before beginning with the detailed description of the invention , let us recall briefly the characteristics of the t . a . d . pipes that differentiate these pipes from the already known pipes . it is known that concrete pipes designed for pressurized conduits belong to two distinct classes : the first ones , utilized in a range of relatively moderated pressures ( for example , for diameters around one meter , not more than 5 - 6 atmospheres ) comprise a concrete wall having therein inserted transversal and longitudinal reinforcement made of iron rods , having a relatively large diameter ; are produced according to different technologies ( centrifugation associated with vibration or rolling , casting in vibrating vertical molds , etc .). the second ones , utilized in a range of pressures greater than those typical for conventional reinforced concrete ( and therefore from 5 - 6 atmospheres up to a maximum of about 20 atmospheres ) normally comprise a core tube , produced according to one of the technologies used for conventional reinforced concrete , whereon a spiral of high strength steel is wound under tensile stress ; the spiral is then protected with a coating of cement . t . a . d . pipes are substantially pipes in conventional reinforced concrete that can withstand the high pressures to which the pre - stressed reinforced concrete pipes are destined . with respect to these latter , the t . a . d . pipes show the following relevant differences in the field of reinforced concrete technology : ( a ) the reinforcement is constituted of thin wires ( having a diameter smaller than 2 millimeters ) continuous in the whole wall thickness of the pipe , i . e . each wire goes from one to the other end of the pipe according to concentric helices , without interruption ; ( b ) the wires are not stretched , contrary to the reinforcement of pre - stressed reinforced concrete ; ( c ) the metallic reinforcement is intimately and tightly diffused in the concrete matrix , contrary to the reinforcement of conventional reinforced concrete and of pre - stressed reinforced concrete wherein the iron is concentrated in the , relatively large , areas of the reinforcement iron members . the pipe is obtained by projecting under high speed ( more than 25 meters / second ) a premium concrete ( a small granulometry , a high cement percentage , a very low water / cement ratio ), with a mechanical process with counter - rotating rolls , on a mandrel rotating around its horizontal axis . the concrete mix is constituted of inert materials up to 3 millimeters , washed and deprived of powders , that are a mixture of quarry and stone crusher products . the proportion of ingredients is around 600 - 700 kg / m 3 of cement , with a water / cement ratio smaller than 0 . 3 . compression stress on a cube : σ c = 650 kg / cm 2 elastic modulus under tensile stress , for a tensile stress up to 0 . 7 σ t : e t = 350 . 000 kg / cm 2 the reinforcement is constituted , as an example , of smooth steel wire having the material defined as conventional reinforced concrete having an evenly distributed steel wire reinforcement constitutes therefore , from the technological standpoint , a new material that provides clearly higher performances with a clearly lower manufacturing cost . indeed the apparatus necessary for the manufacture of t . a . d . pipes is largely less costly , simpler and faster with respect to the apparatus necessary for the manufacture of reinforced concrete pipes either of the ordinary type or the pre - stressed one . in fig1 there is shown a metal mandrel 1 having at its ends two heads 2 , 2 &# 39 ; provided with shaft 3 , 3 &# 39 ; rotatably borne by bearings 4 , 4 &# 39 ;. the head 3 is connected to a motor 5 for the rotation of the mandrel 1 and of the heads 2 , 2 &# 39 ; around the axis passing through the shafts 3 , 3 &# 39 ;. the heads 2 , 2 &# 39 ; are provided with anchorage means 6 , 6 &# 39 ; that are used for the laying - down of the longitudinal wires as it will be described hereinafter . for the manufacture of a t . a . d . pipe on the mandrel 1 there is applied a first layer of concrete by means of a projection apparatus indicated in 8 that projects on the mandrel a jet of coherent concrete 9 , under high speed and having special granulometry and humidity contents characteristics . in the shown exemplary embodiment , it is intended in the figures that , the mandrel rotates around its own axis , that the mandrel is stationary with respect to its longitudinal direction and that the projection apparatus travels along the mandrel in the two senses , in order to distribute the concrete on the mandrel in a circumferential sense because of the rotation of the mandrel and in a longitudinal sense because of the displacement of the apparatus 8 . when the first layer 7 of concrete has been deposited on the mandrel 1 , the winding of circumferential wires is started ( fig2 ). the wires are wound according to the technics disclosed in british pat . no . 1 . 584 . 844 by fastening a bundle of wires 10 to one end of the pipe being formed on the mandrel 1 , which with its rotation will entrain the bundle 10 of wires that is unwound from coils placed on a carriage that travels in the longitudinal direction of the mandrel . when the carriage has performed a full stroke in front of the mandrel , a layer of bundles of wires 10 will be laid - down over the layer 7 . at the same time of the winding of circumferential wires 10 , the projection of concrete is performed by means of the apparatus 8 so that the wires just laid - down on the fresh concrete of the layer 7 of concrete are immediately covered and inglobated in the concrete matrix . at the end of a number of passages a certain thickness of the pipe wall will be formed , wall that is reinforced with the circumferential wires 10 . now one may proceed with the laying - down of a reinforcement layer of longitudinal wires for the manufacture of a t . a . d . pipe according to the present invention . the rotation of the mandrel is stopped , without cutting the wires 10 constituting the circumferential reinforcement , in order to maintain valid the continuity condition of the circumferential reinforcement wires . as it can be seen in fig3 a bundle of wires 11 of longitudinal reinforcement is laid - down by anchoring the ends of the wires 11 to the anchorage means 6 of the heading 2 ( or the heading 2 &# 39 ;) for instance by fastening said wires 11 to a iron bar 12 that acts as a constraint between the wires 11 that are stretched towards the right ( looking fig3 ) and the anchorage means 6 . the anchorage means 6 may be studs or hooks that protrude radially from the headings of the mandrel . the wires 11 are stretched by a machine and are brought towards the opposite heading 2 &# 39 ; and made to pass through the anchorage means 6 &# 39 ; of this head . in fig3 and the following figures only three or four wires 11 have been represented , but it is clear that the anchorage means 6 , 6 &# 39 ; may be arranged in a more tightly packed way on the heads 2 and 2 &# 39 ; and that the wires 11 may be laid - down with one &# 34 ; pass &# 34 ; may also be a large number , for instance six , a dozen or more . fig4 shows the arrangement of the longitudinal wires in a manner corresponding to the representation of fig3 . according to the method of the invention , when the wires 11 have gone beyond the anchorage means 6 &# 39 ; of the head 2 &# 39 ;, the mandrel is rotated through an angle more or less corresponding to the arcle of circle covered by the bundle of wires 11 , while the wires 11 themselves are kept stationary with respect to the mandrel . in this way , as it is shown in fig5 the wires 11 will be bent around the anchorage means 6 &# 39 ;, assuring the fastening of the bundle of wires previously laid - down and subsequently the bundle of wires is stretched in a direction opposite to the previous one , and in this way the ends of the wires of the bundle will be anchored on the anchorage means 6 &# 39 ;. these operations are repeated up to cover the whole surface of the pipe being formed with a layer of longitudinal reinforcement wires , as it is shown schematically in fig6 . obviously also a plurality of layers of wires may be laid - down , each single wire in the layer being continuous in the whole layer . when this operation has come to an end , the wires 11 of the last pass are severed in correspondence of a head and anchored to the respective anchorage means . from this point the formation of the wall of the pipe continues with the winding of the bundle of circumferential wires indicated with 10 &# 39 ; in fig7 and the contemporaneous projection of concrete 9 from the apparatus 8 , resuming the rotation of the mandrel 1 . in this way the longitudinal wires 11 previously laid down are banded by the new layer of circumferential wires 10 &# 39 ; and by the mass of projected concrete . the succession of operations may be repeated at will , up to obtain the desired wall thickness with the desired amount of longitudinal and circumferential reinforcement . it may be remarked that the method for laying - down the longitudinal wires according to the invention may be realized in an automatic way , making thus completely automatic the manufacture of the t . a . d . pipe . a machine for performing this method is described in another patent applied for on the same date of the present application by the same applicant . it should also be remarked that by the method of the present invention , the helix inclination of the circumferential reinforcement may be selected at will and preferably will be a very small one comprised between 2 ° and 10 ° with respect to the axis of the mandrel . it appears therefore resolved in a complete manner the problem of producing pipes in conventional reinforced concrete with evenly distributed steel wire reinforcement provided with a circumferential reinforcement and a longitudinal reinforcement in the desired and suitable amount for providing the article of manufacture with the required strength . it is obvious that the embodiment of the present invention may be subjected to changes that do not depart from the scope and spirit of the same .