Course Book of Foundation for Civil Engineering 2012-2013

COURSE BOOK FOR

th

STAGE CIVIL ENGINEER NG STUDENTS 2012- 013

PREPARED BY ASSIST.

ECTURER OMAR TAHA

Faculty of Engineering School School of Archit Architect ecture ure and Constru Constructio ction n Civil Engineering Department Course Information Academic Year Stage Course Title Course Code Weekly Load Instructor School /Department Inst Instru ruct ctor or Con Conta tact ct Coordin dinator Name Coor Coordin dinat ator or Cont Contac actt Text Book

2012-2013 th 4 Stage Foundation Engineering CE 40 402 4 hrs. (2 hr Theoretical + 2 hr tutorial) Assist. Lecturer : Omar Taha School of Engineering Civil Engineering Department Emai Email: l: omar omar.t .tah aha@ a@ko koya yaun univ iver ersi sity ty.o .org rg Dr. Faris Rashi shied Emai Email: l: fari faris. s.ra rashi shied@ ed@ koyau koyauni nive versi rsity. ty.or org g Joseph Joseph E. Bowles, Bowles, RE.,bS.E RE.,bS.E " Foundati Foundation on Analysis Analysis and Design"5 Design"5Th Th Edition Edition (1997) (1997)

Course Overview This course course is a prerequ prerequisite isite for the the CE 303 soil soil mechanics mechanics course. course. This is a fundame fundamental ntal course course in the Civil Civil and and Geote Geotechni chnical cal Engi Enginee neerin ring g Progra Programs. ms. The course course on "Founda "Foundation tion"" presen presents ts guida guidance nce for selecting selecting and designing foundations foundations for buildings buildings and facilities facilities of all types and associated associated features features for buildings such as earth embankments and slopes, retaining structures. Foundation design differs considerably from design of other elements of a structure because of the interaction between the structure and the supporting medium (soil and rock). The soil and rock medium are highly variable as compared to steel and concrete products above the soil; therefore, much attention is given to presenting subsurface investigation methods to better determine the properties of the soil and rock.

Course Course Obj Object ective ivess The objective of this course is to introduce students that they will be able to: Select boring boring location, location, depth, and associa associated ted laboratory laboratory tests for the project. project.  Select  Select and design the appropriate shallow foundation system and deep foundation system utilizing boring log data and associated laboratory testing and incorporating the following considerations; (a. (a. Soil Soil type type,, b. Sett Settlem lemen entt, c. Loads, d. Alternatives: Alternatives: mat, spread spread footing, footing, combin combined ed footing, footing, e. Cost.) Preparee a geotec geotechnic hnical al engine engineeri ering ng desi design gn repo report rt for for a shallow shallow and/or and/or deep deep foundat foundation ion system system  Prepar including, including, but not limited to, appropria appropriate te engineeri engineering ng analysis, analysis, discussion discussion of alterna alternatives, tives, presentation presentation of field and laboratory data, and final foundation design recommendations.  Perform a time rate of consolidation analysis .  Perform a retaining wall analysis including sliding and overturning considerations.

References "Principles of Foundation Foundation Engineering" Engineering" 7th Edition Edition (2011). (2011). 1. Braja M. Das "Principles "Geotechnical Engineering: Principles and Practices of Soil Mechanics and Foundation 2. V.N.S. Murthy, "Geotechnical Engineering"(2002) "Theoretical Foundation Foundation Engine Engineering" ering" (2007). (2007). 3. Braja M. Das "Theoretical P.E." Soil Engineering: Testing, Design, and Remediation" (1999). 4. Dr. Fu Hua Chen, P.E." (1979). 5. T. William Lambe & Robert V. Whitman "Soil Mechanics" 3rd edition (1979). A A A Assssssi i i ssst t e t O m a r T a h a t ... LLLe eccct t ... O Om ma ar r T T a ah ha a

2

Gradin Grading g Sch Scheme eme:: Exams Exams & Quizzes Quizzes First Semester Second Semester Final Exam

Marks Exam Quizzes 15% 5% 15% 5% 60% -

Course Policies:

1. No Cell Cell Phone Phone is is allowed allowed during during lecture lecture and and exam. exam. Must be OFF OFF (not silence silence or vibrating mode). 2. Be on time time to class. class. Tardy Tardy is strongl strongly y discourage discouraged. d. 3. Exam Examss and Quiz Quizze zess are are clo close sed d boo book k and and close closed d not notes es.. 4. You You shoul should d bring bring calc calcul ulat ator or to ever every y lect lecture ure.. 5. Ten-mi Ten-minut nutes es break break per per each each hour; hour; it will will be given given at at the the end of the the lect lecture ure.. Sylla Syllabus bus of Foun Foundat dation ion Cour Course se & Schedule No. of Weeks

Topic

Four Weeks Five Five We Weeks eks

Site Investigation Bearing Capacity of Foundation

Three Weeks

Shallow Foundation

Three We Weeks Four Four We Weeks eks

Foundation Settlements Deep Deep Foundat Foundation ion (Single (Single Piles) Piles)

Three We Weeks

Deep Fo F oundation (G ( Group pi p iles)

Two Weeks

Lateral Earth Pressure

Two Weeks

Retaining Walls

Two Weeks

Sheet pile Walls

Two Weeks

Slope Stability Analysis

A A A Assssssi i i ssst t e t O m a r T a h a t ... LLLe eccct t ... O Om ma ar r T T a ah ha a

3

Chapter One Site Investigation 1-1Introduction

Investigation of the underground conditions at a site is prerequisite to the economical design of the substructure elements. The field and laboratory investigations required to obtain the essential information on the subsoil is called Soil Exploration or Soil Investigation. 1-2 Obj Object ectives ives:: Genera Generally lly the purpos purposee of a soil soil explor explorati ation on program program is is to provid providee the follow following ings: s:

1) Information to determine determine the type of foundation required (shallow or deep). 2) Information Information to to allow the geotechni geotechnical cal consulta consultant nt to make a recommendati recommendation on on the allowable allowable load load capacity of the foundation. foundation. 3) Sufficient data/laboratory data/laboratory tests to to make settlement predictions. predictions. 4) Locati Location on of the groun ground d water water table table (or determ determina inati tion on of whethe whetherr it is in the the constru constructi ction on zone). zone). 5) Information Information so that the identifi identificati cation on and solution solution of construction construction problems problems (sheeting (sheeting and dewatering dewatering or rock excavation) excavation) can be made. 6) Identif Identifica icatio tion n of potentia potentiall foundat foundation ion proble problems ms (expansi (expansive ve soil, soil, collap collapsib sible le soil, soil, etc.) concerning concerning adjacent adjacent property. property. 7) Identification of construction methods for changing subsoil conditions. 1-3 Execution Execution of Soil Exploratio Exploration n Program

The three limbs of a soil exploration are:1) Plan Planni ning ng.. 2) Execut Execution ion.. 3) Report Report writ writing. ing. 1-4 Methods Methods of Investigations Investigations A- Direct methods. B- Indirect Methods. 1-5 Factors Factors Affecting Affecting the Choice of the Exploratory Exploratory Borings Methods: Methods:

The most suitable suitable method to perform subsoil exploration depends on the following factors: 1) Purpos Purposee and and infor informa mati tion on requ require ired. d. 2) 3) 4) 5) 6) 7) 8) 9)

Equipm Equipment ent avail availabi abilit lity. y. Experience Experience and and training training of available available personal. personal. Dept Depth h of hole hole.. Type Type of soi soill in the the gen gener eral al area area.. Terrai Terrain n and access accessibi ibilit lity. y. The amount amount of money money allocated allocated for for the explorat exploration. ion. Enviro Environm nmenta entall Impact Impacts. s. Disrup Disruptio tion n of existing existing struct structure. ure.


4

1-6 Sampling Sampling and and Samples:Samples:-

1) Disturbed Disturbed Samples. Samples. 2) Undisturbed Undisturbed Samples. Samples. 3) Remolded Remolded Sample Samples. s. 1-7 Number, Number, Spacing Spacing and Depth of Boring Boring

The spacing of borings can not be determined with absolute exactness. They depend upon: 1) Nature and condition of soil. 1) The shape and extent extent of building. building. 2) Importance Importance of the project project (cost of boring). 1-8 Soil Soil Testin Testing g

1) Laboratory Laboratory Tests. Tests. 2) In-situ In-situ Test (Field Tests): Tests): A- Standard Standard Penetrati Penetration on Test Test B- Cone Penetrat Penetration ion Test Test (CPT): 1) Dynamic Cone Penetration Test. 2) Static (Dutch) (Dutch) Cone Cone Penetration Penetration Test. Test. C) Fie Field Vane Shear hear Test esting ing (FV (FVST). ST). D) Fiel Field d Plat Platee Load oad Test. est. 1-9 Housel's Housel's (1929) Method of Determining Determining Safe Bearing Bearing Pressure from Settlement Consideration:

The method suggested by Housel for determining the safe bearing pressure on settleme settlement nt considerati consideration on is based on the following following formula: Q=A m+P n


5

Chapter Two Bearing Bearing Capacity Capacity of Foundation Foundation 2-1 Introduc Introduction tion:: The soil must be capable of carrying the loads from any engineered structure placed upon it without a shear failure and with with the resulting resulting settlements being being tolerable for that structure.

determine ine the allo allowab wable le beari bearing ng capaci capacity ty of soil soil 2-2 Obj Object ectives ives:: To determ 2-3 2-3 Type Typess of Sh Shea earr Fail Failur ure: e: 1) General Shear Failure. 2) Local Shear Failure. 3) Punchin Punching g Shear Failure. Failure. The ultimate bearing capacity, or the allowable soil pressure, can be calculated either from bearing capacity theories or from some of the in situ tests. Each theory has its own good and bad points.

Some of the methods methods for determining ultimate bearing capacity for the soil: 1. Terzaghi's bearing capacity theory 2. The general bearing capacity equation equ ation 3. Field tests 2-4 Terz Terzaghi’s aghi’s Bearing-Cap Bearing-Capacity acity Equation Equation

The equati equations ons for the the ultima ultimate te bearing bearing capaci capacity ty (q foundations foundations as following: following:

.) by

Terzaghi for all shapes of

 For Strip (Continuous) Footing:

q

.=

CN + q N + 0.5 γ B N

 For Square Footing:

q

.=

1.3 CN + q N + 0.4 γ B N

 For For Circu Circular lar Footi Footing ng::

q

.=

1.3CN + q N + 0.3 γ B N

 For For Rect Rectan angu gular lar Footi Footing: ng:

q

.=

CN (1 + 0.3×

) + q N + 0.5 γ B N (1 - 0.2×

)

2-5 Factor Factor of of Safety Safety

The factor of safety safety (F.S) (F.S) with respect respect to shear shear failure failure is defined defined in terms terms of the net ultimate bearing capacity ( q ) .). F.S =

)

.

)

.

=


) )

.

×

.

× 6

2-6 Effect of of Water Table Table on Bearing Bearing Capacity Capacity :

The bearing capacity equations are affected due to the presence of the water table. table. The following following cases may be considered considered here: here: When the the water water table table lies lies abov abovee or at at the base of the founda foundatio tion, n, then then the overbur overburden den Case I: When pressure (q) in the second term of the bearing capacity equations takes the form: (Overburden (Overburden pressure) pressure) q = D × γ

+ D (γ

.-

γ ) G.W.T ∇

Also the value of ( γ) in the third term has to be replaced by (γ .):

γ

.

= (γ

.-

D

Case I

D

γ ) d

D

d

B ∇ G.W.T

G.W.T ∇

Case II

the water water table lies within within depth depth < B below the base base of the Case ase II: II: When the founda foundati tion, on, where whereas as (o < d < B), then then the the over overbur burde den n press pressure ure (q) in the second term of the bearing capacity equations takes the form:

q= γ

×D

The value of (γ) in the third third term of the bearing capacity equations must be replaced *) by the value of (γ which can be calculated as:

ω = 0.5 + 0.5

*

γ =ω

×

γ

Case III: When the water water table table is located at depth depth ≥ B, the water will have no effect on the ultimate bearing capacity. 2-7 Meyerh Meyerhof’s of’s Bearin Bearing-Ca g-Capac pacity ity Equ Equatio ation: n:

P

Meyerhof (1951, 1963) proposed a bearing capacity equation similar to that that of of Terz Terzagh aghii but includ included ed the shape shape factors factors,, depth depth fact factors ors and inclinatio inclination n factors factors for cases where the footing footing load load is inclined inclined from the vertical.

D

Equations:

B

1) For vertical load:

q

.=

C N S d + q N S d + 0.5 γ B N S d

P

°

2) For Inclined load:

D q

.=

C N i d + q N i d + 0.5 γ B N i d B


7

2-8 Hansen's Hansen's Bearing-Capac Bearing-Capacity ity Method:

Hansen (1970) proposed proposed the general bearing-capaci bearing-capacity ty equation. equation. This equation equation is readily readily seen to be a further further extension extension of the earlier Meyerhof Meyerhof (1951) work. work. Equations: 1) For For (C(C-∅) Soi Soil:

q

.=

C N S d i b g + q N S d i b g + 0.5 γ B N S d i b g

2) For For Clay Clay (∅= 0) :

q

.=

′

′

′

′

′

5.14 Su (1+ Sc + dc - ic - bc -gc ) + q

2-9 Bearing Bearing Capacity of Foundations Foundations Subjected to Eccentric Loads: Loads: Genera Generally lly when when the footi footing ng subject subjected ed to eccent eccentric ric loads loads there there are are two appr approac oaches. hes. (1) Convent Convention ional al method method:: Find out the maximum stress and minimum stress under the footing using:

q

=

(1+

q

=

(1-

×

×

+

-

×

×

)

)

≤q

≥ Zero

(2) (2) Meye Meyerh rhof of’s ’s Appr Approa oach ch::

Research and observation [Meyerhof (1953, 1963) and Hansen (1970)] indicate that effective effective footing footing dimensions dimensions obtained obtained as: B′ = B - 2e

q

.=

.

L ′ = L - 2e

≥q

.=

.

×

2-10 Bearing Bearing Capacity Capacity of Footings on on Slopes:

A special problem that may be encountered occasionally is that of a footing footing located on or adjace adjacent nt to a slope. slope. 2-11 Bearing Bearing Capacity Capacity from Field Tests Tests

1) Bearing Capacity from Standard Penetration Test (SPT) 2) Bearing Bearing Capacit Capacity y from Cone Penetrat Penetration ion Test Test (CPT)


8

Chapter Three Shallow Foundation 3-1 Introduc Introduction tion::

Shallow foundations are those foundations are founded near to the finished finished ground surface. 3-2 Obj Object ectives ives of foundat foundation ion:: The objecti objective ve of foundat foundation ion is to transfer transfer the the loads loads of superstructure to the subsoil safely: 1) Without Without exceeding exceeding the load load carrying capacit capacity y of the subsoil strata. strata. 2) Without Without causing causing settlement settlementss which which exceed exceed the permiss permissible ible limit. limit. Foundation : is the lower part of the building or any other structure which transfers the load and distribute it on the soil.

good foundati foundation on design design ensures ensures that that struct structura urall loads loads Foundation Design: a good (including weight of foundations) are transferred to the the ground safely and economically. Foundation can be classified classified according to its depth to the width into two types: 1) Shallow Shallow Foundat Foundation ion (D ≤ B) 2) Deep Deep Foundat Foundation ion (D >> B). 3-3 Types of Shallow Shallow Foundation Foundation::

footing carrying carrying a single single column column is 1) Spread (Isolated (Isolated or Single) Footing: A footing called a spread footing.. footing.... Spread footing footing can be seen as: A) Column Column Footing Footing.. B) Ste Stepped pped Footing Footing.. C) Sloped Sloped Footin Footing. g. D) Wall Footing. Figure Figure (3-1) (3-1) below below shows shows the type typess of the sprea spread d footing footing::

Typical footings, footings, (a) Single Single or spread footings; footings; (b) Stepped Stepped footing; footing; Figure (3-1): Typical (c) Sloped Sloped footing footing;; (d) Wall Wall footi footing ng;; (e) Footing Footing with pedest pedestal. al.


9

2) Combined Combined Footing: Footing: When a footing supports a line of two or more columns, it is called a combined footing. A combined footing may have either rectangular or trapezoidal shape. These several footing types are illustrated as shown below: A) Recta Rectang ngul ular ar Foot Footin ing g B) Tr Trap apez ezoi oida dall Foot Footing ing C) Strap or Cantilev Cantilever er

The figure (3-2) below shows the types of the combined footing:

Figure (3-2) : (A) Rectangular Rectangular Footing (B) Trapezoidal Trapezoidal Footing (C) Strap Strap Footing

3) Raft (Mat) Foundation: A mat foundation is a large concrete slab used to interface one column or more one colum column n in severa severall lines, lines, with with the the base soil. soil. The figure figure below below illus illustra trates tes several several mat configuration configurationss as might be used for buildings. buildings.

Figure (3-3): Common Common types types of mat mat found foundation ations, s, (a) Flat plate; (b) plate thickened thickened under columns; columns; (c) waffle-slab; waffle-slab; (d) plate with pedestals; pedestals; (e) basement basement walls walls as part of of mat. mat.


10

3-4 Design of Dimensions Dimensions of Footings: Footings:

maximum pressure pressure which the soil soil can carry Allowable Bearing Capacity ( ): The maximum safely without risk risk of neither shear failure failure nor excessive settlement settlement (units: kN/m ). V A

≤q

V

The design design of any foundation foundation can be of two approaches: approaches: 1) Uniform Pressure Pressure Intensity: Intensity: This is done by locating the location location of the resulta resultant nt of the colum columns ns loads (R) at the same same location location of the center center of gravity of the plan plan of footing. footing.

q

=

V A

A=B×L

q

≤q

This is is done done when when the the loca locati tion on of the the res resul ulta tant nt of of 2) Increasing Increasing Pressure Pressure Intensity: Intensity: This the column columnss loads loads on a foot footing ing (R) does does not not pass pass thro through ugh the the cent center er of the footin footing, g, the footi footing ng is subjec subjected ted to to what what is called called eccen eccentri tricc loadin loading, g, this this will will develo develop p increasing increasing pressure pressure intensity intensity as shown shown in figure below, below, and this will will cause non uniform pressure. The intensity of the pressure developed under the foundation can be expressed as:

q

=

(1+

q

=

(1-

×

×


+

-

×

×

)

)

≤q

≥ Zero 11

Chapter Four Foundation Settlements 4-1Objectives

Foundation Foundation settleme settlements nts must be estimated estimated with great great care for buildings, buildings, bridges, bridges, towers, towers, power plants plants,, and simila similarr high-cost high-cost structur structures es to avoid avoid the damage damage of the structure. structure. The total total settlem settlement ent of a foundation foundation compris comprises es of three parts as as follows: follows:

S

.=

S +S +S

4-2 Immediate Immediate Settlement: Settlement: This occurs occurs due to elastic elastic deformation deformation of dry soils soils and of moist soils without any change in water content. . ×B (

S= q

)× I

Consolidation ion settlement settlement occurs occurs in saturated saturated clayey 4-3 Cons Consoli olida dati tion on Se Settl ttlem ement ent:: Consolidat soils when when they are subjected subjected to increment increment load load caused caused by foundation foundation construct construction. ion. The final consolidation settlement can be calculated by using one of the following correlations:

S =(

∆

)× H

S = m × ∆p ∆p × H S =

×Hlog

∆

For Normally Normally Consoli Consolidated dated Clay (N.C.C.), (N.C.C.), (O.C.R. (O.C.R. ≤1)

For Over Over Consoli Consolidat dated ed Clay Clay (O.C.C (O.C.C.), .), (O.C.R (O.C.R.. >1) A) If p +∆p≤p , then use;

S =

×Hlog

∆

B) If p +∆p>p , then use;

S =

×Hlog

+

×Hlog

∆

primary consolidation the soil soil structure continues 4-4 Secondary Secondary Settlement: Settlement: After primary to adjust to the load for some additional time.

S = C∝ × H log


12

Chapt Chapter er Five Five Deep Foundation (Single Piles) 5-1 Introduc Introduction tion

Piles are structural members of timber, concrete, and/or steel that are used to transmit surface loads to lower levels in the soil mass. The major uses of piles are: 1. To carry vertical compression load. 2. To resist uplift load. 3. To resist horizontal or inclined loads 5-2 Classification Classification of of Piles: A) According to Their Materials  Timber Piles,  Concrete Piles  Steel Piles. B) According to the method of construction  Driven piles,  Bored Bored pile piless 5-3 Dete Determ rmina inati tion on of Be Bear arin ing g Capa Capaci city: ty:

The ultimate bearing capacity of pile Q ult , is generally represented by the formula: Qult = Q b + Qs Q b: Ultimate bearing resistance available. Qs : Ultimate shaft resistance available. Bearin ing g capac capacit ity y of pile piless in cohe cohesi sive ve soil soilss ( ( = 0) A) Bear Bearin ing g capac capacit ity y of pile piless in cohe cohesi sion onle less ss soils soils (Cu = 0) B) Bear Pile capaci capacity ty in (C (C -  soils) C) Pile 5-4 Obj Object ectives ives:: Upon completion of this semester, students will be able to 

Design and Analysis of Deep Foundations  Calculate side and tip capacity of driven d riven piles in clay  Calculate side and tip capacity of driven piles in sand


13

Chap Chapter ter Six Six Deep Foundation Foundation (Group (Group Piles) 6-1 Introduc Introduction tion

When several pile butts are attached to a common structural element termed a pile cap the result is a pile pile group. Typical arrangements of piles are shown.

6-2 Group Group Actio Action n:

When a pile is installed immediately adjacent to each other the the respective respective bulbs of vertical vertical pressure can overlap as shown in figure. 6-3 Efficiency Efficiency of Pile Group Group (Eg): (Eg):

Since the pile group is not necessarily equal to the sum of the capacities of the piles in the group. In general Eg =

(

)

(

)

×

The efficiency calculates for: Pile group groupss in cohe cohesi sive ve soil soilss ( ( = 0) A) Pile Pile grou groups ps in cohe cohesi sionl onless ess soils soils (Cu = 0) B) Pile 6-4 Pile Groups Groups Subjected Subjected to to Moment:

To calculate the ultimate bearing capacity for each e ach pile in a group subjected su bjected to moment.

P

=

∑

±

× ∑

±

× ∑

6-5 Settlement Settlement of Pile Group 1- Consol Consolida idati tion on settl settleme ement nt of pile pile groups groups 2- Elasti Elasticc settlem settlement ent of pile pile groups groups A A A Assssssi i i ssst t e t O m a r T a h a t ... LLLe eccct t ... O Om ma ar r T T a ah ha a

14

Chap Chapter ter Se Seven ven Lateral Earth Pressure 7-1 Introduc Introduction tion

Earth pressure: pressure: It is pressures pressures of forces which produce from soil and acting acting on the wall which which retained retained it, so it is called called a lateral lateral earth earth pressure. pressure. 7-2 7-2 Type Type of of Late Latera rall Eart Earth h Pres Pressu sure re

It is based on the type and direction movement of retaining wall. 1- Ea E arth Pressureat Rest

Ko =

2- Active Active Earth Earth Pressur Pressuree (Pa) P a = Ka × γ × h

2

∅

2

∅

K a =

= tan ( 45 -

K p =

= tan ( 45 -

)

3- Passive Passive Earth Earth Pres Pressure sure (P p) Pa = Ka × γ × h

)

7-3 Rankine's Rankine's Theory Theory of Earth Pressure Pressure : It considers the equilibrium of an element in a mass of homogenous cohesionless soil of semi-infinite extent.

 If soil surface sloping at angle (  (  )

K a = Cos 

K p = Cos 

























7-4 Coulomb's Coulomb's Theory Theory of Earth Pressure Pressure : This theory takes wall friction into consideration.

K a =

K p =


( (

(∅ (

) (

(

)

∅) ) )

(∅ (

) )

) )

(∅ (

) )

∅) (∅ (

15

Chapt Chapter er Eigh Eightt Retaining Walls 8-1 Introduc Introduction tion

Both the Rankine Rankine and Coulomb Coulomb methods are widely widely used to compute compute the lateral lateral earth pressure on retaining walls. To check the stability of retaining wall, the following steps are used: overturning. 1- Check for overturning

F.S(

for sliding sliding along along the base. 2- Check for

F.S(

bearing capacity capacity failure failure of the base. 3- Check the bearing

F.S(

)

)

=

=

∑ ∑

∑ ∑

)

=

Chapt Chapter er Nine Nine Sheet Pile Wall 9-1 Introduc Introduction tion

Sheet pile walls are retaining walls constructed to retain earth, water or any other fill material. These walls are thinner in section as compared with retaining wall. Sheet pile walls walls are generally used used for the following: following: 1. Water front structures, for example, in building wharfs, quays, and piers 2. Building diversion dams, such as cofferdams 3. River bank protection 4. Retaining the sides of cuts made in earth Sheet piles may conveniently be used in several civil engineering works: 1. Cantilever Cantilever sheet sheet piles: piles: the piles are are fixed only only at the bottom bottom and are are free at the top. 2. Anchored Anchored bulkhe bulkheads ads: the lower ends are are driven driven into into the earth and the upper ends ends are anchored by tie or anchor rods. There are several methods of analyzing cantilever and anchored sheet-pile walls: 1. Free Free earth earth support support 2. Fixed earth support:


16

Chapt Chapter er Te Ten n Slope Stability Stability Analysis Analysis 10-1 10-1 Introduc Introductio tion n

The static stabilit stability y of slopes of earth and rock-fill dams, slopes slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock. This course course is designed designed to give give students students a thorough thorough understanding understanding of of the analysis analysis of the stability stability of natural and engineered engineered slopes. slopes. Emphasis Emphasis will be placed on the use of limit equilibrium methods to analyze slopes using field and laborato laboratory ry data. Discussion Discussion on the probabilist probabilistic ic analysi analysiss of slopes, slopes, along with stabilization stabilization of failed failed slopes, will also be presented. 10-2 Objectives :

1. Learn the principles of of slope stability; stability; factors that affect slope stability; stability; methods of analyzing stability of slopes and embankments. 2. Learn Learn how how to site, site, desi design gn and anal analyze yze eart earth h dams; dams; acquai acquaint nt the student student with with the the basic principles of large earth dam engineering; learn how to evaluate dam stability and seepage. 3. Learn how to continue continue to learn about about slope stability and dams after the course.


17

School of Engineering Civil Eng. Department

Date: -/-/Time: 90 minutes.

Exam

adequacy of four square square spread spread Q1-A): Check the adequacy footing (2×2× 0.5) 0.5) m show shown n belo below w for for the the follow following ing data: data:  Weight of tower = 600 kN k N (weight of foundation not included)  Moment due to wind = 2500 kN.m  Minimum Minimum factor of safety is (3)  concrete = 25 kN/m3 , water = 10 kN/m3

Tower

1.5 m

W.T  = 26º sat. = 17 kN/m3 3 dry= 11.11 kN/m

Wind

4m

7m C= 130  = 30º sat. = 19 kN/m3

7m

8m

(2×2×0.5) m

wall footing shown shown in figure. figure. Find Q1-B): For the wall moment moment (M) to give give equal equal pressure pressure distribution q . = 180 180 kpa kpa..

V = 500 kN/m M =?

1m

following g square footing footing by Q2-A): Check the followin using Terzaghi’s Terzaghi’s bearing bearing capacity capacity equation, given (FS = 2.5), P = 4000 kN.

2m

2m ∇

1m

∇

3×3m Sand ∅= 30° γ = 19 kN/m Gs = 2.7


18

A

Q2-B) Design spread footings for the three columns shown in figure and sketch the layout, q . = 150 150 kpa kpa..

Column A B C

Dimension 0.3 × 0.3 0.3 × 0.3 0.4 × 0.4

Load 500 700 900

3m

B

C

3m

Q3): What is the purpose of the site investigation?


19

Answers:

Tower

Q1-A/

H = 0.5B tan (45 +

∅

)

H = 0.5×2 tan (45 +

) = 1.6 m W.T

The effectiv effectivee depth depth shear (H) (H) within within the first layer. Forc Forces es pe perr leg leg of foun foundat dation ion::

According to weight of tower =

= 150 kN

 = 26º sat. = 17 kN/m3 dry= 12 kN/m3

1.5 m

4m

= 357.14 kN ÷ 2 = 178. 178.6 6 kN

According to moment =

Max. Max. Force Force per leg leg = 150 + 178.6 178.6 = 328.6 328.6 kN kN

C= 130 130  = 30º sat. = 19 kN/m3

8m

Min. Min. Forc Forcee per leg leg = 150 150  178.6 =  = 28.6 28.6 kN Check F.S against uplift: Total weight of footing = (2×2×0.5×25) + (2×2×1×11.11) =94.4 kN Uplift force = 28.6 kN .

F.S again against st uplift uplift =

.

= 3.3 > 3 o.k.

Check F.S against against shear failure: failure:

Wind

7m

qu = C Nc Sc dc + q' Nq Sq dq + 0.5  0.5  B N S d 2

q' = 1.5× 1.5×12 12 =18 =18 kN/m kN/m

7m

(2×2×0.5) m

From Table (2-3), for   = 26º Nq = 11 1 1.8,

N =7.9

Sq = 1 + tan  tan  ( S = 1  1  0.4 ( =

) = 1 + tan 26 × ( ) = 1  0.4× (

) = 1.4877

) = 0.6

1.5 = 0.75 <1 2

Then: A A A Assssssi i i ssst t e t O m a r T a h a t ... LLLe eccct t ... O Om ma ar r T T a ah ha a

20

2

2

dq = 1 + 2tan  2tan  (1- sin sin) (

) = 1 + 2tan (26) (1- sin 26) (

.

) = 1.2 1.23

d =1 2

qult.)g = 18×1 18×11. 1.8× 8×1. 1.48 4877× 77×1. 1.23 23 + 0.5× 0.5× (17 (1710) ×2×7. ×2×7.9×0. 9×0.6×1 6×1= = 421.844 421.844 kN/m kN/m qact)g =

.

=

F.S =

.

2

= 105.75 kN/m ≤ q

×

.)

×

.)

×

.

=

.) g

= 4.6 O.k.

.

Q1-B)

∵ Uniform soil pressure L = (d + e) × 2 V = 500 kN/m

3 = (1 + e) × 2

M =?

∴ e = 0.5 m e= 1m

0.5 =

2m

M = 250 kN.m/m

Q2-A/

γ

=

.

19 =

(γ )

.

(10)

∴ e = 0.88

2m ∇

γ

(γ ) =

=

. .

(10 10)) = 14.3 4.3 kN/m

1m

∇

3×3m

Apply Apply the ulti ultima mate te B.C B.C equati equation on for square square footi footing; ng;

Sand ∅= 30° γ = 19 kN/m

q

Gs = 2.7

.=1.3

CN + q N + 0.4 γ B N

From From Tabl Tablee (2.1) (2.1) for ∅ = 30°

N = 22.5

and

N = 19.7

q = 14.3 × 2 + (19 – 10) × 1 = 37.6 kN/m γ

.=

(γ

.–

γ )


21

γ

.=

19 – 10 = 9 kN/m

q

.=0

+ 37.6 × 22.5 + 0.4 × 9 × 3 × 19.7

= 1058. 1058.76 76 kN/ kN/m Find ( q

q q

)

=

)

=

)

×

qult.)g

+ ( γ ×D )

. .

.

(37.6) 6) = 548.1 548.18 8 kN/ kN/m + (37.

Find the actual actual pressure pressure on soil; soil;

q P

.

.= .

q

= 4000 + 3 × 3× 1× 24 + 3 × 3× 2× 14.3 = 4473.4 kN .

.=

= 497 kN/m < q

×

)

= 548 548.18 kN/ kN/m

ok

Q2-B)

B (m)

L (m ( m)

Col. (A)

Area =

= 3.33

1.83

1.83

Col. (B)

Area =

= 4.66

2.2

2.2

Col. (C)

Area =

= 6.0

2.45

2.45

2.6 – 2.6 – 3 –

.

. .

.

–

.

– –

= 0.46

.

= 0.58 0.585 5

A

= 0.67 0.675 5 0.46 m

0.585 5m 2.6 m 0.58

B

C

0.675 m


22

Q3 / the purpose purpose of a soil exploratio exploration n program is to provide provide the followings: followings:

1) Information to determine determine the type of foundation required (shallow or deep). 2) Information Information to to allow the geotechni geotechnical cal consulta consultant nt to make a recommendati recommendation on on the allowable allowable load load capacity of the foundation. foundation. 3) Sufficient data/laboratory data/laboratory tests to make settlement settlement predictions. 4) Locati Location on of the groun ground d water water table table (or determ determina inati tion on of whethe whetherr it is in the the constru constructi ction on zone). zone). 5) Information Information so that the identifi identificati cation on and solution solution of construction construction problems problems (sheeting (sheeting and and dewatering dewatering or rock excavation) excavation) can can be made. made. 6) Identif Identifica icatio tion n of potentia potentiall foundat foundation ion proble problems ms (expansi (expansive ve soil, soil, collap collapsib sible le soil, soil, etc.) concerning concerning adjacent adjacent property. property. 7) Identification of construction methods for changing subsoil conditions.


23

Course Book of Foundation for Civil Engineering 2012-2013

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