Download presentation

1
**8. Axial Capacity of Single Piles**

CIV4249 ©1998 Dr. J.P. Seidel Modified by J.K. Kodikara, 2001

2
**Methods Pile driving formulae Static load test**

Dynamic or Statnamic load test Static formulae

3
**Pile driving formulae e.g. Hiley formula (Energy balance) Q = e.W.h .**

F (set + tc / 2) Ru= working load, W=weight of the hammer, h= height of the hammer drop (stroke), F=factor of safety tc= elastic (temporary) compression = efficiency F D s tc Ru

4
**Static Load Test Load Deflection What is the failure load?**

Plunging failure Load to specified contract requirement Davisson’s Method Butler and Hoy Chin’s Method Brinch Hanson etc. etc. What is the distribution of resistance? Approximate methods Instrumentation Deflection

5
**Dynamic and Statnamic Testing Methods**

Rapid alternatives to static testing Cheaper Separate dynamic resistance Correlation

6
Pu Axial Capacity W Qs Pu = Qb + Qs - W Qb

7
**Base Resistance Qb Qb = Ab [cbNc + P’ob(Nq-1) + 0.5gBNg + Pob]**

minus weight of pile, Wp but Wp » Ab.Pob Qb and as L >>B, 0.5gBNg << Wp and for f > 0, Nq - 1 » Nq Qb = Ab [cbNc + P’obNq]

8
**Shaft Resistance As Due to cohesion or friction**

Cohesive component : Qsc = As . a . cs Frictional component : Qsf = As .K P’ostan d P’os K.P’os Qs = Qsc + Qsf = As [ a .cs + K P’ostan d ]

9
**Total Pile Resistance Qu = Qb + Qs**

Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’otan d ] How do we compute Qu when shaft resistance along the pile is varying?

10
Mobilization % diam 2 - 5mm Load Total Base Shaft Settlement

11
**Piles in Clay Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’otan d ]**

Qu = AbcbNc + Asa .cs Undrained Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’otan d ] Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’otan d ] Qu = Ab P’obNq + AsK P’ostan d Drained / Effective Qu = Ab P’obNq + AsK P’otan d Qu = AbcbNc + Asa .cs

12
Driven Piles in Clay

13
Driven Piles in Clay

14
**Nc Parameter Nc Compare Skempton’s Nc for shallow foundations**

Nc= 5(1+0.2B/L)(1+0.2D/ B)

15
Adhesion Factor, Aust. Piling Code, AS159 (1978)

16
**Bored Piles in Clay Skempton’s recommendations for side resistance**

= for cu <215 kPa cu =100 kPa for cu>215 kPa Nc is limited to 9. A reduction factor is applied to account for likely fissuring (I.e., Qb = Ab cb Nc)

17
Soil disturbance sampling attempts to establish in-situ strength values soil is failed/remoulded by driving or drilling pile installation causes substantial disturbance bored piles : potential loosening driven piles : probable densification

18
Scale effects Laboratory samples or in-situ tests involve small volumes of soil Failure of soil around piles involves much larger soil volumes If soil is fissured, the sample may not be representative

19
**Piles in Sand Qu = Ab [cbNc+P’obNq] + As [ a .cs+K P’ostan d ]**

Qu = Ab P’obNq] + AsK P’ostan d ]

20
**Overburden Stress P’ob**

Qu = Ab P’obNq] + AsK P’ostan d ] Meyerhof Method : P’ob = g’z Vesic Method : critical depth, zc for z < zc : P’ob = g’z for z > zc : P’ob = g’zc zc/d is a function of f after installation - see graph p. 24

21
Critical Depth (zc)

22
**Bearing Factor, Nq Qu = Ab P’obNq] + AsK P’ostan d ]**

Nq is a function of : Nq is a function of : friction angle, f Total end bearing may also be limited: Layered soils : Nq may be reduced if penetration insufficient. e.g. Meyerhof (p 21) What affects f ? In-situ density Particle properties Installation procedure Meyerhof : Qb < Ab50Nqtanf Beware if f is pre- or post-installation: Nq determined from graphs appropriate to each particular method

23
**Nq factor (Berezantzev’s Method)**

If D/B <4 reduce proportionately to Terzaghi and Peck values

24
**Overburden Stress P’os**

Qu = Ab P’obNq] + AsK P’ostan d ] Meyerhof Method : P’os = g’zmid Vesic Method : critical depth, zc for zmid < zc : P’ob = g’z for zmid > zc : P’ob = g’zc zc/d is a function of f after installation - see graph p. 24

25
**Lateral stress parameter, K**

A function of Ko normally consolidated or overconsolidated - see Kulhawy properties manual see recommendations by Das, Kulhawy (p26) A function of installation driven piles (full, partial displacement) bored piles augercast piles screwed piles

27
**K.tand The K and tand values are often combined into a single function**

see p 28 for Vesic values from Poulos and Davis

28
**Pile-soil friction angle, d**

A function of f See values by Broms and Kulhawy (p26) A function of pile material steel, concrete, timber A function of pile roughness precast concrete Cast-in-place concrete

29
**Pile-soil friction angle**

30
**Example Driven precast concrete pile 350mm square**

Uniform dense sand (f = 40o ; g = 21kN/m3) Water table at 1m Pile length 15m Check end bearing with Vesic and Meyerhof Methods Pile is driven on 2m further into a very dense layer f = 44o ; g = 21.7 kN/m3 Compute modified capacity using Meyerhof

31
**Example Bored pile 900mm diameter**

Uniform medium dense sand (f = 35o ; g = 19.5kN/m3) Water table at 1m Pile length 20m Check shaft capacity with Vesic and Meyerhof Methods By comparsion, check capacity of 550mm diameter screwed pile

32
**Lateral load on single pile**

Calculation of ultimate lateral resistance (refer website/handouts for details) Lateral pile deflection (use use subgrade reaction method, p-y analysis) Rock socketed pile (use rocket, Carter et al method)

Similar presentations

Presentation is loading. Please wait....

OK

TOPIC 2: TYPES OF FOUNDATION

TOPIC 2: TYPES OF FOUNDATION

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on astronomy and astrophysics journals Start a ppt on a remote computer Ppt on viruses and anti viruses Ppt on isobars and isotopes of uranium Hrm ppt on recruitment process Ppt on pricing policy samples Ppt on cloud computing technology Procedure text how to make ppt online Download ppt on mind controlled robotic arms Ppt on endangered species in india