The generic term"manhole", used in the present patent application, is intended to denote in the broadest sense the whole range of manholes, trapdoors and covers used for all types of application.

As is known, such a manhole, usually made from cast iron, essentially consists of a cover which may or may not be perforated, according to the requirements of use, resting horizontally on a supporting frame, whose upper edges are at the level of the road surface, into which the cover is inserted in a complementary way so that it is also aligned with the road surface.

It is known that, with the passage of time, any asphalt road surface requires repair and adjustment of its level. This work is carried out by laying a new layer of asphalt on the existing layer, to eliminate rough areas of the surface while raising its level, or, where this solution cannot be adopted, or can no longer be adopted, because of constraints on the final level of the new layer of asphalt, by using suitable machines to remove the"old"layer and then applying a"new"one.

Whichever of the aforementioned processes is carried out, there will always be a problem of modifying the level of the upper surfaces of manholes to match them to the new situation which is created.

This requires the partial demolition of the concrete structure of the shaft on which the supporting frame of each manhole is fixed, and its reconstruction at a suitable level, resulting in a loss of time due not only to the duration of the aforesaid work but also to the time spent in waiting for the new concrete structures to set.

During such periods of stoppage, it is particularly important to keep the manholes fenced off to prevent random damage to them, and this impedes the ordinary progress of the work and obstructs the passage of vehicles and persons.

The inventor of the present invention has realized that all the aforementioned disadvantages and the associated costs can be avoided by using a manhole in which the cover and supporting frame assembly can be moved reversibly in the vertical direction, by the operation of suitable means fitted to the manhole.

For this purpose, he has devised the object of the present invention, which consists of a manhole for use in roads as described in the attached Claim 1. A preferred example of embodiment is described more fully below, with reference to the attached figures, in which : Fig. 1 shows a partial longitudinal section through the said example of embodiment of a manhole according to the invention ; Fig. 2 shows the same section as that of Fig. 1, with the cover raised vertically, together with the supporting frame, with respect to the other components.

Figure 1 shows a manhole 1 according to the invention, of which only the left-hand half is shown, the other half being a mirror image of it.

A cover 2, in this case a perforated cover for the collection of gutter water, is inserted fully, in a known way, into a supporting frame 5, positioned at the level of the road surface S.

By contrast with the prior art arrangements, the said supporting frame 5 does not rest on the edges 2b of a shaft 2. Instead, a base 6 is fixed on these edges and the supporting frame 5 discharges its weight on to this base by means of a plurality of threaded rods 7, the lower end of each of these rods being screwed into a polygonal nut 8 housed in a recess 10 of complementary shape formed in the upper face of the said base 6.

Each of the aforesaid threaded rods 7 holds up the supporting frame by means of a coaxial part 7a (of truncated conical shape in the present case) which projects radially from it to form a support surface R.

The upper end of each threaded rod 7 terminates in a head 7t shaped (with a square section for example) in such a way that it can be engaged with a screwing tool.

This head 7t passes through a hole 9 formed in the supporting frame 5 and a further hole 4 formed in the cover 5, in such a way that it can be accessed from the outside with the aforesaid screwing tool.

When this tool is used to rotate the threaded rods 7 in the direction of unscrewing, since the aforesaid polygonal nuts 8 cannot rotate in their recesses 10, the cover 3 is raised with respect to the base 6, thus increasing the distance D between them in the vertical direction: Fig. 2 shows the resulting situation after the threaded rods 7 have been unscrewed almost completely from the polygonal nuts 8.

By adjusting this distance D in such a way as to bring the upper face of the cover 3 and its supporting frame 5 to the new level specified for the road surface S, a manhole 1 is immediately positioned at the precise

level of the surface, and the work of laying the road surface can be carried out without any further delay.

If it is subsequently necessary, in the course of later work, to remove a layer of asphalt of a given thickness, thus lowering the level of the road surface, it is simply necessary to carry out the operations as described previously, but with the threaded rods 7 rotated in the opposite direction, in other words in such a way as to screw them into the polygonal nuts 8 and consequently decrease the aforesaid distance D between the supporting frame 5 and the base 6, thus returning the cover 3 to the new level specified for the road surface.

Clearly, the inventor has achieved the desired outcome with his invention, by providing a manhole which can be matched rapidly, and at minimum cost, to any changes in level of a road surface.

The number of the threaded rods 7 can clearly be varied according to the dimensions of the cover 3 and the expected load to be applied to it.

To lock the threaded rods 7 in the desired position corresponding to a specified value of the said distance D, the inventor proposes that a locknut 11, bearing on the upper face of the corresponding polygonal nut 8, be screwed on to each threaded rod 7. The desired locking is achieved in a known way by tightening this locknut 11.

The inventor proposes the use of threaded parts (threaded rods 7, polygonal nuts 8 and locknuts 11) made from stainless steel.

This practice prevents the formation of oxide layers, thus facilitating the operations described previously and reducing maintenance work to a minimum for a manhole constructed according to the invention.