What are the methods included in the mechanical analysis method in the subgrade slope stability anal

The application conditions of each calculation method are different, and the specific selection is based on the form of failure.

Answer] :d Analysis] This question has a certain degree of professionalism, and it is also difficult for candidates with certain professional basic knowledge. It mainly assesses the knowledge points of the definition and application of internal friction angle in geotechnical parameters.

Internal friction angle: the friction characteristics formed by the mutual movement and gluing of particles in the soil, and its value is the angle between the strength envelope and the horizontal line.

The internal friction angle is a shear strength index of soil deficiency, a very important concept in soil mechanics, and an important parameter of engineering design. The internal friction angle of the poor pants soil reflects the friction characteristics of the soil.

The internal friction angle can be mechanically understood as the critical self-stabilizing angle of the block on the inclined plane, and within this angle, the block is stable; Anything greater than this angle will cause the block to slide. Using this principle, the stability of the slope can be analyzed.

Therefore, the correct term of this problem is "d internal friction angle".

1. The compaction quality of the roadbed; The higher the compaction quality of the subgrade, the better the slope stability of the subgrade.

2. a filler for roadbed; The packing of the roadbed should be selected with good permeability and high strength.

3. The level of groundwater level; Where the higher the groundwater level, the greater the influence of the water stability of the roadbed, and the poor stability of the slope.

4. the slope ratio of the subgrade slope; The slower the slope, the better the stability of the subgrade slope.

5. The quality of temporary drainage and slope protection projects.

Answer]: The safety deficiency coefficient of the global arc sliding method is defined by the ratio of anti-sliding moment and sliding moment, and there are still many difficulties in the specific calculation. This method is simple to calculate, but because it ignores the force of soil strips, the calculated safety factor is small.

Because the Swedish strip division method ignores the forces on both sides of the soil strip and cannot meet all the equilibrium conditions, the calculated stability safety factor may be 10% 20% lower than that of other methods with strict hole resistance, and this error increases with the increase of the sliding arc center angle and pore water stress, and in serious cases, the calculated safety factor is half smaller.

After the Bishop strip division method divides the soil slope vertically, the safety factor is defined by the ratio of the anti-slip shear force to the sliding force of the soil strip, which is still based on the premise that the sliding surface is an arc, and the force on both sides of the soil strip is considered, and the calculation results are reasonable. In the analysis, the balance of the vertical force of each soil strip and the moment balance condition of the whole sliding soil were used successively to avoid the EI

and the location of its application point, and assume all xi's

The average is equal to zero, which simplifies the analysis process, but again, it does not meet all the equilibrium conditions, and it is not a strict method, so the error is about 2% 7%. At the same time, the Bishop strip method can also be used for total stress analysis, i.e. the pore water pressure UI is omitted from the above formula

UT and use the total stress intensity C, which can be calculated. The calculation accuracy of this method is high.

The Yangbu strip division method is also called the non-circular sliding method, and the sliding surface is an arbitrary curve. After dividing the soil slope vertically, the safety factor is also defined by the ratio of the anti-slip shear force to the sliding force of the soil strip, and it is assumed that the tangential force on the sliding surface is equal to the shear strength exerted by the soil on the sliding surface, and the action point of the normal force on both sides of the soil strip is located at the height of 1 3 above the bottom surface of the soil strip. It can also be applied to arc sliding.

The method provided by the highway code is based on the simple strip division method, and the ratio of shear force to sliding force is also used to define the safety factor, but the force between the soil strips is not considered, and the stable safety factor obtained is safe.

<>1. Basic situation of rock slope stability analysis

The general understanding of slope stability is that the sliding body in the slope fails along the sliding surface, that is, the ratio of anti-sliding force to sliding force. When the ratio is equal to 1, it is the ultimate equilibrium state; greater than 1, it is a steady state; If it is less than 1, it is unstable. This is a concept of stability in the failure of rock mass.

Second, the basic steps of rock slope stability analysis:

The rock mass structure analysis method was used to divide the slope rock with ballast spike structure types, and the slope failure form was judged according to the type: the block structure slope was composed of multiple groups of structural planes, and the failure of block or wedge occurred (Fig. 1); Layered slopes, which are composed of a single layer or fault, have sliding failure along the plane; The fractured structure slope is composed of multiple groups of dense structural planes, and tracking failure occurs along multiple groups of structural planes (Fig. 3); Scattered structure slope generally refers to a severely weathered rock mass, and the failure form is approximately arc-shaped.

On the basis of the analysis of the rock mass structure, the mechanical analysis method is used to calculate the mechanical analysis method according to the stress conditions of the rock mass, such as the self-weight of the rock mass, the blasting force, the engineering force, the groundwater action, etc. The calculation methods include the limit equilibrium analysis method of the plane; Limit equilibrium analysis of wedge-shaped tetrahedra; The best method of combining the chiping polar projection and the solid proportional projection; Finite element method for stress and strain states of slope rock mass. These methods can give a quantitative evaluation of slope stability.

On the basis of mechanical analysis, from the aspect of geological genesis, the changes of rock properties, transportation, structural plane properties, groundwater dynamic properties and other factors with time are analyzed, the change trend of slope stability is judged, and reinforcement measures are proposed to ensure the stability of slope.

According to the comprehensive analysis results of the above steps, the slope design scheme is selected, and the technical demonstration and economic comparison are carried out to determine the reasonable stable slope angle.