How to calculate the cohesion
Cohesion c and internal friction angle of rock mass φ It can be determined by direct shear, uniaxial compression or triaxial compression experiments
Cohesion, also called cohesion. The calculation method is: in the case of effective stress, the cohesion is obtained by decting the total shear strength from the friction strength. On the other hand, cohesion is the shear strength of the failure surface without any normal stress
The classical expression of internal friction angle is Coulomb's law τ=σ tan φ+ Cfor cohesive soil, C is not 0, for sandy soil, C is 0, φ、 C can be obtained by triaxial test (or direct shear). Under different confining pressures, the maximum principal stress and minimum principal stress can be obtained, and the stress circle can be made. Under at least three different confining pressures, three stress circles can be made, and the common tangent of the three circles can be made. The inclination angle is the internal friction angle
The relationship between repose angle and internal friction angle:1, repose angle and internal friction angle all reflect the internal friction characteristics of granular materials
The concepts of angle of repose and internal friction angle are different. The internal friction angle reflects the friction characteristics between layers of granular materials, and the angle of repose represents the rolling ability of a single granular material on the pile, which is the appearance of the internal friction characteristics3. For similar materials with similar mass and moisture content, the angle of repose is always greater than the internal friction angle, and is greater than the sliding friction angle. The angle of repose is equal to the angle of internal friction for loose materials such as sand which lack cohesion
extended data
determination method of internal friction angle
in order to determine the internal friction angle of granular materials, the Mohr envelope of this material must be determined by experiment. Two methods can be used to determine the Mohr envelope of granular materials
Triaxial compression test the triaxial compression test device is developed by using the device to study the shear characteristics of soil. When the device is used for shearing test of bulk materials such as grain, the pre compacted grain is sealed in the rubber film and put into the compression chamber. The pressure in the compression chamber is graally increased to a predetermined pressure. The axial cutting load is applied to the grain column by universal testing machine or other loading device In this way, the grain column is subjected to air pressure in the radial direction σ Under the combined action of compressed air pressure and axial load in the circumferential direction, the failure time is less than 3 σ The value of 1 can be measured by recorder. Repeat the above procere to get different results σ Principal stress of grain column failure at3 σ The Mohr envelope of bulk material in a certain compaction state is obtained Direct shear test
direct shear test can be carried out on the shear apparatus shown in the figure. The shearing instrument consists of three basic parts: shearing groove, loading device and recorder. The shearing groove comprises a base, a shearing ring and a top cover. The normal pressure is applied to the shear ring by the vertical compaction load, and the shear force is applied to the shear ring by the electric or mechanical transmission device. The transmission device is equipped with a force sensor or dynamometer to measure the shear stress acting on the contact plane between the base and the shear ring
reference source : network cohesion
reference source : network internal friction angle
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in triaxial shear test, the specimen has a clear and flat shear plane, and the angle between the shear plane and the maximum principal stress plane is about 60 degrees. AFwdJte9e
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according to the regression analysis of the test results, the relationship between the cohesion c and the unconfined compressive strength FCU of cement soil is approximately a power function, and the formula is as follows: C = 0.2813 * (FCU ^ 0.7078). The condition of the equation is: FCU = 0.3 ~ 1.3mpa& gt; w< &# 39; 0
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compressive molus of cement soil: when the vertical stress reaches 50% unconfined compressive strength, the ratio of stress to strain of cement soil is called deformation molus E50 of cement soil. When FCU = 0.1 ~ 3.5Mpa, E50 = 10 ~ 550MPa. According to the linear regression analysis of the test results, it is obtained that E50 = 126fcu] 3sp w {= ^ (
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the same explanation is also given in the book of highway foundation treatment manual Foundation treatment and underpinning technology - the third edition has calculation examples for foundation pit slope treatment with mixing piles.
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