■建築研究報告 |
Statistical Observations on Reliablity of Pile Driving Formula Yorihiko OHSAKI 建築研究報告 No.23, 1957 建設省建築研究所 |
＜概要＞ |
In old Japanese Building Code, the determination
of allowable load on pile was governed by the provision that:
The allowable loads on piles driven by drop hammers shall not exceed the value R determined by the following formula;
Where
The pile driving formula (1) specified in this provision is of the type of Engineering News formula. In 1952, the Architectural Institute of Japan issued Standard Design Specifications for Building Foundations, in which Kreuter's formula was proposed for determining the allowable loads on piles. In 1954, the present Building Code has been enforced by the Government and the same formula of Kreuter's is adopted therein. No information, however, is available for the writer on the reason why the old Engineering News had to be withdrawn. According to the present provision, the allowable loads on piles (driven by drop hammers) should not exceed the value R obtained by the following formula except when determined by pile loading tests: Where
The height of fall for zero penetration, H0, should be estimated from a diagram as shown in Fig. 1, in which pile driving should be repeated three times with different heights of fall of the drop hammer. It will be readily known that this height for zero penetration, H0, corresponds to the energy loss during pile driving. However, experienced engineers accustomed to the use of Engineering News formula in the past make complaint quite often that the old formula is far more preferable from the view-point of practice than the new formula of Kreuter's type. The reasons of their complaints may be summarized as follows;
In addition, it may also be undeniable that Engineering News formula was favored because of its simplicity in expression. It is the writer's opinion, however, that the superiority of a pile driving formula over other ones must be judged deliberately on the basis of a large number of accumulated informations on the comparison of computed values and true carrying capacities of the piles under various soil conditions; and, furthermore, the comparison should be made by dealing with accumulated data in a statistical manner. In this paper, experiences of pile driving in two building sites are presented; and deviations in allowable pile loads computed by means of above two pile driving formulas are compared and discussed; furthermore, in one of two sites, the correlation between allowable pile loads determined by tests and computations is discussed to supply a basis for comparing the reliability of pile driving formulas. However, it is not intended in this paper to draw a conclusion immediately, but the scope is limited within just presenting a few examples in a methodological point of view. |