The Dulac System of Concrete Pile Foundations.

Progress, Volume III, Issue I, 1 November 1907, Page 13

The Dulac System of Concrete Pile Foundations.

One of the most interesting of the newer methods of establishing firm foundations for buildings in soft ground was invented by the French engineer, Dulac, and was first used on a large scale in the construction of the buildings of the Paris Exposition of 1900, where much time and money were s?ved by the employment of this novel system. The compression and stiffening of the ground, which are effected by wooden, piling are caused b\ the lateral displacement of

earth as the piles are driven in. Dulac produces the same result by omitting the wooden pile and allowing a conical weight, raised by the pile driver, to fall directly on the earth in which it makes a vertical cylindrical hole, which is deepened by each successive impact of the weight. After the desired depth has been reached the hole is rilled with concrete which is rammed very tightly. The concrete piling thus formed possesses the great advantage of being independent of the height of the ground water. Wooden

piles, on the other hand, must be driven entirely below the lowest water level in order to prevent decay. The Dulac apparatus consists of a pile driver of the usual construction, 30 or 40 feet high, and three weights of a horizontal diameter of about 30 inches. The weight used in the beginning of the operation is conical, sharply pointed, and weighs two

tons. When a hole has attained a depth of a few yards, a weight of parabolic, or sugarloaf .form, also weighing two tons, is substituted and used until the desired depth is reached. The entrance of water can be prevented bythrowing into the hole a quantity of clay which is plastered on the side of the hole by the falling weight. The diameter of the hole, before it is filled with concrete, is only a few inches greater than that of the weights. Holes nearly forty feet deep have been made by this method. The filling is commenced by throwing in a quantity of stones and ramming them down with the third weight, which is flat on the bottom, and weighs one ton. The effect of the ramming is to broaden as well as solidify the successive layers, and thus form a very firm base for the concrete filler. The concrete is then introduced in small portions, each of which is well rammed with both the flat bottomed and the round - bottomed weights, and the process is continued until no more concrete can be forced into the hole. The compression and lateral distension effected by this method are |so great, that the volume of stones and concrete employed is about five times the cubic capacity of the original hole. Thus, two desirable results are produced. In the first place a number of very strong concrete pillars are formed; and in the second, the soil between these pillars is compressed very forcibly so that it becomes capable of aiding materially in the support of the building.

In the new Gospel hall in Punedin, which is being erected from the plans of Basil B. Hooper, special attention had" to be paid to the foundations, which are four feet wide, with expanded metal embedded in the concrete footings. The whole design is carried out in brickwork without cement facings of any kind ****** Two two-storey buildings of very neat design are in course of erection in Victoria avenue, Wanganui ; also several cottages have been erected at Carlton, near the late residence of Mr.^A. Atkins, C.E., Wanganui.