SPT and VST- By Daanyal Umar.pptx

STANDARD PENETRATION TEST (SPT)
FIELD VANE SHEAR TEST (FVST)
May 27, 2021
UNIVERSITY OF ENGINEERING AND TECHNOLOGY PESHAWAR
Peshawar, Pakistan
Engr. Daanyal Umar
BSc. Civil Engineering UET PESHAWAR, MS Geotechnical Engineering NUST
Lecturer, Civil Engineering Department
www.uetpeshawar.edu.pk Department of Civil Engineering

STANDARD PENETRATION TEST
(SPT)
&
Estimation of Shear Strength Parameters

 INTRODUCTION
• The test was first introduced by the Raymond
Pile Company in 1902 and remains today as
the most common in-situ test performed
worldwide.
• In 1947, Terzaghi named the Raymond
Sampler procedure as the ‘‘Standard
Penetration Test’’ (SPT) in a presentation
titled ‘‘Recent Trends in Subsoil Exploration,’’
which he gave at the 7th Conference on Soil
Mechanics and Foundation Engineering at
the University of Texas at Austin.
• The first published SPT correlations
appeared in Terzaghi and Peck (1948).
These were soon followed by correlations
relating SPT blow counts to consistency for
silts and clays and relative density for sands
in Peck et al. (1953). Fig. 1. Standard Penetration Test
For further details about development of SPT: Refer to Subsurface Exploration Using the
Standard Penetration Test and the Cone Penetrometer Test by J. DAVID ROGERS.
The standard procedures for
the SPT are detailed in
• (US)
ASTM D 1586
AASHTO T 206
• (UK and Europe)
EN ISO 22476, Part 3.

 SPT STANDARD PROCEDURE (ASTM)…
Fig. 3. Sequence of driving split barrel sampler during the standard Penetration Test
(Soucre: Professor Paul Mayne, Georgia tech.)
The SPT can be halted when a total of 100 blows have been counted or if the number of
blows exceeds 50 in any given 6 in (150 mm) increment, or if the sampler fails to advance
during 10 consecutive blows. SPT refusal is defined by penetration resistances exceeding
100 blows per 2 in (50 mm), although ASTM D 1586 has re-defined this limit at 50 blows
per 1 in (25 mm).

 SPT SAMPLER AND SPT SHOES
Drive samplers usually employ three types of cutting heads, or shoes, shown here. The sharp
tapered heads are intended for soft soil sampling, while the more blunt tips are designed for
greater longevity when sampling granular soils.

SPT SAMPLE OBTAINED AT FIELD
 SITE INVESTIGATION PROCEDURE ADOPTED IN THE FIELD
1- Selection of Depth & No. of Boreholes.
2- Boring to the required depth by any of the boring
methods.
3- Installation of Casing if required.
4- Removing the drilling tool/bit and
installation of sampler.
5- Conducting SPT at regular depth intervals.
6- Marking & Preserving Soil Samples.
7- Bore Closure.
8- Transportation of soil samples to the Lab.
1-BH-No:
2-Date:
3-Project Name:
4-Sample No.:
5-Depth:

 SELECTION OF DEPTH & NO. OF BOREHOLES

 SELECTION OF DEPTH & NO. OF BOREHOLES…

 SPT PROCEDURE IN FIELD…
• Boringto the required depthby any of the followingboringmethods.
1-Auger Boring.
(Hand operated or Power Driven)

2-Percussion Boring.
(Light or Heavy)

3-Rotary Drilling

 SIGNIFICANCE & USE OF SPT
• Soil borings + laboratory testing.
(most reliable method available to
obtain accurate shear strength
properties for subsurface soils.)
• Many projects, due to limited
budgets, tight schedules, or lack of
concern, do not usually have the
luxury of getting laboratory
recommendations.
• The only subsurface exploration
performed consists of soil borings
with a log recording the soil type and
classification, depth of water table
and SPT blow counts.
• Lack of lab data forces the designer
to estimate the properties of the soil.
SPT
Blows per 30cm
6 6 6
0.0 0.0
50.0 50.0
L E G E N D:
Standard Penetration Test CPT Cone Penetration Test
SPT Number C CPT Number
N Value > 50 UDS Undisturbed Sample
GEOTECHNICAL ENGINEERING DEPARTMENT
6
7
FILLING MATERIAL - Filling material consists of Clay
with by presense of Gravel and Boulder of unnatural
origion.
3
3
CLAY
Brown, Medium Stiff, Moist,
N
VALUES
(inchs)
Depth
(ft)
SAMPLE
TYPE
/
NO.
PROFILE
Subsurface Description
SPT
BLOWS
3.0
5.0 2 3
S-1
S-2
10.0 3 4
7
S-4
2
S-5
20.0 Brown, Stiff, Moist,
21
9
15.0
20.0
5
4
14
12
7
35.0
30.0
9
10.0
7
Remarks
5.0
25.0
40.0
SPT
40.0
45.0
5
35.0
15.0 S-3
Brown, Very Stiff, Moist,
BOREHOLE COMPLETED
30.0
25.0
Filling Material is
encountered upto 4ft
depth as identified by
presence of pieces of
bricks, Gravel and
Boulder of unnatural
origion.
S
SHEET 1 OF 1
R
45.0
0 10 20 30 40 50
Fig. 2. Sample BH-Log.
𝐍 𝐨𝐫 𝐍𝐟𝐨𝐫 𝐍𝐟𝐢𝐞𝐥𝐝

• There are many charts and tables available to make direct correlations between the
SPT blow count (N) and the angle of internal friction (Φ) and undrained cohesion (cu).
However, these estimations should be made by individuals who have a thorough
understanding of soil behaviors.
• The SPT can be used for all types of soil, but in general, the SPT is most often used for
cohesionless deposits. The SPT can be especially of value for soils where the sample
falls or flows out from the sampler when retrieved from the ground such as clean
sand.
 SIGNIFICANCE & USE OF SPT…
ADVANTAGES DISADVANTAGES
1• Obtain both a sample and an N-value 1• Disturbed sample (index tests only)
2• Simple and inexpensive 2• N-value is a crude number for analysis
3• Suitable in many soil types 3• Not applicable in soft clays & loose silts
4• Can be performed in weak rocks 4• High variability and uncertainty
5• Readily available throughout the world 5• Unreliable in gravelly soils
For further details: Refer to
1-Estimating Shear Strength Properties of Soils Using SPT Blow Counts: An Energy Balance
Approach by Timothy Brown and Hiroshan Hettiarachchi.
2-Manual on Subsurface Investigations: FHWA NHI-01-031.

Fig. 2. FACTORS AFFECTING THE N VALUES (NAVY, 1986)
 INFLUENCES ON SPT N-VALUES

 INFLUENCES ON SPT N-VALUES…
We have seen that influences on SPT N-values are due to
• Variations in the test apparatus & procedures
• Disturbance created by boring
• Soil type and properties into which sampler is driven
• Effective stress level
Corrections needs to be applied for these influences

 CONVERSION OF Nf TO N1 ,N60 & N1,60
𝐍𝟏 = 𝐍𝐟 ∗ 𝐂𝐍
𝐍𝟔𝟎 = 𝐍𝐟 ∗ 𝐂𝐄 ∗ 𝐂𝐁 ∗ 𝐂𝐒 ∗ 𝐂𝐑
𝐍𝟏,𝟔𝟎 = 𝐍𝐟 ∗ 𝐂𝐄 ∗ 𝐂𝐁 ∗ 𝐂𝐒 ∗ 𝐂𝐑 ∗ 𝐂𝐍
𝐂𝐄 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧𝐟𝐨𝐫 𝐇𝐚𝐦𝐦𝐞𝐫 𝐄𝐧𝐞𝐫𝐠𝐲.
𝐂𝐁 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 𝐁𝐨𝐫𝐞𝐡𝐨𝐥𝐞 𝐒𝐢𝐳𝐞.
𝐂𝐒 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧𝐟𝐨𝐫 𝐒𝐚𝐦𝐩𝐥𝐞𝐫 𝐔𝐬𝐞𝐝.
𝐂𝐑 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 𝐑𝐨𝐝 𝐋𝐞𝐧𝐠𝐭𝐡.
𝐂𝐍 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 𝐎𝐯𝐞𝐫𝐛𝐮𝐫𝐝𝐞𝐧.
𝐍𝟔𝟎 = SPT N value corrected to 60% of the theoretical free fall hammer energy

 𝐂𝐄 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 𝐇𝐚𝐦𝐦𝐞𝐫 𝐄𝐧𝐞𝐫𝐠𝐲.
If ERf =75(Calculatedinfield)= average transfered energy ratio
𝐂𝐄 =
𝟕𝟓
𝟔𝟎
= 𝟏.𝟐𝟓.

 𝐂𝐁 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 𝐁𝐨𝐫𝐞𝐡𝐨𝐥𝐞 𝐒𝐢𝐳𝐞.
 𝐂𝐒 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 𝐒𝐚𝐦𝐩𝐥𝐞𝐫 𝐔𝐬𝐞𝐝.
 𝐂𝐑 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 𝐑𝐨𝐝 𝐋𝐞𝐧𝐠𝐭𝐡.

• The primary way of using DMT
results is to interpret them in terms
of common soil parameters.
• In this upcoming section, we will
be discussing how we can get the
parameters of our interest i.e.
parameters required for calculating
settlement as well as bearing
capacity, from the DMT result.
• Parameters of interest can be seen
in the Table-2.
Corrected A Pressure (𝑷𝟎)
Corrected B Pressure (𝑷𝟏)
Material Index (𝑰𝑫)
Dilatometer Modulus (𝑬𝑫)
Unit Weight of soil (𝜸)
Total Stress (𝝈) and Effective Stress (𝝈′)
Horizontal Stress Index (𝑲𝑫)
Un-drained Shear Strength (𝑺𝒖)
Friction Angle (∅)
Vertical Drained Constrained Modulus (𝐌)
Table-2: PARAMETERS OF INTEREST
 𝐂𝐍 = 𝐂𝐨𝐫𝐫𝐞𝐜𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 𝐎𝐯𝐞𝐫𝐛𝐮𝐫𝐝𝐞𝐧.

 𝐂𝐎𝐑𝐑𝐄𝐂𝐓𝐈𝐎𝐍 𝐅𝐀𝐂𝐓𝐎𝐑𝐒 (𝐃𝐢𝐟𝐟𝐞𝐫𝐞𝐧𝐭 𝐒𝐨𝐮𝐫𝐜𝐞).

 N55,N70, N60 IN LITERATURE
• 𝐍𝟓𝟓 represents the corrected SPT reading with a standard energy ratio of 55%.
• 𝐍𝟕𝟎 represents the corrected SPT reading with a standard energy ratio of 70%.
• 𝐍𝟔𝟎 represents the corrected SPT reading with a standard energy ratio of 60%.
• For converting 𝐍𝟏 to 𝐍𝟐,
it should be noted that the Energy ratio x Blow Count = Constant for any soil, so
𝐄𝐫𝟏 ∗ 𝐍𝟏 = 𝐄𝐫𝟐 ∗ 𝐍𝟐
 𝐍𝟐 = (𝐄𝐫𝟏/𝐄𝐫𝟐) ∗ 𝐍𝟏
Using this relationship, we can readily convert any energy ratio to any other base, but
we do have to know the energy ratio at which the blow count was initially obtained.
𝐄𝐫 =
Actual hammer energy to sampler,𝐄𝐚
Input Energy,𝐄𝐢𝐧
∗ 𝟏𝟎𝟎
𝐄𝐢𝐧 = W ∗ H is based on the measured hammer velocity at impact with the anvil or as
measured energy in the drill rod just below the anvil.
1- Foundation Analysis & Design (Fifth Edition) by Joseph E. Bowles.
2-History of Progress: Selected U.S. Papers in Geotechnical Engineering edited by W. Allen
Marr.

 APPLICATION OF SPT-N VALUE…
For further details: Refer to Site Investigation (Second Edition) by C. R. I. Clayton, M. C.
Matthews and N. E. Simons.
G= Granular, C= Cohesive, R= Rock
• Liquefaction Analysis.
• Computation of Bearing Capacity and Settlements for Shallow & Deep Foundations.

But SPT is not likely to be abandoned for several reasons:
1. The test is very economical in terms of cost per unit of information.
2. The test results provides soil samples, which can be tested for index
properties and visually examined.
3. Long service life of the enormous amount of equipment in use.
4. The accumulation of a large SPT database that is continually expanding.
5. The results of the SPT have been correlated with a number of soil properties
to provide estimates of the values of those properties. The estimated values
are often used for preliminary designs in lieu of values obtained from tests
run specifically to determine those properties.
6. The fact that other methods can be readily used to supplement the SPT
when the borings indicate more refinement in sample/data collection.
 TIME TO RETIRE SPT…

ANGLE OF INTERNAL FRICTION (Φ)
CORELATIONS WITH SPT

 ANGLE OF INTERNAL FRICTION CORELATIONS…

Source: Karol (1960)-No Correction Applied to N.

The following bullets provide help in determining which value to select for a
given N160 and soil type (Bowles,1977):
• Use the maximum value for GW
• Use the average for GM and SP
• Use the minimum for SC
• Use the minimum + 0.5 for ML
• Use the average +1 for SW
• Use the average -1 for GC
• Use the Maximum -1 for GP

NAVFAC DM 7.1, 1982

• HATANAKA AND UCHIDA (1996)
A fairly good correlation between the N1 value and the φd(FS) was established. Finally,
based on the test results, a simple equation to relate the N1 value and φd(FS) of sandy
soils in the range of N1 between 3.5 and 30, for this study.
• Shioi and Fukui (1982)
In Japan the Road Bridge Specifications (Shioi and Fukui 1982) suggests for N > 5,
Design Standards for Structures (Shioi and Fukui, 1982)
http://www.roads.maryland.gov/opr_research/md-02-sp007b49-updating-bearing-capacity-
spt-graphs-report.pdf

• WOLF
The angle of friction of granular soils, ϕ, has been correlated to the standard
penetration number. Peck, Hanson, and Thornburn (1953) gave a correlation between
N and ϕ in a graphical form, Fig 2.1, which can be approximated as (Wolff, 1989)
://www.roads.maryland.gov/opr_research/md-02-sp007b49-updating-bearing-capacity-spt-
graphs-report.pdf

• HATANAKA AND UCHIDA (1996)
N and ϕ in a graphical form, which can be approximated as (Wolff, 1989)
• HATANAKA AND UCHIDA (1996)modified
N and ϕ in a graphical form, Fig 2.1, which can be approximated as (Wolff, 1989)
Hatakanda, M. and Uchida, A., 1996: Empirical correlation between penetration resistance
and effective friction angle of sandy soil. Soils and Foundations 36 (4): 1-9

• JAPAN ROAD ASSOCIATION
• GIBBS AND HOLTZ
From this equation we will get angle of internal friction in RADIANS. We have to then
convert it into degrees so that to compare it with Phi value obtained from various other
correlations.
• CHEN 2004
https://link.springer.com/content/pdf/10.1007%2Fs12205-017-1899-5.pdf
http://www.nrcresearchpress.com/doi/pdf/10.1139/cgj-2016-0318

• MOSTAFAABDOU ABDEL NAREIN MAHMOUD (2013)
http://www.ipublishing.co.in/ijcserarticles/twelve/articles/volthree/EIJCSE3150.pdf

• MOSTAFAABDOU ABDEL NAREIN MAHMOUD (2013)…
Another correction n6 is for blow count frequency that applies for soils including sands below the
water table (Aggour and Radding, 2001)
• POUYASALARI, GHOLAM REZA LASHKARIPOUR, MOHAMMED GHAFOORI (2015)
http://www.ipublishing.co.in/ijcserarticles/twelve/articles/volthree/EIJCSE3150.pdf
http://file.scirp.org/pdf/OJG_2015050614431300.pdf

• POUYASALARI, GHOLAM REZA LASHKARIPOUR, MOHAMMED GHAFOORI (2015)…
http://file.scirp.org/pdf/OJG_2015050614431300.pdf

• OTHERS
EXCEL SPREADSHEET

0
5
10
15
20
25
30
35
0 10 20 30 40 50 60
DEPTH
PHI VALUE
DEPTH VS PHI
DEPTH VS HATANAKA & UCHIDA (FINE SAND) DEPTH VS WOLF (1989)
DEPTH VS JAPAN ROAD ASSOCIATION (1990) DEPTH VS KULHAWAY & MAYNE
DEPTH VS HATANKA & UCHIDA (1996) DEPTH VS CHEN (2004)
DEPTH VS HATANAKA ET AL (1998) DEPTH VS AVERAGE PHI VALUE
DEPTH VS LAB PHI DEPTH VS HATANAKA & UCHIDA (MEDIUM SAND)
DEPTH VS HATANAKA & UCHIDA ( DENSE SAND) DEPTH VS MOSTAFA (2013)
DEPTH VS POUYA 2015 (SP SOILS) DEPTH VS POUYA 2015 (SC SOILS)
DEPTH VS OTHERS (SANDY) DEPTH VS OTHERS (GRANULAR)
DEPTH VS SANDY SOIL PARTICLES DEPTH VS ANGULAR SOILS

0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40
DEPTH
PHI VALUE
DEPTH VS PHI
DEPTH VS AVERAGE PHI VALUE DEPTH VS LAB PHI

0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40
DEPTH
PHI VALUE
DEPTH VS PHI
DEPTH VS JAPAN ROAD ASSOCIATION (1990) DEPTH VS AVERAGE PHI VALUE DEPTH VS LAB PHI

0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40 45
DEPTH
PHI VALUE
DEPTH VS PHI
DEPTH VS AVERAGE PHI VALUE DEPTH VS LAB PHI DEPTH VS OTHERS (SANDY)

0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40
DEPTH
PHI VALUE
DEPTH VS PHI
DEPTH VS AVERAGE PHI VALUE DEPTH VS LAB PHI DEPTH VS MOSTAFA (2013)

0
5
10
15
20
25
30
35
0 10 20 30 40 50 60
DEPTH
PHI VALUE
DEPTH VS PHI
DEPTH VS KULHAWAY & MAYNE DEPTH VS AVERAGE PHI VALUE DEPTH VS LAB PHI DEPTH VS ANGULAR SOILS

 CONCLUSIONS for SPT and phi
• For identification of shear strength parameter of sand using SPT is adequate rather
than using laboratory tests because SPT is carried out in the field on the
undisturbed samples.
• SPT is considerable reliable test in determining Phi value & Shear strength of the
soil.
• The equation for sandy soil is most suitable to estimate the Phi value as the phi
value using this correlation falls exactly between the Average Phi value and Phi
value calculated in the lab.
φ = (12 𝑁1,60)0.5
+ 20 𝑓𝑜𝑟 𝑆𝑎𝑛𝑑𝑦 𝑆𝑜𝑖𝑙
• The phi values calculated using the Japan road association correlation was very
close to the average phi value.
• The correlations which showed the highest departure from the average value on
the positive side are kulhaway and Mayne & the one which is provided for angular
soils.

• The correlation which showed the highest departure from the average value on
the negative side is Mostafa. (2015)
• It was also seen that as the overburden stress increases with depth the Phi value
decreases. Due to increase in overburden stress the coarser particles are
crushed to finer particles under high stress and we know that the Phi value for
finer particles have phi values less than the coarse particles.
 CONCLUSIONS for SPT and phi

UNDRAINED SHEAR STRENGTH
(Su) CORELATIONS with SPT

 UNDRAINED SHEAR STRENGTH (Su)
CORELATIONS

CORELATIONS…

SPT Capability to Estimate Undrained Shear Strength of Fine- Grained Soils of
Tehran, Iran- Frazad Nassaji
CORELATIONS…
Stroud and Butler (1975)

Hara et. al
CORELATIONS…

CORELATIONS…
AASHTO SOIL CLASSIFICATION
system

CORELATIONS…
AASHTO SOIL CLASSIFICATION system

CORELATIONS… Terzaghi 1996
FHWA/OH-2009/7

CORELATIONS…
Dept. of Navy- 1982
FHWA/OH-2009/7

FIELD VANE SHEAR TEST
(VST)
&
Estimation of Undrained Shear Strength

• Field Vane Shear test is a quick method
to estimate undrained shear strength of
soft saturated clays.
• One of the most widely used test.
• A four-bladed vane is inserted into the
ground and rotated counter clockwise
to measure the resisting torque.
• Peak and residual strengths are
measured.

• The standard vane has a
height-to-diameter ratio of 2
(H/D=2) and is 55 or 65 mm
in diameter and 110 or 130
mm in height
• Standard blades consist of
1.95 mm thick, high-strength
steel plate welded to a steel
rod.

Procedure – ASTM D2573
• The vane is pushed into the ground to the desired depth and is rotated at a
standard rate of 0.1 degrees per second and the torque is measured
• Vane can be inserted from bottom of a borehole or may be pushed directly
into the ground
• Soil is failed along a cylindrical surface circumscribed in circle with
diameter equal to diameter of vane blades
• The peak torque developed is related to the peak shear strength of the
soil which is function of shape and dimension of blades
• After the peak torque has been measured, the blades are rotated
rapidly several times (about 10 times) to measure the residual strength
• Process is repeated for the next depth; usually, a test can be done every
0.5m

Shear stress corresponding to the failure
condition is called shear strength.
Shear Strength of Soils
Mohr’s Hypothesis
'
tan
'
' 

 
 c
f

Shear Strength of Soils
• Shear resistance in soils is the result of resistance to movement
at the inter-particle contacts.
• Each contact can transmit normal force from one particle to
another across an area which increases or decreases as normal
force increases or decreases.
• Any mechanism that increases contact area contributes to
shear resistance.
• Increase in effective stress produces an increase of interparticle
contact area and thus increase in shear resistance.

• Occurs when the pore water is unable to drain out of the
soil.
• In an undrained condition, the rate of loading is much
quicker than the rate at which the pore water is able to
drain out of the soil.
• As a result, most of the external loading is taken by the pore
water, resulting in an increase in the pore water pressure.
The tendency of soil to change volume is suppressed during
undrained loading.
• For a rate of loading associated with a normal construction
activity, saturated coarse-grained soils (e.g. sands and
gravels) experience drained conditions and saturated fine-
grained soils (e.g. silts and clays) experience undrained
conditions.
Undrained condition

• The shear strength of a fine-grained soil under undrained
condition is called the undrained shear strength and is
denoted by Su.
• Su is the radius of the
• Mohr’s Circle of Total Stress:
Undrained Shear Strength
The undrained shear
strength depends only on
the initial void ratio or
the initial water content
of the soil.

• Unlike the critical state
angle of friction, the
undrained shear strength is
not a fundamental soil
parameter.
• Its value depends on the
values of the effective
confining stresses.
• An increase in effective
confining stresses causes a
decrease in void ratio and
an increase in undrained
shear strength as shown in
the figure.

• The Atterberg limits (Liquid Limit
and Plastic Limit) define the range
of undrained shear strengths for a
fine-grained plastic soil.
• At its Liquid Limit (i.e. Liquidity
Index IL = 1), a clay has Su
approximately equal to 1.5 kPa.
• At its Plastic Limit (i.e. IL = 0),a
clay has Su approximately equal to
150 kPa.
• Therefore, approximate estimate of
Su can be obtained by knowing the
water content of the soil.

strength is
the following
• Undrained
shear
estimatedby using
relation:
where T = torque measured, and
D = diameter of vane blades
• Sensitivity (St) of soil can be
ascertained by diving peak strength
with residual strength
St = su(FV)peak / su(FV)remolded
Well defined peak
and reduction
afterwards
No peak and lesser
torque as
compared to UD

• The maximum measured torque (T) in VST is used to
calculate the undrained shear strength (su) as follows;
where;
T = Torque in N.m or lb.ft
k = constant depending upon dimensions and shape of the vane (m3 or ft3)

 Conventional Interpretation by Chandler, 1988 depends upon
recorded maximum torque (T), it assumes a uniform distribution of
shear stresses both top and bottom along the blades and a vane with
height to width ratio H/D = 2.
 The test is normally reserved for soft to stiff materials with
suv < 200kPa (2tsf). The general expression for all types of vanes:
where
iT = angle of taper at top (with respect to horizontal)
iB = angle of bottom taper

• For the commercial vanes in common use, above equation reduces to
the following expressions for vanes with blade heights that are twice
their widths (H/D = 2) ;

○ Thicker the blades, more
 Influences
 Blade Thickness
○ Insertion of Blades causes
disturbance of soil
will be the disturbance and
thus less strength will be
indicated
SMIEP,3rd Edition, 1996
Greater thickness
Greater disturbance
Lesser Shear strength

 Influences
 Wait Time
○ Insertion of blades generates excess porewater pressure
○ With time, this excess porewater pressure dissipates
and
the soil strength increases
SMIEP, 3rd Edition,1996

 Correlations
Su can be found
from equation
And than Plasticity
Index and pre-
consolidation
pressure can be
found if one is
known of the two

 Correlations for
incorporating FS in
your result
PI less, u greater , lesser FS
incorporated
PI great, u less, more
FSincorporated

 Correlations
Not unconfined
compressive strength

Based on Skempton’s work
Based on Chandler’s work
 Correlations

Bjerrum
Correction Factor
 Correlations

 Other Correlations
Skempton and Bjerrum (1957)

 Other Correlations
Bjerrum & Simmons (1960)

SPT and VST- By Daanyal Umar.pptx

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