No abstract

The vibration test is more than an integrity test because it also gives a measurement of soil-pile interaction. Of particular importance is the measurement of pile head stiffness E', which is a dynamic measurement of the initial load settlement characteristic of the pile. It is useful to plot pile head stiffnesses of a population of piles of similar dimensions on a site where the geological profile is fairly uniform. Fig. 18 shows what was done on a site at Rossano de Calabro in southern Italy where 730 piles were tested. They varied in length from 14 m to 17 m and they had a ,diameter varying between 520 mm and 540 mm. These were cast in situ end bearing piles passing through soft alluvium and founded in a conglomerate.The water/cement ratio of 0.33-0.40 was rather lower than one would use in the UK and this, without doubt, accounted for some of the troubles that were experienced in installing these piles. The range of pile head stiffnesses was quite considerable. The average value was 0.60 MN/mm and the standard deviation was 0.23.72. It seems that for the first time one has a means of obtaining information enabling one to select piles intelligently and rationally for load testing. The problem until now has been that when a pile has been selected for load testing there has been no way of knowing whether or not that particular pile is an average pile, a good pile or a defective one. The load test results therefore could give no indication of the relative load carrying characteristics of the other piles. On the site in Italy it would have been possible to select one or two piles having a stiffness of 0.25 MN/mm knowing that 97% of the population of piles had a stiffness greater than this. Dr DavisSince the Paper was written, two modifications have been made to the equipment. First, it is no longer necessary to ensure that there are no extraneous vibrations on site, because an extra item in the recording circuit smooths out any spurious signals. Second, it is now possible to test raker piles using a special harness to position the vibrator in the line of the pile axis. Inclined piles up to a rate of one in four have similar values for pile stiffness as vertical piles on the same site.74. One of the major restrictions of the method is the unlikelihood of receiving a reflected signal from the bottom of the pile when the pile length to diameter ratio is too great. A likely limiting upper ratio of 30 to 1 was suggested in the Paper. Subsequent testing in the Thames Estuary has shown that good results have been obtained for ratios up to 50 to 1, where a very soft lateral soil has resulted in little damping, and the pile toe was founded in a stiff stratum. This is not the case for piles founded in stiffer lateral soils such as London Clay.

This berth is noteworthy not only for its depth as a bulkhead structure but also because it is a solid wharf alongside a deep channel which has been created over the years.68. The development of the Tees estuary from the treacherous waste of shifting sandbanks in the 1850s to the present controlled deep channel for the current and next generation of bulk carriers represents a striking example of the intelligent use of training walls and an understanding of the balance of tidal forces as shown by generations of engineers. Outstanding in their contributions to this achievement were John Fowler, who by 1887 had established a trained channel 20 feet deep; James Meadows Rendel (1855), for the Care breakwaters and harbour of refuge; A. J. Barry who with Frederick Palmer discredited the '1920 theory' that further channel improvements could not be reconciled with large-scale reclamation; and John Clarke, the present Engineer and his predecessor Don Burdis, who have added thousands of acres of land adjacent to deep water-so valuable and appropriate for industrial development at this time.69. As to the construction of the berth I would like to add a word of appreciation to both the Contractors for their co-operative and helpful attitude in dealing with the unfamiliar requirements of such an unorthodox structure. Mr KnowlesTwo field trials (Figs 17 and 18) were held. In each test, a concrete panel 17 m deep was jacked into a trench filled with bentonite slurry. Guide walls (not shown) were jacked apart to remove restraint and a concrete bearing provided a rotation point. Although six earth pressure cells were installed to record ground pressures they were not completely satisfactory, as at least one hydraulic lead was ruptured on reinforcement. Also, it was impossible to ensure soil contact where cavitation occurred. Consequently no firm conclusion was reached on stress distribution.71. Comparing the 17 m test depth in recent hydraulic fill with the 42 m depth of structure it was concluded that frictional resistance to tilting was likely to be 4 t/ma or greater and Professor C. Veder of the Technische Hochschule, Graz, Austria, who was consulted, concurred.72. The second test was in two stages; first a 'push-over' and secondly a 'pullout'. The standard panel connector between elements A and B was disconnected at 8 m depth to reduce the vertical jacking force, for practical reasons. Inclinometer readings in element A revealed a structural failure during the first stage of the test. Considering that the 'push-over' test was thus carried out on an 8 m deep panel and in varying soils, compared with 17 m on the previous test and a final structure up to 42 m deep, the test value of just under 2 t/mz was regarded as satisfactory.

DiscussionMr G. A. Wilson (Chief Engineer, Port of London Authority), in opening the discussion, said that on first looking at the Paper he had been delighted with the design. It was undoubtedly most interesting but on reading the Paper the problems which such an elegant design had presented were brought out and he began to wonder if it were as satisfactory as the first glance had suggested. 72.The old work, built with screw piles, had lasted:45 years, and as a dock engineer he thought that could be considered an excellent design because after 45 years alterations to meet more exacting conditions were generally needed. Those who made the screw pile design could be well satisfied with their achievement.73. The Authors pointed out that because of the generally corrosive and destructive conditions they could not recommend any of the normal designs and adopted prestressed concrete but he wondered if, when the job was finished, they remained content with the method of construction. He had a practical interest in the cost of the design because he was about to build a quay wall about 48 ft high where the duty would be similar. He proposed to continue with the design described in I.C.E. Paper No. 62511, No. 1 Berth, Tilbury Dock, in which costs were quoted. The Authors' design involved a good deal of divers' work and tidal work both of which he always endeavoured to avoid. The Paper stated the cost to be M25 per ft length of quay, but did not say if this figure included the surface of the quay or other work such as crane tracks. In the Tilbury design simple 30 ft square concrete monoliths were sunk into the ground, with a concrete slab top supported on the monolith and cantilevered over the back to make a 50 ft wide surface. The cost of this was M39 per ft run so that allowing for all the variables there did not seem to be any great saving in the prestressed design. The monoliths provided such a very solid wall and quay surface that the design did not fulfil his first requisite, that it should be ready to be renewed in about 50 years; it would probably last 150 years.74. In the Tilbury design the surcharge on the deck was taken as 4 cwtlsq. ft and he noted that the Authors had used 2 cwt/sq. ft but tested to 5. The Authors mentioned protecting the steel in the concrete from the corrosion but did not say what cover had been used. The drawings were small so it was difficult to tell but it seemed doubtful if any greater cover than usual had been possible in the R.C. beams between piles. He was interested by the remark about the synthetic rubber compound to stop leaks in slabs and wondered whether it had been successful.75. There were many interesting records in the Paper, particularly about the testing of earth pressures and he hoped that other speakers would take this point. Information on the number and type of jacks used to get the stress in the cables would be useful. The t Proc. Instn civ.

No abstract