Calculations

<< Click to Display Table of Contents >>

Navigation:  Chapter 9 Geotechnical Data Management > Geotechnical Tests > Entering Test Data > Rock Tests > Unconfined Compressive Strength >

Calculations

Previous pageReturn to chapter overviewNext page

The following calculations are used in this test:

 

Deformation

 

The lateral and axial deformations can be specified directly or using deformation dial readings. When using dial readings they are converted to actual deformations using a dial constant.

 

DL = (RLi - RL) * LDC                        Lateral Deformation

 

DA = (RA - RAi) * ADC                        Axial Deformation

 

where,

DL        = Lateral deformation

DA        = Axial deformation

RL        = Lateral dial reading

RLi        = Initial lateral dial reading

LDC        = Lateral dial constant

RA        = Axial dial reading

RAi        = Initial axial dial reading

ADC        = Axial dial constant

 

 

Axial Load

 

The axial loads can be specified directly or using readings from a load ring. When using readings from a load ring the readings are converted to axial loads either using load ring constants or a linear equation.

 

Load Ring Constant

 

If P < Crossover        P = R * LRC1                

 

If P > Crossover                P = Crossover * LRC1 + (R - Crossover) * LRC2

 

Linear

 

P = M * R + C

 

where,

P        = Axial load

R        = Axial dial reading

LRC1        = Load ring constant 1

LRC2        = Load ring constant 2

M        = Linear multiplier

C        = Linear constant

 

 

Axial Strain

 

εa = (DA - DA0) / h                

 

where,

εa        = Axial strain

DA        = Axial deformation

DA0        = Initial axial deformation (first deformation)

h        = Sample height

 

 

Lateral Strain

 

εl = (DL - DL0) / d                        Diameter lateral strain method

 

εl = ((DL/π) - DL0) / (d/π)                Circumference lateral strain method

 

where,

εl        = Lateral strain

DL        = Lateral deformation

DL0        = Initial lateral deformation (first deformation)

d        = Sample diameter

 

 

Axial Stress

 

σa = P / A

 

where,

σa        = Axial stress

P        = Axial load

A        = Sample cross-sectional area

 

 

Compressive Strength

 

Compressive strength = maximum σd

 

 

Water Content

 

wi (%) = 100 * (Mbwt - Mbdt) / (Mbdt - Mbt)                

 

where,

wi        = Initial percentage water content

Mwt        = Mass of tare and wet specimen

Mdt        = Mass of tare and dry specimen

Mt        = Mass of tare

 

 

Dry Density

 

ρd = Mw / V / (1+ w)

 

where,

ρd        = Dry density

Mw        = Wet sample mass

V        = Sample volume

w        = Water content

 

 

Dry Unit Weight

 

γd = ρd * γw

 

where,

γd        = Dry unit weight

γw        = Unit weight of water (9.807 kN/m3)

 

 

Saturation

 

Si (%) = 100 * Vwi / Vvi                                

 

where,

Si        = Initial saturation

Vwi        = Initial volume of water in sample = (Mw - Ms) / ρw

Vvi        = Initial volume of voids = Vi - Vs

Vs        = Volume of solids = Ms / (SG * ρw)

Ms        = Mass of solids = Mw / (1 + wi / 100)

ρw        = Density of water (1.0 g/cm3)

SG        = Specific gravity

 

 

Void Ratio

 

ei = Vvi / Vs                                        

 

where,

ei        = Initial void ratio