Effects of soil mechanical properties on the height and tractive performance of rubber grouser at different moisture contents

Rubber tracked vehicles are commonly used on agricultural machinery that perform agricultural operations such as rice harvesting in soft paddy fields with low bearing capacity.Research was carried out to assess the influence of soil moisture content and mechanical properties on the tractive performance of a rubber grouser with three heights(45 mm,55 mm,60 mm).The direct shear test and penetration test were used in this study,which was based on a semi-empirical approach of determining tractive parameters.Direct shear tests were used to measure soil shear strength parameters such as cohesion,adhesion,internal and exterior friction angles.The results of the penetration test were used to determine tractive parameters such as soil thrust,running resistance,and traction,for the penetration test,a device was designed and developed.The experimental results revealed that soil cohesion and adhesion increased linearly with increasing soil moisture content,however adhesion dropped after 30.7%.Similarly,the soil thrust initially increased till 21.5%then decreased.Furthermore,running resistance had a decreasing trend over soil moisture content whereas maximum traction achieved for 45 mm grouser height at 21.5%moisture content.It was concluded that a rubber grouser with 45 mm height had better traction rather than 55 mm and 60 mm,it can be suitably used for designing a track system for a crawler vehicle(e.g.,harvester)leading to its greater adoption among the farmers.

Experimental study of the effects of non-uniformly distributed fine soil on mechanical properties of Shenyang–Dandong Railway coarse-grained soil

The stress produced by repeated train loads decreases with increasing railway subgrade bed depth, and slightly weathered coarse particles of subgrade bed fillings can be broken at different levels under continuous load. Thus, the mass of fine soil, with a diameter of not more than 0.075 mm, is different at different depths. Fine soil is also sensitive to frost heave and thaw settlement. In order to study the effects of non-uniformly distributed fine soil on the mechanical properties of coarse-grained soil of the Shenyang-Dandong Railway, triaxial tests were conducted with three types of specimens, un- dergoing six freeze-thaw cycle numbers （0, 1, 3, 7, 9, 12） and three confining pressures （100, 200, 300 kPa）. The freezing temperature is -5 ~C and the thawing temperature is ＋15 ~C. The stress-strain behavior, static strength, resilient modulus, cohesive force and the angle of internal friction were measured for different tested specimens. As a result, the law of static strength and resilient modulus of different specimens following the increase of freeze-thaw cycles under three confining pressures is obtained. The changing law of cohesive force and friction angle of three specimens following the increase of freeze-thaw cycles is also calculated, and the different results of different specimens are also compared.

Mechanical behavior of iron ore tailings under standard compression and extension triaxial stress paths

The disposal of mining tailings has increasingly focused on the use of dry stacks.These structures offer more security since they use filtered and compacted material.Because of the construction method and the heights achieved,the material that compounds the structure can be subjected to different stress paths along the failure plane.The theoretical framework considered in the design of these structures generally is the critical state soil mechanics(CSSM).However,the data in the literature concerning the uniqueness of critical state line(CSL)is still controversial as the soil is subjected to different stress paths.With respect to tailings,this question is even more restricted.This paper studies two tailings with different gradings due to the beneficial processes over extension and compression paths.A series of drained and undrained triaxial tests was conducted over a range of initial densities and stress levels.In the q-p'plane,different critical stress ratio(M)values were obtained for compression and extension stress paths.However,the critical state friction angle is very similar with a slightly higher critical state friction angle for extension tests.Curved stress path dependent CSLs were obtained in the n-lnp0 plane with the extension tests below the CSL defined in compression.Regarding the fines content,the studied tailings presented very similar M and critical state friction angle values.However,the fines content af-fects the volumetric behavior of the studied tailings and the CSLs on the n-lnp0 plane shift downwards with the increasing fines content for compression and extension tests.In relation to dilatancy analysis,the fines content did not present an evident influence on the dilatancy of the materials.However,different values of mean stress ratio N were obtained between compression and extension tests and can corroborate the existence of non-unique CSLs for these materials.

The Effects of Farmyard Manure and Mulch on Soil Physical Properties in a Reclaimed Coastal Tidal Flat Salt-Affected Soil

Careful soil management is important for the soil quality and productivity improvement of the reclaimed coastal tidal flat saline land in northern Jiangsu Province, China. Farmyard manure（ FYM） and mulch applications, which affect soil characteristics and plant significantly, are regard as an effective pattern of saline land improvement. As a conventional management in the study region, FYM and mulch are used for the amendment of the new reclaimed tidal flat regularly, but little is known about their effects on soil physical properties functioning. A study was conducted on a typical coastal tidal flat saline land, which was reclaimed in 2005, to evaluate the effects of FYM, polyethylene film mulch（PM）, straw mulch（SM）, FYM combined with PM（FYM＋PM）, FYM combined with SM（FYM＋SM）, on soil hydraulic properties and soil mechanical impedance. CK represented conventional cultivation in study area without FYM and mulch application and served as a control. The experiment, laid out in a randomized complete block design with three replications, was studied in Huanghaiyuan Farm, which specialized in the agricultural utilization for coastal tidal flat. Result showed that capillary water holding capacity（CHC）, saturated water content（SWC）, saturated hydraulic conductivity（ Ks） and bulk density（BD）, cone index（CI） were affected significantly by the FYM and mulch application, especially in the 0-10 cm soil layer. FYM and mulch management increased CHC, SWC and Ks over all soil depth in the order of FYM＋SM〉FYM＋PM〉FYM〉SM〉PM〉CK. With the contrary sequence, BD and CI decreased significantly; however, FYM and mulch application affected BD and CI only in the upper soil layers. CHC, SWC and Ks decreased significantly with the increasing of soil depth, BD and CI, and a significant liner equation was found between CHC, SWC, Ks and BD, CI. With the highest CHC（38.15%）, SWC（39.55%）, Ks（6.00 mm h-1） and the lowest BD（1.26 g cm-3） and CI（2.71 MPa）, the combined management of FYM and SM was recommend to be an effective method for the melioration of reclaimed coastal tidal flat saline soil.

Determination of critical state line(CSL)for silty-sandy iron ore tailings subjected to low-high confining pressures

The disposal of filtered tailings in high dry stacks can induce particle breakage,changing the material's behaviour during the structure's lifetime.The grading changes influence material properties at the critical state,and this is not mature for intermediate artificial soils(tailings)in a broad range of confining pressures.In this paper,it aims to describe the behaviour of iron ore tailings in a spectrum of confining pressures broader than the reported in previous studies.A series of consolidated drained(CD)triaxial tests was carried out with confining pressures ranging from 0.075 MPa to 120 MPa.These results show that the amount of breakage plays an essential role in the response of iron ore tailings.The existence of curved critical state line(CSL)in both specific volume(ν)-logarithm of mean effective stress(p′)and deviatoric stress(q)-mean effective stress(p′)planes,and different responses in the deviatoric stress-axial strain-volumetric strain curves were verified.An inverse S-shaped equation was proposed to represent the silty-sandy tailings'behaviour up to high pressures onν-lnp′plane.The proposed equation provides a basis for enhancing constitutive models and considers the evolution of the grading up to severe loading conditions.The adjustment considered three regions with different responses associated with particle breakage at different pressure levels.

Random checkerboard based homogenization for estimating effective thermal conductivity of fully saturated soils

This paper proposes homogenization scheme for estimating the effective thermal conductivity of fully saturated soils. This approach is based on the random checkerboard-like microstructure. Two modeling scales and two modeling approaches are distinguished and used, i.e. microscale and mesoscale and 1-step and 2-step homogenizations, respectively. The 2-step homogenization involves sequential averaging procedure, i.e. first, at microscale, a mineralogical composition of soil skeleton is considered and averaging process results in estimation of the skeleton effective thermal conductivity, and then, at mesoscale, a random spatial packing of solid skeleton and pores via random checkerboard microstructure is modeled and leads to evaluation of the soil overall thermal conductivity. The 1-step homogenization starts directly at the mesoscale and homogenization procedure yields evaluation of the overall soil thermal conductivity. At the mesoscale, the distinct nature of soil skeleton, as composed of soil separates,is considered and random variability of soil is modeled via enriched random checkerboard-like structure.Both approaches, i.e. 1-step and 2-step homogenizations, interrelate mineralogical composition with the soil texture characterized by the volume fractions of soil separates, i.e. sand, silt and clay. The probability density functions(PDFs) of thermal conductivity are assumed for each of the separates. The soil texture PDF of thermal conductivity is derived taking into consideration the aforementioned functions. Whenever the random checkerboard-like structure is used in averaging process, the Monte Carlo procedure is applied for estimation of homogenized thermal conductivity. Finally, the proposed methodology is tested against the laboratory data from our measurements as well as those available from literature.

Dynamic Finite Element Analysis for Interaction between Two Phase Saturated Soil Foundation and Platform

In this paper, the foundation soil of offshore structure is simulated as a two phase saturated porous medium. The dynamic equations of porous medium and finite element formulation are given. For structural analysis, the technique of multilevel substructure is used, and the saturated soil analysis is set in the highest level substructure model. Based on these theories a dynamic finite element analysis program DIASS for the analysis of interaction between two phase ocean soil foundation and platform structures has been developed. A numerical example is given here to illustrate the influence of the pore water in soil on the structural response of an ocean platform.

Three-dimensional cellular automata based particle flow simulations of mechanical properties of talus deposit

Based on three-dimensional cellular automata （CA）, a new stochastic simulation model to simulate the microstructures and particle flow of talus deposit is proposed. Ill addition, an auto-modeling program CARS is developed, with which nunaerical simulations can be conducted conveniently. For the problem of simulating mechanical behaviors of talus deposit, spatial anangement or sphere shapes should be considered. In the new modeling method, four sphere anangement models are developed for the particle flow simulation of talus deposit. Numerical results show that the talus deposit has the mechanical characteristics of typical stress-strain curves, as other rock-like materials. The cohesion of talus deposit decreases with increasing rock content, while the internal friction angle increases with increasing rock contents. Finally, numerical simulation is verified with the results of field test.

Review and prospect of the effects of freeze-thaw on soil geotechnical properties

Freeze-thaw hazard is one of the main problems in cold regions engineering and artificial ground freezing engineering.To mitigate freeze-thaw hazards,it is essential to investigate the effects of freeze-thaw on soils engineering properties.This paper summarizes the effects of freeze-thaw on the physical and mechanical properties of soils reported in recent studies.The differences of freeze-thaw conditions between freezing shaft sinking and cold regions engineering are discussed.Based on the technological characteristics of freezing shaft sinking in deep alluvium,we further attempt to identify key research needs regarding the freeze-thaw effects on the engineering properties of deep soils.

Consolidation and Creep Behaviors of Two Typical Marine Clays in China

This paper presents an experimental investigation into the deformation characteristics of two typical marine clays obtained from Dalian and Shanghai, respectively, in China. Three kinds of laboratory tests, i.e. conventional oedometer tests, one-dimensional and triaxial creep tests were carried out. The results obtained from consolidation tests demonstrate linear e−logσv relationships for Shanghai clay at normally consolidated state, while partly or even global non-linear relationships for Dalian clay. The compression index Cc for both clays follows the correlation of Cc = 0.009(wL −10) where wL is the liquid limit of soil. The relationship between logkv (kv is the hydraulic conductivity of soil) and void ratio e is generally linear and the hydraulic conductivity change index Ckv can be described by their initial void ratio for both clays. The secondary compressibility of Dalian clay lies in medium to high range and is higher than that of Shanghai clay which lies in the range of low to medium. Furthermore, based on drained triaxial creep tests, the stress-strain-time relationships following Mesri’s creep equation have been developed for Dalian and Shanghai clays which can predict the long-term deformation of both clays reasonably well.

Treatability of volatile chlorinated hydrocarbon-contaminated soils of different textures along a vertical profile by mechanical soil aeration：A laboratory test

Mechanical soil aeration is a simple, effective, and low-cost soil remediation technology that is suitable for sites contaminated with volatile chlorinated hydrocarbons（VCHs）. Conventionally, this technique is used to treat the mixed soil of a site without considering the diversity and treatability of different soils within the site. A laboratory test was conducted to evaluate the effectiveness of mechanical soil aeration for remediating soils of different textures（silty,clayey, and sandy soils） along a vertical profile at an abandoned chloro-alkali chemical site in China. The collected soils were artificially contaminated with chloroform（TCM） and trichloroethylene（TCE）. Mechanical soil aeration was effective for remediating VCHs（removal efficiency 〉 98%）. The volatilization process was described by an exponential kinetic function.In the early stage of treatment（0–7 hr）, rapid contaminant volatilization followed a pseudofirst order kinetic model. VCH concentrations decreased to low levels and showed a tailing phenomenon with very slow contaminant release after 8 hr. Compared with silty and sandy soils, clayey soil has high organic-matter content, a large specific surface area, a high clay fraction, and a complex pore structure. These characteristics substantially influenced the removal process, making it less efficient, more time consuming, and consequently more expensive. Our findings provide a potential basis for optimizing soil remediation strategy in a cost-effective manner.

Engineering practice of mechanical soil aeration for the remediation of volatile organic compound-contaminated sites in China： Advantages and challenges

In recent years, many industrial enterprises located in the urban centers of China have been relocated owing to the rapid increase in urban development. At the sites abandoned by these enterprises, volatile organic compounds have frequently been detected, sometimes at high concentrations, particularly at sites abandoned by chemical manufacturing enterprises. With the redevelopment of sites and changes in land-use tvpe associated with these sites, substantial amounts of contaminated soils now require remediation. ＂Since China is a developing country, soil remediation warrants the usage of techniques that are suitable for addressing the unique challenges faced in this country. Land shortage is a common problem in China; the large numbers of contaminated sites, tight development schedules, and limited financial resources necessitate the development of .cost-effective methods for land reclamation.Mechanical soil aeration is a simple, effective, and low-cost soil remediation tectm^que mat is particularly suitable for the remediation of large volatile organic compound-contaminated sites. Its effectiveness has been confirmed by conducting laboratory studies, pilot tests, and full-scale projects.This study reviews current engineei-ing practice and developmental trends of mechanical soil aeration and analyzes the advantages and disadvantages of this technology for application in China as an emerging soil remediation market. The findings of this study might aid technology development in China, as well as assist other developing countries in the assessment and implementation of costeffective hazardous waste site soil remediation programs.

Dynamic Analysis of Submarine Pipelines on an Elastic / Viscoelastic Foundation

This paper presents a new finite element method for solving static and dynamic problems in laying operation of pipelines. The effect of the viscoelastic soil behavior is considered by using the Pasternak foundation model. Some examples are also presented.

Influence of fabric anisotropy on seismic responses of foundations

Earthquakes, as one of the well-known natural disasters, are highly destructive and unpredictable.Foundation failure due to liquefaction induced by earthquakes can cause casualties as well as significantdamage to the building itself. Fabric anisotropy of soil grains is considered to be an important factor indynamic soil response based on previous researches and laboratory tests. However, the limited availabilityof real physical data makes it less persuasive. In this study, a shake table installed on ageotechnical centrifuge is used to provide the designed seismic motions, and therefore, to simulate therealistic earthquake motion to foundations. Important parameters in the responses such as acceleration,excess pore pressure and deformation are evaluated to investigate the influence. Implications for designare also discussed. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Proctor cone penetrometer for in-situ soil strength studies in Nigeria

Investigations of in-situ or laboratory soil strength properties,particularly the resistance of soil to penetration,usually referred to as cone index(CI)are often required in soil tillage and traction studies.This helps in the analysis of the interactions of both tillage tools and tractive elements with the soil.However,penetrometer,the instrument used for measuring this important parameter(CI),is not readily available in Nigeria.Following the recommendations in ASAE standards,a functional proctor cone penetrometer for soft soils has been developed and calibrated.The major parts include the handle,made of half-inch galvanized pipe,constructed in such a way that it can be screwed on and off the pressure shaft conveniently,the graduated pressure and penetration shafts made of stainless steel;the spring loaded pressure chamber,and a cone probe.The penetrometer was calibrated by applying known forces on the handle while noting corresponding penetrations and displacements on the graduated pressure shaft.A performance test was carried out on a clayey loam soil to compare the readings obtained from the developed penetrometer and an imported one.The major difference between the two is that while one is very expensive and scarce to come by,the other is produced locally with locally sourced materials and technology.The cost of the imported one is ten times more than that of the local one.The mean CI obtained for twenty-four random samples on the soil surface for the test area at 18 cm depth was found to be 1.4358 MPa for the local,and 1.5096 MPa for the imported.Regression analysis of the two sets of values of CI for the local and the foreign showed a strong correlation(R2=0.779,P<0.05).This implies that the locally produced proctor penetrometer is reliable for measurements of CI at 0-18 cm soil depth for soft soils.

Behavior of materials for earth and rockfill dams:Perspective from unsaturated soil mechanics

The basis of the design of earth and rockfill dams is focused on ensuring the stability of the structure under a set of conditions expected to occur during its life.Combined mechanical and hydraulic conditions must be considered since pore pressures develop during construction,after impoundment and in drawdown.Other instability phenomena caused by transient flow and internal erosion must be considered.The prediction of the hydromechanical behavior of traditional and non-traditional materials used in the construction of dams is therefore fundamental.The materials used for dam’s construction cover a wide range from clayey materials to rockfill.In a broad sense they are compacted materials and therefore unsaturated materials.A summary of the current level of knowledge on the behavior of traditional materials used in the construction of dams is presented in the paper.Regular compacted materials(with a significant clay fraction),rockfill and compacted soft rocks are studied with more detail.The latter are non-traditional materials.They are analysed because their use,as well as the use of mixtures of soil and rock,is becoming more necessary for sustainability reasons.

Analytical solution for upheaval buckling of shallow buried pipelines in inclined cohesionless soil

Upheaval buckling of pipelines can occur under thermal expansion and differential ground settlement.Research on this phenomenon has usually assumed the pipes are buried in horizontal ground.For long-distance transmission pipelines across mountainous areas,the ground surface is commonly inclined.Based on the Rankine earth pressure theory and Mohr-Coulomb failure criterion,analytical formulae for calculating the peak uplift resistance and the slip surface angles for a buried pipe in inclined ground are presented in this paper.Analyses indicate that the slip surfaces in inclined ground are asymmetric and rotate towards the downhill side.Under a shallow burial depth,the failure plane angle is highly impacted by the ground inclination.When the embedment ratio(H/D)is more than 4,the influence of the ground slope on the failure plane angle is negligible.The peak uplift resistance reduces in inclined ground,especially when H/D is less than 1.Finally,a simple equation considering the impact of ground inclination is proposed to predict the peak uplift resistance.

Effects of sediment characteristics on the sediment transport capacity of overland flow

The transport of sediments is a crucial part of soil erosion.Accurately calculating the sediment transport capacity is key to the construction of soil erosion process models.Research on Tc has focused mainly on the dynamics of a single particle of sediment and hydraulic variables.There have been few studies of the impact of soil aggregates on the Tc.To clarify how sediment characteristics,including those for single particles and aggregates,affect the Tc of overland flow with no raindrop import,flume experiments were implemented at slope gradients varying from 5.24%to 26.80%and flow discharges ranging from 0.68 to 5.41×10^(-3)m^(2)s^(-1).The experimental materials were five typical soils in China.The results indicated that the correlation between the measured Tc and sediment mechanical composition indexes of the five soils was indistinctive in this study.The sediment settling velocity with aggregates has a significant corre-lation with the measured Tc.New equations,including for the sediment settling velocity with aggregatesωud75,were established to calculate the Tc.The empirical equation that includedωud75,slope gradient and unit discharge performed greatly in predicting Tc(R^(2)=0.93,NSE=0.90).ωud75 can effectively improve the calculation accuracy of Tc.The new equation including flow and sediment properties obtained through dimensional analysis performed well in predicting Tc(R^(2)=0.99,NSE=0.91),and the calculation accuracy was better than that of the empirical model derived in this study.These findings indicate that the sediment settling velocity is an important variable in the equation for predicting sediment transport capacity of overland flow.

STUDY ON STARTING VELOCITY OF COHESIVE SEDIME-NTATION

In this paper, with the starting velocity experiments of natural cohesive sedimentation, an assumption concerning the starting mechanism of cohesive sedimentation was proposed and a formula to determine the starting velocity of compact clay was given. It is pointed out that the fluctuating function of flow is a main factor for the starting of sedimentation. The component and structure of cohesive sedimentation are also the affecting factors for the starting. Consequently, the modern results of soil mechanics, clay mineralogy and fluid mechanics are helpful in the investigation of this kind of engineering problem.

Eco-geotechnics for human sustainability

As a result of climate change and increasing engineering activities, soil-related disasters such as slope failures and sandstorms have become more frequent worldwide. These disasters have caused not only loss of life, but also have led to serious economic losses as well as ecological and environmental damage. To sustain mankind, a new discipline, eco-geotechnics, has rapidly become established and developed in recent years. It integrates scientific knowledge from soil mechanics, rock mechanics,ecology, biology, and atmospheric science to develop cross-disciplinary theories and carry out experiments to tackle grand world challenges such as the effects of climate change. Through the development of eco-geotechnics, various eco-friendly technologies have been developed to mitigate sandstorms and to improve the performance of earthen structures such as embankments, slopes and landfill covers. This state-of-the-art review introduces and discusses the important advances in the field of eco-geotechnics,covering theoretical developments, laboratory testing, centrifuge modelling, field monitoring and engineering applications.Finally, the research gaps and future needs of eco-geotechnics are highlighted and discussed.