CHAILEELINSX010424AWJ12D03TT5 (3)

7/27/2019 CHAILEELINSX010424AWJ12D03TT5 (3)

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CHAPTER 5

RESULT AND ANALYSIS

5.1 Introduction

For analysis purpose, the relevant data and test results are collected from six

selected sites. The data and test results are obtained from the soil investigation, pile

driving records and pile load test results on site. Besides, all the data are also from

the same source. Thus, for a particular site, the driving record used in pile driving

formula should be from the same pile that selected for load testing. Also, the

designed pile length in static analysis should be same as the driven length that

obtained from the driving record. Ultimate capacity of a pile was calculated based

on the method selected as mentioned in Chapter four, which are Meyerhofs Method

for static analysis, Modified Engineering News Record (ENR) Formula, Hiley

Formula and Gates Formula for pile driving formula and Professor Chins Method

for interpretation of the load test result.

For comparison purpose, summary of the ultimate capacity for the entire site

are presented in table form, which the ultimate capacities that obtained from different

methods are compared to each other and the differences in percentages are


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established. Finally, the analysis results are presented in bar chart form for

convenient reading.

5.2 Calculations Example

For easy understanding purpose, a calculation example for each of those

selected methods that showing all the detail steps in obtaining the ultimate capacities

are attached.

5.2.1 Static Analysis

5.2.1.1 Calculation Example Meyerhofs Method

Project 4:

FromEquation 3.1:

Ultimate pile capacity, Qult = Qs + Qb

Nominal surface area of the pile in soil layer, As = 2j x L

= 2 (0.35/2) x L= 1.1 L m2

Frictional Resistance, Qs

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Assumption 1:

Skin friction is mobilized to the whole length of the driven pile.

For 0 10.2 m,

Cu = 18.67 Kpa,

From Figure 3.4: = 1.179

From Equation 3.13 : Qs = p

L = 18.67 x 1.179 x 1.1 x 10.2

= 247.05 KN

For 10.2 29.60 m,

Cu = 23.44 Kpa,


From Equation 3.13 : Qs = pL = 23.44 x 1.07 x 1.1 x 19.4

= 535.22 KN

For 29.6 35.0 m,

Take N avg = 8, Cu = correlation factor x N

= 6.67 x 8 = 53.36 kPa

From Figure 3.4: = 0.825From Equation 3.13 : Qs = pL

= 53.36 x 0.825 x 1.1 x 5.4

= 261.49 KN

For 35.0 43.1 m,


= 6.67 x 12 = 80.04 kPaFrom Figure 3.4: = 0.6

64

350 mm spun pile


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= 427.89 KN

For 43.1 48.9 m,


= 6.67 x 15 = 100.05 kPa



= 319.16 KN

For 48.9 52.42 m,

The soil is silty sand, therefore from the SPT test,

The SPT N-value = 60.75, N = 0.6 x 60.75

= 36.45

cu = 2N = 72.90

From Equation 3.13 : Qs = p

L = 72.90 x 1.1 x 2.52

= 282.27 KN

Assumed bedding level, RL= - 52.42 m

Ap = j2

= (0.35/2)2

= 0.096 m2

The soil is dense sand, N = 65.22, therefore, N' = 65.22 x 0.6 = 39.13

bu = 40N x Db/B

= 40 x 39.13 (1/0.35)

= 4471.97 KN

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< 400N = 13200 ok.

Pbu = Apbu

= 0.096 x 4471.97= 429.31 KN

FromEquation 3.1:

Ultimate pile capacity, Qult = Qs + Qb

Qult = 247.05 + 535.22 + 261.49 + 427.89 + 319.16 + 282.27 + 429.31

= 2502.39 KN

Assumption 2:

Skin friction mobilized only in the stiff layers

Skin friction lost from 0 23 m,

= Qs(0-8) + (12.8 x 2j x x Cu)

= 247.05 + (23.44 x 1.07 x 1.1 x 12.8)

= 600.19 KN

Remaining ultimate pile capacity = 2502.39 600.19

= 1902.2 KN

* The calculation for the correlation factor is attached in Appendix H.

* The depth of down drag in the soil is determine by the software named CONSOL

(a special software to determine the consolidation and rate of consolidate).

5.2.1.2 Summary Of Ultimate Capacity From Static Analysis

On the basis of the comparison of ultimate capacity using the static analysis

and in situ testing, it is proposed to use the assumption two, thus Skin friction

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mobilized only in the stiff layers, to achieve a practical results. The results of

ultimate capacity for all the six selected sites are summarized in Table 5.1 below

showing, while the breakdown of skin friction and end bearing capacity value are

attached in Appendix I-1 to I-6 for reference.

Table 5.1: Summary of ultimate capacity from static analysis

Project Name Ultimate Capacity, Qu (KN)

Project 1 1450.38

Project 2 1651.57

Project 3 1656.54

Project 4 1902.20

Project 5 1335.07

Project 6 1648.22

5.2.2 Pile Driving Formula

Three driving formulas were chosen in this study, thus Modified ENR

Formula, Hiley Formula and Gates Formula. The ultimate capacity are calculated

based on the driving records on site and calculation example for each of those

formula used are showing in the following part. The ultimate capacity for every

selected site that obtained from the three mentioned methods is summarized in Table

5.2 for comparison purpose. While summary of driving record and calculation steps

for the three formulas for all the selected sites are attached in Appendix J to O-3.

5.2.2.1 Modified ENR Formula

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(0.8)(36.75) 24.5 + (0.5)2 (82.278)

0.008 + 0.0254 24.5 + 82.278

Project 4:

Pile No : BP1Pile Size : 350 mm Diameter

Hammer : K-25

Table 3.2 : Hammer efficiency, E = 0.8

Table 3.3 : Coefficient of restitution, n = 0.5

Appendix P : Weight of ram, WR = 24.5 KN

Appendix J : Pile Length, L = 52.42 m

( Penetration of pile per hammer blow, S = 0.008 m

Solution:

From Modified ENR formula:

EWRh WR+ n2WP

S + C WR+ WP

From the Standard Products Properties (Appendix Q),

Nominal weight of 350mm diameter Spun pile = 160 kg/m

= 1.5696 KN/m

The pile weight = 1.5696 KN/m * L

= 1.5696 *52.42

= 82.278 KN

From Table D.5 in Appendix P, for diesel hammer,

Weight of ram, WR = 24.5 KN

Height of hammer drop, h = 1.5 m

WRh = 24.5 * 1.5 = 36.75 KNm

Therefore,

=

880.2

4 * 0.4221

=

371.5

4 KN

68

Qu =

Qu =


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5.2.2.2 Hiley Formula

Table 3.2 : Hammer efficiency, eh = 0.8

Table 3.3 : Coefficient of restitution, n = 0.5

Appendix P : Weight of ram, Wr = 24.5 KN

Appendix J : Pile Length, L = 52.42 m

Penetration of pile per hammer blow, s = 0.008 m

Solution:

FromHiley formula:

From the Standard Products Properties given (Appendix Q),

Nominal weight of 350mm dia. Spun pile = 160 kg/m

= 1.5696 KN/m

The pile weight = 1.5696 KN/m * L

= 1.5696 * 52.42= 82.278 KN


Weight of ram, Wr = 24.5 KN


WRh = 24.5 * 1.5 = 36.75 KNm

From Table 3.4 - Manufacturer Printed Manual,

The driving on site is in the category of Medium Driving - 0.006 'l'

Cap compression, c1 = 0.10 inch = 0.00254 m

Length of pile = 52.42 m = 171.94 ft

0.006 'l' = 0.006 (171.94) = 1.0316

Pile compression, c2 =1.0316 inch = 0.02620 m

Ground compression, c3 = 0.15 inch = 0.00381 m

Therefore,

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eh Eh Wr + n2 Wp

s + 1/2 (c1 + c2 + c3) Wr + WpQu =

(0.8)(36.75) 24.5 + (0.5)2 (82.278)

0.008 + 1/2 (0.03255) 24.5 + 82.278 Qu =


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= 1211 * 0.4221

=

511.1

6 KN

5.2.2.3 Gates Formula

Solution:

From Gates formula:

Qu = a [EHE ] (b log S)

Qu is in KN, therefore a = 104.5, b = 2.4 and E = 0.85 for diesel hammer


Weight of ram, Wr = 24.5 KN


Rated hammer energy = WRh = 24.5 * 1.5 = 36.75 KNm

From Appendix J,

Penetration of pile per hammer blow, s = 8 mm

Therefore,

Qu = a [EHE ] (b log S)

= 104.5 [0.85 * 36.75 ] (2.4 log 8)

= 874.27 KN

5.2.2.4 Comparison Of Ultimate Capacity From Pile Driving Formulas

Table 5.2: Summary of ultimate capacity from pile driving formulas

Project Name QU FROM PILE DRIVING FORMULAS (KN)

Modified ENR Hiley Diff. (%) Gates Diff. (%)

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Project 1 243.03 322.49 32.70 575.29 136.72

Project 2 232.04 259.39 11.79 595.61 156.69

Project 3 364.73 485.80 33.19 874.27 139.70

Project 4 371.54 511.16 37.58 874.27 135.31

Project 5 354.70 486.74 37.23 817.67 130.53

Project 6 268.15 334.70 24.82 629.49 134.75

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Comparison Of Ultimate Capacity Based On

Different Pile Driving Formulas

0

100

200

300

400

500

600

700

800

900

1000

Project 1 Project 2 Project 3 Project 4 Project 5 Project 6

Selected Project

Ultimate

Capacity,Qu(KN)

Modified ENR Hiley Gates

Figure 5.1: Comparison of ultimate capacity from pile driving formulas

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5.2.3.2 Interpretation Of Load Test Result By Chins Method Stability Plot

Stability Plot For Spun Pile at BP1, Project 4(Chin's Method)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 2 4 6 8 10 12 14 16 18 20

Settlement (mm)

/P(mm/T

First Cycle Minus Residual

Figure 5.2: Stability plot74


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5.2.3.3 Estimation Of Ultimate Pile Capacity From Stability Plot

From the stability plot,

For 1st Cycle:

Slope of the plot = (0.1111 - 0.0832) / (8.33 - 1.56)

= 0.0279 / 6.77

= 0.0041 ton-1

Know that the inverse slop of the plot gives the ultimate capacity,

Thus,Ultimate Capacity of the pile, Qult = 1/ 0.004 ton

-1

= 242.652 ton

= 2426.52 KN

For Minus Residual:

Slope of the plot = (0.0965 - 0.0535) / (14.5 - 2)

= 0.0430 / 12.5

= 0.0034 ton-1

Know that the inverse slop of the plot gives the ultimate capacity,

Thus,

Ultimate Capacity of the pile, Qult = 1/ 0.003 ton-1

= 290.698 ton

= 2906.98 KN

From the load test results, it is found that the head settlement for first cycleand second cycle of spun piles is quiet near to each other. For example, from Table

5.3 above, the residual settlement after the first cycle is 3.53 mm. Which as for

second cycle, the residual settlement is 4.83 mm. The difference is considered very

small and exhibited similar initial residual strengths. In this condition, it is reasonable

to say that the driven pile has achieved its capacity at a constant stage. Hence, the

interpretation of ultimate capacity by using first cycle result is considered reliable.

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5.2.3.4 Summary Of Ultimate Capacity From Load Test Results

Similar with the example calculation for Project 4, all the ultimate capacities

for the other selected sites are interpret from static load test results that carried out

for that particular pile by using Chins Method. The related data, stability plot as

well as the interpretation results are shown in Appendix R-1 to V-3. While the

summary of the ultimate capacity for the six selected sites are shown in Table 5.4

below.

Table 5.4: Summary of ultimate capacity from load test results

Project Name Ultimate Capacity, Qu (KN)

Project 1 1904.76

Project 2 2285.71

Project 3 2230.77

Project 4 2426.52

Project 5 1818.18

Project 6 2105.26

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5.3 Comparison Of Ultimate Pile Capacity, Qu

5.3.1 Comparison Of Ultimate Capacity Between Theoretical Formula And In-Situ Testing

Table 5.5 : Summary of ultimate capacity from load test results, pile driving formula and static analysis

Project Name

ULTIMATE CAPACITY, QU (KN)

Load Test

(Chin Method)

Pile Driving Formula Static Analysis

(Meyerhof's Method)Modified ENR Hiley Gates

Project 1 1904.76 243.03 322.49 575.29 1450.38

Project 2 2285.71 232.04 259.39 595.61 1651.57

Project 3 2230.77 364.73 485.80 874.27 1656.54

Project 4 2426.52 371.54 511.16 874.27 1902.20

Project 5 1818.18 354.70 486.74 817.67 1335.07

Project 6 2105.26 268.15 334.70 629.491648.22


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Ultimate Capacity From Load Test Result, Pile Driving Formulas

And Static Analysis

0

500

1000

1500

2000

2500

1 2 3 4 5 6

Selected Project

UltimateCapacity,Qu

Load Test (Chin Method) Modified ENR Hiley Gates Static Analysis (Meyerhof's Method)

Figure 5.3: Ultimate capacity from load test result, pile driving formulas and static analysis78


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From Table 5.5 and Figure 5.3 above, it is found that ultimate capacity

determined from pile load test result show the highest value compare with the other

two methods. This followed by static analysis and pile driving formula respectively.

Ultimate capacity, Qu obtained from Chins method is more reliable as it is

determined through the load test where installed pile are load to twice the working

load as desired by the designer. It is always more convincing the designer as the pile

has been loaded and the soil partial at the pile shaft or pile toe has been adequately

mobilized to gain its strength.

As for ultimate capacity obtained from the static analysis and pile driving

formulas, both are lower than the load test results. However, ultimate capacity from

static analysis shown a closer value to ultimate capacity from load test results as it is

based on bearing capacity theory and the soil parameters used in the analysis were

predicted from the borehole data. But pile driving formulas only a prediction of

energy transfer from the hammer drop to the driven pile only. Various empirical

assumptions may not be found satisfactory to correlate to field condition.

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5.3.2 Comparison Between Static Analysis And Load Test Results

Table 5.6: Comparison of ultimate pile capacity, Qu from load test results and static analysis

Project Driving

Soil Characteristic Ultimate Capacity (KN) ComparisonDifferences (%)

Name Depth Type Of Soil Along Type Of Soil At Average Static Load Test Static Analysis vs

(m) Middle Strata Bedding Level SPT-N Value Analysis Results Load Test Results

Project 1 46.00 Silty Clay Silty Sand 16.37 1450.38 1904.76 23.85

Project 2 68.10 Stiff Silty Clay Stiff Silty Clay 7.38 1651.57 2285.71 27.74

Project 3 55.62 Sandy Silty Clay Sandy Silty Clay 16.67 1656.54 2230.77 25.74

Project 4 52.42 Silty Clay Silty Gravelly Sand 21.88 1902.20 2426.52 21.61

Project 5 50.50 Silty Clay Silty Clay 6.15 1335.07 1818.18 26.57

Project 6 52.00 Soft Silty Clay Clayey Silty Sand 17.40 1648.22 2105.26 21.71

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Comparison between ultimate capacities from interpretation of load test

results (Chins method) and static analysis (Meyerhofs method) show the

percentages difference ranging from 21.61% to 27.74%.

As stated in Geotechnical Information Of The Selected Sites in Chapter 4,

type of soils for the selected sites are silty clay with lamination of sand at certain

layers. In purpose of studying the soils characteristics factor to the differences

between these two methods, few criteria have been highlighted, thus the driving

depth, type of soil along middle strata, type of soil at bedding level as well as

average SPT-N value. As observed in Table 5.6, Project 2 and 5 can be categorized

in a different group from Project 1, 3, 4 and 6. These two projects achieved a lower

value in standard penetration test as well as having the same type of soil at both the

middle strata and bedding level of pile, thus silty clay while the other projects were

bedding on a sand strata. From the table, it is found that ultimate capacity calculated

from static analysis for Project 2 and 5 achieved a lower value when their piles were

bedding on clayey strata, even though they were driven deeper. At the same time, a

higher percentage of differences achieved when compared to the load test results.

As from Meyerhofs formula, calculation of end bearing capacity in clayey

soil is using equation of 9 Cu Ap while sandy soil is using 40N (Db/B)Ap. It is found

the larger difference was established when the base stratum is of clayey soil where

the clay formula needs to be used. This is because the clay formula for end bearing

capacity in Meyerhofs Method gave a lower value, which is therefore

underestimated.

81

81

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CORRELATION CHART

y = 0.76 x

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 250 500 750 1000 1250 1500 1750 2000 2250 2500

Qu Load Test (Chin's Method), KN

Q

uStaticAnalysis(Meyerhof'sMethod),K

Figure 5.4: Correlation factor for ultimate capacity from load test result and static analysis 82


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5.3.3 Comparison Between Static Analysis And Pile Driving Formulas

Table 5.7: Comparison of ultimate capacity from static analysis and pile driving formulas

Project Name


Static Analysis Pile Driving Formulas

(Meyerhof's Method) Modified ENR Diff.(%) Hiley Diff.(%) Gates Diff.(%)

Project 1 1450.38 243.03 83.24 322.49 77.77 575.29 60.34

Project 2 1651.57 232.04 85.95 259.39 84.29 595.61 63.94

Project 3 1656.54 364.73 77.98 485.80 70.67 874.27 47.22

Project 4 1902.20 371.54 80.47 511.16 73.13 874.27 54.04

Project 5 1335.07 354.70 73.43 486.74 63.54 817.67 38.75

Project 6 1648.22 268.15 83.73 334.70 79.69 629.49 61.81


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COMPARISON OF ULTIMATE CAPACITY BASED ON

STATIC ANALYSIS AND PILE DRIVING FORMULAS

0

250

500

750

1000

1250

1500

1750

2000


SELECTED PROJECT

ULTIMATECAPACITY,

Qu(K

Static Analysis (Meyerhof's Method) Modified ENR Formula Hiley Formula Gates Formula

Figure 5.5: Comparison of ultimate capacity based on static analysis and pile driving formulas 85


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From the comparison between static analysis and pile driving formulas, it is

shown that static analysis by Meyerhofs method has a higher ultimate capacity, Qu

as compared to the three selected pile driving formulas. While among the three

driving formulas, Gates Formula shows a closer value to static analysis.

Static analysis is based on bearing capacity theory and the soil parameters

were predicted from the borehole data. These are not happening for analysis by pile

driving formulas where its assumptions depends only on types of piling equipment

and its efficiency as well as the slenderness of pile.

Pile driving formulas give the value of ultimate capacity during the driving

process. The values are significantly lower due to the soil that has been remolded

during the driving process especially when involving clayey soils. This can be

observed from the calculated ultimate capacity that using driving formulas in Project

2 always shows the lowest value as compared with other projects even though it

achieved the highest value of driving depth. Besides, Project 2 also indicated a

highest percentage of difference when compared to the value from static analysis.

As described in Geotechnical Information Of The Selected Sites in Chapter 4 and

Table 5.4 in previous part, Project 2 obtained the clayey soil at both along the middle

strata and bedding level of pile. As therefore, the significantly lower value and

higher percentage of difference established in Project 2 is because of the remolding

of soil that due to the driving works has created greater disturbance to clayey soil.

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5.3.4 Comparison Between Load Test Result And Pile Driving Formulas

Table 5.8 : Comparison of ultimate capacity from load test results and pile driving formulas

Project Name


Load Test Results Pile Driving Formula

Stability Plot Modified ENR Diff.(%) Hiley Diff.(%) Gates Diff.(%)

Project 1 1904.76 243.03 87.24 322.49 83.07 575.29 69.80

Project 2 2285.71 232.04 89.85 259.39 88.65 595.61 73.94

Project 3 2230.77 364.73 83.65 485.80 78.22 874.27 60.81

Project 4 2426.52 371.54 84.69 511.16 78.93 874.27 63.97

Project 5 1818.18 354.70 80.49 486.74 73.23 817.67 50.03

Project 6 2105.26 268.15 87.26 334.70 84.10 629.49 70.10

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COMPARISON OF ULTIMATE CAPACITY BASED ON

LOAD TEST RESULT AND PILE DRIVING FORMULAS

0

250

500

750

1000

1250

1500

1750

2000

2250

2500


SELECTED PROJECT

ULTIMATECAPACITY,

Qu(K

Load Tes t Res ults Modified ENR Formula Hiley Formula Gates Formula

Figure 5.6: Comparison of ultimate capacity based on load test result and pile driving formulas88


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From the comparison between load test and pile driving formulas, it is noted

that ultimate capacity from interpretation of load test results by Chins method

achieved a 60% to 90% higher value as compare to the three selected pile driving

formulas. As the comparison between static analysis and pile driving formulas, the

ultimate capacity from Gates Formula still shows a closer value from load test result

than the other two methods.

The pile driving formulas are only the prediction of pile capacity to be

achieved during the driving process and significantly affected by the type of piling

equipment but the relationship of pile to the soil properties is not precisely described.

However, the ultimate capacity from these driving formulas would be even lower

when the sites involved more clay layer. This can be observed from the calculated

ultimate capacity of Project 2, which it shown a lowest value as compared with other

projects as well as obtained a highest difference when compared with load test results

even though it achieved the highest value of driving depth. The significant lower

value and higher percentage of difference established in Project 2 may be able to be

explained by the remolding of soil that due to the driving works has created greater

disturbance to clayey soil as compared to sandy soil.

The load test results are more reliable due to the following reasons:

The pile has been driven and loaded,

The actual behavior of pile will be established based on the actual site

condition,

Although it does not pre-determine the pile slenderness, the effect still will

be reflected during the load test.

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