting a low additional value.Using RP-based solidifying material can not only improve its utilization efficiency,but also reduce the cost of commercial solidifying materials.To date,this is the best solidifying material utilized to dispose the original waterworks sludge(OWS)with high moisture contents(60%),and the product could be used to fabricate non-fired bricks.This has become a new environment-friendly technology of“using waste to treat waste”.In this paper,the influence of different particle sizes and dosages of RP on the prepared solidifying material was studied.Besides,unconfined compression strength(UCS),volume stability,chemical composition,and heat of hydration,pore structure of the solidifying material were characterized.Then,non-fired bricks were prepared by using the solidifying material,recycled aggregate,and original waterworks sludge.The UCS and softing coefficient(SC)of the non-fired bricks were evaluated.As a result,the 28-day UCS of the solidifying material with optimal(M30)was 35.40 MPa,which could reach 84.37%of Portland cement(PC).The addition of RP increased the volume stability of the solidifying material.The addition of a large amount of RP reduced the heat flux and cumulative heat release of the solidifying material,while its porosity increased.The UCS of non-fired brick(NF20)in 28 days was 15.19 MPa and the SC after 28 days was 78.35%.In conclusion,the preparation of solidifying material using RP could be a promising approach and has a great potential in disposal of original waterworks sludge.
基金This study was funded by the National Natural Science Foundation of China(Grant Number 51568044)the first-class subjects of Lanzhou University of Technology(Grant Number 25-225209)Research project of China Municipal Engineering Northwest Design and Research Institute Co.Ltd.(Grant Number XBSZKY2031).
文摘Lime-fly ash stabilized loess has a poor early strength,which results in a later traffic opening time when it is used as road-base materials.Consideration of the significant early strength characteristics of sulphate aluminum cement(SAC),it is always added into the lime-fly ash mixtures to improve the early strength of stabilized loess.However,there is a scarcity of research on the mechanical behavior of lime-fly ash-SAC stabilized loess and there is a lack of quantitative evaluation of loess stabilized with binder materials.This research explored the effects of the amount of binder materials,curing time and porosity on the unconfined compressive strength(UCS),splitting tensile strength(STS),cohesion(c)and friction angle(φ)of lime-fly ash-SAC stabilized loess by a series of unconfined compressive tests(UCT)and splitting tensile tests(STT).The results indicate that an increase in curing time and a decrease in porosity lead to a continuous increase in the UCS and STS for lime-fly ash-SAC stabilized loess.The addition of SAC has a prominent enhancement in the early strength of lime-fly ash-SAC stabilized loess.When the curing time,porosity,and binder content were constant,the UCS and STS increase with increasing SAC content;For a stabilized loess with 30%binder content and 5%SAC content after 1 day of curing,the UCS was greater than 0.7 MPa,which meets the requirement of opening traffic,so lime-fly ash-SAC stabilized loess could be used as an excellent maintenance material for road-base;In accordance with the analysis of testing data,empirical relationships between the UCS and STS of lime-fly-SAC stabilized loess and key effect factors(binder materials content,curing time and porosity)were developed,which can provide references for reasonably selecting the amount of binder materials,compaction degree and curing period to meet the required strength of practical engineering.Finally,based on the Mohr-Coulomb theory and the above empirical relationships,a simpler method for calculating the c andφof stabilized loess was proposed,with which,the shear strength parameters can be determined only by UCT or STT.
文摘With the industrialisation,industrial byproducts are produced in large quantities and create nuisance to natural habitats.The disposal of these wastes like fly ash,marble powder,construction and demolition(C&D)waste,brick powder,agricultural wastes etc.has become the potential threat to the ecosystem and need some real solutions.The direct disposal of such wastes into open land or water bodies causes circumambient pollution.One of the potential solutions is to utilise these wastes in the construction industry on large scale as subgrade rehab or additive to cement based materials.In the present study,the compaction and strength characteristics of stabilised soil have been studied by using various waste materials i.e.lime,cement,plastic waste,industrial waste,fibre,mushroom waste,wet olive pomace etc.and reviewed.The addition of additives improved the engineering properties of soil significantly.
基金Projects(51208333,51078253)supported by the National Natural Science Foundation of China
文摘In order to simulate and study the mechanism of cement stabilized soils polluted by different contents of magnesium sulfate(MS), a series of tests were conducted on the cemented soil samples, including unconfined compression strength(UCS) tests of blocks, X-ray diffraction(XRD) phase analysis of powder samples, microstructure by scanning electronic microscopy(SEM),element composition by energy dispersive spectrometry(EDS), and pore distribution analysis by Image Processed Plus 6.0(IPP 6.0)software. The UCS test results show that UCS of cemented soils reaches the peak value when the MS content is 4.5 g/kg. While, the UCS for Sample MS4 having the MS content of 18.0 g/kg is the lowest among all tested samples. Based on the EDS analysis results,Sample MS4 has the greater contents for the three elements, oxygen(O), magnesium(Mg) and sulfur(S), than Sample MS1. From the XRD phase analysis, C-A-S-H(3Ca O·Al2O3·3Ca SO4·32H2O and 3Ca O·Al2O3·Ca SO4·18H2O), M-A-H(Mg O·Al2O3·H2O), M-S-H(Mg O·Si O2·H2O), Mg(OH)2 and Ca SO4 phase diffraction peaks are obviously intense due to the chemical action associated with the MS. The pore distribution analysis shows that the hydrated products change the distribution of cemented soil pores and the pores with average diameter(AD) of 2-50 μm play a key role in terms of the whole structure of cemented soil. The microscopic structure of the cemented soil with MS exhibits the intertwined and embedded characteristics between the cement and granular soils from the SEM images of cemented soils. The microstructure analysis shows that the magnesium sulfate acts as the additive, which is beneficial to the soil strength when the MS content is low(i.e., Sample MS2). However, higher MS amount involving a chemical action makes samples crystallize and expand, which is adverse to the UCS of cemented soils(i.e., Sample MS4).
文摘Micaceous soil is a problematic soil due to its low strength and poor ductility.In this context,the performances of micaceous soils were improved by applying a combination of granulated blast furnace slag,fiber and polymer additive.The dosages examined included 0%e30%mica,3%e15%slag and 0.25%e1.25%fiber by weight,and 0.1e0.5 g/L polymer additive.Most of the combinations were found to increase the material strength and ductility,yet to be optimized.To refine the dosage,response surface method was used to conduct experimental design and develop predictive models for material strength.The developed models formulate the material strength as a nonlinear function of dosages and,by interrogating it,can optimize additive contents in terms of target requirements.The models were verified through trials and can be used to determine dosages to upscale micaceous soils to field conditions.
基金supported by the Opening Funds of Jiangsu Key Laboratory of Construction Materials(No.CM2018-02)the Key Project of Natural Science Foundation of Zhejiang Province,China(No.LZ22E080003)the General Project of Natural Science Foundation of Zhejiang Province,China(No.LY20E080002).
文摘Because of the high cost of cultivating urease-producing bacteria(UPB),this paper proposes soybean-urease-induced carbonate precipitation(SUICP)as a novel biocement for treatment of nickel contaminants and cementation of sandy soil.We found the optimal soaking time and soybean-powder content to be 30 min and 130 g/L,respectively,based on a standard of 5 U of urease activity.The most efficient removal of nickel ions is obtained with an ideal mass ratio of urea to nickel ions to soybean-powder filtrate(SPF)of 1:2.4:20.The removal efficiency of nickel ions can reach 89.42%when treating 1 L of nickel-ion solution(1200 mg/L with the optimal mass ratio).In incinerated bottom ash(IBA),the removal efficiency of nickel ions is 99.33%with the optimal mass ratio.In biocemented sandy soil,the average unconfined compressive strength(UCS)of sand blocks cemented with soybean urease-based biocement can reach 118.89 kPa when the cementation level is 3.Currently,the average content of CaCO_(3)in sand blocks is 2.52%.As a result,the SUICP process can be applied to remove heavy metal ions in wastewater or solid waste and improve the mechanical properties of soft soil foundations.
基金Alchemy Polymers Company,LLC for their financial support
文摘A series of tests were carried out on sulfate rich,high-plasticity clay and poorly-graded natural sand to study the effectiveness of a methylene diphenyl diisocyanate based liquid polymer soil stabilizer in improving the unconfined compressive strength(UCS) of freshly stabilized soils and aged sand specimens.The aged specimens were prepared by exposing the specimens to ultraviolet radiation,freeze-thaw,and wet-dry weathering.The polymer soil stabilizer also mitigated the swelling of the expansive clay.For clay,the observations indicated that the sequence of adding water and liquid polymer had great influence on the gained UCS of stabilized specimens.However,this was shown to be of little importance for sand.Furthermore,sand samples showed incremental gains in UCS when they were submerged in water.This increase was significant for up to 4 days of soaking in water after 4 days of ambient air curing.Conversely,the clay samples lost a large fraction of their UCS when soaked in water;however,their remaining strength was still considerable.The stabilized specimens showed acceptable endurance under weathering action,although sample yellowing due to ultraviolet radiation was evident on the surface of the specimens.Except for moisture susceptibility of the clay specimens,the results of this study suggested the liquid stabilizer could be successfully utilized to provide acceptable strength,durability and mitigated swelling.
基金This research was supported by the National Natural Science Foundation of China(Grant Nos.KCA313017533 and C16A300190).
文摘Facial support in slurry shield tunneling is provided by slurry pressure to balance the external earth and water pressure.Hydraulic fracturing may occur and cause a significant decrease in the support pressure if the slurry pressure exceeds the threshold of the soil or rock material,resulting in a serious face collapse accident.Preventing the occurrence of hydraulic fracturing in a slurry shield requires investigating the effects of related influencing factors on the hydraulic fracturing pressure and fracture pattern.In this study,a hydraulic fracturing apparatus was developed to test the slurry-induced fracturing of cohesive soil.The effects of different sample parameters and loading conditions,including types of holes,unconfined compressive strength,slurry viscosity,and axial and circumferential loads,on the fracturing pressure and fracture dip were examined.The results indicate that the fracture dip is mainly affected by the deviator stress.The fracturing pressure increases linearly with the increase in the circumferential pressure,but it is almost independent of the axial pressure.The unconfined compressive strength of soil can reflect its ability to resist fracturing failure.The fracturing pressure increases with an increase in the unconfined compressive strength as well as the slurry viscosity.Based on the test results,an empirical approach was proposed to estimate the fracturing pressure of the soil.
