CONSOLIDATION AND SETTLEMENT ANALYSIS - FOR GATE

CONSOLIDATION AND SETTLEMENT ANALYSIS

             

 

Soil consolidation refers as the mechanical process by which soil changes its volume.

In other words soil consolidation is the process in which the volume of soil decreases due to removable of water molecules from the pores of the soil, It is the function of the effective pore water pressure. When the water are removed from the soil then soil particles are packed more closely to each other under the action of static load. This term was introduced by the karl Tarzaghi and he is also known as  “the father of soil mechanics”.

When the load is  applied on the saturated soil there is an increase in the pore water water pressure and this excess pressure is dissipated as water drains away from the soil void’s and pressure transferred to the soil that result in the settlement of soil.

DEFINITION OF SOIL CONSOLIDATION

Soil consolidation refers the process by which the volume of saturated soil it may be fully or partially saturate is decreases under pressure of static load.

Odeometre is the device that uses to measure the soil consolidation.

The consolidation is mainly divided into three stages which are discussed below :-

1-     Initial consolidation of soil

2-     Primary consolidation of soil

3-     Secondary consolidation of soil

 

INITIAL CONSOLIDATION OF SOIL

Initial consolidation is the sudden reduction in the volume of the soil after  load applied on the soil because of expulsion  air from the voids of soil . the Initial consolidation is a elastic in nature.

PRIMARY CONSOLIDATION OF SOIL

Primary consolidation is the main phase of the soil , the compression and expulsion of pore water are done in this phase . Primary consolidation is the time settlement phenomenon that means it increase the passing times. Primary consolidation is non-elastic in nature.

SECONDARY CONSOLIDATION OF SOIL

The Secondary consolidation stage starts after the Initial and Primary consolidation of the soil. This stage starts when the air present in the soil voids and pore water are expelled out.

It is complex process and thought to be done because of the adjustment of internal structure of soil.

KARL TERZAGHI THEORY OF CONSOLIDATION

Karl Terzaghi who is known as the father of soil mechanics gives a theory that is known as the Karl terzaghi theory of consolidation of soil . This theory computes the amount of consolidation occurs in the soil, after any given time t.

It based on the fact that consolidation is directly based on the expulsion of pore water.

Assumption of Karl Terzaghi theory

1-     The soil is Homogeneous and Isotropic.

2-     The flow is one dimensional that is vertical.

3-     The vertical flow may be one way flow or two way flow.

4-     The change will happen in depth.

5-     The plastic readjustment of soil is required.

6-     Darcy’s law is valid

7-     Permeability is constant over the range of effective stress

 

DRAINAGE PATH

The drainage path is the path through which water expelled out from the soil.

The drainage path of two types

1-One way drainage path

2-Two way drainage path

ONE WAY DRAINAGE PATH

In one way  drainage path water goes out of soil only through one way it may be upward or downward flow.

The value of drainage path is the thickness of soil mass.

TWO WAY DRAINAGE PATH

In two way drainage path water goes out of soil through both  upward and downward flow.

The value of drainage path is half the thickness of soil mass because water expelled out through two path.

 AS PER TERZAGHI :-

 

 

C_V = COEFFICIENT OF CONSOLIDATION

M_V = COEFFICIENT OF VOLUME OF COMPRESSIBILITY

K = HYDRAULIC CONDUCTIVITY

DEGREE OF CONSOLIDATION

A degree of consolidation is defined in terms of time and drainage path. A degree of consolidation is directly Proportional to time and inversely proportional to square of drainage path.

There are four cases which described he degree of consolidation.

CASE-1

                    BASED ON THE SETTLEMENT

 

⃤  H = Ultimate settlement at T=∞ after 100% degree of consolidation

⃤   G = It is the settlement at time T  Where (0<T<∞)

CASE-2

           DEGREE OF CONSOLIDATION BASED ON THE VOID RATIO

                        

_e༠ = Initial void ratio at t=0

 _e100 = void ration after 100% degree of consolidation at t=∞

e = void ratio at any time 0<t<∞

CASE-3

DEGREE OF CONSOLIDATION BASED ON PORE WATER PRESSURE

u༠ = pore water pressure at t=0

u100 = pore water pressure at at t=∞ after 100% degree of consolidation

 

TIME FACTOR

Time factor is defined as the time which relates consolidation and  the pore water pressure and time required to that degree of consolidation.

 

Where,

C_V  = coefficient of consolidation

D² = drainage path

T = time required for given drainage