Study On Anisotropy Of Compressive And Tensile Properties Of Malan Loess In Shanxi

With national economic development transferring to the Midwest,the Loess Plateau has become the main battlefield for construction.The construction of highways,airports and embankment dams in the loess area is booming,and people have put forward higher requirements for the tensile resistance and crack resistance of these buildings.The tensile strength of loess is generally small and not easy to measure,which is often neglected in engineering.But studies show that the,occurrence and development of geological hazards such as falling,landslides,debris flows and ground fissures are closely related to the tensile properties of soil.Tensile cracks have occurred before the gravity erosion such as collapse and effusion.During the settlement of loess foundation,there are not only shear cracks,but also local tensile cracks.The compressive strength is a characterization of the amount of the structural strength of soil.The lateral or axial deformation failure of soil under the upper load condition is actually the decrease of pore volume and the change of pore water and gas.It leads to the destruction of particles relationship and inter-particle bonding force.Therefore,studying the compression and tensile strength characteristics of loess is of great significance not only for improving the strength theory of soil,but also for solving practical engineering problems.There are many factors that affect the tensile strength and compressive strength of loess,including the internal factors such as the material composition,microstructure,compactness degree,depositional age and void ratio,and the external factors such as moisture content.In this paper,the difference of ultrasonic wave velocity,compressive strength and tensile strength of undisturbed Malan loess in different directions was analyzed based on laboratory test,and then the anisotropy of undisturbed loess structure was discussed.The results show that: The compressive strength of dryness specimens of undisturbed Malan loess is between 350-1000 kPa.And tensile strength is far less than the compressive strength,and its range is between 75-120 kPa.There are significant anisotropy in the compressive strength and tensile strength of Malan Loess: the strength of the sedimentary direction(vertical)is generally greater than that in the horizontal direction.The ultrasonic velocity of Malan loess is anisotropic.Under dry condition and natural water content,the vertical wave velocity of specimens is greater than the horizontal wave velocity of specimens.After specimens drying to 0% from natural water content,the range of its wave velocity increased from 0.49-0.83 km/s to 0.78-1.13 km/s,and the overall increase of wave velocity was about 36.5%.The structure of undisturbed Malan loess has anisotropy.The vertical soil-particles are more closely arrayed,and the soil skeleton is more solid.And there are so many vertical joints in the loess mass.So the ultrasonic wave velocity,compressive strength and tensile strength of undisturbed Malan loess show anisotropy.