Pile Foundation DesignUsing Microsoft Excel

HANIFI CANAKCI

Department of Civil Engineering, University of Gaziantep, 27310 Gaziantep, Turkey

Received 14 September 2006; accepted 20 May 2007

ABSTRACT: This article presents a program called Pile-D developed for the teaching of

pile foundation design to undergraduate level geotechnical engineering students. The program

performs drained and undrained analysis for frictional resistance of the pile in clay, and uses

critical depth approach for the analysis of the pile in sand. � 2007 Wiley Periodicals, Inc. Comput

Appl Eng Educ 15: 355�366, 2007; Published online in Wiley InterScience (www.interscience.wiley.com); DOI

10.1002/cae.20206

Keywords: pile foundation; geotechnical engineering; spreadsheet application; clay; sand

INTRODUCTION

Pile foundation design is considered as one of the

state-of-the-art areas of the geotechnical engineering.

There are different theoretical and empirical methods

used in pile foundation design. The design procedure

requires use of different soil and pile material

properties. Teaching this course in a classroom

environment with limited time and practicing few

examples makes it difficult for students to understand

the concepts of pile foundation design.

Pile foundation design in some cases is lengthy,

which is always a limiting factor in an educational

environment and there is not much we can do to

change this. However, we may increase the student

experience by exposing the students to many more

cases and variations with the help of user-friendly

computer programs. Computer programs with visual

interface are easy to use even for students with little

experience with personal computer. It allows effective

presentation of fundamental principles underlying the

design and operation of different engineering appli-

cations. These type of programs not only give students

the opportunity to learn fast, but also enable them to

tackle a broad range of applications by employing

various types of problem in very short time period.

Thus, problem solving is no longer time-consuming

and boring for the students.

Many different programs were developed as

courseware and teaching tools for geotechnical engi-

neering students. The software Geocal [1] developed

as a joint project of several universities from UK

covers many areas of soil mechanics and geotechnical

engineering. Budhu’s [2] soil mechanics courseware

contains multimedia material for a typical university

undergraduate level soil mechanics course. Sharma

and Hardcastle [3] developed a geotechnical labo-

ratory software module. It covers common soil

mechanics tests, which are presented in a multimedia

format. Masala and Biggar [4] also developed a virtual

geotechnical laboratory for simulation of permeability

test. Most of these programs are prepared using visual

interface for ease of use.Correspondence to H. Canakci (canakci@gantep.edu.tr).

� 2007 Wiley Periodicals Inc.

355

Pile-D is developed using Microsoft Excel

for more effective teaching of pile foundation design

and it makes use of all the advantageous of visual

programs. There are various programs in the market

performing advanced calculations on the topic.

However, they are not much use for the teaching of

pile foundation design. The program presented here is

a simple tool for more effective teaching of pile

foundation design, which is what a student needs

during an undergraduate level program.

The program is developed for undergraduate level

civil engineering students who already have back-

ground knowledge in pile design analysis. It allows

the user to practice the solution procedures of pile

design typically used in manual calculations. The

Pile-D is designed to play an active role in dealing

with user-defined problems. The main advantage of

this is that it facilitates active and experiential

learning. Below, we present the theory of the design

procedure for clay and sand as used by the program

and explain the modules of the program.

PILE FOUNDATION

In most of the Civil Engineering projects, loads

coming from the super structure are transferred to soil

through foundation that can be either spread or pile.

Although spread footings are more commonly used,

engineers often encounter circumstances where pile

foundation is more appropriate. Following conditions

can be given as examples:

* The upper soils are so weak and/or the structural

loads are so high that spread footing would be too

large.* The upper soil is subjected to score or under-

mining.* The foundation must penetrate through water.* Large uplift capacity is required.* There will be future excavation adjacent to the

foundation, and this excavation would under-

mine shallow foundation.

Pile foundations typically extent to depths in the

order of 15 m below ground surface but in some cases

they can be as deep as 45 m. Even greater lengths have

been used in some offshore structures such as oil

drilling platforms [5].

Engineers and contractors have developed many

kinds of pile foundations each of which is best suited

to certain loading and soil conditions. Construction

and design of these pile types are different. Although

numerous theoretical and experimental investigations

have been conducted in the past to predict the

behavior and load carrying capacity of piles in

granular and cohesive soils, the mechanism are not

entirely understood. Pile foundation is considered as

an art because of the uncertainties involved in working

with some soil conditions [6].

ESTIMATION OF PILE LOADCARRYING CAPACITY

The load is transmitted to the soil surrounding the pile

by friction or adhesion between the soil and the sides

of the pile or/and the load is transmitted directly to the

soil just below the pile tips. This can be expressed by

Qult ¼ Qs þ Qp ð1Þ

where Qult is the ultimate bearing capacity of a single

pile, Qs is the bearing capacity gained by friction or

adhesion, and Qp is the bearing capacity furnished

by the soil just below the pile tip. The term Qs in

Equation (1) can be evaluated by multiplying the unit

skin friction or adhesion between the soil and the sides

of the pile f by the pile surface area As. The term Qp

can be evaluated by multiplying the ultimate bearing

capacity of the soil at the tip of the pile q by Ab.

Hence, Equation (1) can be expressed as follows:

Qult ¼ f � As þ q � Ab ð2Þ

The calculation of Qs and Qp values has been the

subject of numerous published studies. Equation (1) is

a general relation and applicable to all soils.

PILES IN CLAY

The bearing capacity at the tip of the pile can be

calculated from:

Qp ¼ cu � Nc � Ab ð3Þ

where cu is undrained cohesion of the clay below the

pile tip, Nc is the bearing capacity factor and has a

value of about 9, and Ab is the base area of the pile [7].

There are several methods available for the calcu-

lation of the unit frictional resistance of pile in clay.

Some of the accepted procedures are discussed briefly

below.

�� Method

This method is based on drained shear strength. When

piles are driven into saturated clay, pore water

pressure in the soil around the pile increases.

However, within a month or so, this pressure gradually

356 CANAKCI

dissipates. Hence, the unit frictional resistance for

the pile can be determined on the basis of the effective

stress parameters of the clay in a remolded state

(c¼ 0). Thus, at any given depth unit, frictional

resistance can be expressed by

f ¼ � � �0v ð4Þ

where �0v is the vertical effective stress at any depth,

’R is the drained friction angle of remolded clay, K is

the earth pressure coefficient, and

� ¼ Kðtan’RÞ ð5Þ

The value of K can be conservatively taken as the

earth pressure coefficient at rest, or

Ks ¼ 1� sin�R ðfor normally consolidated claysÞð6Þ

Ks ¼ ð1� sin�RÞffiffiffiffiffiffiffiffiffiffi

OCRp

ðfor overconsolidated claysÞð7Þ

where OCR is overconsolidation ratio.

Combining Equations (4)�(7), the unit frictional

resistance for normally consolidated clay may be

given as

f ¼ ð1� sin�RÞtan�R � �0v ð8Þ

For overconsolidated clays

f ¼ ð1� sin�RÞtan�R

ffiffiffiffiffiffiffiffiffiffi

OCRp

� �0v ð9Þ

Once the value of f is determined, the total

frictional resistance may be evaluated from

Qs ¼ Sf � p � DL ð10Þ

where p is the perimeter of the pile section, DL is the

incremental pile length over which p and f are taken

constant.

�� Method

Although a drained strength analysis is theoretically

more accurate, it is also possible to analyze frictional

resistance based on empirical correlation with the

undrained strength, cu. This method is extensively used

because of the large base of experience and because

the test required obtaining cu is simple and inex-

pensive. In this method, the unit frictional resistance is

determined from

f ¼ a � cu ð11Þ

where � is the empirical adhesion factor. The

approximate variation of the value of � is shown in

Figure 1. For normally consolidated clays with cu less

than or equal to about 50 kPa, the value of � is equal to

one. Thus

Qs ¼ S� � cupDL ð12Þ

�� Method

This method combines drained and undrained analy-

sis. It computes average unit frictional resistance from

favg ¼ lð��0v þ 2cuÞ ð13Þ

where �0v is the mean effective stress for entire

embedded length and l is the coefficient which

depends on entire embedded depth of the pile (Fig. 2).

Care should be exercised in obtaining the value of �0v

and cu in layered soil. This can be explained with the

help of Figure 3. Using Figure 3, the mean value of cumay be determined from

cuðavgÞ ¼ ðcuð1ÞL1 þ cuð2ÞL2 þ cuð3ÞL3 þ . . .Þ=L ð14Þ

Figure 3 shows the plot of the variation of

effective stress with depth. The mean effective stress

should be determined from

��0v ¼

A1 þ A2 þ A3 þ . . .

Lð15Þ

where A1, A2, A3, . . . are the areas in the vertical

effective stress diagram.

PILES IN SAND

The bearing capacity at the tip of the pile can be

calculated by

Qp ¼ cu � Nc � Ab ð16Þ

Figure 1 Variation of alpha factor with undrained cohe-

sion.

PILE-D 357

In the case of piles driven in sand, the unit frictional

resistance at a given depth for a pile can be expressed

as

Qs ¼ K � �0v � tan � ð17Þ

where K is the earth pressure coefficient, �0v is the

effective vertical stress at the depth under consid-

eration, and � is the friction angle developed at soil-

pile interface. The value of K changes with depth. It is

approximately equal to the Rankine passive pressure

coefficient at the top of the pile. It may be less than the

at rest earth pressure coefficient at the pile tip. Based

on presently available results, the coefficient of lateral

earth pressure is assumed to vary between 0.60 and

1.25, with lower values used for silty sand, and higher

values for other deposits.

Effective stress normally increases as the depth

increases. In the case of pile driven in sand, it has been

determined that effective pressure of soil adjacent to a

pile does not increase without limit as depth increases.

Instead, effective vertical stress increases as depth

increases until a certain depth of penetration is

reached. Below this depth, which is called critical

depth and denoted Dc, effective vertical stress more or

less remains constant (Fig. 4). The critical depth is

dependent on the field condition of the sand and

pile size. Tests indicate that critical depth ranges

from about 10 piles diameter for loose sand to about

20 piles diameter for dense compacted sand.

The coefficient of friction between sand and the

pile surface may be obtained from Table 1.

The load bearing capacity at the pile tip can be

calculated from

Qp ¼ �0v � Nq � Ab ð18Þ

where �0v is the mean effective stress for entire

embedded length, Nq is the bearing capacity factor,

and Ab is the base area of the pile. Although many

more different approaches are proposed for the design

of pile foundation in sand and clay, the program uses

only the methods explained above.

THE PROGRAM Pile-D

Two essential characteristics are considered while

developing the program. These are the capability

of promoting interactivity with the user and easily

producing interfaces with a pleasant layout [8]. The

layout can strongly influence the improvement of

user’s motivation. Concerning these characteristics,

Microsoft Excel is chosen as programming platform.

Readiness of a wide group of functions for different

tasks such as graphic capacities, two-dimensional

array with the capacity to link rows and columns,

handling of data, accessibility, and manageability are

considered as advantages of Microsoft Excel [9].

Figure 2 Variation of � with embedded length of the pile.

Figure 3 Application of l method in layered clayey soil.

358 CANAKCI

These advantageous of Microsoft Excel are mostly

used in Pile-D.

The program interfaces are developed in such a

way that it is not only easy to use but also provides an

environment where students feel motivated to explore.

The visual graphics used in the pages ensure a

motivating environment. In the developed program

Pile-D, a consistent screen layout is designed to

provide effective instruction, appropriate navigational

tools, and visual aesthetics. The screen is organized

into functional areas. These areas appear in the same

locations throughout the program for consistency.

Pile-D has two sections. These are pile in clay

and pile in sand. Pile in clay section has six sub-

sections, namely geotechnical data input, pile pro-

perties input, alpha and lambda values selection,

presentation of results, and calculation check. Pile in

sand has four subsections namely, geotechnical and

pile properties input, bearing capacity factor selec-

tion, presentation of results, and calculation check.

Pile in clay section is designed to solve vertical

downward axial load carrying capacity of a single pile

embedded in layered clay. Frictional resistance of the

pile in clay is analyzed using three different theories

known as Alpha, Beta, and Lambda. The user can

obtain the solution using all these three methods. End

bearing capacity of the pile in sand is calculated using

user selected bearing capacity factor. To allow para-

metric studies, four different bearing capacity factors

proposed by different researchers are included in the

program. The user can easily move between the

subsections and change soil and pile properties and

observe changes in the result immediately. The

program can be used for back calculation for existing

pile if soil and pile properties are known. Also, the

length of a pile can be calculated for a specific load by

trying different pile shapes and materials.

DEMONSTRATING EXAMPLES

In this section, two examples are given to demonstrate

the computational and graphical utilities of Pile-D.

The first example is for pile design in clay and

the second one is for pile design in sand. Cells and

combo boxes used in the program are explained while

going through examples.

Example Calculation for Pile in Clay

Example 9-4 of Reference [6] is selected for

demonstrating example calculation. The problem

requires the calculation of ultimate point resistance

and frictional resistance of a 30 m long circular pipe

pile embedded into two different clay layers. The

frictional resistance of the pile is to be determined

using alpha, beta, and lambda methods. We notice that

the water table remains within the embedded length of

the pile.

To start the solution of the problem, ‘‘pile design

in clay’’ section is called from the main page (Fig. 5).

Given soil data and ground water level are entered as

an input data into provided cells as shown in Figure 6.

The user is allowed to choose pile shape from the

combo box (Fig. 7). Three most widely used pile

shapes are placed into the combo box. These are cir-

cular, square, and octagonal. After selecting the shape

of the pile, the user can input size of the pile into the

provided cell. If the user wants to choose alpha and

lambda factor he/she simply clicks on ‘‘Chose �factor’’ or ‘‘Chose l factor’’ buttons and calls alpha

and lambda graphs. From these graphs, he/she reads

corresponding alpha and lambda values depending on

the undrained cohesion and total embedded length of

the pile, and enters these values into the provided cell

(Fig. 8). This option of the program encourages the

Table 1 Coefficient of Friction Between Sand and Pile

Materials

Coefficient of friction between

sand and pile material tan �

Concrete 0.45

Wood 0.40

Steel (smooth) 0.20

Steel (rough, rusted) 0.4

Steel (corrugated) Use tan� of sand

Figure 4 Variation of vertical effective stress adjacent to

pile with depth.

PILE-D 359

user to contribute to the solution. To obtain the

solution, the user simply clicks on ‘‘Calculate’’ button

and the page with results comes on to the screen

(Fig. 9).

The results page contains point resistance; fric-

tional resistances calculated using three methods,

ultimate capacity, and allowable capacity values. The

user may change the factor of safety value and

Figure 5 Main page of the program Pile-D.

Figure 6 Pile design in clay section soil data entrance page.

360 CANAKCI

recalculate allowable capacity. The screen also

contains frictional resistance values calculated using

the coefficients read by the user. This allows the user

compare these resistances by those calculated by the

program. In the computer solution, the coefficients are

determined using best fit curve functions of the alpha

and lambda graphs. The program allows the user to go

back to previous data entrance screens and change soil

or pile properties using the buttons located at the

bottom part of the screen, and obtain the new results.

When the user clicks on the ‘‘check your

calculation’’ button, the screen shown in Figure 10

comes on. This page contains selected parameters

and certain intermediate results obtained during the

calculations. This page allows the student to compare

his hand calculation with that of the program. This

way the student has opportunity to identify his/her

mistakes and correct them.

Example Calculation for Pile in Sand

Example 10-2 of Reference [7] is used to illustrate the

use of program for pile in sand problems. The problem

statement is as follows: A concrete pile is to be driven

into a medium dens to dens sand. The diameter of the

pile is 305 mm, and its embedded length is 7.62 m.

Unit weight of the sand is 20.1 kN/m3 and, its internal

angle of friction is 388. K is assumed as 0.95. Ground

water table is 3 m below ground surface. Calculate

pile’s axial load carrying capacity assuming factor of

safety is 2.

The problem requires the calculation of frictional

resistance, tip resistance, ultimate load, and allowable

load carrying capacity of circular concrete pile driven

into medium to dense sand.

First, ‘‘pile in sand’’ section is called from main

page of the program. Geotechnical properties and

depth of the water table are entered to appropriate

cells provided in the data entrance page (Fig. 11). The

user is allowed to choose bearing capacity factor from

the graph that comes on by clicking ‘‘For bearing

capacity factor click’’ button. Four different bearing

capacity factors are presented in the graph (Fig. 12)

proposed by different researchers and the user can

select any of them. Two options including loose and

medium to dense for the in situ state of sand are

provided in the same page. This selection affects the

value of critical depth. The combo box provided at

the top right corner of the window allows the user to

choose a pile material. The options are concrete,

wood, corrugated steel, smooth steel, and rusted steel.

The program assigns a specified friction coefficient

between pile-soil interfaces depending on the selected

pile material. The user can select the shape of the pile

Figure 7 Selection of pile shape and dimension.

PILE-D 361

from the same page. The options provided are square,

circular, and hexagonal cross-sections. Once the user

enters the pile diameter into the provided cell he/she

can click ‘‘Calculate’’ button to call results page

(Fig. 13). The page contains point resistance, fric-

tional resistance, ultimate capacity, and allowable

capacity values. The user may change the factor of

safety value and recalculate allowable capacity.

As in ‘‘pile in clay’’ section, the user can move

between the pages and change soil or pile properties,

and obtain new results. Also, ‘‘check your calcula-

tion’’ button allows the student to compare his/her

hand calculation with that of the program (Fig. 14).

INSTRUCTOR’S EXPERIENCE ANDSTUDENT EVALUATIONS

Pile-D program is used in CE 466 Foundation

Engineering II course, which is offered every

Figure 8 Selection of design parameters (a) alpha parameter and (b) lambda parameter.

362 CANAKCI

Figure 9 Output page for pile design in clay.

Figure 10 Calculation checking for pile design in clay.

PILE-D 363

academic year. This is an elective course and an

average of 20 students in their senior year takes the

course. After teaching the theory of load carrying

capacity of a single pile in sandy and clayey soil, some

examples considering various cases are solved.

Next, new example is given to students to solve it

in the classroom in a 30-min period. When the

given time is over, same sample problem is solved

Figure 11 Data entrance for pile design in sand.

Figure 12 Selection of bearing capacity factor.

364 CANAKCI

while demonstrating the use of Pile-D program in the

classroom. This takes only about 20 min, and thus the

use of this program does not affect the content that

needs to be covered during the classroom time.

The students taking the course obtain the program

from the instructor and they are allowed to install it

in their personal computer. They are assigned some

homework problems and they are asked to solve the

Figure 13 Output page for pile design in sand.

Figure 14 Calculation checking for pile design in sand.

PILE-D 365

problems by hand and check their solutions using

Pile-D program. They are supposed to submit both

hand and Pile-D solutions. As part of the homework

assignments, the students are also asked to perform

some analytical studies by varying some soil and pile

material parameters and observe their effects on the

results.

Verbal feedback from students is usually sought

after they complete their assignments on the use of

Pile-D. Almost all of the students find the program

user-friendly. The navigation through the program is

found easy. They say they have no problems with

understanding the meaning of buttons and icons

within the program. The automatic generation of a

plot showing the effective stress with depth consid-

ering critical depth in sandy soil and a plot showing

the change in effective stress with depth in layered

clayey soil are favored features. The students also

pointed out that the use of this program helped them to

understand the load carrying capacity of single pile in

sandy and clayey soil much better.

CONCLUSIONS

Microsoft Excel is a useful programming platform

due to its easy accessibility and execution on any type

of computers. It is well-suited to perform Geo-

technical Engineering calculations. Pile-D is a Micro-

soft Excel based educational computer program

module. It is developed as a courseware for more

effective teaching of pile foundation design in clayey

and sandy soil in undergraduate level geotechnical

engineering courses. The program allows the user to

change various parameters used in the calculations

and observe their effects on load carrying capacity of

pile in sand and clay. Using the program, the user can

configure and conduct his/her own examples inter-

actively instead of following a limited number of

examples selected by the instructor.

REFERENCES

[1] GeotechniCAL, Educational technology for ground

engineering. http://www.uwe.ac.uk/geocal/geocal.htm

2002.

[2] M. Budhu, Soil mechanics and foundations, Wiley,

New York, 2000.

[3] S. Sharma and J. H. Hardcastle, Computer based

instruction for consolidation testing, Proceedings of

the 36th Annual Symposium on Engineering Geology

and Geotechnical Engineering, Las Vegas, Nevada,

March 2001, 28�30.

[4] S. Masala and K. Biggar, Geotechnical virtual

laboratory. I. Permeability, Comp Appl Eng Educ

11 (2003), 132�143.

[5] D. P. Coduto, Foundaton design principles and

practices, Prentice Hall, Englewood Cliffs, NJ, 1994.

[6] B. M. Das, Principles of foundation engineering,

4th ed., PWS-KENT, Boston, 1999.

[7] C. Liu and J. B. Evett, Soils, foundations, 5th ed.,

Prentice Hall, Englewood Cliffs, NJ, 2001.

[8] S. A. Brretto, R. Piazzalunga, and V. G. Ribeiro, A

web-based 2D structural analysis educational software,

Comp Appl Eng Educ 11 (2003), 83�92.

[9] K. Y. Kabalan and A. El-Hajj, Digital filter design

using spreadsheets, Comp Appl Eng Educ 7 (1999),

9�15.

BIOGRAPHY

Hanifi Canakci received his BSc degree in

civil engineering fromMiddle East Technical

University, Turkey, in 1989, and his MSc

and PhD in geotechnical engineering from

University of Strathclyde, Glasgow, United

Kingdom, in 1992 and 1996, respectively.

He is currently an assistant professor in

the Department of Civil Engineering at The

University of Gaziantep in Turkey. His

current research interests are computer-aided learning and ground

improvement.

366 CANAKCI