US2502757A - Revetment - Google Patents

Description

April 4, 1950 D. MCD. SHEARER 2,502,757

REVETMENT Filed Feb. 7, 1947 6 Sheets-Sheet 1 Curren f a Zirecf/on o pera/r017 f EN TOR.

April 1950 D. MCD. SHEARER 2,502,757

REVETMENT Filed Feb. 7, 1947 6 Sheets-Sheet 2 T E LLTQL T 12:1 1; T .T T 7 m k 6 1 6 1 T? SubmayedJa/l/f Aprii 4, 1950 D. MED. SHEARER REVETMENT Filed Feb. 7, 1947 April 4, 1950 D. MCD. SHEARER REVETMENT 6 Sheets-Sheet 5 Filed Feb. 7, 1947 4 NN AMN w ll 1 t1 II III II April 4, 1950 D. MQD. SHEARER REVETMENT 6 Sheets-Sheet 6 Filed Feb. 7, 1947 Patented Apr... 4, 1950 UNITED STATES PATENT OFFICE I REVETMENT David McD. Shearer, San Antonio, Tex.

Application February 7, 1947, Serial No. 727,043

16 Claims. 1

This invention relates to the protection from current erosion of the subaqueous banks of alluvia1 streams with strong currents and deep waters, by means of articulated slab revetment mats placed over the critical area of the submerged banks. The revetment of the banks of such streams involves large scale engineering problems of great difficulty and complexity. The success of such operations depend not only upon the quality and efllcient performance of the revetment mats after they have been placed in position on the submerged banks to be protected, but is also dependent upon extensive coordination in design of both the placement plant and the revetment, as well as upon the methods employed in the production and assembly of the parts of the latter. In these respects the undertaking differs fundamentally from the revetment of exposed upper banks, or the banks of small streams, canals and the like where the revetment is placed in the dry or in very shallow water, where no particular problem in placement is involved. In such cases almost any kind of superficial covering of rip-rap, concrete, and the like is suitable.

Experience indicates that for practical reasons an articulated slab revetment mat intended for successful application in the field of the art to which this invention relates should possess the following characteristics:

The mat should be susceptible to practical placement in deep waters and strong currents by means, methods and plant known to the art.

The constituent parts of the mat, and thereforethe structure as a whole, must be durable under water and be much heavier than the displaced water, preferably with the specific gravity and compactness of stone, in order to resist displacement by strong currents and turbulent flow.

It must be flexible, tough and strong, in order to take the surge and lash of the current in the course of placement, and thereafter when in place, follow subsequent adjustments in the slope of repose of the lower or submergedhank without disintegration.

Its surface should be as smooth as possible and hug closely the bank which it covers in order to offer minimum obstruction to the flow of water above it and thereby avoid creating local turbulence in the flow and consequent agitation through openings between its parts.

The mat must be a continuous structure in order to assure positive coverage after placement, and for the same reason the unit structural ele- 2 ments thereof should be as extensive in area as practicable.

The slab elements of the mat structure must be firmly but flexibly united in order to follow closely the irregular surface of the submerged bank when placed, and thereafter to conform closely to its changing slope -as the stream continues to deepen beyond the toe of the revetment thus altering the slope of repose of the materials composing the re'veted bank. This flexibility is also required to enable the structure to pass through two changes of direction in course of placement without damage to its parts, and in order to further yield without rupture by the pressure of the current in the course of placement.

The bodies of the parts composingthe mat structure must be integrally formed with a skeletal structure of wire in order to avoid their local movement after placement which would make openings in the mat resulting in progressive disintegration or raveling of the mat by reason of the possible parting of one or more wires or cables in localized areas.

The texture of the mat structure must be close enough to prevent excessive leaching or filtering of underlying sands, or other loose materials composing the submerged slope, through interstices or openings in the mat structure to ultimately undermine the structure, and at the same time it must be sufliciently permeable to prevent flotation from the building up of unbalanced hydrostatic pressures beneath the structure on a falling river or in the presence of "weeping soil strata.

The mat structure must be capable of complete fabrication in the dry for reasons of accessibility and the need of thorough visual inspection of the structure before immersion.

The structure by its design must lend itself to positive control during placement in deep water and strong currents in order to assure proper positioning and coverage under water.

The mat structure must be so formed in its constituent parts that it may be launched over the curved sheave studded side of a launching float and suspended therefrom on the launching cables during descent to position on the submerged bank without damage to its parts through introduction of eccentric stresses in the zone of the sheaves or the accumulation or transmission of stresses thru the bodies of the slabs in descent.

The unit mat structure must be capable of rapid placement under positive control in order to minimize its exposure to possible destruction by currents in'the course of the laying operation. To this end the structure must be composed of an assembly of well cured prefabricated parts, the manufacture and seasoning of which are independent of the assembly and placement of the structure.

The launching cables of the mat structure must lie within the bodies of the slabs of the mat structure tangent to or coinciding with the plane of the skeletal reinforcing grid by which the slabs are joined together and to the cables in order to avoid destructive eccentric stresses in the slabs.

The launching cables must be exposed in order to bear directly on the sheaves of the curved side of the launching float.

Continuous channels must be provided in the mat structure for accommodation of both launching cables and the sheaves of the launching float, and for the additional purposes of cooperating with the sheaves in guiding the structure in its descent from the float and in preventing lateral displacement of the mat structure along the curved side of the launching float by the drag of the current.

The parts of the mat structure must be joined together by rigidly secured fastenings, in order to carry the weights and stresses and prevent subsequent shifting of the position of the parts with respect to one another and the structure as a whole.

The design of the mat structure must include provisions for securely fastening its parts together by accommodating such fastenings without detriment to the efliciency of the structure as a whole in its primary mission of protecting submerged banks from erosion.

The design of the prefabricated parts of the mat structure must include provisions for the engagement of grapples or suitable lifting and moving devices without detracting from the efflciency of the mat structure in which incorporated.

Heretofore articulated slab revetment mats in this category of revetments necessarily have had open spaces between the sections and between the several slabs of each section at their adjathe bank through said openings by strong andturbulent currents flowing over the submerged structure, and also by surface wave agitation along the inside edge of the structure which is exposed at low water.

Experience, so far, has developed no practical cure for this condition. It is the broad purpose of this invention to remedy this deficiency by means of a novel revetment structure possessing all of the essential characteristics listed above as well as being proof against leaching.

More specifically, one purpose of the present invention is to provide a revetment mat of articulated unit slabs which are formed in such a manner that connections between contiguous unit slabs and the joinder of groups of such unit slabs prefabricated into unit sections of a mat structure are effected to avoid intervening interstices in the structure through which water may 4 circulate to undermine it, especially when the revetment is subject to the action of strong 'or turbulent currents or to low water wave wash along its inner edge.

Another purpose of the invention is to provide an articulated slab revetment mat havins closed or contact joints between the articulated ele-- ments of the structure, without interfering with its flexibility and adaptability to irregular surfaces, its ability to equalize water pressures through the structure, and its suitability for rapid and economical manufacture and placement in deep waters and strong currents.

Another purpose of the invention is to provide an articulated slab revetment mat having launching cables disposed in covered channels, and fastenings disposed in closed walls through which water may seep to equalize pressures but without flowing freely to undermine the structure.

Another purpose of this invention is to provide a novel prefabricated unit section of an articulated slab revetment mat having the above characteristics, and which section is capable of being cast, formed or reproduced in quantity in tiers, accurately, cheaply and rapidly, one section being molded above another, by means of novel mold-forms disclosed in my co-pending application No. 7 27,042.

A further purpose of this inventio i is to provide a prefabricated unit section of an articulated slab revetment mat composed of any desired number of unit slabs which are initially rigidly interconnected but which may subsequently move relative to each other by fracturing zones of weakness formed between them to provide requisite flexibility within the section and within a mat structure composed of an assembly of such sections, without creating spaces between the several unit slabs of the section through which a circulation of water may circulate with sufllcient force to undermine the revetment structure.

To these and other ends my invention embodies further improvements and arrangement of parts as shown in the accompanying drawings and described in the accompanying specification, the novel features thereof being set forth in the appended claims.

In the drawings:

Figure 1 is a small scale plan view of a single prefabricated unit of construction or section in which the minor details have been omitted. The unit section consists of a plurality of similar unit slabs, arranged in contact side by side and interconnected.

Figure 2 is a small scale side view of a tier or stack of such prefabricated unit mat sections, one cast section being superimposed upon another.

Figure 3 is an end view of the tier of sections shown in Fig. 2 supported on a template.

Figure 4 is a small scale view of a typical bank revetment operation employing my invention, three unit revetment mat structures being shown assembled in overlapping upstream succession and a fourth being shown under construction and in course of placement.

Figure 5 is a sectional view of the operation described above showing in elevation the plant engaged in placing a revetment mat structure.

Figure 6 is an enlarged sectional diagram showing the curved side of the launching float with the sheaves thereon.

Figure 7 is an enlarged sectional detail view along the plane I -P of Fig. 6, showing the relative position of the sheaves and a launching cable in the undercut channel of the slabs.

Figure 8 is a plan view somewhat diagrammatic, showing an enlargement of the parts 01 two mats overlapping at their edges and illustrating the launching cables initially anchored to deadmen placed in the upper or exposed, part of a river bank.

Figure 9 is an end view of the two mats shown in Fig. 8 parallel to the bank line of a river featuring the overlapping of the upstream structure over the preceding downstream structure.

Figure 10 is a longitudinal'cross section taken on the line IO -I Ii of Fig. 8 featuring the integration of slabs into the structure as a whole.

Figure 11 is an enlarged plan view of atypical unit mat section drawn to scale, featuring employment of the preferred type of wire reinforcing-bonding grid.

Figure 12 is a fragmentary end view shown in plan of another similar unit mat section illustrating a modified form of the wire reinforcingbonding grid.

Figure 13 is a fragmentary plan view of an end of another unit mat section illustrating another modified form of the wire grid.

Figure 14 is an enlarged isometric view of one end of a unit section shown in Figure 11 depicting the characteristic form of unit slabs composing the unit mat section and in particular the shape and position of the clip fastening well recesses.

Figure 15 is an isometric view of one corner of the end slab of the mat section of Figure 14 showing details of side and end clip wells.

Figure 16 is a fragmentary view of part of a longitudinal cross section of a tier of mat sections cast in superimposed relation showing the transverse joints between the slabs of a section.

Figure 17 shows a top plan view on an enlarged scale of the area II outlined in dotted lines on Fig. 8 for the purpose of illustrating parts of six prefabricated unit mat sections along the jointure of two launches of a completed mat structure embodying my present invention.

Figure 18 is a longitudinal section through the revetment structure shown in Fig. 1'7 taken in the plane indicated by the section line la -l8.

Figure 19 is another longitudinal section through the mat structure of Fig. 1'7 taken on the line l9 l9*.

Figure 20 is a transverse section through the structure of Fig. 17 taken on the line ID ZO Figure 21 is a transverse sectional view taken on line 2 I= 2 i of Fig. 17.

Figure 22 is an enlarged fragmentary cross section taken on the line 22 of Fig. 17 featuring the longitudinal vertical contact joint between ends of slabs of adjacent sections.

Figures 23 and 24 are similar views featurin modifications in the design of the ends of the slabs of adjacent sections to provide a range of upward articular movement between the slabs tional view featuring in side elevation one of the cable clip fastenings also shown in Fig. 21.

Figure 26 is a top plan view of the subject of Fig. 25.

Figure 27 is a cross section taken on the line 6 looped ends of the longitudinal grid members of contiguous sections of the mat assembly at the meeting ends of successive sections and the meeting sides of successive launches.

Figure 29 is an enlarged fragmentary cross sectional view taken at an intermediate point ill -l I. on section line ll of Fig. 17, featuring the ordinary transverse joint between the adiacent slabs of the unit mat sections.

Figure 30 is a fragmentary transverse cross section taken on the line SP-Jl of Fig. 29.

Figure 31 is a detail elevation showing portions of the ends of slabs of two superposed unit mat sections showing the alined clip wells and a lifting grapple stirrup engaged with the looped end of a transverse grid member of the upper section.

Similar reference characters in the several figures indicate similar parts.

The preferred dimensions of the unit mat sections referred to herein are: Length 25 feet, width 4 feet and thickness 3 inches.- The preferred number of slabs per section runs from 20 to 25, depending upon the width selected. The preferred dimension of the unit slab of the section arc: length 4 feet, width 12 to 15 inches, thickness 3 inches.

The preferred material of which the bodies of the slabs .are composed is ordinary good quality concrete made of Portland cement, sand and gravel or crushed stone. However, it is to be understood that any other suitable initially plastic material having substantially the same density, durability and spaciflc gravity of good concrete may be so employed.

The width (parallel to-the river bank) of any unit revetment mat structure embodying my invention is dependent upon the length of the launching apparatus float available for its placement. In general, narrow mats may be made to fit the irregularities of a shore line more closely than wide mats, but faster progress and greater economy in their installation results from the use of wide unit mats. Although mats as wide as 600 feet are not impracticable, the preferred width in the general case is about 200 feet. Under average conditions the length of the unit mat structure (normal to a shore line) may be as great as desired within the limitations of available plane and the skill of the operating personnel.

The members of the reinforcing-bonding grid included in the unit mat sections may be rods or wires, preferably the latter, of any suitable commercial metal possessing the requisite strength, ductility, yield tolerance and durability, but non-corrosive metals and particularly noncorrosive wires are preferred.

The manner in which revetment mats embodying my invention are constructed will become apparent by a more detailed explanation of the several figures of the drawings. In Fig. 1 I have shown a single prefabricated unit I, consisting of a plurality of unit slabs 2. The mat sections I may be cast in superimposed relation as shown in Fig. 2 with separating layers of paper between them and built up into a stack 3 to any desired height, as indicated in Figs. 2 and 3, on a casting template 4.

These sections may be manufactured in a suitably laid out casting yard conveniently located on the river bank and later moved to decks of barges nearby and transported by barge to the site' of the revetment; or they may be cast in tiers directly on the decks of the barges by means of a floating casting plant. Power machinery is employed in lifting and moving the tiers of sections. Grapples are available for lifting the sections singly, in groups of several sections broken off a tier, of. the whole tier as a unit, as and when desired.

The ultimate assembly of the mat sections is illustrated in Fig. 4 which shows these unit mat structures Nos. A. B and C and a fourth section under construction. Each unit mat structure consists of an assembly or the prefabricated unit mat sections i arranged side by side in successive rows or launches" 5, securely Joined together and to launching cables 6 disposed in channels in the lower face of the structure and in coincidence with the contacting long sides of the sections. These launching cables are controlled in unison by the machinery of the launching apparatus on a float I. Float I is equipped to move under control along the lower or downstream sides of the movable mooring barges l which are suspended from the fixed set of mooring barges 9 by means of cables Hi at a variable distance therefrom as determined by taking up or paying out said cables. The launching plant is served successively by a number of material barges H loaded with tiers of mat sections I,

from which the sections are lifted and moved individually by a locomotive crane I! to position in the launch assembly 5 on the ways of the float I. In connection with the operation of the crane I2, a special grapple is employed for lifting and moving the sections. The special grapple is equipped along its sides with hook like stirrups 42 (Fig. 31) which engage the edges of the sections through the recesses l'l (Figs. 11, 14).

It will be observed in Fig. 4 that the mat as constructed in successive increments of "launches 5, must pass over the curved side i3 of the float I in its descent to final position on the submerged bank, and in so doing changes its direction twice through nearly 90 degrees each time. After the mat has been placed the current continues to erode the submerged bank [4 beyond the outer edge of the mat, so that the mat must follow the erosion and finally adjust itself to the new slope of repose 15. In addition to their other functions, the launching cables 6 incorporated into the mat structure now provide the additional strength necessary to resist this strain and prevent rupture of the mat in the areas of the subsidence. The launching apparatus employed is described in U. S. Letters Patent No. 1,229,152, Apparatus for launching revetment mats, issued to me June 29, 1917.

The purpose of the sheaves i5 is to carry and support the launching cables 6 on which the mat structure rides, around the eas curve IS in changing its direction while launching, from approximately horizontal to approximately vertical without damage to the parts of the mat structure. In order to avoid destructive eccentric stresses entering the slabs the cables must be supported around the curve at the plane of the incorporated wire reinforcing grid which carries the weight of each unit slab 2 directly to the cable to which it is joined. This necessitates forming channels IS in the ends of the slabs for accommodation of both sheaves and cables. An additional function served by these channels include keying the mat to the curved side of the float i in order to prevent lateral displacement of the structure along the side of the float. It will be noted that the ends of he slabs 2 extend into contact above the underlying launching cable 6, thus forming the covered or undercut channe1 It. In Figs. 8 and 7 I have illustrated the necessary coordination in design between the mat structure and the launching plant. The relation of mat to plant is comparable to the relation of ammunition to a gun which fires it.

Figure 8 shows two mats Nos. A and B (Fig. 4) with the down stream edge of the latter overlapping the upstream edge of the former, as indicated at I! in Fig. 9. This diagrammatic view also illustrates the interconnected side to side arrangement of the successive launches I, the meeting edges of their constituent unit section; I being connected by fastenings such as shown in Fig. 28. Figure 8 also shows the launching cables I initially extended at their shore ends and anchored to dead men 20 placed in the upper or exposed part of a river bank. This is a useful expedient in making the first launch and thereafter on steep slopes to restrain the mat from sliding down the slope. Ordinarily the upper banks are graded to fairly flat, stable slopes. in which event the great weight of the structure is usually suflicient to anchor it in place.

Observing Fig. 11 it will be seen that I employ a suitable form of reinforcement or bonding preferably formed of wires 22 extending lengthwise of the unit sections l and wires 23 extending transversely of the individual slabs 2. These wires comprise straps formed by doubling a single strand back on itself with ends lapped or welded near the middle. This design makes possible use of wire of smaller diameter for the same strength in the member when of non-corrosive material. The longitudinal members 22 extend continuously through all slabs of the section from end to end and serve to hinge the adlacentslabs together articulately at contact joints 2G and to provide the means of connecting the unit sections together end to end. The transverse members 23 serve to reinforce the individual slabs 2 along their Weakest dimension and at the same time their looped ends provide means for joining the unit sections together along their sides.

A permissible modification of the above bonding wires is shown in Fig. 12 in which a single strand of heavier gauge wire is used with its ends bent around the clip well openings or recesses I1 and only extend a short distance back into the section. Another modification illustrated in Fig. 13 shows the reentrant end of the wire in rear of the loops twisted around the main strand.

Each unit slab 2 is provided at its opposite ends with recesses I! for clip fastenings and those slabs at the extremities of each unit section have other recesses 21 which cooperate with and complement similar recesses in adjoining unit sections of a mat structure to form wells for gaining access to the looped ends 22 and 23 of the grid members 22 and 23, respectively, and for seating therein the clip fastenings (Figs. 25-28) which join the adjacent sections of the mat structure together and to the launching cables and of which the characteristic diaphragm like plates substan tially close the openings of the wells.

It will be seen from Figs. 14 and 15 that the clip well recess l'l terminates in the top of the launching cable channel [8 formed in the lower edge of the slab, whereas the clip well recess 21, formed in the side of the slab which constitutes the end of the unit mat section, extends entirely through the slab from the upper to the lower face thereof. It will also be noted that the transverse grid wire 23 terminates at right angles in the rectangular end 23 which crosses the open side bers 22 of the wire grid (Fig. 16);

9. of the recess I I in the plane of the projecting end 28 of the slab and in coincidence with the top of the undercut recess l8, whereas the longitudinal grid wire 22 terminates in the rectangular end 22 which crosses the open face of the clip well recess 21 in extension of the line defining the intersection of the bevel planes 29 and 30 which in turn define the side of the slab and the end of the section. Along the sides of both recesses I1 and 21, the grid members preferably lie within the side walls of said recesses and are wholly or partly encased in the material of the slab. The exposed 100p ends 22' and 23 of the reinforcing wires cooperate with similar ends of wires in the :contiguous sections of a mat structure, and constitute the parts which are included in the grip of the launching cables, as hereinafter more specifically described.

120 The unit slabs 2 are formed by two oppositely disposed, complementary, similar but unequal;

angular grooves, V-shaped in cross section, separated by the thickness of the longitudinal mem- The upper groove 26 is necessarily larger than the lower groove 26 in order to enable the cross bar 3| of the demountable mold forms to be detached from the groove 26 of the upper casting and dropped into the underlying larger groove 26 of the preceding casting from which it may be withdrawn endwise for repeated use in the successive castings of the tier. Equal angular openings in the grooves above and below the plane of the wire grid assures equal upward and downward articulation between adjacent slabs, regardless of the position of the grid. Another reason for placing the grid well below the median horizontal plane of the slabs is to make feasible the use of a shallow launching cable channel i 8, a feature which improves the efficiency of the contact joint 32 (Fig. 22) between the meeting ends of the adjacent slabs 2 as best shown in Fig; 22, thus adding to the strength of the faces at the ends 20 of the slab.

Referring to Fig. 17 it will be seen that the sides of the unit sections l are joined together in contact and to the launching cables 6 by clip fastenings in wells i1 and are connected to the underlying launching cables 6 disposed in the channels l8 recessed into the lower face of the structure. It will also be observed that the successive launches are joined together in contact at their meet ng beveled ends bymeans of the clip fastenings in clip wells 21. \;=All connections are effected by the clip fastenings including within their grips the stirrup-like looped ends of the meeting grid members where exposed in the clip wells and in contact side by side therein.

Figure 18 features the connections between the contiguous edges of the unit slabs 2 and also shows the unit between two of the slabs lying at the united ends of unit mat sections. In this figure "it will be seen that the longitudinal grid members 22 lie in an area between the opposing V-shaped grooves 26 and 26 which cooperate to constitute the transverse joints (Figs. 17-29) and extend continuously through the length of the sections I and throughout the mat structure by being connectcd at the meeting ends of sections by means of clip fastenings in clip wells 21 (Fig. 17), thereby joining the sections together in contact at their meeting ends. It is also to be noted that the transverse grid members 23 pref- Figure 19 shows in elevation a given length of one of the launching cables 6 lying in recess I! under the projecting ends 20 of slabs 2 with the clip fastenings seated in clip wells l1 and gripping their grid members. 23 together and uniting them to the launching cable. There is preferably one such fastening to each slab 2 in the middle of the slab end. Launching cables 6 run continuously throughout the mat structure and are a constituent part thereof, and in addition to its other important functions, heretofore described, adds strength to the mat structure'in the direction where mostneeded, normal to the shore line. Againgreverting tol igs. 1'7 and Fig. 20. and with parti'euiar refercnce to the latter which showan I I view-tremor the slabs forming'ithe end unit: section" with similar adjacent units joined th ereto. This is thepoint of jointure between launches 5 where such end slabs are conneoted by clip fastenings located in clip wells 21 "which join together thelooped ends 22 of the longitudinal grid members 22 of successive laimches to form the continuous uniform mat structure. Figure 20 also shows the launching cables'li lying in the channels I 8 and covered over by the projecting ends of the slabs 2. The engagement of-these ends of the slabs form the articular joint 32 directly above the cable.

Figure 21 shows the relative position of the transverse grid wires 23 above the longitudinal wires 22 and the clip fastenings in the access wells II. These fastenings. serve the dual purpose of bringing together the adjacent looped ends 23 of transverse grid wires 23 and also uniting them to the underlying cables.v In this way each end of each unit slab 2 is connected to a launching cable 6. Hence, as the successive launches 5 are fed overboard the channels I8 in which the cables are enclosed accommodate the sheaves i6 (as shown in dotted lines in Fig. 22) and the ends of the unit slabs 2 are supported on the idler r'olls 34 adjacent the sheaves (Fig. '7).

In Figs. 23 and 24 I have shown how the ends of the slabs 2 may be chamfered or beveled in cases where it is desired to add to the flexibility of the mat structure as a whole without sacrificing its strength and at the same time effectively closing the joints immediately above the launching cables. Inthese figures I have also shown suggested changes in the cross sectional contours of the cable channels which may be made to compensate for any strength that may be lost in chamfering the ends of the slabs. However, it will be apparent from a comparison of Figs. 22, 23 and 24 that in all cases the width of the channel I8 is determined by the thickness of the sheaves I 6 and its depth or vertical dimension is governed by the position of the wire grid in the bodies of the slabs, the grid being placed as close to their lower faces as is consistent with the preservation of maximum strength and other considerations. The preferred location of the grid is approximately one-third of the thickness of the slab from its bottom face. I

Clip wells One half of each clip well I! and 21, best shown in Figs. 25, 26 and 27, is recessed into the meeting edges of each of the two adjacent slabs of adjacent mat sections. The clip wells result from cooperation of its two halves in substantially perfect registration when mat sections are placed side by side and end to end. The method and forms employed in the manufacture of the sections makes this result automatic and certain during construction (see my copending application Serial No. 727,042, Method and mold forms for prefabricating sections of an articulated revetment mat without spacings between slabs). It will be 'observed that clip wells I! along the meeting sides of mat sections above the launching cables, terminate downwardly in the top of the channel I8 which is otherwise closed over throughout by the projecting end-s 20 of the slabs extending over the channelway to form the contact joint 32. On the other hand the clip wells 21 (Fig. 28) along the meeting ends of the contiguous sections, likewise formed by cooperating recesses in adjoining sections, extend clear through the sections from top to bottom. An ad- I ditional function of clip well recesses H in the ends of the slabs of the unit mat sections is to provide means for engagement of the legs of the handling grapples as heretofore described.

Longitudinal contact joint 32 as shown in Figs. 22 and 25 provides for downward articulation of one section with respect to the adjoining section through full 90 degrees of are without opening sufliciently to permit harmful circulation of water. In all normal relative movements of these parts in a revetment in place the design of the joint assures positive contact of the adjacent slabs. The limited need for upward articulation between the elements of a mat structure along the contact joint 32 normal to the bank is adequately met by the yield tolerance of the fastenings. However, any desired range of upward articulation may be provided for positively by beveling back the ends 20 of the meeting slabs, as indicated by 35 and 36, from a contact point just above the launching cable 6 as shown in Figs. 23 and 24, without forming spaces through which water may circulate to undermine the structure in place. These figures also show permissible variations in the design of the channelway 18 in the interest of strengthening the slab ends and the joint 32.

Fastenings for the unit sections The common characteristic of the fastenings employed in the wells formed by the meeting recesses H, in the ends of slabs 2, and the recesses 21, in the edges of those slabs forming the ends of the units I, is that they function to draw together the loops or stirrup ends of the transverse and longitudinal reinforcing wires and also substantially close the wells allowing only minimum spaces for the circulation of water through the wells.

The preferred type of clip fastening is illustrated in Figs. 25, 26 and 27. It consists of a U-bolt 31 fitted with nuts and a special plate 38, which may be rolled, out and bent, stamped out, forged or cast in quantity. The clips may be lighter in design than somewhat similar commercial varieties and are preferably made of noncorrosive metals. The plate 38 is designed to close the openings in clip wells l1 and 21 with small clearance thus forming an effective bafiie checking the circulation of water therein to harmless velocities. In addition, the plate is equipped with the downwardly turned wings or flanges 39 set wide apart to fit comfortably within the sides of the looped ends of grid members 22 or 23, as the case may be, and at the same time fit snugly over and hold said ends of the grid members firmly together. The flanges or wings 39 are notched at the center to embrace the respective stirrup ends 22' and 22 of said grid members. It will be noted that the rectangular form of the end of the grid members together with the positioning of the plate wings ll, near, but not directly in contact with the sides, provides a connection of great strength with limited but desirable tolerance of yield under strain. The use of shorter U-bolts in the clips shown in Fig. 28, at the ends of the mat sections, is desirable, but not a The launching cables 8, best shown in Figs. 25 and 27, are preferably commercial wire strands of suitable size and strength, the individual wires of which are preferably of non-corrosive materials identical in composition to the wires of the grid in order to avoid electrolysis at contacts on immersion. It will be noted that the launching cable contacts the lower faces of the grid members 23 and therefore lies in the plane of the longitudinal grid members 22. The ends of ad jacent grid members 22 of adjacent mat sections are joined together and to the underlying launching cables by means of clip fastenings which must be set up tightly beyond the possibiliis of slippage. In this way the weight of each individual slab is transmitted through grid member 23 directly to the'launching cable which carries the weight of all slabs individually and cumulatively when, in launching, the mat is suspended over the side of the launching apparatus float I (Fig. 5), thus preventing the accumulation and transmission of destructive stresses through the slabs along the longitudinal grid members 22, as would otherwise occur to defeat the operation of successful placement. The launching cables being thus firmly incorporated into the mat structure, provide the additional strength to the emplaced structure, in the direction normal to the bank line, where needed to resist the disrupting effects produced by the usual lower bank subsidence to new slopes of repose inducted by continued erosion beyond the toe of the revetment.

Artimuatmg the slabs of mat sections This is eflected by'the characteristic features of the transverse contact joint 26 between the slabs 2 as well as between the meeting ends of the unit mat sections of the mat structure which may be recognized best by referring to Figs. 16, 29 and 30. The joint consists of a large angular groove above and a similar but smaller angular groove oppositely disposed in the same vertical plane below it and spaced therefrom by the thickness of the interposed longitudinal grid members 22, which hinge the adjacent slabs together articulately in the contact zone 33. Since the angular openings in these grooves are the same, equal upward and downward vertical articulation between adjacent slabs is assured in the direction normal to the river bank line wherever this is important in the mat structure. The relative size and position of the angular grooves, as shown, makes possible the casting of the sections of the mat in tiers of sections, one section superimposed above another, as shown in Fig. 16, and as more fully disclosed in my copending application. Positioning the grid nearer the lower face of the structure makes possible a shallow undercut cable and sheave channel l8 which is essential to the efllciency of contact joint 32 and also avoids excessive weakness in the projecting ends 20 of the slabs which cover said channelway, as shown in Figs. 22 and 25. The contact zone 33 will be 13 clearly understood from Fig. 80. Its width may be increased as desired by lifting the bottom of the upper groove 2', or by otherwise increasing vertically the space between grooves. The areas it constitute zones of weakness between the slabs I initially joined rigidly together by continuity therein of the materials composing the slabs, and which laterfracture to form contact joints between adjoining slabs when the sections are moved or worked in the revetment mat structure.

The placement operation (Figs. 4 and 5) The revetment mat should be preferably laid at a time when the water in the stream is at or near a seasonal low level. Thesiteof; the work should be cleared thoroughly eftrees, brush,

stumps, logs, snags, wreckage or other obstructions. The upper, or exposed bank should then be graded back to a satisfactory slope, the flatter the better and preferably graded at not less than 3 to 1. The slope should then be extendeddown over the submerged lower bank and well out into the stream and to the limits of the proposed revetment if practicable, by dredging, filling or mechanically grading under water. At best the resulting submerged slope will be rough, unstable and possibly considerably damaged by erosion before covered by the revetment.

The position for the first "setting of the plant is selected at a distance above th lower end of the site equal to the practicable reach of the launching plant. The assembled plant is then moored alongside the bank and parallel to it and extending upstream from the selected point. Cables l8 are then run out from mooring barge 8 and made fast to suitable dead men placed well upstream in the top of the adjacent bank. In this position the fixed mooring barges 8, the movable mooring barges 8 and the launching apparatus float 1, lie sid by side temporarily lashed together, with mooring barges 9 next to the bank. The entire plant is now swung pivotally from its lower end, with the current out into the stream until positioned normal to the bank line with the inner end of the upper barges 8 bearing'thereon, and made fast thereto. Next, the lower mooring barges 8 with the launching float I appended thereunder, are dropped down stream by payin out cables 48 until correctly positioned above the site of mat No. A. Mooring barges 8 are then temporarily made fast to the bank and the outboard end inclined slightly down stream. The first barge ll loaded with tiers 3 of prefabricated mat sections I is then run in alongside of and made fast to the launching float I, and both float and material barge are moved inboard across mooring barges 8 until the float 1 grounds against the bank.

The launching cables 6 are then run out to the temporary or permanent fastenings 20 in the adjacent bank. The first launch 5 is then built up on the ways of the float I, and consists of a single row of prefabricated mat sections l arranged side by side and interconnected along their contact edges to the launchin cables lying thereunder by means of the clip fastenings. The several launching cables are then payed out in unison by the machinery of the launching float I, until the first launch, under action of gravity, assisted manually as necessary, moves over the curved side l3 of float l and its inside edge comes to rest on the bank at the water line. The cables to the bank anchors are then taken up and adjusted. The launching float 1 is then drawn outboard by other machinery of the apparatus and at the same time the launching cables are again payed out in unis n until the outboard edge of the launch arrives at a selected point just above the beginning of the downward curve iii in the side of float I, where the movement is arrested and everything made fast. The second launch is then built up in the same manner on the ways of the float in continuation of the flrstlaunch to which it is joined in contact by joining the meeting ends of the corresponding mat sections of each launch by clip fastenings (Fig. 28) as heretofore described. The launching cables are again payed The operation described is repeated f desired length of the mat has been attainedjia'ta,

which point the further assembly of "launches".

is discontinued, the launching cables are payed out in unison as the float I is moved back or out- I I board, thus lowering the structure to its final position at rest on the submerged bank or river bottom.

The launching cables are then cut and the mooring barges 8 with appended plant are then drawn upstream a distance of one mat width, less the width of the overlap, by actuating machinery to take up or shorten cables 48. The operations described in the construction of mat No. A are now repeated in the construction of mat No. B, and so on successively for mat No. C and mat No. D, after which the entire plant is shifted upstream to the next successive setting, where the whole operation is repeated, and so on to the completion of the entire revetment project. In launching it is desirable to incline the float. I slightly to the current in order that the current may slightly inflate the suspended mat structure, or flll it like a sail to steady it and assist the outboard movement. It is also desirable to run cables (not shown) from the upstream edge of the portion of the mat structure suspended from the float, under'mooring barges 8 to fastenings on mooring barges 9 as additional means of steadying the mat structure against the current and preventing folding at the upstream edge as well as displacement downstream under severe conditions. After a mat has been placed the current continues to erode the submerged bank H beyond the outer edge of the structure, so that it becomes necessary for the mat to follow the erosion closely and adjust itself to the new slope of repose l5 under great strain on the structure in this direction. The additional strength needed to resist this is provided by the launching cables 6 firmly incorporated into the structure in this direction as heretofore de scribed.

Handling the mat unit sections The special construction I have provided in my unit sections provides a ready means for sides of the mat units 1 and are spaced in accord-,-

the curve at ance with the distances between the wells II on all of the slabs 2 of such units. Their lower ends 42 are beveled and provided with shoulders extending parallel with the edges of the unit. when the grappling device I! is lowered the several legs pass downwardly throughthe loops 23a and their hooked ends engage beneath the top of the channel I! and the embedded reinforcement wires 23. Thus when the grappling device is elevated the unit i is supported throughout its length for transportation. When the unit is lowered into position on the deck of the assembly float 1 the several grappling hooks ll may be readily disengaged by moving them laterally, as will be understood. This arrangement of cooperating parts on the unit mat sections and the handling apparatus provides a means for lifting the units vertically and shifting them laterally in a rapid and safe manner.

The life of such a revetment employed on a fully regulated stream will be very long and the annual maintenance small. On the other hand it is the destiny of every isolated revetment employed as a local expedient on the constantly shifting banks of unregulated meandering alluvial streams to be ultimately fianked" or left behind by the stream as it wanders from side to side of the valley floor.

Thus, it will be understood from the foregoing specifications and the accompanying drawings, that my present invention consists of an articulated slab revetment mat with launching cables incorporated therein, composed of an assembly of prefabricated unit sections, each section consisting of a plurality of similar slabs, so formed and interconnected within the section and continuously throughout the revetment mat, as to exclude from the resulting mat structure all openings through which water may circulate freely to undermine the revetment mat when in place on the submerged banks of streams with deep water and strong currents, and which at the same time meets all other conditions essential to practical manufacture and placement of such a structure.

I claim:

1. An oblong body of material molded in a relatively thin flat form as a unit section of a revetment mat said body being divided transversely into a plurality of unit slabs by V-shaped grooves forming planes of weakness between adjacent slabs, said section being provided at its sides and ends with recesses for the reception of securing devices for uniting said section with other similarly formed sections, longitudinally extending reinforcing wires embedded in the section serving as a means of articulation between the several slabs of a section, and carrying at their ends loop portions located in the end recesses, other transversely extending reinforcing wires embedded in the respective slabs and having loop portions lying in the side recesses, said loop portions of the two sets of wires being adapted to cooperate with the aforesaid securing devices.

2. A rectangular body of molded material forming a unit section of a revetment mat, said body being divided transversely into a plurality of unit slabs by grooves extending inwardly from the opposite faces of the body without meeting to form intermediate zones of weakness, longitudinally extending reinforcing wires embedded in said zones and transversely extending wires embedded in each slab, said body being provided at its ends and sides with recesses in alinement with the reinforcing wires, and the latter being formed with stirrup portions extending across the outer edges of the recesses and serving as securing elements.

3. A body of molded material forming a unit section of a revetment mat divided transversely into a plurality of unit slabs by oppositely disposed grooves of V shape extending inwardly from the opposite faces of the body without meeting and creating intermediate zones of weakness in said material, defining slab divisions thereof, longitudinally extending reinforcing wires passing through said zonesand forming a means of articulation between the adjacent unit slabs, reinforcing wires extending transversely of each slab, said section being provided with recesses at its ends and sides and said two sets of wires having end portions extending respect'.vely across said recesses and serving as elements by means of which contiguous unit sections may be secured to each other in contact to form a revetment mat. I

4. An oblong body of material molded witha relatively thin cross section and forming a unit s ction of a revetment mat divided transversely into a plurality of unit slabs by V-shaped grooves extending inwardly from its opposite faces and creating weakened zones located at approximately two-thirds of the thickness of the body below its upper surface, said section having lon itudinally extending channels in its lower bottom edges and provided with recesses in said edges above the channels and also provided with recesses in its ends, and connecting means embedded in the body having portions extending across the recesses adjacent the outer planes of said sides and ends.

5. A revetment mat composed of a series of similar unit sections, each section comprising an oblong body divided by transverse grooves, extending inwardly from its opposite faces, into unit slabs connected by intermediate zones of .weakness and having longitudinally extending channels in its lower or bottom edges and provided with recesses located above the channels, the ends of said units being provided with beveled faces, said faces having corresponding recesses therein, longitudinal reinforcing wires embedded in the zones of weakness forming means of articulation between the several unit slabs and having loop portions extending across the end recesses, other reinforcing wires in the unit slabs likewise having loop portions extending across the side recesses, launching cables located in the longitudinal channels formed between adjacent sections, clips embracing them and the loops in the side recesses of adjacent sections and other fastenings embracing the loops in the end recesses of preceding and trailing units, said clips comprising plates adapted to close the clip recesses in which they are located.

6. A revetment mat composed of a series of similar oblong unit sections located in parallel and consecutive arrangement, each section composed of suitable molded material, having at its ends upper and lower faces beveled to form a projecting edge intermediate to the upper and lower faces of the section, the latter having recesses extending across said beveled faces, said section having at its sides longitudinally extending channels with their upper walls coincident with said projecting edge, said section also having-recesses above and communicating with said channels, and being further provided with V I aw -m i spaced transverse grooves in'lts top and bottom races forming intermediate zones of weakness which define between them unit slabs, longitusections, securing clips fitted in the side recesses of adjoining sections embodying fastenlngs embracing the cables and the connecting elements in said recesses and other securingv devices fitted in the end recesses of preceding and trailing sec tions for pivotally uniting the connecting elernents therein to secure said end portions in substantially meeting engagement of their respective projecting edges.

7. A revetment mat composed of a plurality of prefabricated unit sections, united at their ad= Jacent ends and sides, each unit being cast over and integral with a continuous reinforcing wire grid, said grid of each section forming bonding elements at the sides and ends or the sections, the sections being each divided into a plurality of slabs continuous in. the zone of the wire grid interconnected by the grid and separated by cooperating transverse grooves lying above and below the plane of their respective grids, and connection between the bonding elements of the several unit sections.

8. A revetment mat composed oi a plurality of prefabricated unit sections, united at their adjacent ends and sides, each unit comprising a plurality of slabs cast over and integral with a reinforcing wire grid, said sections having alined upper and lower V-shaped grooves forming con-= tact points between adjacent slabs and further provided with recesses in its ends and sides re-=- ceiving portions of the grid which form bonding elements, and connections between the bonding elements of adjacent unit sections including plates which substantially close said recesses against the circulation of water therethrough.

9. A revetment mat composed of longitudinally and transversely disposed series of oblong unit sections with bevel pointed ends articulately con-= nected at their ends and sides in contact, each unit section being composed of molded material having recesses in its ends and sides for the accommodation of fastenings joining the ends of the reinforcing grid wires embedded in said material and which have portions extending across the recesses to form fastening elements, each of said unit sections being also provided with V-shaped grooves in their upper and lower faces on opposite sides of their grids dividing the sections into interconnected unit slabs, said lower grooves being of lesser cross sectional area than the upper grooves and securing devices connecting the grid wires of adjacent sections.

10. An articulated slab revetment mat consisting of an assembly of rectangular prefabricated unit sections, each section consisting of a series of similar rectangular unit slabs cast over and integral with a wire reinforcing-bonding grid coextensive with the unit and lying below its horizontal center plane, the edges of the successive slabs contacting in the zones of said grids and being beveled back above and below said zone and at the ends of the sections and undercut below said zone at the longitudinal sides of the sections, said sections being also provided at their ends and sides with recesses exposing por- 18 tions of said grids, launching cables disposed in said undercuts, and connecting devices between the exposed gridparts at the meeting ends of successive sections and other connections uniting the exposed grid portions at the contiguous side edges of adjacent sections and-to the underlying launching cables.

11-. An articulated slab revetment mat consisting or an assembly of preiabrieated unit sections articulately connected end to end and side by side, the meeting longitudinal edges of each section having underlying cable recesses which cooperate to form channels in lower side of the mat, parallel launching cables lying therein, said sections being provided in their contiguous side edges with registering recesses and having at their ends other registering recesses, longitudinal and transverse reinforcing bonding wires embedded in the sections having portions extend ing across said several recesses to form fastening elements, said units also being provided at upposite sides of the plane of said wires with allned transversely extending ii-shaped grooves form ing connected articulated unit slabs, plates in said recesses-overlying the fastening elements and connecting devices embracing said elements and passing through the plates, the connecting elements in the side recesses also embracing the launching cables.

12. An articulated slab revetment mat is: posed of an assembly of prefabricated unit sec= tions close jointed and flexibly interconnected along their meeting borders, said sections having channels recessed into the under face of the mat structure along the longitudinal meeting sides of the unit sections, launching cables disposed in said channels and running continuously in one direction through the mat structure, each l unit mat section consisting of a plurality of identical rectangular slabs flexibly interconnected and in contact side to side, each section including within its body integral and coextensive therewith a unit wire grid, recesses along the borders of said unit mat sections exposing border portions of said grids and cooperating between sections at their meeting sides to form openings, metal clip tastes seated in said openings including plates which fit therein and join together the adjacent unit t sections at their meeting ends by clamping together the adjacent portions of the wire grids exposed in said cooperating recesses, similar clip fastenings at the meeting sides of the unit sections clamping the units together and to the adjacent launching cable with the exposed border portions of said wire grids, the meeting sides of the several slabs of each unit mat section and the meeting ends of the sections being bluntly pointed outwardly and in contact in the horizontal zone of the wire grid and formed with facial planes above and below the zone of the grid beveled back from the zone of contact.

13. A revetment mat composed of a plurality of prefabricated unit sections each composed of a plurality of slabs with alined upper and lower v shaped grooves forming contact joints between adjacent slabs, each unit section being assembled 'in contacting engagement at its borders with other like contiguous sections, means for yieldingly connecting the adjacent ends and sides of the different sections together, continuous launching cables lying along the under side of the mat assembly coincident with the meeting sides of the sections and to which the adjacent sections are rigidly fastened.

14. A revetment mat composed of a plurality oi prefabricated unit sections each molded with underlying channels extending upwardly from the bottoms of the sections and terminating in shoulders assembled in contacting engagement at their borders, the channels in the assembled or abutting units extending continuously for the length of the mat, launching cables lying in said channels beneath said shoulders and means for yieldingly connecting the adjacent edges or said sections to each other and to said cables.

15. An articulated slab revetment mat composed of a plurality of prefabricated unit sec tions of such articulated slabs each molded with underlying channels open along the undersides of the ends of the slabs, said unit sections being assembled in contacting engagement at their borders, the channels in the assembled units extending continuously for the length of the mat, launching cables lying in said channels and means for yieidingly connecting the adjacent edges of such sections to each other and rigidly to said launching cables.

16. A prefabricated unit section of a revetment 20 mat comprising a body formed of a plurality of flexibly united similar unit slabs with alined upper and lower V-shaped contact Joints between adjacent slabs, the ends or the slabs and the sides of the sections being undercut at their lower portions to form downwardly opening cable channels when assembled into the mat structure.

DAVID McD. SHEARER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Engineering News-Record, pages 124-128, September 20, 1945.

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