Influence of fines content on the anti-frost properties of coarse-grained soil

This paper aims to determine the optimal fines content of coarse-grained soil required to simultaneously achieve weaker frost susceptibility and better bearing capacity. We studied the frost susceptibility and strength properties of coarse-grained soil by means of frost heaving tests and static triaxial tests, and the results are as follows： （1） the freezing temperature of coarse-grained soil decreased gradually and then leveled off with incremental increases in the percent content of fines; （2） the fines content proved to be an important factor influencing the frost heave susceptibility and strength properties of coarse-grained soil. With incremental increases in the percent content of fines, the frost heave ratio increased gradually and the cohesion function of fines effectively enhanced the shear strength of coarse-grained soil before freeze-thaw, but the frost susceptibility of fines weakened the shear strength of coarse-grained soil after freeze-thaw; （3） with increasing numbers of freeze-thaw cycles, the shear strength of coarse-grained soil decreased and then stabilized after the ninth freeze-thaw cycle, and therefore the mechanical indexes of the ninth freeze-thaw cycle are recommended for the engi- neering design values; and （4） considering frost susceptibility and strength properties as a whole, the optimal fines content of 5% is recommended for railway sub,fade coarse-~rained soil fillings in frozen re^ions.

Prediction model of moisture content of dead fine fuel in forest plantations on Maoer Mountain,Northeast China

Preventing and suppressing forest fires is one of the main tasks of forestry agencies to reduce resource loss and requires a thorough understanding of the importance of factors affecting their occurrence.This study was carried out in forest plantations on Maoer Mountain in order to develop models for predicting the moisture content of dead fine fuel using meteorological and soil variables.Models by Nelson(Can J For Res 14:597-600,1984)and Van Wagner and Pickett(Can For Service 33,1985)describing the equilibrium moisture content as a function of relative humidity and temperature were evaluated.A random forest and generalized additive models were built to select the most important meteorological variables affecting fuel moisture content.Nelson’s(Can J For Res 14:597-600,1984)model was accurate for Pinus koraiensis,Pinus sylvestris,Larix gmelinii and mixed Larix gmelinii—Ulmus propinqua fuels.The random forest model showed that temperature and relative humidity were the most important factors affecting fuel moisture content.The generalized additive regression model showed that temperature,relative humidity and rain were the main drivers affecting fuel moisture content.In addition to the combined effects of temperature,rainfall and relative humidity,solar radiation or wind speed were also significant on some sites.In P.koraiensis and P.sylvestris plantations,where soil parameters were measured,rain,soil moisture and temperature were the main factors of fuel moisture content.The accuracies of the random forest model and generalized additive model were similar,however,the random forest model was more accurate but underestimated the effect of rain on fuel moisture.

CPT-Based estimation of undrained shear strength of fine-grained soils in the Huanghe River Delta

The Huanghe River(Yellow River)Delta has a wide distribution of fine-grained soils.Fluvial alluviation,erosion,and wave loads affect the shoal area,resulting complex physical and mechanical properties to sensitive finegrained soil located at the river-sea boundary.The cone penetration test(CPT)is a convenient and effective in situ testing method which can accurately identify various soil parameters.Studies on undrained shear strength only roughly determine the fine content(FC)without making the FC effect clear.We studied four stations formed in different the Huanghe River Delta periods.We conducted in situ CPT and corresponding laboratory tests,examined the fine content influence on undrained shear strength(S_(u)),and determined the cone coefficient(N_(k)).The conclusions are as follows.(1)The fine content in the area exceeded 90%,and the silt content was high,accounting for more than 70%of all fine particle compositions.(2)The undrained shear strength gradually increased with depth with a maximum of approximately 250 kPa.When the silt content was lower than 60%–70%,the undrained shear strength decreased.(3)The silt and clay content influenced undrained shear strength,and the fitted f_(s)h/q_(t) function model was established,which could be applied to strata with a high fine content.The cone coefficients were between 20 and 25,and the overconsolidated soil layer had a greater cone coefficient.

Predicting lateral displacement caused by seismic liquefaction and performing parametric sensitivity analysis:Considering cumulative absolute velocity and fine content

Lateral displacement due to liquefaction(D_(H))is the most destructive effect of earthquakes in saturated loose or semi-loose sandy soil.Among all earthquake parameters,the standardized cumulative absolute velocity(CAV_(5))exhibits the largest correlation with increasing pore water pressure and liquefaction.Furthermore,the complex effect of fine content(FC)at different values has been studied and demonstrated.Nevertheless,these two contexts have not been entered into empirical and semi-empirical models to predict D_(H)This study bridges this gap by adding CAV_(5)to the data set and developing two artificial neural network(ANN)models.The first model is based on the entire range of the parameters,whereas the second model is based on the samples with FC values that are less than the 28%critical value.The results demonstrate the higher accuracy of the second model that is developed even with less data.Additionally,according to the uncertainties in the geotechnical and earthquake parameters,sensitivity analysis was performed via Monte Carlo simulation(MCS)using the second developed ANN model that exhibited higher accuracy.The results demonstrated the significant influence of the uncertainties of earthquake parameters on predicting D_(H).

Influence of the rolling-resistance-based shape of coarse particles on the shear responses of granular mixtures

Shear responses of dense granular mixtures of spherical coarse particles with the rolling resistance and spherical fine particles are studied via triaxial compression tests using the discrete element method.The macroscale responses(shear strength and dilatancy)are examined.Comparing the results with those in the literature indicates that granular mixtures with a rolling resistance coefficient of 0.5 have similar macroscale responses to those of gravel-shaped coarse particle mixtures.We quantify the microscale responses including the percentage contributions of contact types,partial coordination number,average particle rotation,average degree of interlocking,and local structural properties,A detailed analysis of the force-fabric anisotropy reveals the mechanisms of the variations in the shear strength with the rolling resistance coefficient and the fines content.The mechanism of the variation in the shear strength with the fines content for granular mixtures with a rolling resistance coefficient of 0.5 is different from that for gravel-shaped coarse particle mixtures.Finally,we find that a rolling resistance linear model weakens the linear relationship between the stress ratio and the fabric anisotropy of strong and non-sliding contacts when the fines content is 30% and 40%.

Investigation of the hydro-mechanical behaviour of fouled ballast

In this study,a fouled ballast taken from the site of Sénissiat,France,was investigated.For the hydraulic behaviour,a large-scale cell was developed allowing drainage and evaporation tests to be carried out with monitoring of both suction and volumetric water content at various positions of the sample.It was observed that the hydraulic conductivity of fouled ballast is decreasing with suction increase,as for common unsaturated soils.The effect of fines content was found to be negligible.For the mechanical behaviour,both monotonic and cyclic triaxial tests were carried out using a large-scale triaxial cell.Various water contents were considered.The results were interpreted in terms of shear strength and permanent axial strain.It appeared that the water content is an important factor to be accounted for since any increase of water content or degree of saturation significantly decreases the shear strength and increases the permanent strain.Constitutive modelling has been attempted based on the experimental results.The model in its current state is capable of describing the effects of stress level,cycle number and water content.

An insight into the mechanical behavior of binary granular soils

This paper investigates the participation of the fines fraction in the load-carrying structure of binary mixtures of granular soils. For this purpose, various fractions of two fine sands were added to two coarse sands with the same particle size distribution, but different particle shape characteristics. Based on the results of 144 direct shear tests, it was found that fines participation in the load-bearing structure increases with fines content. At the same fines content, the participation of the fines in the load-carrying structure of loose mixtures is greater than in samples that were initially compacted. In addition, it was observed that fines participation rises with the increase in the average size of the fines fraction.