ONE DIMENSIONAL CONSOLIDATION TEST

A small Insight

DECEMBER 22, 2015

One Dimension Consolidation Test

1 Azaz Ahmed

ONE DIMENSIONAL CONSOLIDATION TEST

To determine

Voids ratio and Coefficient of volume change

Coefficient of consolidation

Coefficient of permeability

1. VOIDS RATIO FOR APPLIED PRESSURE

Use the ‘Height of Solids Method’ for calculation of final void ratio at the end of each pressure

increment.

Calculation of Dial Change, ΔH

∆𝐻 = 𝐻𝑗 − 𝐻𝑖

Here Hj and Hi are the consecutive dial gauge readings.

Calculation of Height of solid specimen, Hs

𝐻𝑠 =𝑊𝑑

𝐺 × 𝐴

Here Wd is the weight of dried specimen, A is cross sectional area and G is the Specific Gravity

of soil.

Calculation of voids ratio, e at each pressure interval

𝑒 =𝐻 − 𝐻𝑠

𝐻𝑠

Table for Calculation of Voids ratio by height of solids method

Applied

Pressure σ’

(kN/m2)

Final Dial

Reading

(10-2mm)

Dial Change

ΔH

(mm)

Specimen

Height,

H=H1±ΔH(mm)

Height of Voids

H-Hs

(mm)

Voids ratio

𝑒 =𝐻 − 𝐻𝑠

𝐻𝑠

Remarks

0.0 10.0 20.0 50.0 100.0 200.0 400.0 600.0 800.0 0.0

*Applied Pressure, σ” should be in kN/m2.

One Dimension Consolidation Test

2 Azaz Ahmed

2. CALCULATION OF VOLUME CHANGE (THICKNESS METHOD)

The coefficient of volume change mv can be calculated as

𝑚𝑣 = −∆𝐻

𝐻𝑜×

1

∆𝜎′

*mv is expressed in m2/kN

3. COEFFICIENT OF CONSOLIDATION

Denoted as cv

Determined by comparing the characteristics of the theoretical relationship between Tv

and U to the relationship between elapsed time t and degree of consolidation of

specimen in laboratory.

Square root time fitting method is used

Tv is the constant known as time factor

U is the degree of consolidation expressed in percentage as U(%)

Square root of time fitting method

It consists of drawing the curve between root of time √𝑡 as abscissa and the dial reading R,

representing the compression of the specimen, as ordinate for any pressure increment in the

consolidation test.

Determination of coefficient of consolidation

Elapsed time

t (minutes)

Dial Reading

R (10-2) √𝑡

Prepare Time-Consolidation Curve from above table

Square root of time is plotted as abscissa

Dial reading is plotted as the ordinate

One Dimension Consolidation Test

3 Azaz Ahmed

Time Consolidation curve

Ro corresponds to the time t=0 and U=0

The curve is straight up to U(60%)

Abscissa at U(90%) is equal to 1.15 times the abscissa at U(60%)

The straight line portion (line A) is produced back to meet ordinate at Rc

Initial consolidation equals difference between Rc and Ro

Abscissa of line B equals 1.15 times of line A

Intersection of Line B with consolidation curve gives point P

Point P corresponds to U (90%) with designated dial readings as R90 and t90 respectively

d = average drainage path for the pressure increment

𝑑 =1

2× [

𝐻𝑖 + 𝐻𝑓2

]

One Dimension Consolidation Test

4 Azaz Ahmed

Time Factor (Tv)90 is obtained from table below

t90 is obtained from point P corresponding to U(90%)

Calculation of Coefficient of Consolidation

𝑐𝑣 =(𝑇𝑣)90𝑡90

× 𝑑2

4. COEFFICIENT OF PERMEABILITY

It is usually calculated as

𝑘 = 𝑐𝑣 ×𝑚𝑣 × 𝛾𝑤

Here k is the coefficient of permeability, cv is the coefficient of consolidation, mv is the

coefficient of volume change and γw is the unit weight of water.

REFERENCES

Punmia B.C., Jain A.K., and Jain A.K. “Soil Mechanics and Foundations” Laxmi Publications

(P) limited, ISBN: 81-7008-791-0, pp 339-394