How to calculate the cohesion of soil

1. The internal friction angle is measured by triaxial test. Step 1: fix the confining pressure, that is, the small principal stress (the small principal stress and the medium principal stress in the ordinary triaxial test are equal), and add the axial pressure until the specimen is destroyed, so as to determine the large principal stress. In this way, a group of small principal stress and large principal stress are obtained. Step 2, increase the confining pressure twice to determine the large principal stress of soil samples under the two confining pressures, and then get the values of two groups of small principal stress and large principal stress. Step 3, make Mohr circle according to the three groups of principal stress values. Step 4, draw the common tangent of three different Mohr circles above the coordinate axis. The angle between the common tangent and the horizontal direction is the internal friction angle, and the intercept between the common tangent and the Y axis is the cohesion. If you still don't understand, please continue to ask. If you solve your problem, please adopt it.

2. 1. Shear strength of cement soil: the shear strength of cement soil increases with the increase of compressive strength. When FCU = 0.30 ~ 4.0Mpa, its cohesion c = 0.10 ~ 1.0MPa, which is generally about (20 ~ 30)%, and its internal friction angle changes between 20 ~ 30 degrees. &# 39; S/g  mn
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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.

3. tf=atanp+c

tf'= a' tanp'+ c'
it was originally indicated by Greek letters, but it doesn't seem to come out here
shear strength = normal stress * Tan internal friction angle + cohesion
the following formula is effective, and it is used more now, which is close to the actual situation.

4. Shear strength of cement soil: the shear strength of cement soil increases with the increase of compressive strength. When FCU = 0.30 ~ 4.0Mpa, its cohesion c = 0.10 ~ 1.0MPa, which is generally about (20 ~ 30)%, and its internal friction angle changes between 20 ~ 30 degrees.

5. The internal friction angle is about 20 and the cohesion is more than 20

6. Drucker Prager model can reflect clay, and the parameters in Drucker Prager model have the input terms of internal friction angle and cohesion. The material follows Coulomb Moore criterion

7.

According to engineering experience, the internal friction angle of silty clay is calculated φ Generally 18-25 ° Friction coefficient f = Tan φ= 46), and the cohesion c is generally 5-10kpa

The internal friction angle of silty clay is generally higher than that of clay, but its cohesion is lower than that of clay, and its value is often different e to the different particle size (i.e. viscosity) and water content of silty clay

extended data:

characteristics of silty clay:

timeliness is an important feature of soft soil deformation, which is mainly given by the stress of soft soil in the historical process and its own physical properties. Due to the timeliness of soft soil deformation, when the structure is built on the soft soil foundation, the settlement may graally increase with the passage of time, resulting in problems such as structural stability of the structure, affecting the normal use of the structure, and even leading to serious accidents such as damage and collapse of the structure

8. It seems to calculate the effective stress. That is to subtract the pore water pressure!

9. Lime, sand and soil are stronger than clay

10.

Internal friction angle of silt φ Generally 18-25 °， The cohesion is generally 5-10kpa

Internal friction angle of

round soil φ Generally 18-22 °， The cohesion is very small, which can be regarded as 0

The value of internal friction angle depends on the frictional resistance and interlocking action between soil particles, and the internal friction angle reflects the frictional resistance property of soil. Cohesion is the characteristic index of cohesive soil, which includes the original cohesion formed by the molecular gravity between soil particles and the solidified cohesion formed by the cementation of compounds in soil

Therefore, internal friction angle and cohesion are two mechanical indexes of soil shear strength. The shear strength of soil refers to the ultimate resistance of soil to shear failure. The essence of the strength of soil is the shear capacity of soil

Shear strength index of

soil internal friction angle φ、 Cohesion c φ—— Internal friction angle of soil ° C -- cohesion of soil (kPa)

φ、 C is related to the properties of soil, the experimental methods and conditions. Therefore, when we talk about the strength index, we should indicate its test conditions Extended data:

the shear strength of soil can be considered to be composed of internal friction between particles and cohesion caused by molecular gravity of cement and bound water film, Among them, the interaction among clay particles, water and electricity system is the most common. The interaction between particles may be attractive force or repulsive force

The cohesive force of

soil is e to the combined action of attraction and repulsion between soil particles. Gravity in clay mainly includes the following types:

1, electrostatic gravity

it includes Coulomb force and ion electrostatic force. Because the clay mineral particles are flaky, they have negative charges in the plane part and positive charges in the corners of both sides, and they will attract each other when they contact each other

The van der Waals force is the intermolecular attraction. The opposite dipole attraction between the polarizing molecule and the adjacent polarizing molecule may be inced. When the polarizing molecule approaches the nonpolarizing molecule, it may also ince the latter to attract the opposite dipole

The cementation between particles is a kind of chemical bond. Intergranular cementation includes oxides of carbon, silicon, lead and iron and organic mixtures. These cementitious materials may come from the soil itself, i.e. formed in the process of mineral dissolution and reabsorption, and may also come from the water solution in the soil

When the normally consolidated soil is unloaded after consolidation and becomes overconsolidated soil, its shear strength does not decrease proportionally with the decrease of effective normal stress, but retains most of the strength

The cohesion does not come from the cementation and chemical bonding between clay particles, but from the friction strength as cohesion. It includes the strength caused by suction in unsaturated soil and the strength of occlusal performance in coarse-grained soil