so as to give more interior space at the bottom. For a short stretch in each tube near Hicks street, where the most marked variations occurred the upper half of the tunnel lining was forced outward and upward by heavy hydraulic pressure sufficiently far into the surrounding soil to permit the construction of a new masonry roof providing increased clearance. The total length of tunnel reconstructed is 2,919 feet, of which 1,957 feet are in the north tube, and 962 feet in the south tube. The time occupied by the work was thirteen months; and this, as well as the cost, was considerably less than for any other method suggested. The principal advantage of the particular method followed, however, was found in the fact that the regular work of finishing the tunnel was not materially interfered with in the meantime.

Those portions of the tubes where undue flattening or other defects occurred as a result of settlement have been largely remedied by the process of reconstruction; and at all points it is found practicable to strengthen doubtful sections to such an extent that they will become relatively the strongest parts of the tubes. This latter work is now in progress.

Considerable difficulty has been ex; erienced in making certain sections of the tubes watertight before lining them with concrete. This is particularly the case where the tubes pass through two beds of extremely fine sand, each about 800 feet long, which show on the boring profile, included in the original contract drawings, as occcurring on either side of the rock formation encountered on the Brooklyn side. This material exhibits a marked tendency to run in through leaks in the lining, even though the openings are very small, and this in turn produces a slight settlement of the tube in the vicinity. There is no reason, however, to doubt that the efforts now being made by the contractor will prove successful in providing the absolute watertightness guaranteed by the terms of the contract, so far as future settlement is concerned.

The matter of the stability of the above described material under the loads that will be brought upon it from the operation of trains having been questioned by the officials of the Rapid Transit Subway Construction Company, it was considered advisable by them to provide some auxiliary means of support, such as piles reaching to rock or hard material, at intervals under the tubes where they pass through the fine sand. This view was not concurred in by your engineer, but as the cost of the piles could not properly be a charge against the tunnel work, and as experiments showed that they might be driven rapidly without materially delaying completion, no objection was made, and the work was allowed to proceed. At the present time nearly half the piles have been driven, and it is expected to finish the remainder during July.

In passing it may be remarked that material of this character is depended upon for a foundation under many of the high buildings in the lower part of the city, where the loads per square foot are many times in excess of any load that can be brought upon the tunnel. Nor is its action under similar conditions unknown, as it constitutes a foundation for the subway structure in lower Broadway and Battery Park, through which trains have been operating for two years without developing any defects.

It having been recognized early in the work that suitable means of ventilation must le provided for the river tunnels. sites for permanent shafts were chosen at the location fixed upon for working shafts at South Ferry and at

the foot of Joralemon street, Brooklyn. Because of the depth of ground water at the latter place and the probability of the construction at that point interfering with the regular use of the working shafts, it was deemed advisable to select another site further up the street. After three new locations were chosen and abandoned because of the opposition of property owners along the street, a site was finally secured between Hicks street and Willow place, opposite No. 60 Joralemon street. The building at that number was purchased by the contractor and will be altered to serve as an intake and outlet for the air in the tunnel. At present both shafts, the one at South Ferry and the one in Joralemon street, are under construction.

Section 3.- Clinton street, Fulton street, and Flatbush avenue to Atlantic

avenue.

Work on this section at the beginning of the year had been in progress two years and nine months. Much of this time, however, was lost on account of the change of plan from a two-track to a four-track structure and work on the latter basis had been in progress only a year and three months. In general, it may be said that the work done prior to the change in plan has operated to retard progress rather than to increase it, by reason of the time required to alter the original structure and underpin it where new tracks adjoin it at a lower level. Slow deliveries of steel also continued to hamper the work until early in the present year, when all shipments of the material were received.

In Joralemon street the structure had been completed and surface damage repaired, as noted in the last annual report. The walls and ceiling have since been finished with waterproofing cement, a section of track laid, and signaling apparatus installed. The interior finish of the Borough Hall station is practically complete.

Except near the turn into Flatbush avenue, little remains to be done in Fulton street. In this locality the work is exceptionally difficult on account of the necessity for supporting the two elevated structures and surface-car tracks while carrying on the construction under cover and excavating below ground-water level for the lower track crossing the spur for the Manhattan bridge connection. It has been necessary to maintain the shaft at DeKalb avenue to handle the excavation at this point. The wings of the Hoyt street station were built early in the year, and the interior finish is well advanced.

On Flatbush avenue favorable progress was made between Livingston and State streets. Extensive pipe changes have to be made before the street can be restored to its normal condition. Considerable excavation remains at the site of the Atlantic avenue station, where construction has been delayed by the slow deliveries of steel. At the Nevins street station, where work was delayed for the same reason, good progress is now being made.

The methods in use by the sub-contractors for handling and removing excavated material and temporarily supporting the elevated structure remain the same as described in previous reports and have been found altogether satisfactory. It has been necessary to continue in service the shafts at DeKalb avenue, Lafayette avenue and Livingston street. The shaft at Borough Hall was discontinued early in the year, when the structural portion of the station at that point was completed.

The important and difficult task of underpinning the piers of the buildings adjoining the subway was completed in May. At each of the four stations, and for the greater part of the length of the depressed track connections, the subway excavation is close up to and below the foundations of front walls of buildings. In order to avoid damage by settlement it was necessary to underpin these in nearly every instance, and in many cases to carry the underpinning piers of concrete below the level at which water would stand in the soil. This was accomplished by temporarily supporting the piers on double I-beam girders running parallel to the building lines, thus transferring their loads to new bearings carefully wedged up on either side; after which rectangular sheeted pits were excavated below the original foundations to the required depth and filled with concrete, leaving the sheeting in place. Where the pits were dug below the level of ground water, interlocking steel sheeting was used for the bottom length of about six feet, and the water level was lowered by careful pumping as much as was required to finish the excavation and place the concrete. In all these operations the greatest skill had to be exercised to prevent incipient movement of the surrounding soil, and the sub-contractor's efforts in this direction proved successful.

The chief items for both regular and extra work on each section of Contract No. 2, for which the contractor has been paid from the beginning of construction to June 30, 1907, are given in the following table: