An insight to the One dimension consolidation test. The processes is summarized from the book "Soil Mechanics and Foundations" by Punmia et al. It def...
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ONE DIMENSIONAL CONSOLIDATION TEST A small Insight
DECEMBER 22, 2015
Azaz Ahmed
One Dimension Consolidation Test
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
∆ = − Here H j and Hi are the consecutive dial gauge readings.
Calculation of Height of solid specimen, H s
= × Here Wd is the weight of dried specimen, A is cross sec tional area and G is the Specific Gravity of soil. Calculation of voids ratio, e at each pressure interval
= − Table for Calculation of Voids ratio by height of solids method Applied Pressure σ’ (kN/m2) 0.0 10.0
Final Dial Reading (10-2mm)
Dial Change ΔH (mm)
20.0 50.0 100.0 200.0 400.0 600.0 800.0 0.0 *Applied Pressure, σ” should be in kN/m2.
Specimen Height, H=H1±ΔH(mm)
Height of Voids H-Hs (mm)
Voids ratio
− =
Remarks
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Azaz Ahmed
One Dimension Consolidation Test 2. CALCULATION OF VOLUME CHANGE (THICKNESS METHOD)
The coefficient of volume change m v can be calculated as
1 = − ∆ × ∆′ *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
√ 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)
Prepare Time-Consolidation Curve from above table
Square root of time is plotted as abscissa
Dial reading is plotted as the ordinate
√
2
Azaz Ahmed
One Dimension Consolidation Test
Time Consolidation curve
R o 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 R c
Initial consolidation equals difference between R c and R o
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 re adings as R 90 and t90 respectively
d = average drainage path for the pressure increment
= 21 × [ +2 ]
3
Azaz Ahmed
One Dimension Consolidation Test Time Factor (T v)90 is obtained from table below
t90 is obtained from point P corresponding to U(90%)
Calculation of Coefficient of Consolidation
= (90)90 × 4. COEFFICIENT OF PERMEABILITY
It is usually calculated as
= × × 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
