(2)

where:

RF = Reduction factor.

Q_{mod} = Modified Chin’s value of ultimate capacity.

Q_{ch} = Chin’s value of ultimate capacity.

5.5. Decourt’s Extrapolation (1999)

Applying Decourt’s Extrapolation by dividing each load by its corresponding settlement and ploting the resulting values against the applied load. A linear regression over the apparent line (last three points) determines a line. Decourt identified the ultimate load as the intersection of this line with load axis as shown in Figures 11 for working test pile #3 [13].

6. Proposed Method for Determination of Ultimate Pile Capacity from Load Test

The load vs settlement behavior of the pile is extrapolated using an empirical method. The estimation of ultimate load consists of two steps as given below:

1) Plotting load settlement curve from field load test data as shown in Figures 12-14.

2) The ultimate pile capacity is given by the empirical formula:

(3)

where:

Q_{u} = ultimate load capacity (kN).

m = slope of the trend straight line.

y = y-intercept of the straight line (as a value without sign).

7. Comparison between Different Methods for Determination of Ultimate Pile Capacity

The calculation of the ultimate capacity of piles and the corresponding factors of safety using the above mention methods are summarized in Table 5.

The ultimate loads obtained by various methods from the pile load test results are shown in Figure 15.

8. Load Carried by End Bearing and Friction along Shaft

From Table 6 the values of the ultimate pile capacity were taken to evaluate the percentage of friction and end bearing capacity from Figure 3. Based on the above findings, it was found that the percentage of load carried by friction along the pile shaft and the end bearing are shown in the following Table 6.

Figure 10. Ultimate pile capacity by Ahmad and Pise method for non-working test pile #1.

Figure 11. Ultimate pile capacities by Decourt’s extrapolation method for working test pile #3.

Figure 12. Ultimate pile capacity using proposed method for non-working test pile #1.

9. Conclusions

From the testing program and comparable study conducted, the following conclusions are arrived at:

1) The percentage of friction load carried by the shaft is approximately 85% to 90% and the percentage of load carried by the end bearing is 15% to 10%.

2) Hansen (1963) method gives higher values of ultimate capacity carried by the pile than the other methods.

3) A new proposed method to calculate the ultimate capacity of pile from pile load test is presented.

4) The proposed method for determining the ultimate capacity of friction piles appears to give results that are in good agreement with the analytical predictions.

5) The proposed method is good to apply, easier, quicker, more reliable, does not give max or min numbers as compared to some others.

Figure 13. Ultimate pile capacity piles using proposed method for working test pile pile #2.

Figure 14. Ultimate pile capacity pile using proposed method for working test pile #3.

Table 5. Ultimate capacity and factor of safety (F.S.) of pile using different methods.

Figure 15. Comparison of ultimate pile loads using different methods.

Table 6. Percentage of ultimate load carried by end bearing and friction.

10. Acknowledgements

The author would like to acknowledge the Fetih Construction Company and Pauer-Egypt Company for their valuable assistance.

REFERENCES

- U. A. A. Mirza, “Pile Skin Friction in Clays,” International Journal of Offshore and Polar Engineering, Vol. 7, No. 1, 1997, pp. 538-540.
- D. M. Dewaikar and M. J. Pallavi, “Analysis of Pile Load Tests Data,” Journal of Southeast Asian Geotechnical Society, Vol. 6, No. 4, 2000, pp. 27-39.
- F. I. Nabil, “Axial Load Tests on Bored Piles and Pile Groups in Cemented Sands,” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 127, No. 9, 2001, pp. 766-733. doi:10.1061/(ASCE)1090-0241(2001)127:9(766)
- G. E. Abdelrahman, E. M. Shaarawi and K. S. Abouzaid, “Interpretation of Axial Pile Load Test Results for Continuous Flight Auger Piles,” Emerging Technologies in Structural Engineering, Proceedings of the 9th Arab Structural Engineering Conference, Abu Dhabi, 29 November- 1 December 2003, pp. 791-802.
- M. Wehnert and P. A. Vermeer, “Numerical Analysis of Load Test on Bored Piles,” Proceedings of the Ninth International Symposium on “Numerical Models in Geomechanics”, Ottawa, 25-27 August 2004, pp. 1-6.
- A. M. Radwan, A. H. Abdel-rahman, M. Rabie and M. F. Awad-Allah, “New Suggested Approach for Design of Large Diameter Bored Piles Based on Finite Element Analysis,” Twelfth International Colloquium on Structural and Geotechnical Engineering (12th ICSGE), 10-12 December 2007, Cairo, pp. 340-357.
- Egyptian Code, “Soil Mechanics and Foundation,” Organization, Cairo, 2005.
- A. Akbar, S. Khilji, S. B. Khan, M. S. Qureshi and M. Sattar, “Shaft Friction of Bored Piles in Hard Clay,” Pakistan Journal of Engineering and Applied Science, Vol. 3, 2008, pp. 54-60.
- H. H. Al Jairry, “Exact Probability Equation for Friction Piles in Clay,” Iraqi Journal of Civil Engineering, Vol. 6, No. 1, 2009, pp. 791-802.
- J. B. Hansen, “Discussion on Hyperbolic Stress-Strain Response, Cohesive Soils,” Journal for Soil Mechanics and Foundation Engineering, Vol. 89, 1963, pp. 241- 242.
- F. K. Chin, “Estimation of the Ultimate Load of Piles from Tests Not Carried to Failure,” Proceedings of Second Southeast Asian Conference on Soil Engineering, Singapore City, 11-15 June 1970, pp. 81-92.
- F. Ahmed and P. J. Pise, “Pile Load Test Data-Interpretation & Correlation Study,” Indian Geotechnical Conference, Vadodara, 17-20 December 1997, pp. 443-446.
- L. Decourt, “Behavior of Foundations under Working Load Conditions,” Proceedings of the 11th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, Foz DoIguassu, August 1999, Vol. 4, pp. 453-488.