believed that the model experiments described in the Paper were the first to have been carried out in connexion with sheet-pile walls where the experimental work had been done under carefully controlled conditions and the walls had been tested right up to failure.In interpreting the results and applying them to the design of full-size walls, the following limitations should be realized:(i) the experiments had been performed on very small scale walls;(ii) the soil throughout had been a uniform stratum of sand in a loose state of compaction; and (iii) the sand had been completely dry. (In an actual wall there was usually a water level or water-table, resulting in part of the soil penetrated by the piling being in a submerged state and thus having a lower effective density.) With reference first to the experimental work itself, Mr Cornfield made the following (1) Since no soil-pressure gauges had been used, the pressure distributions on the walls were not known at failure. The actual distribution at the failure condition (when yield B had been reached) would be very instructive and would assist in determining the most suitable method of design.(2) It was not clear how the "end effects" of the model (the effect of fiiction of the side walls of the containing bin) had been eliminated, with regard especially to the accuracy of the tie-rod load readings.(3) There was some doubt as to the error resulting by neglecting the effect of stress concentrations at the root of the notches in the model steel plate wall. (4) The method of determining yield A was stated on p. 288 as being "that point at whirh a definite divergenre from the almost linear initial relation could be detected on plotting the results, whereas the ultimate yield B was that associated with a visible 'yield hinge' where an angle from the straight about 10' or greater formed at a notch". (See also Fig. 6d.) However, from examination of Fig. 12a the positions of points representing yield A did not appear to agree with the above statement. The curves given in that figure suggested that it comments : t
Consulting Engineers I shall make my comments from the point of view of a customer who has used the Pilemaster.87. About 18 months ago my firm was responsible to the Ministry of Transport for the reinstatement of two short lengths of river wall at Wisbech. The design finally adopted was steel sheet piling and the Pilemaster was used to install the piles.88. Frodingham No. 4 N piles, 55 ft long were required which had to penetrate between 30 ft and 40 ft into sandy silt. The site was virtually in the town centre and there was a great mass of very old property immediately adjoining the works, some of it being listed as of historic interest. Consequently, when our thoughts turned towards using sheet piling, having regard to noise and vibration the possibility of using the Pilemaster was attractive.89. However, the site had three potentially serious obstacles. First, the adjoining lengths of the river showed ample evidence of earlier structures and we anticipated a lot of timber and stone debris in the upper layers. Secondly, whilst the River Board had been very co-operative and most helpful in allowing us to come forward into the river with our new work, they had no choice but to insist that we put our piles to the same batter as the existing piles. They could not let us have vertical piles. Thirdly, over the second length of wall, the raking piles had to follow a curved line in plan, so we were setting quite a task for sheet piling. 90.Because of these difficulties we thought that a full-scale test was desirable before committing ourselves to the Pilemaster, and in February 1967 the Ministry of Transport arranged for the purchase of a panel of eight piles to be pushed down byPilemaster. As this was completely successful, the project went forward to tender with the Pilemaster specified. 91. The job was completed without undue incident. As the Authors mentioned, we did have to resort to percussive driving on several occasions and it was very noticeable that every time the hammer came on, the Contractors' telephone began to ring with calls from a wide area around Wisbech, but these complaints stopped as soon as the hammering stopped. 92.In the first length of wall we found that the first pile in each new panel refused after about 15 ft penetration and had to be hammered. We never really established why, but two contributory reasons might have been, first, that we had female clutches leading and the outstanding clutch of the previous panel may well have become clogged; also there was a definite tendency for the piles to lean in the line of driving, so that if a panel finished with a slight lean and we attempted to keep the next one vertical, the connecting pile may well have acted as a wedge.93. In the second half of the job we arranged for male clutches to lead, and took greater care to keep the piles vertical, and the job went more expeditiously. Also we introduced a modified form of Pilemaster, so it is not possible to identify the cause of our previous difficulty nor what effected the cure. 94. The modified form of...
The two submarine pipelines described by the Authors in 5 75 represent a total capital investment of about L14 000 000 and they appear to be the largest examples of this class of work yet undertaken in British waters.95. Increasing use is now being made of submarine pipeline techniques in other fields and it would be useful if the Authors could give some more information about the design of the natural gas pipelines in relation to sea bed conditions. In 5 78 trenching depths of from 4 to 10 ft, according to location, were mentioned and it would be interesting to know what minimum depths of cover were specified. From 5 81 it appears that the pipelines may remain exposed for several months before becoming buried by natural sand movements. Were the pipelines in operation during this period and was the risk of damage by ships' anchors considered to be negligible?96. Finally, it appears from 5 77 that the thickness of the weight coat has been increased where the pipelines are within territorial waters. The limit of territorial waters is a notional line, not connected directly with either depth or sea conditions, and it would be helpful if the Authors would explain the reasons for the adoption of a more expensive form of construction within this line. M r A. M. Muir Wood, Sir William Halcrow and PartnersAn unsuspecting reader of $5 45-49 might suppose that a fully sufficient theory was available for the calculation of wave force against a drilling platform. I suggest to the Authors that the following factors are among those that require considerably more study before there can be any complacency among engineers responsible for designing such structures.98. While the higher order wave theories (or Cnoidal wave theory in shallow water) may appear better to represent the particle motions of steep regular symmetrical waves, they take no account of important modifying effects such as eddy viscosity. Moreover, in many marine applications, the irregular, short-crested and asymmetric wave of the open sea is found to have significantly different effects on structures than the long regular wave of the wave theories.99. Considerable doubt is attached to the evaluation of the inertia and drag coefficients and it is highly improbable, from fundamental considerations, that these are each constant through a wave cycle as frequently assumed for marine structures.100. Knowledge of the motions of the incipiently breaking wave relies more on experiment than on theory; this is often the most critical type of wave for an offshore platform but is such a rare event at the situation of a platform that few full-scale recdrds are available.101. Where, on account of steepness of the wave or the slope of the structural member, the motion of the water is inclined obliquely to the axis of the member, the inertial and drag coefficients will be varied in consequence.102. The vortex street that forms in the wake of a cylinder in a steady current causes a cyclical variation in drag and in lift (i.e. the lateral force perpendicular to the direction of ...
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