Formation of Tianwen-1 landing crater and mechanical properties of Martian soil near the landing site

After landing in the Utopia Planitia,Tianwen-1 formed the deepest landing crater on Mars,approximately 40 cm deep,exposing precious information about the mechanical properties of Martian soil.We established numerical models for the plume-surface interaction(PSI)and the crater formation based on Computational Fluid Dynamics(CFD)methods and the erosion model modified from Roberts’Theory.Comparative studies of cases were conducted with different nozzle heights and soil mechanical properties.The increase in cohesion and internal friction angle leads to a decrease in erosion rate and maximum crater depth,with the cohesion having a greater impact.The influence of the nozzle height is not clear,as it interacts with the position of the Shock Diamond to jointly control the erosion process.Furthermore,we categorized the evolution of landing craters into the dispersive and the concentrated erosion modes based on the morphological characteristics.Finally,we estimated the upper limits of the Martian soil’s mechanical properties near Tianwen-1 landing site,with the cohesion ranging from 2612 to 2042 Pa and internal friction angle from 25°to 41°.

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.

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.

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.

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.