Should geological survey with how many experimental criteria?

Should geological survey with how many experimental criteria?

Should geological survey with how many experimental criteria?

25/05/2021

Determining how many indicators depends on the designer, what parameters are needed. Therefore, the identification of 7 indicators, 9 indicators or 17 real indicators is not mentioned exactly. Below is a classification of 7 indicators, 9 indicators and 17 indicators in the most "common" way.

7, 9 AND 17 MECHANICAL INDICATORS OF SOIL ???

 

07 physical and mechanical parameters of soil applied to soil samples that are not intact and have no stickiness

  1.  1. Particle composition of soil (TCVN 4198 - 2014)
  2.  2.Soil moisture (TCVN 4196 – 2012)
  3.  3. Natural density (wet density) of soil (TCVN 4202 – 2012)
  4.  4. Density of soil (TCVN 4195 – 2012)
  5.  5.Calculation of soil compaction (TCVN 4200 – 2012)
  6.  6. Angle of internal friction of the soil (TCVN 4199 – 1995)
  7.  7. Soil cohesion (TCVN 4199 – 1995)

For non-cohesive sandy soil, there are experiments to determine the natural resting angle (dry rest angle and wet rest angle) by sand pouring method (TCVN 8724 – 2012) and there are no results of internal friction angle and adhesive force.

09 physico-mechanical parameters of soil applied to intact soil samples include

  1.  1. Particle composition of soil (TCVN 4198 - 2014)
  2.  2.Soil moisture (TCVN 4196 – 2012)
  3.  3.Natural density (wet soluble) of soil (TCVN 4202 – 2012)
  4.  4.Density of soil (TCVN 4195 – 2012)
  5.  5.Liquid limit of soil (TCVN 4197 – 2012)
  6.  6. Plastic limit of soil (TCVN 4197 – 2012)
  7.  7.Calculation of soil compaction (TCVN 4200 – 2012)
  8.  8.Angle of internal friction of the soil (TCVN 4199 – 1995)
  9.  9.Soil cohesion (TCVN 4199 – 1995)

For non-cohesive soils (clay content < 10%) the yield-plasticity test will not be performed.

For mixed clay containing a lot of gravel (content > 30%), there will be no shear and compression test. In case of gravel with content > 50%, there will be no flow-plasticity test.

17 physico-mechanical parameters of soil, including 09 experimental parameters and 08 parameters calculated from 09 experimental criteria

  1.  1. Particle composition of soil (TCVN 4198 - 2014)
  2.  2.Soil moisture (TCVN 4196 – 2012)
  3.  3. Mass (density) volume of soil (TCVN 4202 – 2012)
  4.  4. Density of soil (TCVN 4195 – 2012)
  5.  5.Dry density of soil
  6.  6. The buoyant capacity of the soil
  7.  7. Soil void ratio
  8.  8. Soil porosity
  9. 9.Saturation of the soil
  10.  10.Liquid limit of soil (TCVN 4197 – 2012)
  11.  11. Plastic limit of soil (TCVN 4197 – 2012)
  12.  12.Plasticity Index                                                                            
  13.  13. Viscosity                                                                                    
  14.  14.Angle of internal friction of the soil (TCVN 4199 – 1995)
  15.  15.Soil cohesion (TCVN 4199 – 1995)
  16.  16. Soil compaction coefficient (TCVN 4200 – 2012)
  17.  17.Module of total deformation of the soil                                        

CONTENTS OF SOME MECHANICAL INDICATORS OF SOIL

To understand these criteria, it is necessary to consider the relationship between the phases in the soil.

           Soil consists of solid, liquid and gaseous phases. The solid phase can be mineral crystals, organic matter, and both. The spaces between the solid phase are called voids. In the solid phase, water predominates and air predominates in the gas phase. If the voids in the soil are filled with water, it is called saturated soil, otherwise it is unsaturated. If all the voids are air, we call it dry soil

Thus, total volume ( V ) of soil samples including solid phase volume ( S ) , the volume of liquid ( W ) and gas-phase volume ( a )

      V = V s  + V w  + V a  = V s  + V v

 

Where  v  = V w  + V a  is the pore volume.

The mass of the soil sample includes the mass of the solid phase ( s ) and the mass of the liquid phase ( w ) . Therefore:

  W = W S  + W W

 

1. Soil moisture (w) - (Water content or Moisture content)

Is the amount of water contained in the soil, expressed in (%) of the dry soil mass.

2. Soil void ratio (e) – (Void ratio)

Is the ratio between the volume of pores in the soil and the volume of soil particles in that soil sample.

3. Porosity (n) – (Porosity)

Soil porosity is the ratio between the pore volume in the soil and the soil volume in its natural state.

4. Particle density (G s ) – (Specific gravity)

It is the ratio of the mass of a unit volume of soil in the solid, completely dry and tightly packed state without voids.

In other words, it is the ratio of the weight of an absolute dry solid particle to the weight of water of the same volume.

5. Soil Saturation (S) – (Degree of saturation)

It is the ratio between the volume of water in a soil mass and the volume of soil pores in that soil mass.

6. Natural density (wet density – natural volumetric weight) – (Unit weight – Bulk unit weight)

Is the mass of a unit volume of soil with natural texture and moisture.

7. Saturated unit weight

Is the density of the soil when the pores of the soil are filled with water. In this case the soil consists of only two components: solid particles and water.

8. Effective unit weight of the soil

Is the density of the soil when submerged under free water, i.e. the ratio between the floating weight of the solids in the soil mass and the volume of that soil mass.

9. Dry unit weight of soil

The dry density of the soil is also known as the dry weight of the soil. Is the ratio between the mass of solid particles in the soil and the volume of the soil in its natural state.

10. Plasticity Index - Liquidity Index

           The physical and mechanical properties of cohesive soils are associated with four distinct states: hard, semi-hard, plastic, and flowing. If we plotted the mass with water content as shown below, we can determine the initial liquid state is  point A .

           At  point B , the soil becomes so hard that it is no longer able to flow. The water content (moisture) at the point  B boundary   is called  the liquid limit  ( LL ).

 As the soil continues to dry, there is a wide range of water content at which the soil can be molded into any desired shape without cracking. Soils in this state are said to exhibit plastic behavior, the ability to continuously deform without cracking. But if drying is continued beyond the water content range for plastic behavior, the soil becomes semi-hard. Soil cannot be cast now without cracks appearing. The water content at which the soil changes from plastic to semi-hard is called  the plastic  limit ( Plastic limit - symbol PL ).

          The range of water content over which the soil plastically deforms is called  the plasticity  index ( PI ):

    PI = LL – PL

 

As the soil continues to dry, it turns into a solid state called the hard state. In this state, no further volume change occurs since almost all the water in the soil has been removed. The water content at which the soil changes from semi-hard to hard is called the  shrinkage limit (symbol SL) . Shrinkage limits are useful for determining soil swelling and shrinkage. The yield and plastic limits are called the Atterberg limits; named after the initiator, Swedish soil scientist, A. Atterberg (1911).

          We can associate specific strength properties with each state of the soil. In the flowing state, the soil has the lowest strength and greatest deformation. In the hard state, the soil has the greatest strength and the lowest deformation. A measure of the intensity of land using Atterberg limits called  viscosity  ( Liquidity Index - symbol LI ).

11. Internal friction angle and soil cohesion (Internal friction angle – Coefficient cohesive)

Two parameters of internal friction angle and soil cohesion represent the shear strength of the soil.

To determine the shear strength of the soil, one can use the direct shear test on a plane cutter.

           After compressing the above soil sample with a certain vertical load P, wait for the soil sample to completely stabilize to settlement deformation. Then cut the soil sample directly with increasing horizontal load to a certain maximum position ( Q ) , the soil sample is completely cut. The value of shear stress  τ  at a point on the slip surface, when the soil is sliding under compressive pressure  σ  is determined by dividing the shear force by the cross-sectional area of ​​the soil sample.

where  F  is the cross-section of the soil sample

           Just like that, we perform many experiments to determine the maximum shear strength of the soil for each different compressive pressure (usually 3-4 samples). Based on soil shear test results, can build graphs of the dependence between the compressive stress  σ  and shear stress  τ .

  • For loose land:

Inside:

S  is the maximum shear strength of the soil;

τ gh  is the ultimate shear stress;

σ  is the compression pressure;

φ  is the internal friction angle of the soil.

            The above expression is the expression of shear resistance of loose soil first discovered by CA Coulomb in 1773 called the shear law of soil, also known as Coulomb's law.

“ The ultimate shear strength of loose soil is the frictional resistance, which is proportional to the vertical compressive pressure ”

  • For sticky soil

           Cohesive soil differs from loose soil in that the soil particles are bound together by adsorbed water films, colloidal substances and cementitious substances. Therefore, even when the shear strain is very small, the cohesive soil already has a certain shear strength. Therefore, for cohesive soils, in addition to the internal friction component, there is also a cohesive force component that also participates in the shear resistance of the soil.

By experiments similar to loose soils, a graph of the dependence between shear stress  τ  and vertical compressive stress is obtained in the form of a straight line that cuts through the vertical axis by a distance of C.

Where: C is the unit cohesive force of the soil

Coulomb's law for cohesive soils is stated as follows:

“The maximum shear strength of cohesive soils is a first-order function of vertical compressive pressure and consists of two components: the cohesive force C is independent of the vertical compressive pressure and σ.tgφ is proportional to the compressive force. straight."

12. Coefficient of compressibility and Modulus of Deformation

Consider a elemental soil sample of height h and assume that this elemental soil sample consists of two parts: the solid particle volume and the pore volume corresponding to the initial void ratio e 0 . Under the effect of load P, the deformation of the soil sample is caused only by the decrease in pore volume, while the solid particle volume is unchanged.

But V = h.F  and  V = hF 

F  is the cross-sectional area of ​​the soil sample;

Δh  is the height difference before and after compaction of the soil sample.

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