This paper presents experimental studies on a compacted expansive soil,from Nanyang,China for investigating the at-rest lateral earth pressureσL of expansive soils.The key studies include(i)relationships between the...This paper presents experimental studies on a compacted expansive soil,from Nanyang,China for investigating the at-rest lateral earth pressureσL of expansive soils.The key studies include(i)relationships between theσL and the vertical stressσV during soaking and consolidation,(ii)the influences of initial dry densityρd0 and moisture content w 0 on the vertical and lateral swelling pressures at no swelling strain(i.e.σV0 andσL0),and(iii)evolution of theσL during five long-term wetting-drying cycles.Experimental results demonstrated that the post-soakingσL-σV relationships are piecewise linear and their slopes in the passive state(σL>σV)and active state(σL<σV)are similar to that of the consolidationσL-σV relationships in the normal-and over-consolidated states,respectively.The soakingσL-σV relationships converge to the consolidationσL-σV relationships at a thresholdσV where the interparticle swelling is restrained.TheσL0 andσV0 increase monotonically withρd0;however,they show increasing-then-decreasing trends with the w 0.The extent of compaction-induced swelling anisotropy,which is evaluated byσL0/σV0,reduces with an increase in the compaction energy and molding water content.TheσL reduces over moisture cycles and the stress relaxation in theσL during soaking is observed.An approach was developed to predict the at-rest soakingσL-σV relationships,which requires conventional consolidation and shear strength properties and one measurement of theσL-σV relationships during soaking.The proposed approach was validated using the results of three different expansive soils available in the literature.展开更多
Earthquake-induced slope failures are common occurrences in engineering practice and pre-stressed anchor cables are an effective technique in maintaining slope stability,especially in areas that are prone to earthquak...Earthquake-induced slope failures are common occurrences in engineering practice and pre-stressed anchor cables are an effective technique in maintaining slope stability,especially in areas that are prone to earthquakes.Furthermore,the soil at typical engineering sites also exhibit unsaturated features.Explicit considerations of these factors in slope stability estimations are crucial in producing accurate results.In this study,the seismic responses of expansive soil slopes stabilized by anchor cables is studied in the realm of kinematic limit analysis.A modified horizontal slice method is proposed to semi-analytically formulate the energy balance equation.An illustrative slope is studied to demonstrate the influences of suction,seismic excitations and anchor cables on the slope stability.The results indicate that the stabilizing effect of soil suction relates strongly to the seismic excitation and presents a sine shape as the seismic wave propagates.In higher and steeper slopes,the stabilizing effect of suction is more evident.The critical slip surface tends to be much more shallow as the seismic wave approaches the peak and vice versa.展开更多
Geotechnical engineering data are usually small-sample and high-dimensional,which brings a lot of challenges in predictive modeling.This paper uses a typical high-dimensional and small-sample swell pressure(P s)datase...Geotechnical engineering data are usually small-sample and high-dimensional,which brings a lot of challenges in predictive modeling.This paper uses a typical high-dimensional and small-sample swell pressure(P s)dataset to explore the possibility of using multi-algorithm hybrid ensemble and dimensionality reduction methods to mitigate the uncertainty of soil parameter prediction.Based on six machine learning(ML)algorithms,the base learner pool is constructed,and four ensemble methods,Stacking(SG),Blending(BG),Voting regression(VR),and Feature weight linear stacking(FWL),are used for the multi-algorithm ensemble.Furthermore,the importance of permutation is used for feature dimensionality reduction to mitigate the impact of weakly correlated variables on predictive modeling.The results show that the proposed methods are superior to traditional prediction models and base ML models,where FWL is more suitable for modeling with small-sample datasets,and dimensionality reduction can simplify the data structure and reduce the adverse impact of the small-sample effect,which points the way to feature selection for predictive modeling.Based on the ensemble methods,the feature importance of the five primary factors affecting P s is the maximum dry density(31.145%),clay fraction(15.876%),swell percent(15.289%),plasticity index(14%),and optimum moisture content(13.69%),the influence of input parameters on P s is also investigated,in line with the findings of the existing literature.展开更多
Numerous engineering cases have demonstrated that the expansive soil channel slope remains susceptible to damage with the implementation of a rigid or closed protective structure. It is common for the protective struc...Numerous engineering cases have demonstrated that the expansive soil channel slope remains susceptible to damage with the implementation of a rigid or closed protective structure. It is common for the protective structure to experience bulging failure due to excessive swelling pressure. To investigate the swelling pressure properties of expansive soil, the constant volume test was employed to study the influence of water content and reserved expansion deformation on the characteristics of swelling pressure in strong expansive soils, and also to explore the evolution mechanism of the swelling pressure. The findings demonstrate that the swelling pressure-time curve can be classified into swelling pressure-time softening and swelling pressure-time stability type. The swelling pressuretime curve of the specimen with low water content is the swelling pressure-time softening type, and the softening level will be weakened with increasing reserved expansion deformation. Besides, the maximum swelling pressure Psmax decreases with increasing water content and reserved expansion deformation, especially for expansion ratio η from 24% to 37%. The reserved deformation has little effect on reducing Psmax when it is beyond 7% of the expansion rate. The specimen with low water content has a more homogeneous structure due to the significant expansion-filling effect, and the fracture and reorganization of the aggregates in the specimens with low water content cause the swelling pressure-time softening behavior. In addition, the proposed swelling pressure-time curve prediction model has a good prediction on the test results. If necessary, a deformation space of about 7% expansion rate is recommended to be reserved in the engineering to reduce the swelling pressure except for keeping a stable water content.展开更多
The wide engineered application of compacted expansive soils necessitates understanding their behavior under field conditions.The results of this study demonstrate how seasonal climatic variation and stress and bounda...The wide engineered application of compacted expansive soils necessitates understanding their behavior under field conditions.The results of this study demonstrate how seasonal climatic variation and stress and boundary conditions individually or collectively influence the hydraulic and volume change behavior of compacted highly expansive soils.The cyclic wetting and drying(CWD)process was applied for two boundary conditions,i.e.constant stress(CS)and constant volume(CV),and for a wide range of axial stress states.The adopted CWD process affected the hydraulic and volume change behaviors of expansive soils,with the first cycle of wetting and drying being the most effective.The CWD process under CS conditions resulted in shrinkage accumulation and reduction in saturated hydraulic conductivity(k sat).On the other hand,CWD under CV conditions caused a reduction of swell pressure while has almost no impact on k sat.An elastic response to CWD was achieved after the third cycle for saturated hydraulic conductivity(k sat),the third to fourth cycle for the volume change potential under the CV conditions,and the fourth to fifth cycle for the volume change potential under the CS conditions.Finally,both swell pressure(s s)and saturated hydraulic conductivity(k sat)are not fundamental parameters of the expansive soil but rather depend on stress,boundary and wetting conditions.展开更多
When expansive soils in the original location are artificially transferred to landfill in different seasons,and subject to engineering activities afterwards,the corresponding deformation and stability of retaining str...When expansive soils in the original location are artificially transferred to landfill in different seasons,and subject to engineering activities afterwards,the corresponding deformation and stability of retaining structures become unpredictable.This necessitates the determination of lateral pressure coefficient at rest(k_(0) value)for expansive soils in landfill.Considering compaction,excavation of expansive soils,as well as construction of landfill in different seasons,series of stepwise loading and unloading consolidation tests at various moisture contents were carried out in this work to explore the evolution characteristics of k_(0) value and assess the dependence of k_(0) value on vertical stress and moisture content.Besides,scanning electron microscope(SEM)was used to track the change in microstructural features with vertical stresses.The results indicated that the k_(0) value of expansive soil shows a pronounced nonlinearity and is inextricably linked with vertical stress and moisture content,based on which a prediction formula to estimate the variation in k_(0) value with vertical stress during loading stage was proposed;there is a significant exponential increase in k_(0) value with overconsolidation ratio(OCR)during unloading stage,and OCR dominates the release of horizontal stress of expansive soil;SEM results revealed that with an increase in vertical stress,the anisotropy of expansive soil microstructure increases dramatically,causing a significant directional readjustment,which is macroscopically manifested as an initially rapid increase in k_(0) value;but when vertical stress increases to a critical value,the anisotropy of microstructure increases marginally,indicating a stable orientation occurring in the soil microstructure,which causes the k_(0) value to maintain a relatively stable value.展开更多
Unsaturated expansive soil is widely distributed in China and has complex engineering properties.This paper proposes the unified hydraulic effect shear strength theory of unsaturated expansive soil based on the effect...Unsaturated expansive soil is widely distributed in China and has complex engineering properties.This paper proposes the unified hydraulic effect shear strength theory of unsaturated expansive soil based on the effective stress principle,swelling force principle,and soil–water characteristics.Considering the viscoelasticity and structural damage of unsaturated expansive soil during loading,a fractional hardening–damage model of unsaturated expansive soil was established.The model parameters were established on the basis of the proposed calculation method of shear strength and the triaxial shear experiment on unsaturated expansive soil.The proposed model was verified by the experimental data and a traditional damage model.The proposed model can satisfactorily describe the entire process of the strain-hardening law of unsaturated expansive soil.Finally,by investigating the damage variables of the proposed model,it was found that:(a)when the values of confining pressure and matric suction are close,the coupling of confining pressure and matric suction contributes more to the shear strength;(b)there is a damage threshold for unsaturated expansive soil,and is mainly reflected by strength criterion of infinitesimal body;(c)the strain hardening law of unsaturated expansive soil is mainly reflected by fractional derivative operator.展开更多
To improve the soil and water stability of expansive soil slopes and reduce the probability of slope failure,novel protection systems based on polymer waterproof coatings(PWC)were used in this study.Herein,three group...To improve the soil and water stability of expansive soil slopes and reduce the probability of slope failure,novel protection systems based on polymer waterproof coatings(PWC)were used in this study.Herein,three groups of expansive soil slope model tests were designed to investigate the effects of polyester nonwovens and PWC(P-PWC)composite protection system,three-dimensional vegetation network and PWC(T-PWC)composite protection system,and nonprotection on the soil and water behavior in the slopes under precipitation–evaporation cycles.The results showed that the moisture change of P-PWC and T-PWC composite protected slopes was significantly smaller than that of bare slope,which reduced the sensitivity of slope moisture to environmental changes and improved its stability.The soil temperature of the slope protected by the P-PWC and T-PWC systems at a depth of 70 cm increased by 5.6℃ and 2.7℃,respectively.Using PWC composite protection systems exhibited better thermal storage performance,which could increase the utilization of shallow geothermal resources.Moreover,the maximum average crack widths of the bare slopes were 7.89 and 3.17 times those of the P-PWC and TPWC protected slopes,respectively,and the maximum average crack depths were 6.87 and 3 times those of the P-PWC and T-PWC protected slopes,separately.The PPWC protection system weakened the influence of hydro–thermal coupling on the slopes,inhibited the development of cracks on the slopes,and reduced the soil erosion.The maximum soil erosion of slopes protected by P-PWC and T-PWC systems was 332 and 164 times lower than that of bare slope,respectively.The P-PWC and T-PWC protection systems achieved excellent"anti-seepage and moisture retention"and anti-erosion effects,thus improving the soil and water stability of slopes.These findings can provide important guiding reference for controlling rainwater infiltration and soil erosion in expansive soil slope projects.展开更多
Sixteen groups of comprehensive tests have been conducted to investigate the modifications in the physical properties of a weak expansive soil due to the addition of a cement jute fiber.The tests have been conducted t...Sixteen groups of comprehensive tests have been conducted to investigate the modifications in the physical properties of a weak expansive soil due to the addition of a cement jute fiber.The tests have been conducted to analyze the liquid plastic limit,the particle distribution and the free expansion rate.The results show that:(1)With an increase in the cement-jute fiber content,the free expansion rate of the modified expansive soil gradually decreases,however,such a rate rebounds when the fiber content exceeds 0.5%and the cement content exceeds 6%.(2)With an increase in the cement percentage,the particle unevenness coefficient(Cu)and curvature coefficient(Cc)of the modified expansive soil tend to grow gradually.The Cc coefficient reaches 1.0 when the cement content is 6%.The unevenness coefficient of 16 soil samples is greater than 5.0,however,the Cu coefficient decreases when the cement content reaches 6%.(3)The plastic limit of soil increases as the cement content is made higher,while the liquid limit and plastic index decrease gradually.When the content of the modified material is 2%+0.1%~2%+0.7%(Cement content+jute fiber content),the change of particle size distribution is most obvious.(4)When the contents of cement and jute fiber are is 6%and 0.5%,respectively,the modification induced in the physical properties of soil samples corresponds to the best case.展开更多
This study examined the effects of using bagasse ash in replacement of ordinary Portland cement(OPC)in the treatment of expansive soils.The study concentrated on the compaction characteristics,volume change,compressiv...This study examined the effects of using bagasse ash in replacement of ordinary Portland cement(OPC)in the treatment of expansive soils.The study concentrated on the compaction characteristics,volume change,compressive strength,splitting tensile strength,microstructure,California bearing ratio(CBR)value,and shear wave velocity of expansive soils treated with cement.Different bagasse ash replacement ratios were used to create soil samples.At varying curing times of 7,14,and 28 days,standard compaction tests,unconfined compressive strength tests,CBR tests,Brazilian split tensile testing,and bender element(BE)tests were carried out.According to X-ray diffraction(XRD)investigations,quartz and crystobalite make up the majority of the minerals in bagasse ash.Bagasse ash contains a variety of grain sizes,including numerous fiber-shaped particles,according to a scanning electronic microscope(SEM)test.For all of the treated specimens with various replacement ratios,the overall additive content has not changed.The results of the Brazilian split tensile tests demonstrate improved tensile strength for all specimens with various replacement proportions.A lower maximum dry density and a greater optimal water content would result from the substitution of bagasse ash.When the replacement ratio is not more than 20%,the CBR values of the parts replaced specimens are even higher than the cement treatments.The results of BE testing on the treated soils show that there is significant stiffness anisotropy but that it steadily diminishes with curing time and replacement ratio.According to the study,bagasse ash is a useful mineral additive,and the best replacement ratio(CBA20)is 20%.展开更多
A dynamic triaxial instrument was used to study the effects of different concentrations of sodium chloride and stress amplitudes on the dynamic properties of an expansive soil under cyclic loading.In particular,four p...A dynamic triaxial instrument was used to study the effects of different concentrations of sodium chloride and stress amplitudes on the dynamic properties of an expansive soil under cyclic loading.In particular,four parameters were considered in such a parametric investigation,namely,hysteresis curve morphology characteristic non-closure degreeεp,the ratio of the short and long axisα,the slope of the long axis k and the enclosed area S.The results show that with an increase in the sodium chloride concentration,the soil particle double electric layer becomes thinner,the distance between soil particles decreases,and the whole sample becomes denser.Theεp-N,α-N and S–N relation curves all show a decreasing trend.The ratio of plastic deformation to total deformation grows with increasing the dynamic stress amplitude,and the curves show an upwards trend.The k-N relationship curve displays an increasing trend with the concentration and a general downwards trend as the dynamic stress amplitude is made higher.This also indicates that sodium chloride solutions can improve the engineering properties of expansive soil to a certain extent.With an increase in the vibration times N,the shape of the hysteretic curve becomes narrower,and the whole soil exhibits a cyclic strain hardening.With the help of an exponential function,a model is introduced to predict the relationship between the concentration and the hysteretic curve.展开更多
Volume instability of expansive soils due to moisture fluctuations is often disastrous,causing severe damages and distortions in the supported structures.It is,therefore,necessary to adequately improve the performance...Volume instability of expansive soils due to moisture fluctuations is often disastrous,causing severe damages and distortions in the supported structures.It is,therefore,necessary to adequately improve the performance of such soils that they can favorably fulfil the post-construction stability requirements.This can be achieved through chemical stabilization using additives such as lime,cement and fly ash.In this paper,suitability of such additives under various conditions and their mechanisms are reviewed in detail.It is observed that the stabilization process primarily involves hydration,cation exchange,flocculation and pozzolanic reactions.The degree of stabilization is controlled by several factors such as additive type,additive content,soil type,soil mineralogy,curing period,curing temperature,delay in compaction,pH of soil matrix,and molding water content,including presence of nano-silica,organic matter and sulfate compounds.Provision of nano-silica not only improves soil packing but also accelerates the pozzolanic reaction.However,presence of deleterious compounds such as sulfate or organic matter can turn the treated soils unfavorable at times even worser than the unstabilized ones.展开更多
Phase change materials(PCMs)can store large amounts of energy in latent heat and release it during phase changes,which could be used to improve the freeze-thaw performance of soil.The composite phase change material w...Phase change materials(PCMs)can store large amounts of energy in latent heat and release it during phase changes,which could be used to improve the freeze-thaw performance of soil.The composite phase change material was prepared with paraffin as the PCM and 8%Class C fly ash(CFA)as the supporting material.Laboratory tests were conducted to reveal the influence of phase change paraffin composite Class C fly ash(CFA-PCM)on the thermal properties,volume changes and mechanical properties of expansive soil.The results show that PCM failed to establish a good improvement effect due to leakage.CFA can effectively adsorb phase change materials,and the two have good compatibility.CFA-PCM reduces the volume change and strength attenuation of the soil,and 8 wt.%PCM is the optimal content.CFA-PCM turns the phase change latent heat down of the soil and improves its thermal stability.CFA-PCM makes the impact small of freeze-thaw on soil pore structure damage and improves soil volume change and mechanical properties on a macroscopic scale.In addition,CFA-8 wt.%PCM treated expansive soil has apparent advantages in resisting repeated freeze-thaw cycles,providing a reference for actual engineering design.展开更多
This laboratory study examines the potential use of an anionic polyacrylamide(PAM)-based material as an environmentally sustainable additive for the stabilization of an expansive soil from South Australia.The experime...This laboratory study examines the potential use of an anionic polyacrylamide(PAM)-based material as an environmentally sustainable additive for the stabilization of an expansive soil from South Australia.The experimental program consisted of consistency limits,sediment volume,compaction and oedometer cyclic swell-shrink tests,performed using distilled water and four different PAM-to-water solutions of P_(D)=0.1 g/L,0.2 g/L,0.4 g/L and 0.6 g/L as the mixing liquids.Overall,the relative swelling and shrinkage strains were found to decrease with increasing number of applied swell-shrink cycles,with an‘elastic equilibrium’condition achieved on the conclusion of four cycles.The propensity for swelling/shrinkage potential reduction(for any given cycle)was found to be in favor of increasing the PAM dosage up to P_(D)=0.2 g/L,beyond which the excess PAM molecules self-associate as aggregates,thereby functioning as a lubricant instead of a flocculant;this critical dosage was termed‘maximum flocculation dosage’(MFD).The MFD assertion was discussed and validated using the consistency limits and sediment volume properties,both exhibiting only marginal variations beyond the identified MFD of P_(D)=0.2 g/L.The accumulated axial strain progressively transitioned from‘expansive’for the unamended soil to an ideal‘neutral’state at the MFD,while higher dosages demonstrated undesirable‘contractive’states.展开更多
This study explores the coupling effect of pond ash(PA)and polypropylene(PP)fiber to control the strength and durability of expansive soil.The PA is used to chemically treat the expansive soil and PP fiber is adopted ...This study explores the coupling effect of pond ash(PA)and polypropylene(PP)fiber to control the strength and durability of expansive soil.The PA is used to chemically treat the expansive soil and PP fiber is adopted as reinforcement against tensile cracking.The sustainable use of PA and PP fiber are demonstrated by performing mechanical(i.e.unconfined compressive strength,split tensile strength and ultrasonic pulse velocity),chemical(pH value,electrical conductivity and calcite content),and microstructural analyses before and after 2nd,4th,6th,8th and 10th freezing-thawing(F-T)cycles.Three curing methods with 7 d,14 d and 28 d curing periods are considered to reinforce the 5%,10%,15%and 20%PA-stabilized expansive soil with 0.25%,0.5%and 1%PP fiber.In order to develop predictive models for mechanical and durability parameters,the experimental data are processed utilizing artificial neural network(ANN),in association with the leave-one-out cross-validation(LOOCV)as a resampling method and three different activation functions.The mechanical and durability properties of the PA-stabilized expansive soil subgrades are increased with PP fiber reinforcement.The results of ANN modeling predict the mechanical properties perfectly,and the correlation coefficient(R)approaches up to 0.96.展开更多
The characteristics of soil treated with cationic polyacrylamide(CPAM)mass content of 0%,0.2%,0.4%,0.6%,0.8%,and 1%were investigated through a series of laboratory tests to explore the practical engineering effect of ...The characteristics of soil treated with cationic polyacrylamide(CPAM)mass content of 0%,0.2%,0.4%,0.6%,0.8%,and 1%were investigated through a series of laboratory tests to explore the practical engineering effect of an expansive soil amended with environmental protection material CPAM.The results indicate that with the increasing CPAM content,the liquid limit and plasticity index of soil decrease,the plastic limit increases,and the free swelling ratio and loaded swelling ratio decrease.Besides,the improved soil has less disintegrating property and better water stability.The shear strength increases as the content increases,and the optimal content is 0.6%.Meanwhile,the cohesion of the soil first increases and then decreases,and the internal friction angle increases.Additionally,the unconfined compressive strength first increases and then decreases.The improved soil presents the characteristics of brittle failure and reaches the peak value(410.1 kPa)at the content of 0.8%after curing for 14 days.Scanning electron microscope(SEM)exhibits that the number of curved and wrinkled sections of the expansive soil is reduced after CPAM improvement.Simultaneously,the arrangement of the superimposed polymer changes from face-face to side-angle or side-face-angle,and the reticular structure formed improves the strength and spatial stability of the soil.Therefore,adding appropriate cationic polyacrylamide could improve expansive soil in engineering.展开更多
In this paper,the discrete element method(DEM)is used to study the microstructure of expansive soils.The results of the numerical calculations are in agreement with the stress-strain triaxial test curve that is obtain...In this paper,the discrete element method(DEM)is used to study the microstructure of expansive soils.The results of the numerical calculations are in agreement with the stress-strain triaxial test curve that is obtained for a representative expansive soil.Biaxial compression tests are conducted for different confining pressures(50 kpa,100 kpa,and 150 kpa).Attention is paid to the following aspects:deviatoric stress,boundary energy,friction energy,bond energy,strain energy,kinetic energy,and the contact force between grains when the test specimen is strained and to the effect of the different confining pressures on the internal crack expansion.The results of this research show that the cross-section of the specimen is destroyed along the middle part of the specimen itself.When the confining pressure is higher,the impulse is stronger,and this leads to more effective destruction.展开更多
Expansive soils can pose tough issues to civil engineering applications. In a typical year, expansive soils can cause a greater financial loss than earthquakes, floods, hurricanes and tornadoes combined. Various means...Expansive soils can pose tough issues to civil engineering applications. In a typical year, expansive soils can cause a greater financial loss than earthquakes, floods, hurricanes and tornadoes combined. Various means have been studied to tackle problems associated with expansive soils. The majority of the methods are based on treatment of the soils. While the methods may be effective in some cases, their limitations are also obvious: The treatment normally involves complex processes and may not be eco-friendly in the long run. In many cases, the effectiveness of the treatment is uncertain. A retaining system that maintains a constant lateral pressure is proposed, which consists of three components: the retaining sheet, the slip-force device and the bracing column. The retaining sheet bears the pressure exerted by expansive backfills and is not embedded into the soils. Placed between the retaining sheet and bracing column, the slip-force device permits displacement of the retaining sheet but keeps the force on the sheet and the bracing column constant. The governing equation of the motion of the piston in the slip-force device is derived and a numerical simulation of a practical case is conducted based on the derived governing equation. Numerical results show that as the expansive soil swell, the spring force will increase and the piston will move accordingly. When the pressure of the oil in chamber reach<span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">es</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> the open threshold of the unidirectional relief valve, the valve will open and the spring force and the oil pressure in the chamber will keep constant. The results also show that some parameters, such as damping ratio, have very slight influences on the device behavior, say 2 × 10</span><sup><span style="font-family:Verdana;">-6</span></sup><span style="font-family:Verdana;"> or even 4.8 × 10</span><sup><span style="font-family:Verdana;">-9</span></sup><span style="font-family:Verdana;">. Theoretical and numerical studies prove the effectiveness of the proposed retaining system.</span></span></span></span>展开更多
Expansive soils undergo high volume change due to cyclic swelling and shrinkage behavior during the wet and dry seasons.Thus,such problematic soils should be completely avoided or properly treated when encountered as ...Expansive soils undergo high volume change due to cyclic swelling and shrinkage behavior during the wet and dry seasons.Thus,such problematic soils should be completely avoided or properly treated when encountered as subgrade materials.In the present study,the biomedical waste incinerator ash and lime combination was proposed to stabilize expansive soil.Particle size analysis,Atterberg limits,free-swell,compaction,unconfined compression strength,and California bearing ratio tests were conducted on the natural soil and blended with 3%,5%,7%,9%,and 11%biomedical waste incinerator ash(BWIA).The optimum content of BWIA was determined based on the free-swell test results.To further investigate the relative effectiveness of the stabilizer,2%and 3%lime were also added to the optimum soil-BWIA mixture and UCS and CBR tests were also conducted.In addition,scanning electron microscopy(SEM)tests for representative stabilized samples were also conducted to examine the changes in microfabrics and structural arrangements due to bonding.The addition of BWIA has a promising effect on the index properties and strength of the expansive soil.The strength of the expansive soil significantly increased when it was blended with the optimum content of BWIA amended by 2%and 3%lime.展开更多
Construction and demolition waste(CDW)are the largest waste products in the world today and competes as a viable recycled additive material in place of natural aggregates.Due to the increase in compressive strength of...Construction and demolition waste(CDW)are the largest waste products in the world today and competes as a viable recycled additive material in place of natural aggregates.Due to the increase in compressive strength of different mix proportions of CDW,it is also considered for reuse in concrete and subbase construction.This study shows the effect of CDW in expansive soil stabilization.The chemical and mechanical properties of these materials have shown that they are capable of developing compressive strength properties for replacement of cement with significant reduction in carbon emission.The inherent compositional properties of recycled CDW compared in this review suggests that CDW have good filler properties in highly expansive soils.Mixtures of crushed brick and recycled aggregates characterised based on chemical properties of different replacement ratios suggests that CDW of good-quality aggregates reduces swell potential of expansive soils and increased mechanical strength in pavement construction.展开更多
基金sponsored by the National Natural Science Foundation of China(Grant Nos.52378365 and 52179109)Jiangsu Province Excellent Postdoctoral Program(Grant No.2023)China Scholarship Council-University of Ottawa Joint Scholarship.
文摘This paper presents experimental studies on a compacted expansive soil,from Nanyang,China for investigating the at-rest lateral earth pressureσL of expansive soils.The key studies include(i)relationships between theσL and the vertical stressσV during soaking and consolidation,(ii)the influences of initial dry densityρd0 and moisture content w 0 on the vertical and lateral swelling pressures at no swelling strain(i.e.σV0 andσL0),and(iii)evolution of theσL during five long-term wetting-drying cycles.Experimental results demonstrated that the post-soakingσL-σV relationships are piecewise linear and their slopes in the passive state(σL>σV)and active state(σL<σV)are similar to that of the consolidationσL-σV relationships in the normal-and over-consolidated states,respectively.The soakingσL-σV relationships converge to the consolidationσL-σV relationships at a thresholdσV where the interparticle swelling is restrained.TheσL0 andσV0 increase monotonically withρd0;however,they show increasing-then-decreasing trends with the w 0.The extent of compaction-induced swelling anisotropy,which is evaluated byσL0/σV0,reduces with an increase in the compaction energy and molding water content.TheσL reduces over moisture cycles and the stress relaxation in theσL during soaking is observed.An approach was developed to predict the at-rest soakingσL-σV relationships,which requires conventional consolidation and shear strength properties and one measurement of theσL-σV relationships during soaking.The proposed approach was validated using the results of three different expansive soils available in the literature.
基金National Natural Science Foundation of China under Grant Nos.52208345,52008124,52268054the Opening Fund of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection under Grant No.SKLGP2022K002+1 种基金the Natural Science Foundation of Jiangsu Province under Grant No.BK20210479the Fundamental Research Funds for the Central Universities under Grant No.JUSRP121055。
文摘Earthquake-induced slope failures are common occurrences in engineering practice and pre-stressed anchor cables are an effective technique in maintaining slope stability,especially in areas that are prone to earthquakes.Furthermore,the soil at typical engineering sites also exhibit unsaturated features.Explicit considerations of these factors in slope stability estimations are crucial in producing accurate results.In this study,the seismic responses of expansive soil slopes stabilized by anchor cables is studied in the realm of kinematic limit analysis.A modified horizontal slice method is proposed to semi-analytically formulate the energy balance equation.An illustrative slope is studied to demonstrate the influences of suction,seismic excitations and anchor cables on the slope stability.The results indicate that the stabilizing effect of soil suction relates strongly to the seismic excitation and presents a sine shape as the seismic wave propagates.In higher and steeper slopes,the stabilizing effect of suction is more evident.The critical slip surface tends to be much more shallow as the seismic wave approaches the peak and vice versa.
基金great gratitude to National Key Research and Development Project(Grant No.2019YFC1509800)for their financial supportNational Nature Science Foundation of China(Grant No.12172211)for their financial support.
文摘Geotechnical engineering data are usually small-sample and high-dimensional,which brings a lot of challenges in predictive modeling.This paper uses a typical high-dimensional and small-sample swell pressure(P s)dataset to explore the possibility of using multi-algorithm hybrid ensemble and dimensionality reduction methods to mitigate the uncertainty of soil parameter prediction.Based on six machine learning(ML)algorithms,the base learner pool is constructed,and four ensemble methods,Stacking(SG),Blending(BG),Voting regression(VR),and Feature weight linear stacking(FWL),are used for the multi-algorithm ensemble.Furthermore,the importance of permutation is used for feature dimensionality reduction to mitigate the impact of weakly correlated variables on predictive modeling.The results show that the proposed methods are superior to traditional prediction models and base ML models,where FWL is more suitable for modeling with small-sample datasets,and dimensionality reduction can simplify the data structure and reduce the adverse impact of the small-sample effect,which points the way to feature selection for predictive modeling.Based on the ensemble methods,the feature importance of the five primary factors affecting P s is the maximum dry density(31.145%),clay fraction(15.876%),swell percent(15.289%),plasticity index(14%),and optimum moisture content(13.69%),the influence of input parameters on P s is also investigated,in line with the findings of the existing literature.
基金financially supported by the National Key R&D Program of China (Grant No. 2019YFC1509901)。
文摘Numerous engineering cases have demonstrated that the expansive soil channel slope remains susceptible to damage with the implementation of a rigid or closed protective structure. It is common for the protective structure to experience bulging failure due to excessive swelling pressure. To investigate the swelling pressure properties of expansive soil, the constant volume test was employed to study the influence of water content and reserved expansion deformation on the characteristics of swelling pressure in strong expansive soils, and also to explore the evolution mechanism of the swelling pressure. The findings demonstrate that the swelling pressure-time curve can be classified into swelling pressure-time softening and swelling pressure-time stability type. The swelling pressuretime curve of the specimen with low water content is the swelling pressure-time softening type, and the softening level will be weakened with increasing reserved expansion deformation. Besides, the maximum swelling pressure Psmax decreases with increasing water content and reserved expansion deformation, especially for expansion ratio η from 24% to 37%. The reserved deformation has little effect on reducing Psmax when it is beyond 7% of the expansion rate. The specimen with low water content has a more homogeneous structure due to the significant expansion-filling effect, and the fracture and reorganization of the aggregates in the specimens with low water content cause the swelling pressure-time softening behavior. In addition, the proposed swelling pressure-time curve prediction model has a good prediction on the test results. If necessary, a deformation space of about 7% expansion rate is recommended to be reserved in the engineering to reduce the swelling pressure except for keeping a stable water content.
文摘The wide engineered application of compacted expansive soils necessitates understanding their behavior under field conditions.The results of this study demonstrate how seasonal climatic variation and stress and boundary conditions individually or collectively influence the hydraulic and volume change behavior of compacted highly expansive soils.The cyclic wetting and drying(CWD)process was applied for two boundary conditions,i.e.constant stress(CS)and constant volume(CV),and for a wide range of axial stress states.The adopted CWD process affected the hydraulic and volume change behaviors of expansive soils,with the first cycle of wetting and drying being the most effective.The CWD process under CS conditions resulted in shrinkage accumulation and reduction in saturated hydraulic conductivity(k sat).On the other hand,CWD under CV conditions caused a reduction of swell pressure while has almost no impact on k sat.An elastic response to CWD was achieved after the third cycle for saturated hydraulic conductivity(k sat),the third to fourth cycle for the volume change potential under the CV conditions,and the fourth to fifth cycle for the volume change potential under the CS conditions.Finally,both swell pressure(s s)and saturated hydraulic conductivity(k sat)are not fundamental parameters of the expansive soil but rather depend on stress,boundary and wetting conditions.
基金supported by the National Key Research and Development Program of China(Grant No.2019YFC1509901)。
文摘When expansive soils in the original location are artificially transferred to landfill in different seasons,and subject to engineering activities afterwards,the corresponding deformation and stability of retaining structures become unpredictable.This necessitates the determination of lateral pressure coefficient at rest(k_(0) value)for expansive soils in landfill.Considering compaction,excavation of expansive soils,as well as construction of landfill in different seasons,series of stepwise loading and unloading consolidation tests at various moisture contents were carried out in this work to explore the evolution characteristics of k_(0) value and assess the dependence of k_(0) value on vertical stress and moisture content.Besides,scanning electron microscope(SEM)was used to track the change in microstructural features with vertical stresses.The results indicated that the k_(0) value of expansive soil shows a pronounced nonlinearity and is inextricably linked with vertical stress and moisture content,based on which a prediction formula to estimate the variation in k_(0) value with vertical stress during loading stage was proposed;there is a significant exponential increase in k_(0) value with overconsolidation ratio(OCR)during unloading stage,and OCR dominates the release of horizontal stress of expansive soil;SEM results revealed that with an increase in vertical stress,the anisotropy of expansive soil microstructure increases dramatically,causing a significant directional readjustment,which is macroscopically manifested as an initially rapid increase in k_(0) value;but when vertical stress increases to a critical value,the anisotropy of microstructure increases marginally,indicating a stable orientation occurring in the soil microstructure,which causes the k_(0) value to maintain a relatively stable value.
基金financially supported by Sichuan Huaxi Group Co.,ltd.(No.HXKX2019/015,No.HXKX2019/019,No.HXKX2018/030)the Open Fund of Sichuan Provincial Engineering Research Center of City Solid Waste Energy and Building Materials Conversion and Utilization Technology(No.GF2022ZC009)the Open Fund of Sichuan Engineering Research Center for Mechanical Properties and Engineering Technology of Unsaturated Soils(No.SC-FBHT2022-04)。
文摘Unsaturated expansive soil is widely distributed in China and has complex engineering properties.This paper proposes the unified hydraulic effect shear strength theory of unsaturated expansive soil based on the effective stress principle,swelling force principle,and soil–water characteristics.Considering the viscoelasticity and structural damage of unsaturated expansive soil during loading,a fractional hardening–damage model of unsaturated expansive soil was established.The model parameters were established on the basis of the proposed calculation method of shear strength and the triaxial shear experiment on unsaturated expansive soil.The proposed model was verified by the experimental data and a traditional damage model.The proposed model can satisfactorily describe the entire process of the strain-hardening law of unsaturated expansive soil.Finally,by investigating the damage variables of the proposed model,it was found that:(a)when the values of confining pressure and matric suction are close,the coupling of confining pressure and matric suction contributes more to the shear strength;(b)there is a damage threshold for unsaturated expansive soil,and is mainly reflected by strength criterion of infinitesimal body;(c)the strain hardening law of unsaturated expansive soil is mainly reflected by fractional derivative operator.
基金the financial supports from the Key Research and Development Program of Guangxi(No.GUIKE AB22080061)the Guangxi Transportation Industry Key Science and Technology Projects(No.GXJT-2020-02-08)+2 种基金the National Natural Science Foundation of China(No.52268062)the Guangxi Key Project of Nature Science Foundation(No.2020GXNSFDA238024)。
文摘To improve the soil and water stability of expansive soil slopes and reduce the probability of slope failure,novel protection systems based on polymer waterproof coatings(PWC)were used in this study.Herein,three groups of expansive soil slope model tests were designed to investigate the effects of polyester nonwovens and PWC(P-PWC)composite protection system,three-dimensional vegetation network and PWC(T-PWC)composite protection system,and nonprotection on the soil and water behavior in the slopes under precipitation–evaporation cycles.The results showed that the moisture change of P-PWC and T-PWC composite protected slopes was significantly smaller than that of bare slope,which reduced the sensitivity of slope moisture to environmental changes and improved its stability.The soil temperature of the slope protected by the P-PWC and T-PWC systems at a depth of 70 cm increased by 5.6℃ and 2.7℃,respectively.Using PWC composite protection systems exhibited better thermal storage performance,which could increase the utilization of shallow geothermal resources.Moreover,the maximum average crack widths of the bare slopes were 7.89 and 3.17 times those of the P-PWC and TPWC protected slopes,respectively,and the maximum average crack depths were 6.87 and 3 times those of the P-PWC and T-PWC protected slopes,separately.The PPWC protection system weakened the influence of hydro–thermal coupling on the slopes,inhibited the development of cracks on the slopes,and reduced the soil erosion.The maximum soil erosion of slopes protected by P-PWC and T-PWC systems was 332 and 164 times lower than that of bare slope,respectively.The P-PWC and T-PWC protection systems achieved excellent"anti-seepage and moisture retention"and anti-erosion effects,thus improving the soil and water stability of slopes.These findings can provide important guiding reference for controlling rainwater infiltration and soil erosion in expansive soil slope projects.
基金supported by the National Natural Science Foundation of China(Grant No.41877251,Li,https://www.nsfc.gov.cn/)the Key Scientific Research Projects of Colleges and Universities in Henan Province(Grant No.22A560021,Yang,http://jyt.henan.gov.cn/,Grant No.23A560014,Cheng,http://jyt.henan.gov.cn/)+1 种基金the Key Scientific and Technological Support Projects of Tianjin Key R&D Plan(Grant No.19YFZCSF00820,Li,https://kxjs.tj.gov.cn/)the Special Fund for Basic Scientific Research and Young Backbone Teachers of Zhongyuan University of Technology(K2020QN015,2020XQG14,Cheng,https://www.zut.edu.cn/).
文摘Sixteen groups of comprehensive tests have been conducted to investigate the modifications in the physical properties of a weak expansive soil due to the addition of a cement jute fiber.The tests have been conducted to analyze the liquid plastic limit,the particle distribution and the free expansion rate.The results show that:(1)With an increase in the cement-jute fiber content,the free expansion rate of the modified expansive soil gradually decreases,however,such a rate rebounds when the fiber content exceeds 0.5%and the cement content exceeds 6%.(2)With an increase in the cement percentage,the particle unevenness coefficient(Cu)and curvature coefficient(Cc)of the modified expansive soil tend to grow gradually.The Cc coefficient reaches 1.0 when the cement content is 6%.The unevenness coefficient of 16 soil samples is greater than 5.0,however,the Cu coefficient decreases when the cement content reaches 6%.(3)The plastic limit of soil increases as the cement content is made higher,while the liquid limit and plastic index decrease gradually.When the content of the modified material is 2%+0.1%~2%+0.7%(Cement content+jute fiber content),the change of particle size distribution is most obvious.(4)When the contents of cement and jute fiber are is 6%and 0.5%,respectively,the modification induced in the physical properties of soil samples corresponds to the best case.
基金funded by the National Natural Science Foundation of China(Nos.11672066,12172085).
文摘This study examined the effects of using bagasse ash in replacement of ordinary Portland cement(OPC)in the treatment of expansive soils.The study concentrated on the compaction characteristics,volume change,compressive strength,splitting tensile strength,microstructure,California bearing ratio(CBR)value,and shear wave velocity of expansive soils treated with cement.Different bagasse ash replacement ratios were used to create soil samples.At varying curing times of 7,14,and 28 days,standard compaction tests,unconfined compressive strength tests,CBR tests,Brazilian split tensile testing,and bender element(BE)tests were carried out.According to X-ray diffraction(XRD)investigations,quartz and crystobalite make up the majority of the minerals in bagasse ash.Bagasse ash contains a variety of grain sizes,including numerous fiber-shaped particles,according to a scanning electronic microscope(SEM)test.For all of the treated specimens with various replacement ratios,the overall additive content has not changed.The results of the Brazilian split tensile tests demonstrate improved tensile strength for all specimens with various replacement proportions.A lower maximum dry density and a greater optimal water content would result from the substitution of bagasse ash.When the replacement ratio is not more than 20%,the CBR values of the parts replaced specimens are even higher than the cement treatments.The results of BE testing on the treated soils show that there is significant stiffness anisotropy but that it steadily diminishes with curing time and replacement ratio.According to the study,bagasse ash is a useful mineral additive,and the best replacement ratio(CBA20)is 20%.
文摘A dynamic triaxial instrument was used to study the effects of different concentrations of sodium chloride and stress amplitudes on the dynamic properties of an expansive soil under cyclic loading.In particular,four parameters were considered in such a parametric investigation,namely,hysteresis curve morphology characteristic non-closure degreeεp,the ratio of the short and long axisα,the slope of the long axis k and the enclosed area S.The results show that with an increase in the sodium chloride concentration,the soil particle double electric layer becomes thinner,the distance between soil particles decreases,and the whole sample becomes denser.Theεp-N,α-N and S–N relation curves all show a decreasing trend.The ratio of plastic deformation to total deformation grows with increasing the dynamic stress amplitude,and the curves show an upwards trend.The k-N relationship curve displays an increasing trend with the concentration and a general downwards trend as the dynamic stress amplitude is made higher.This also indicates that sodium chloride solutions can improve the engineering properties of expansive soil to a certain extent.With an increase in the vibration times N,the shape of the hysteretic curve becomes narrower,and the whole soil exhibits a cyclic strain hardening.With the help of an exponential function,a model is introduced to predict the relationship between the concentration and the hysteretic curve.
文摘Volume instability of expansive soils due to moisture fluctuations is often disastrous,causing severe damages and distortions in the supported structures.It is,therefore,necessary to adequately improve the performance of such soils that they can favorably fulfil the post-construction stability requirements.This can be achieved through chemical stabilization using additives such as lime,cement and fly ash.In this paper,suitability of such additives under various conditions and their mechanisms are reviewed in detail.It is observed that the stabilization process primarily involves hydration,cation exchange,flocculation and pozzolanic reactions.The degree of stabilization is controlled by several factors such as additive type,additive content,soil type,soil mineralogy,curing period,curing temperature,delay in compaction,pH of soil matrix,and molding water content,including presence of nano-silica,organic matter and sulfate compounds.Provision of nano-silica not only improves soil packing but also accelerates the pozzolanic reaction.However,presence of deleterious compounds such as sulfate or organic matter can turn the treated soils unfavorable at times even worser than the unstabilized ones.
基金This research was funded by the National Natural Science Foundation of China(51879166)the Open Fund of the State Key Laboratory of Frozen Soil Engineering of China(SKLFSE201909).
文摘Phase change materials(PCMs)can store large amounts of energy in latent heat and release it during phase changes,which could be used to improve the freeze-thaw performance of soil.The composite phase change material was prepared with paraffin as the PCM and 8%Class C fly ash(CFA)as the supporting material.Laboratory tests were conducted to reveal the influence of phase change paraffin composite Class C fly ash(CFA-PCM)on the thermal properties,volume changes and mechanical properties of expansive soil.The results show that PCM failed to establish a good improvement effect due to leakage.CFA can effectively adsorb phase change materials,and the two have good compatibility.CFA-PCM reduces the volume change and strength attenuation of the soil,and 8 wt.%PCM is the optimal content.CFA-PCM turns the phase change latent heat down of the soil and improves its thermal stability.CFA-PCM makes the impact small of freeze-thaw on soil pore structure damage and improves soil volume change and mechanical properties on a macroscopic scale.In addition,CFA-8 wt.%PCM treated expansive soil has apparent advantages in resisting repeated freeze-thaw cycles,providing a reference for actual engineering design.
基金funded by the Australian Research Council(ARC),Project No.DP140103004。
文摘This laboratory study examines the potential use of an anionic polyacrylamide(PAM)-based material as an environmentally sustainable additive for the stabilization of an expansive soil from South Australia.The experimental program consisted of consistency limits,sediment volume,compaction and oedometer cyclic swell-shrink tests,performed using distilled water and four different PAM-to-water solutions of P_(D)=0.1 g/L,0.2 g/L,0.4 g/L and 0.6 g/L as the mixing liquids.Overall,the relative swelling and shrinkage strains were found to decrease with increasing number of applied swell-shrink cycles,with an‘elastic equilibrium’condition achieved on the conclusion of four cycles.The propensity for swelling/shrinkage potential reduction(for any given cycle)was found to be in favor of increasing the PAM dosage up to P_(D)=0.2 g/L,beyond which the excess PAM molecules self-associate as aggregates,thereby functioning as a lubricant instead of a flocculant;this critical dosage was termed‘maximum flocculation dosage’(MFD).The MFD assertion was discussed and validated using the consistency limits and sediment volume properties,both exhibiting only marginal variations beyond the identified MFD of P_(D)=0.2 g/L.The accumulated axial strain progressively transitioned from‘expansive’for the unamended soil to an ideal‘neutral’state at the MFD,while higher dosages demonstrated undesirable‘contractive’states.
文摘This study explores the coupling effect of pond ash(PA)and polypropylene(PP)fiber to control the strength and durability of expansive soil.The PA is used to chemically treat the expansive soil and PP fiber is adopted as reinforcement against tensile cracking.The sustainable use of PA and PP fiber are demonstrated by performing mechanical(i.e.unconfined compressive strength,split tensile strength and ultrasonic pulse velocity),chemical(pH value,electrical conductivity and calcite content),and microstructural analyses before and after 2nd,4th,6th,8th and 10th freezing-thawing(F-T)cycles.Three curing methods with 7 d,14 d and 28 d curing periods are considered to reinforce the 5%,10%,15%and 20%PA-stabilized expansive soil with 0.25%,0.5%and 1%PP fiber.In order to develop predictive models for mechanical and durability parameters,the experimental data are processed utilizing artificial neural network(ANN),in association with the leave-one-out cross-validation(LOOCV)as a resampling method and three different activation functions.The mechanical and durability properties of the PA-stabilized expansive soil subgrades are increased with PP fiber reinforcement.The results of ANN modeling predict the mechanical properties perfectly,and the correlation coefficient(R)approaches up to 0.96.
基金funded by the National Natural Science Foundation of China(41977236,41672278,41271071)the Science and Technology Planning Project of Housing and Urban-Rural Development of Anhui Province(2019-YF023)+1 种基金the Major Universities Natural Science Research Project in Anhui Province(KJ2016SD19)the Natural Science Foundation of Jiangxi Province(2019ACBL20002).
文摘The characteristics of soil treated with cationic polyacrylamide(CPAM)mass content of 0%,0.2%,0.4%,0.6%,0.8%,and 1%were investigated through a series of laboratory tests to explore the practical engineering effect of an expansive soil amended with environmental protection material CPAM.The results indicate that with the increasing CPAM content,the liquid limit and plasticity index of soil decrease,the plastic limit increases,and the free swelling ratio and loaded swelling ratio decrease.Besides,the improved soil has less disintegrating property and better water stability.The shear strength increases as the content increases,and the optimal content is 0.6%.Meanwhile,the cohesion of the soil first increases and then decreases,and the internal friction angle increases.Additionally,the unconfined compressive strength first increases and then decreases.The improved soil presents the characteristics of brittle failure and reaches the peak value(410.1 kPa)at the content of 0.8%after curing for 14 days.Scanning electron microscope(SEM)exhibits that the number of curved and wrinkled sections of the expansive soil is reduced after CPAM improvement.Simultaneously,the arrangement of the superimposed polymer changes from face-face to side-angle or side-face-angle,and the reticular structure formed improves the strength and spatial stability of the soil.Therefore,adding appropriate cationic polyacrylamide could improve expansive soil in engineering.
基金financially supported by the National Science Foundation of China(41877251)the science and technology innovation fund project of Xinxiang University(15ZA06).
文摘In this paper,the discrete element method(DEM)is used to study the microstructure of expansive soils.The results of the numerical calculations are in agreement with the stress-strain triaxial test curve that is obtained for a representative expansive soil.Biaxial compression tests are conducted for different confining pressures(50 kpa,100 kpa,and 150 kpa).Attention is paid to the following aspects:deviatoric stress,boundary energy,friction energy,bond energy,strain energy,kinetic energy,and the contact force between grains when the test specimen is strained and to the effect of the different confining pressures on the internal crack expansion.The results of this research show that the cross-section of the specimen is destroyed along the middle part of the specimen itself.When the confining pressure is higher,the impulse is stronger,and this leads to more effective destruction.
文摘Expansive soils can pose tough issues to civil engineering applications. In a typical year, expansive soils can cause a greater financial loss than earthquakes, floods, hurricanes and tornadoes combined. Various means have been studied to tackle problems associated with expansive soils. The majority of the methods are based on treatment of the soils. While the methods may be effective in some cases, their limitations are also obvious: The treatment normally involves complex processes and may not be eco-friendly in the long run. In many cases, the effectiveness of the treatment is uncertain. A retaining system that maintains a constant lateral pressure is proposed, which consists of three components: the retaining sheet, the slip-force device and the bracing column. The retaining sheet bears the pressure exerted by expansive backfills and is not embedded into the soils. Placed between the retaining sheet and bracing column, the slip-force device permits displacement of the retaining sheet but keeps the force on the sheet and the bracing column constant. The governing equation of the motion of the piston in the slip-force device is derived and a numerical simulation of a practical case is conducted based on the derived governing equation. Numerical results show that as the expansive soil swell, the spring force will increase and the piston will move accordingly. When the pressure of the oil in chamber reach<span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">es</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> the open threshold of the unidirectional relief valve, the valve will open and the spring force and the oil pressure in the chamber will keep constant. The results also show that some parameters, such as damping ratio, have very slight influences on the device behavior, say 2 × 10</span><sup><span style="font-family:Verdana;">-6</span></sup><span style="font-family:Verdana;"> or even 4.8 × 10</span><sup><span style="font-family:Verdana;">-9</span></sup><span style="font-family:Verdana;">. Theoretical and numerical studies prove the effectiveness of the proposed retaining system.</span></span></span></span>
文摘Expansive soils undergo high volume change due to cyclic swelling and shrinkage behavior during the wet and dry seasons.Thus,such problematic soils should be completely avoided or properly treated when encountered as subgrade materials.In the present study,the biomedical waste incinerator ash and lime combination was proposed to stabilize expansive soil.Particle size analysis,Atterberg limits,free-swell,compaction,unconfined compression strength,and California bearing ratio tests were conducted on the natural soil and blended with 3%,5%,7%,9%,and 11%biomedical waste incinerator ash(BWIA).The optimum content of BWIA was determined based on the free-swell test results.To further investigate the relative effectiveness of the stabilizer,2%and 3%lime were also added to the optimum soil-BWIA mixture and UCS and CBR tests were also conducted.In addition,scanning electron microscopy(SEM)tests for representative stabilized samples were also conducted to examine the changes in microfabrics and structural arrangements due to bonding.The addition of BWIA has a promising effect on the index properties and strength of the expansive soil.The strength of the expansive soil significantly increased when it was blended with the optimum content of BWIA amended by 2%and 3%lime.
文摘Construction and demolition waste(CDW)are the largest waste products in the world today and competes as a viable recycled additive material in place of natural aggregates.Due to the increase in compressive strength of different mix proportions of CDW,it is also considered for reuse in concrete and subbase construction.This study shows the effect of CDW in expansive soil stabilization.The chemical and mechanical properties of these materials have shown that they are capable of developing compressive strength properties for replacement of cement with significant reduction in carbon emission.The inherent compositional properties of recycled CDW compared in this review suggests that CDW have good filler properties in highly expansive soils.Mixtures of crushed brick and recycled aggregates characterised based on chemical properties of different replacement ratios suggests that CDW of good-quality aggregates reduces swell potential of expansive soils and increased mechanical strength in pavement construction.
