Erosion Control

Abstract

The invention relates to an erosion-controlling protective surfacing for the soil comprising flexible liquid-permeable supporting sheet means conforming to the contour of the soil and a mat of blocks on said supporting sheet means, said mat having drainage passageways therethrough so that water can pass through the surfacing. Preferably, the surfacing includes filter means and the blocks are secured to the supporting sheet means.

Parent Case Text

This application is a continuation-in-part of my copending application Ser. No. 564,167, filed July 11, 1966 now U.S. Pat. No. 3,421,417.

Description

This invention is directed to controlling or preventing erosion of soil, and more particularly, it is directed to an erosion-controlling protective surfacing for the soil and a method of controlling soil erosion.

In general, erosion control is directed to one or more of the following:

1. Prevention of good soil, such as arable, grazing or forestry soil or land from being washed away by water (water erosion), or from being blown away by wind (wind erosion).

2. Prevention of washing or blowing away of poor or uncultivatable soil and its deposition on good soil, thereby causing ill effects on the good soil.

3. Improvement, wherever possible, of poor, uncultivatable and/or arid soil to render such soil usable for agricultural purposes.

4. Prevention of the silting up or cluttering of land or soil with soil brought from other locations by water and maintaining desirable vertical drainage of the soil.

5. Prevention of undesirable runoff of rain and surface water to obtain desirable absorption of such water in the soil, as well as judicious distribution of the water.

6. Prevention of undesirable changes in the contour of the land caused by movement of the soil and water.

It will be appreciated, therefore, that control of soil erosion encompasses or involves soil conservation, as well as controlling of waterflow.

In nature, erosion is prevented largely by natural growth of vegetation. The roots or grasses, trees and other vegetation hold the particles of soil together so as to prevent soil movement or erosion by wind and water. This also renders the soil porous so that surface water can be absorbed and properly drained. The cover of leaves, twigs and other external growth and the partly humidified organic waste also serve to control flow of surface water to produce a proper distribution and absorption of water as well as prevention of erosion. In the course of time, the vegetation decomposes to form humus, a valuable part of the soil for storing and dispersing water, food and oxygen for the vegetable matter, as well as providing anchorage for vegetation.

Bare land or land poorly covered with vegetation is particularly subject to erosion, especially during torrential rains and strong winds, since such land does not have the vegetation to prevent movement of the particles of the soil. Such land can absorb the water only poorly. This occurs not only on sloped terrain, but on flat terrain as well. In those areas which have only a relatively thin layer of topsoil, the high runoff speed of excess water washes away this thin layer. Erosion always occurs in nature even in areas untouched by man, but in the those areas the erosion is not necessarily as serious because of the balanced situation occurring in nature. Man destroys this balance of nature by cutting down forests, overgrazing the land, burning, and, in general, by destroying the natural protective crop cover and this disturbance of the natural balance has caused large areas of originally good soil to become useless because of erosion.

Many attempts have been made to control erosion by various means. One approach is to imitate nature as much as possible by sowing plants, bushes and other vegetation. Attempts have been made to control erosion by using special methods of tillage contouring, terraining, drainage, laying out of spillway systems, stripcropping, crop rotation, etc.

In addition to the basically agricultural methods of controlling erosion, various mechanical and/or chemical techniques have been tried, either alone or together with agricultural techniques, so as to ultimately obtain a growth of vegetation for controlling the erosion. Some of these mechanical or chemical methods comprise mixing cellulose or alginates with the soil to form an idealized seedbed: placing burlap or jute netting on slopes (mostly on a small scale): placing prefabricated or formed in situ asphalt membranes, facings, linings, or revetments, use of rigid or flexible concrete revetments: use of riprap, dumped rubble, etc.

None of these methods is satisfactory. Chemical methods do not give sufficient mechanical strength and in the case of torrential rains the protective layer is easily washed away. The burlap and jute methods, because of the light weight of the fabric are easily understreamed. Nylon matting is similarly understreamed, although in some cases reasonable results are obtained by weighing these with riprap, but the matting does not have sufficient strength to withstand the sharp edges of the stones and becomes torn.

Riprap and dumped rubble, usually in the form of a graded filter construction, have the disadvantages of not being readily available everywhere, are difficult to keep in place, are high in maintenance costs, and are never really soil retaining. Asphalt and concrete constructions of the impermeable type are costly because of the necessary weight and thickness to withstand hydrostatic pressure and even when weep holes are provided, cracks and ruptures frequently appear suddenly. It is difficult in this type of construction to include structure for slowing down current of flowing surface water and/or further sedimentation.

There is currently in use what is called a flexible concrete mattress for riverbank revetments, as shown in U.S. Pat. Nos. 2,674,856 and 2,876,628, comprising slabs of concrete wired together and placed on the soil. Although this construction is admittedly an improvement over rigid constructions, it is still not satisfactory. It is well known that in such constructions, when a crack appears in an individual slab there is tremendous erosion. Since there is no provision for the equalization of hydrostatic pressure, the entire mattress can be picked up by the currents. Neither is there a specific device to augment sedimentation and/or slow down currents.

When dealing with erosion, I have found that erosion can be successfully controlled and often eliminated by applying to the surface of the ground a protective surfacing having the following characteristics:

1. The surfacing should be sufficiently flexible to form to the contour of the underlying soil and form a good contact therewith, thereby preventing understreaming.

2. The surfacing should have sufficient strength and weight properties to prevent displacement of the elements thereof by heavy water currents or wave action and such properties can be supplied by the weight of the elements.

3. The surfacing should permit the passage of surface water into the underlying soil, that is, maintain good vertical drainage.

4. Means should be provided to permit the passage of water upwardly from beneath the surfacing to release hydrostatic pressure formed underneath the surfacing. This is of particular importance on dikes and riverbanks, since hydrostatic pressure can cause great damage (slip erosion).

5. Means should be provided to prevent the underlying soil from being carried away by the movement of the water.

In addition to the above, depending upon the prevailing conditions, the following additional characteristics are significant:

6. Where there is excessive movement of water on the surfacing, means should be provided for slowing down such movement and/or for furthering sedimentation.

7. Where vehicles are to run over the surfacing, the surfacing should have an appropriate wear surface.

In many instances means should be provided to permit the growth of vegetation through the surfacing, so that the vegetation can assist in the prevention of erosion, or in many applications, eventually take over the entire job of erosion control, so that the originally applied surfacing is only temporary.

According to one aspect of the present invention, there is provided an erosion-controlling protective surfacing applied to the soil, said surfacing comprising flexible liquid-permeable supporting sheet means conforming to the contour of the soil and a mat of blocks on said supporting sheet means, said mat being constituted by a plurality of blocks in a side-by-side substantially abutting arrangement, said mat having drainage passageways therethrough extending from an upper surface of said mat to the bottom surface thereof to provide communication from said upper surface to said supporting sheet means whereby liquid can pass, in either direction, between said upper surface and the soil through said supporting sheet means and said mat. According to the preferred embodiment, this surfacing includes filter means and means for securing the blocks to the supporting sheet means.

According to another aspect of the invention, there is provided an erosion-controlling protective surfacing to be applied to the soil to prevent erosion thereof, comprising flexible liquid-permeable supporting sheet means positionable on the soil and a plurality of blocks in a side-by-side substantially abutting arrangement superposed on said supporting sheet means forming a mat of blocks thereon, each of said blocks being secured to said supporting sheet means, said mat having drainage passageways therethrough extending from an upper surface thereof to the bottom surface thereof to provide communication from said upper surface to said supporting sheet means whereby, when said assembly is applied to the soil, liquid can pass in either direction between said upper surface and the soil through said supporting sheet means and said mat, said assembly being sufficiently flexible to conform to the contour of said soil. According to a preferred aspect of the invention, the surfacing includes filter means.

According to another aspect of the invention, there is provided a method of controlling erosion of soil by applying thereover an erosion controlling protective surfacing, comprising applying to the soil flexible liquid-permeable supporting sheet means conforming to the contour of the soil and positioning thereover a plurality of blocks in a side-by-side substantially abutting arrangement to form a mat of blocks on said supporting sheet means, said mat having drainage passageways therethrough extending from an upper surface thereof to the bottom surface thereof to provide communication from said upper surface to said supporting sheet means whereby liquid can pass in either direction between said upper surface and the soil through said supporting sheet means and said mat. Preferably, filter means is also provided and the blocks are secured to the supporting sheet means.

These and other aspects of the invention will be readily apparent from the following description in connection with the accompanying drawings, wherein:

FIG. 1 shows a perspective view of one embodiment of the surfacing of the invention, showing only one block secured to a supporting sheet;

FIG. 2 shows a plan view of the structure of FIG. 1, but shows a plurality of blocks, one being shown in detail and the remainder in phantom;

FIG. 3 schematically shows one manner in which blocks are secured to the supporting sheet and shows the manner in which adjacent assemblies are positioned on the soil;

FIG. 4 shows a perspective view of another embodiment of the invention, showing a different form of block;

FIG. 5 is a diagrammatic cross section showing another manner in which the blocks are secured to the supporting sheet;

FIG. 6 is a diagrammatic cross-sectional view showing one manner in which adjacent assemblies may be secured to each other;

FIG. 7 is a diagrammatic cross-sectional view showing an embodiment of the invention showing two supporting sheets;

FIG. 8 is a diagrammatic cross-sectional view showing an embodiment of the invention showing three supporting sheets;

FIG. 9 is a diagrammatic cross-sectional view showing another embodiment where there are two layers of blocks;

FIG. 10 is a diagrammatic cross-sectional view showing an embodiment where there are sheets on both sides of the mat of blocks.

In this application the word "soil" will be used in a broad sense to mean particles of the type which make up the earth, whether such particles constitute arable, good soil or poor, uncultivatable soil, and includes such materials as sand, since frequently the ground which is to be protected is essentially sand.

Referring to FIGS. 1 and 2, according to one embodiment of the invention, there is provided a supporting sheet means 10 which, in this embodiment, is shown as a net. Superposed on net 10 in a side-by-side substantially abutting arrangement are a plurality of blocks B, for convenience only one block being shown in FIG. 1, FIG. 2 showing a plurality of blocks with only one block being shown in detail, the others being shown in phantom. Each block or element or module B, in this embodiment, is generally square, having a substantially flat bottom so that the bottom will make substantially continuous contact with the upper surface of sheet 10. Through the center of the block there is a vertical, longitudinal channel 12, circular in cross section. On each side of the block, substantially in the center thereof, there are semicircular, longitudinal channels 14 and on each corner of the block there are vertical quarter circular vertical channels 16.

Across the upper surface of blocks B there are horizontally disposed grooves 18 and 20, the grooves intersecting channels 14 at the sides of the block. Also in the top surface of the block there are grooves 22 and 24 along the edges, said grooves intersecting side channels 14 and corner channels 16.

When the blocks B are positioned in a side-by-side abutting relationship, as shown in FIG. 2, the vertical channels around the periphery of one block cooperate with the vertical channels on an adjacent block to form enclosed channels. For example, half channels 14 on adjacent blocks form full channel 26 and quarter channels 16 at the corners of adjacent blocks form or define full channel 28. It will be appreciated that the side-by-side arrangement of blocks B define a mat of blocks and that the channels in the blocks, either by themselves or when cooperating with channels of adjacent blocks, define passageways through the mat of blocks extending from an upper surface of the mat to the bottom surface, thereby providing communication from said upper surface to said supporting sheet 10, whereby liquid can pass in either direction between said upper surface and the supporting sheet.

In the construction illustrated in FIGS. 1 and 2, the sheet 10 extends in two adjacent directions from the mat of blocks to form along two edges of the assembly margins 30 and 32 where there are no blocks. Although these margins are not essential, they are convenient when placing the assembly of blocks on the ground, as shown in FIG. 3. In FIG. 3 there are shown several assemblies of sheet 10 and blocks B as used according to the invention. When utilizing the assembly of the invention the surface of the ground or soil to be protected is prepared in any convenient manner to receive the assemblies, that is, the ground is graded to provide the desirable contour. On the prepared ground or soil S there is then positioned an assembly comprising sheet 10 and blocks B. Adjacent thereto there is positioned another assembly of blocks B' on sheet 10' with the outer row of blocks B' of the second assembly being positioned on the margin 30 of sheet 10 so that the adjacent blocks B and B' of the adjacent assemblies substantially abut. In this manner there is provided beneath the layers of the blocks a substantially continuous overlapping supporting sheet.

Each of the blocks of each assembly is secured to its supporting sheet by any desirable means and two such means are shown in FIG. 3. The blocks B are secured to sheet 10 by means of adhesive 33 interposed between the bottom of blocks B and sheet 10, either in spaced-apart locations, as shown in FIG. 3, or coextensively with the bottom of each block B (not shown). Alternatively, instead of using adhesive securing means, the blocks can be secured to their supporting sheet by means of mechanical fasteners such as nails 34 which secure blocks B' to sheet 10'. Although in FIG. 3 the blocks of the two assemblies are shown secured to their respective supporting sheets by different means, it will be appreciated that normally in any one job similar securing means are used to secure the blocks to the supporting sheets. Although FIG. 3 only shows two assemblies on the soil, it will be appreciated that as many assemblies are used as are necessary to cover the ground which is to be protected. Other securing means can be used to secure the blocks to their supporting sheets, as will be hereinafter described.

It is readily apparent that although the blocks in the mat of blocks abut each other, the blocks are free to move a small amount in a vertical direction and this results in the entire assembly of blocks and supporting sheet means as being flexible and able to conform to the contour of the soil on which the assembly is positioned. It is also apparent that the assembly need not be made on the job, but can be prefabricated and shipped to the job. In this manner it is simple to grade and substantially smooth the surface of the soil and apply thereto the assembly of blocks and supporting sheet means. This can be done in a facile manner, using a minimum of skilled labor. In fact, most of the labor can be relatively unskilled. When the assembly is applied to the soil it readily conforms thereto. Any surface water which flows over the top of the mat of blocks, either from streams or rainwater, can readily flow through the passageways to be absorbed and distributed in the soil below. The roughened contour of the upper surface of the mat, by virtue of the grooves in the blocks, serves to impede the flow of water, further assisting in the vertical drainage of the soil.

If, because of the conditions in which the surfacing is applied, the hydrostatic pressure beneath the mat of blocks increases, such pressure is readily relieved by the water flowing upwardly through the passageways. In the even there is a small amount of understreaming or other conditions which cause the underlying soil to move upwardly or downwardly, the mat or, in some cases, individual blocks, can move upwardly or downwardly to conform to the contour of the underlying soil, thereby preventing further understreaming.

The supporting sheet means 10 has thus far been described as a net. This sheet can be made of any desirable material, such as perforated flexible foil or sheet or fabric of metal or plastic or any other sheet which is permeable to liquid. For example, it can be made of metal screening, metal net, expanded metal mesh, plastic net or screen, or woven or netted or any similar type of sheet made of natural or synthetic fibers. It can even be made of a sheet of fibers not interwoven but merely felted, as long as it is permeable to liquid. Nylon net or screen has been found to be a particularly desirable material, in view of its strength, ease of handling and resistance to deterioration.

It will be appreciated that supporting sheet means supports the blocks when the assembly is placed on the ground and also may support the mat of blocks if the assembly is prefabricated.

According to a preferred construction, the supporting sheet means comprises filter means. For example, in the embodiment shown in FIGS. 1--3, the sheet 10 can have its water-permeable openings therethrough of such a dimension that it will permit the passage of liquid therethrough but will substantially prevent the passage therethrough of particles of soil and in this application the words "filter" or "filter sheet" will refer to an element which is permeable to liquid but substantially impermeable to soil particles. When sheet 10, therefore, has the openings therethrough to constitute such sheet as a "filter sheet," water flowing upwardly from the oil through the protective surfacing will not carry along with it the particles of soil. Obviously, this prevents the formation of areas beneath the protective surfacing devoid of soil which is a cause of understreaming. It therefore can be said, when the supporting sheet means includes or comprises a filter sheet, that the assembly of sheet and blocks comprises a protected filter construction, the blocks protecting the filter.

The blocks can be made of any desirable material, such as molded or cast concrete, brick and even such materials as adobe or material or synthetic plastics, depending upon the nature of the conditions in which the surfacing is used. Preferably, the blocks are concrete, either high or low density, and in areas where the blocks comprise a wear surface for vehicles the blocks should have high compressive strength. In areas where there is a heavy movement of surface water, such as revetments for dikes, canals and waterways and for streambed protection the blocks are preferably made of high density material such as concrete with the weight of the blocks serving to keep the assembly in place against the movement of the current.

As has been stated previously, in ideal erosion control it is desirable, wherever possible, to simulate the protection afforded by nature. Therefore, in most locations after the assembly is placed on the soil it is desirable to encourage growth of vegetation in the passageways. In some locations, normally the forces of nature will create a condition where grass or other vegetation will grow in these passageways. To accelerate such growth it can be desirable to at least partially fill the passageways with vegetation-growth-producing materials such as fertilizer, soil, seed, bacteria, fungi, weedkiller, etc. In many cases however it is merely sufficient to place soil in the passageways, whereupon natural vegetation follows.

Ultimately, therefore, the vegetation will fill up the passageways. This vegetation serves as an additional primary filter means for regulating the vertical drainage and serves to maintain the blocks in position. In fact, in many locations, because of the protected environment created by the blocks, the vegetation can flourish and ultimately there will be sufficient vegetation to take over the entire job of erosion control. In such locations it may not be necessary for the blocks and/or the supporting sheet means to be permanent, since they merely have to last only until the vegetation takes over. In such locations the sheet 10 can be made of material which will deteriorate in time, as can the blocks. In such locations the blocks can even be made of such organic materials as compressed compost or even compressed garbage, since the blocks only need to last sufficiently long for the vegetation to take over. The blocks can deteriorate under the influence of light, weather, or other climatic phenomena.

In order to assist in the even absorption of water through the protective surfacing, the blocks can even be made of porous materials which help the absorption of the surface water and will retain moisture to assist in the vegetational growth. For example, the blocks can be made of such porous materials as foamed phenolic resins or polyester resins. An additional advantage of using such porous materials for the blocks is that the pores can be initially impregnated with vegetation-growth-producing materials such as fertilizer to provide a reserve of such materials as the vegetation grows.

In the embodiment of the block shown in FIGS. 1 and 2, grooves 22 and 24 are along edges of the block and grooves 18 and 20 are spaced from edges of the block. All the grooves intersect, with the intersections of grooves 22 and 24 being at the corners of the block and with the intersections of grooves 22, 24 and 18, 20 being at the edges of the block, and with the intersection of grooves 18 and 20 being spaced from the edges of the block. Each of the channels 12, 14 and 16 extends from the bottom of a groove intersection through the bottom surface of the block. In this way water in any of the grooves will always be able to flow into a channel. Furthermore, vegetation growing in a channel or passageway will always be able to be bent into a groove when a vehicle passes over the tops of the blocks. Since the vegetation bends into the grooves, such vegetation is not cut by the abrasive action of the vehicles against the upper extremities of the blocks. Preferably, in order to avoid cutting the vegetation, the upper edges of the grooves are rounded.

It will be appreciated, therefore, that broadly, the block shown in FIGS. 1 and 2 has a substantially flat bottom surface, an upper surface, and at least two intersecting grooves extending in the plane of the upper surface, at least one of said grooves being spaced from the edges of the block, and at least one channel extending from the bottom of the intersection of said grooves through said bottom surface. The channels define passageways for the passage of water. Vegetation may grow in the passageways. Preferably, there are one or more channels on the periphery of the block so that when the blocks are assembled in their ultimate location, channels from adjacent blocks together define closed channels or passageways.

Although, in FIG. 1 and 2, the blocks have been shown as square, they obviously may have other shapes, such as rectangular (not shown) or hexagonal (not shown). The blocks may be assembled in a side-by-side arrangement, as shown in FIG. 1 and 2, or in any other arrangement conventionally used for blocks or bricks, that is, a zigzag arrangement, diagonal arrangement, etc. Although preferably the blocks are arranged so that the channels of one block cooperate with the channels of an adjacent block to form enclosed channels, it will be appreciated that even when a channel on the periphery of one block is adjacent a flat side portion of an adjacent block, there still will be produced enclosed channels which act as passageways.

By way of example of dimensions, excellent results have been obtained with a concrete block wherein the height is 10 cm.; length and width, 20 cm.; width of grooves 18 and 20, 5.2 cm.; width of grooves 22 and 24, 2.6 cm.; depth of grooves 20 and 24, 2.8 cm.; depth of grooves 18 and 22, 1.4 cm.; radius of channel 12, 2.5 cm. The radius of the enclosed channels formed by the abutting channels of adjacent blocks is about 3.3 cm. These dimensions, obviously, can be varied, depending on the conditions. It is noted that channels 20 and 24 are deeper than channels 18 and 22. This is an optional feature which can be used where it is desirable to direct the flow of water more in one direction than in another direction. It will also be appreciated that the order of the width of a channel does not substantially exceed the order of the width of the groove where the two of them intersect. These relative widths serve to prevent vegetation growing in the channels from being abraded by vehicular traffic. The width of the channel determines the width of the vegetation growing therein and, obviously, if the width of a channel is less than the width of a groove, substantially all of the vegetation growing in a channel can bend into a groove. On the other hand, if the order of the width of the channel substantially exceeds the order of the width of the groove, a substantial amount of the vegetation growing in said channel will not be able to bend into the groove and will be subject to being cut off by vehicular traffic.

The blocks are not bonded to each other along their sides as are bricks when bricks are laid in a pattern. The blocks are therefore somewhat free to move to a small extent relative to each other in a vertical direction. Nevertheless, since the blocks abut, such movement is restricted by mechanical or frictional forces, but the abutment is sufficient to prevent lateral movement of the blocks which would ultimately result in block being forced out of the mat with consequent destruction of the protective surfacing.

As illustrated, the peripheries of the blocks are such that although the blocks abut each other, passageways still are provided between adjacent blocks for the passage of liquid through the mat of blocks.

The size and number of passageways will, of course, depend upon the volume of water to be handled by the protective surfacing and in many locations it is unnecessary to provide the central channel 12 or, in fact, any other channel in the body of the block, other than those formed on the periphery.

When the surfacing is applied in a location where there will be no vehicular traffic along the tops of the blocks, such as in a streambed or on a slope of a stream or dike, it is not necessary to provide the upper surface of the blocks with the grooves, provided it is not imperative for slowing down currents and/or sedimentation. In such cases each block can have a substantially flat top and this embodiment is shown in FIG. 4, wherein blocks B" have substantially flat tops and bottoms and are secured to supporting sheet 10", the mat of blocks having the passageways therethrough for the flow of water, as in the previously described embodiments. Blocks B" are secured to supporting sheet 10" in the manner as was described in connection with the previously described embodiments.

It will be appreciated that in any particular installation different types of blocks can be used side by side. For example, if the protective surfacing is to be applied in a streambed, along the bank of the stream where there is no vehicular traffic and on a road adjacent the bank where there is vehicular traffic, the blocks in the streambed and along the bank can have the construction shown in FIG. 4, while the roadway can have the blocks shown in FIG. 1. In a similar manner, since vegetation would not normally grow in the passageways of the surfacing of the streambed, that surfacing should be of a permanent nature. On the other hand, the surfacing on the bank where vegetation may grow rather quickly and would not be subject to damage by vehicular traffic, the protective surfacing may be of a relatively temporary nature, as previously described, having to last only sufficiently long enough for the vegetation growing in the passageways to take over the job of erosion control. This clearly illustrates the versatility and adaptability of the present invention to various problems of erosion control.

When the blocks are bonded to the supporting sheet by adhesive, any suitable adhesive can be used. Excellent results are obtained using synthetic resins, although in many cases bitumen and other adhesives can be used. Instead of using such mechanical or penetrating fasteners, such as nails 34, as shown in FIG. 3, obviously fasteners such as staples (not shown) can be used. Another form of penetrating fastening means which can be used can loosely be called "sewing," as shown in FIG. 5, where blocks B are secured on supporting sheet 10 by passing or intertwining cord, cable or wire 36 through the channels in the blocks and the sheet 10.

It is frequently desirable to secure one assembly of blocks to an adjacent assembly and this can be done, for example, in the manner shown in FIG. 6. One assembly is placed on the soil, the next assembly is placed adjacent thereto on the margin 30, and a U-shaped clamp or staple 38 has its branches 40 pass through the passageways of adjacent blocks and the ends of the branches are bent as shown at 42.

In the embodiments thus far described the supporting sheet means has been shown as a single sheet. However, this may comprise a plurality of sheets, two of which sheets 44 and 46, one superposed on the other being shown in FIG. 7 and three sheets 48, 50 and 52, superposed on each other, being shown in FIG. 8. In those locations where it is not necessary to use a filter sheet, either because of the soil and/or water conditions or because the vegetation growing in the passageways serves as the filter, both sheets 44 and 46 serve not only to hold the blocks together during shipment, but more importantly, serve to maintain the blocks in place on the soil. In such instances, sheets 44 and 46 are merely selected for the strength characteristics and the size of the water-permeable openings therethrough is immaterial. However, where filtering action is desired, either sheet 44 or sheet 46, or both, may have their pores or openings of such a size that either or both of the sheets act as a filter sheet. In a similar manner any one, two or three of sheets 48, 50 or 52 can be a filter sheet, or any one, two or three can serve merely as a supporting sheet. It is emphasized that any one or all of the sheets can have sufficient strength to provide for the mechanical support of the blocks and at the same time have pores or openings sufficiently small to serve as a filter sheet.

An excellent advantage of the structures shown in FIGS. 7 and 8 is that the filter sheet, if it is relatively weak, such as felted mat, can be positioned between the blocks and a stronger sheet on the other side thereof. In some constructions, where the weight of the blocks is sufficient to keep the assembly in place, all of the supporting sheets, or a single one if only one is used, can be of relatively little strength and can serve primarily as filter sheets.

It has been found that synthetic mesh (whether made by weaving, knitting, netting, extrusion or bonding of synthetic filaments) is excellent material for use as one or more of the sheets, since not only can the pores be sufficiently small for the sheet to act as a filter sheet, but these synthetic meshes have excellent strength characteristics so that such sheet can give the appropriate mechanical support.

The sheets which constitute the supporting sheet means can not only be made in the materials as described, but it can be made of such sheetlike structures as weftless fabrics, parallel strands or wires, etc., so constituted as to act substantially as a sheet.

As stated previously, to be a filter sheet the sheet must be permeable to liquid but substantially impermeable to soil particles. The size of the pores or openings through the filter sheet will therefore vary somewhat, depending on the granularity of the soil. For most applications it has been found that satisfactory filtration is obtained when the average diameters of the openings or pores through the filter sheet do not exceed about 250 microns, although in many cases average diameters as large as 1 1/2 mm. are satisfactory. When any of the sheets are to be of a relatively temporary nature, any sort of fabric, such as burlap, hemp, sisal, permeable kraft paper, etc., can be used either in their natural forms or impregnated with materials such as asphalt.

In FIG. 9 there is shown a construction where there are two mats of blocks, one over the other with supporting sheet means 54 between the mats. Such construction is useful where an especially strong and heavy construction is necessary.

In FIG. 10 there is shown a construction wherein there is a sheet 56 beneath the blocks B and a sheet 58 above the blocks B. This construction at times facilitates the prefabrication and handling of the assemblies for delivery onto the job. Sheet 56 can be the principal mechanical support and/or filter sheet, while sheet 58 would be more or less temporary in nature, to be destroyed by the elements or by vegetation growing in the passageways in the mat of blocks.

In all the embodiments shown in FIG. 6 through 10, the blocks may have the structure as described in any of the other embodiments and the blocks may be united to the various sheets by adhesives or mechanical fastening means as previously described.

According to the preferred embodiment, the blocks are assembled and fastened on the supporting sheets before being laid on the soil. Such assemblies may be delivered to the mob as sheets or in rolls and on the job it will only be necessary to grade the soil and place the assemblies thereover. In the case of rolls, in order to maintain abutted arrangement of the blocks after unrolling, it is of course advisable to at least partially bevel the sides of the abutting blocks. After the assemblies are placed on the soil the passageways therein can be at least partially filled with vegetation-growth-producing materials to assist in the start or maintenance of the vegetation. In some cases, especially when using porous blocks, either the pores of the blocks or the passageways can be at least partially filled with such materials prior to placing the assemblies on the soil.

In those locations, as has been mentioned previously, where there is no need for immediate filter action and where the vegetation growth in the passageways would be relatively rapid, the vegetation filling the passageways can act as the filter, preventing movement of the particles of the soil from beneath the surfacing to the exterior.

In all the embodiments described thus far the blocks are fastened to the supporting sheet means. Occasionally the conditions of the soil are such that it is not necessary to fasten the blocks to the supporting sheet means. In such cases the protective surfacing can be laid down completely in situ by first applying to the soil one or more of the sheets which in such cases would generally be filter sheets, and then placing the blocks thereover and lastly at least partially filling the passageways with vegetation-growth-promoting materials.

It will thus be appreciated that the erosion-controlling surfacing of the present invention is useful in hydraulic engineering where the main problem is erosion caused by water, such as in dikes, canals, waterways and streambeds; in agricultural engineering, wherein it is merely desirable to obtain temporary erosion control until vegetation takes over; and in road engineering, such as pavements for medians and shoulders, recreational areas, etc., where there is vehicular and/or pedestrian traffic.

Claims

I claim:

1. An erosion-controlling protective surfacing applied to the soil, said surfacing comprising flexible liquid-permeable supporting sheet means conforming to the contour of the soil and a mat of blocks on said supporting sheet means, said mat being constituted by a plurality of blocks in side-by-side substantially abutting arrangement, means securing each of said blocks to said sheet-supporting means, said mat having drainage passageways therethrough extending from an upper surface of said mat to the bottom surface thereof to provide communication from said upper surface to said supporting sheet means whereby liquid can pass, in either direction, between said upper surface and the soil through said supporting sheet means and said mat, no portion of any block overlying any portion of any block adjacent thereto so that each block can move vertically relative to each block adjacent thereto.

2. A surfacing according to claim 1, including filter means.

3. A surfacing according to claim 2, wherein said filter means comprises vegetation growing in said passageways.

4. A surfacing according to claim 2, wherein said filter means is a filter sheet beneath said mat of blocks.

5. A surfacing according to claim 1, wherein said securing means comprises an adhesive.

6. A surfacing according to claim 1, wherein said securing means comprises penetrating fastener means.

7. A surfacing according to claim 1, wherein said supporting sheet means comprises a plurality of sheets.

8. A surfacing according to claim 1, wherein said supporting sheet means includes at least one filter sheet.

9. A surfacing according to claim 1, wherein said supporting sheet means includes at least one sheet of synthetic mesh.

10. A surfacing according to claim 1, wherein there is another mat of blocks beneath said supporting sheet means.

11. A surfacing according to claim 1, wherein there is a sheet secured to the top surface of the mat of blocks.

12. A surfacing according to claim 1, wherein the periphery of each of said blocks is so shaped that portions of the peripheries of the blocks are spaced apart from portions of peripheries of adjacent blocks, such spaced-apart peripheries defining said passageways.

13. A surfacing according to claim 1, wherein each block has a bottom surface and an upper surface and at least two intersecting grooves extending in the plane of said upper surface, at least one of said grooves being spaced from the edges of said block, and at least one channel extending from the bottom of the intersection of said grooves through said bottom surface, the channels of said blocks defining said passageways.

14. A surfacing according to claim 1, wherein each block has a bottom surface and an upper surface and at least two intersecting grooves extending in the plane of said upper surface, at least one of said grooves being spaced from the edges of said block, and at least one channel extending from the bottom of the intersection of said grooves through said bottom surface, the channels of said blocks defining said passageways.

15. A surfacing according to claim 1, wherein said surfacing includes vegetation-growth-producing material.

16. An erosion-controlling protective surfacing to be applied to the soil to prevent erosion thereof, comprising a flexible liquid-permeable supporting sheet means positionable on the soil and a plurality of blocks in a side-by-side substantially abutting arrangement superposed on said supporting sheet means forming a mat of blocks thereon, each of said blocks being secured to said supporting sheet means, said mat having drainage passageways therethrough extending from an upper surface thereof to the bottom surface thereof to provide communication from said upper surface to said supporting sheet means whereby, when said assembly is applied to the soil, liquid can pass in either direction between said upper surface and the soil through said supporting sheet means and said mat, said assembly being sufficiently flexible to conform to the contour of said soil, no portion of any block overlying any portion of any block adjacent thereto so that each block can move vertically relative to each block adjacent thereto.

17. A surfacing assembly according to claim 16, including filter means.

18. A surfacing according to claim 17, wherein said filter means is a filter sheet beneath said mat of blocks.

19. A surfacing according to claim 18, wherein said filter means comprises at least one filter sheet positioned beneath said mat of blocks.

20. A surfacing according to claim 16, wherein said supporting sheet means comprises a plurality of sheets.

21. A surfacing according to claim 16, wherein said supporting sheet means includes at least one filter sheet.

22. A surfacing according to claim 16, wherein said supporting sheet means includes at least one sheet of synthetic means.

23. A surfacing according to claim 16, wherein there is a sheet secured to the top surface of the mat of blocks.

24. A surfacing according to claim 16, wherein the periphery of each of said blocks is so shaped that portions of the peripheries of the blocks are spaced apart from portions of peripheries of adjacent blocks, such spaced-apart peripheries defining said passageways.

25. A surfacing according to claim 16, wherein each block has a bottom surface and an upper surface and at least two intersecting grooves extending in the plane of said upper surface, at least one of said groove being spaced from the edges of said block, and at least one channel extending from the bottom of the intersection of said grooves through said bottom surface, the channels of said blocks defining said passageways.

26. A surfacing surfacing according to claim 16, wherein each block has a bottom surface and an upper surface and at least two intersecting grooves extending in the plane of said upper surface, at least one of said grooves being spaced from the edges of said block, and at least one channel extending from the bottom of the intersection of said grooves through said bottom surface, the channels of said blocks defining said passageways.