Drilled Shafts Foundation

Department of Civil Engineering, University Putra Malaysia, Malaysia 

The advantages of this type of foundation over other similar t)q)es are as follows  

2 DESIGN OF A DRILLED SHAFT Axial load carrying capacity of drilled shafts 

The primary load on a drilled shaft is usually axial, either downward or uplift. Therefore, it is necessary to select a diameter and length that produce sufficient skin friction and end bearing capacities. There are several methods of determining the axial capacity of drilled shaft. The important methods are  

The most common method of designing a drilled shaft is based on soil properties obtained from field and laboratory tests. The analyses are similar to those of driven piles and are subject to similar uncertainties. End bearing and skin friction resistances are computed, though the methods of computing these factors are different because of their construction dissimilarities. 

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Osterberg, J.O. 1984. A new simplified method for load testing drilled shafts. Foundation drilling. Association of drilled shaft contractors. Dallas. 

Carter, J. R, and Kulhawy, F. H. 1988. Analysis and Design of Drilled Shaft Foundations Socketed into Rock, Report No. EL-5918, Empire State Electric Engineering Research Corporation and Electric Power Research Institute, New York, NY. 

Drilled shaft foundations are the most versatile types of foundations. The length and size of the foundations can be tailored easily. Disturbance to the nearby structures is small compared with other types of deep foundations. Drilled shafts can be constructed very close to existing structures and can be constructed under low overhead conditions. Therefore, drilled shafts are often used in many seismic retrofit projects. However, drilled shafts may be difficult to install under certain ground conditions such as soft soil, loose sand, sand under water, and soils with boulders. Drilled shaft will generate a large volume of soil cuttings and fluid and can be mess. Disposal of the cuttings is usually a concern for sites with contaminated soils. 

Drilled shaft foundations are usually comparable or more expensive than driven piles. For large bridge foundations, their cost is at the same level of caisson foundations and spread footing foundations combined with cofferdam construction. Drilled shaft foundations can be constructed very fast under normal conditions compared with caisson and cofferdam construction. 

The following design requirements shall apply (ATC-32 1996) to bridges on drilled shaft foundations ... 

In recent years, there have been a number of innovative piling systems in addition to the already established driven piles, drilled shafts and caisson foundations. A variant of the pile support system is the Augeo pile system. According to Abdullah et al. (2003), the Augeo pile system is theoretically cheaper than the conventional pile system. 

Chin (2004) presents results of a static load test on a 825 mm diameter drilled shaft and assessed it with regard to the relevant settlement acceptance criteria of Table 11.1. The Malaysian PWD specification for piling works was adopted as the standard specification governing the testing and foundation pile performance. 

The most common source of dynamic loading is a pile hammer, because it is already on site and thus represents little or no additional cost. Therefore, these tests are most commonly performed on driven pile foundations. However, dynamic loads also can be obtained with drop hammers that enable testing of drilled shafts and other types of deep foundations. 

Another factor which has exacerbated the problem is that in some foundations, e.g. drilled shafts (or bored piles) and caisson, part of the constmction process, take place out of sight below ground. Furthermore, for all pile foundations, the pile shafts below ground are not visible or accessible after completion. Such lack of visibility hamper quahty control although special measures, such as sonic logging, may be adopted to alleviate the problem. 

A pile extension pier consists of a drilled shaft as the foundation and the circular column extended above the shaft to form the substructure. An obvious advantage of this type of pier is that they occupy a minimal amount of space. Widening an existing bridge in some instances may require pile extensions because space limitation precludes the use of other types of foundations. 

A shaft is a type of foundation that is constructed with cast-in-place concrete after a hole is first drilled or excavated. A rock socket is a shaft foundation installed in rock. A shaft foundation is also called a drilled pier foundation. 

Kulhawy, F. H. and K. K. Phoon. 1993. Drilled Shaft Side Resistance in Clay Soil or Rock, Design and Performance of Deep Foundations Piles and Piers in Soil to Soft Rock, Eds. P.P Nelson, T.D. Smith and E.C. Clukey, ASCE, Reston, VA. pp. 172-183. 

Horvath, R. G. and T. C. Kenney. 1979. Shaft Resistance of Rock-Socketed Drilled Piers, Symposium on Deep Foundations, ASCE National Convention, Atlanta, GA, pp. 182-214. 

Bridge Drilled Non-linear Soil Equivalent Coupled Foundation Shaft System Spring Model Cantilever Stiffness Matrix... 

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