BACKGROUND ART In general, scouring continuously happens in the vicinity of the foundation of submerged structures such as a bridge, a breakwater or a protecting bank built in a riverside or seaside. Such scouring may cause an evacuation of the sand and gravels at the base of the foundations of the submerged structures to give detrimental effects on the stability of said structures.

Therefore, it has been devised to riprap the foundations of submerged structures or the surface of a breakwater or a protecting bank in a riverside and seaside by using stones or mesh bags filled with stones. However, such riprapping cannot be a radical countermeasure of scouring since stones or a mesh bag filled with stones can be moved or swept away by the waves because of its light weight compared to its volume.

In addition, protecting blocks having a weight of about 5 ton or more are thrown at a seaside or breakwater, in which the velocity of flow and waves are high, to protect the

breakwater from the waves or torrent. Since conventional protecting blocks for removing waves generally have a star-shaped structure and several protrusion radially popped out, they are very big and massive. Further, since there are large rooms between the blocks after constructing them, there is still a problem that a scouring and an evacuation of the sand and gravels at the foundations of a breakwater cannot be prevent in spite of a certain extent of removing or alleviating the waves or torrents.

The present invention is envisaged to solve the above problems. The object of the present invention is to provide a method for the construction of an anti-scour protection of a bridge and for the stabilization of stream bed in a river or stream, by paving block mats on the stream bed in the vicinity of submerged bridge piers and abutments to prevent the vicinity of submerged bridge piers and abutments from scouring by the water flow and to stabilize the ground in the vicinity of the foundations of the bridge piers.

DISCLOSURE OF THE INVENTION In order to achieve the above object, the method for the construction of an anti-scour protection of a bridge and for the stabilization of stream bed by using block mats according to the present invention is characterized by that it comprises: linking a large number of unit block, which is nearly rectangular in its plan view and has protrusion parts and concave groove parts adjacent to said protrusion part formed on the upper and lower faces of its body, a through-hole having a predetermined size formed in the center of its body, and interlocking members for coupling with an adjacent unit block provided on the front, rear, left and right side faces of its body, in a two-dimensional direction by means of said interlocking members to form a large number of block mats having a predetermined size; and paving said block mats on stream bed in the vicinity of the foundation of a submerged structure.

In the present invention, it is preferable to previously pave base mat made of an engineering fiber on the overall construction area of the stream bed to avoid a local sinking of the soft ground owing to the weight of the block mat itself before the block mats are paved.

In addition, when the above block mats are laminated in a multilayer, it is preferable to position the upper and lower unit blocks of the block mats so that their protrusion part and the concave groove part are interlockedly matched together.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an apparent perspective view of a unit block which is employed in the method for the construction of an anti-scour protection of a bridge and for the stabilization of stream bed according to the present invention.

Figure 2 represents a block mat in which a large number of unit block represented in Figure 1 are linked.

Figure 3 represents a construction shape in which several block mats represented in Figure 2 are paved on stream bed in the vicinity of the foundation of a bridge pier and/or abutment.

Figure 4 represents a change of stream bed in the vicinity of the foundation of a bridge pier and/or abutment when the flow amount is increased (at a flood state) after block mats are paved as represented in Figure 3.

Figure 5 shows a change of stream bed in the vicinity of the foundation of a bridge pier when the flow amount is decreasingly recovered to the original state (at a normal state) after the flood state of Figure 4 has passed.

Figure 6 is a front view of a debris barrier constructed by applying the method of the present invention.

Figure 7 is a sectional view of a fire prevention dam constructed by applying the method of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be illustrated more specifically by referencing the drawings attached.

Figure 1 is an apparent perspective view of a unit block which is employed in the method for the construction of an anti-scour protection of a bridge and for the stabilization of stream bed according to the present invention.

Referring to Figure 1, the block (100) used in the method of the present invention is nearly rectangular in its plan view, and the upper and lower faces of its body are provided with protrusion parts (101) and concave groove parts (102) adjacent to said protrusion part, by which the block is somewhat stuck into the ground of stream bed to resist the water flow and maintain the paving state as well as a unit block is matched with the upper and lower blocks so that the overall integrated structure of blocks becomes firm. Further, a through- hole (103) having a predetermined size is formed in the center of the body of the block, by which the buoyancy of the block is reduced when it is submerged under water as well as the stream bed can be stabilized due to a deposition of sand or small gravels therein. And an interlocking member (104) for coupling with the adjacent unit block is provided at each side face of the front, rear, left and right of the body. Said interlocking member (104) can be made of deformed bar. When the block is used in see water (salty water), the deformed bar can be covered with a stainless steel or the interlocking member itself can be made of a stainless steel.

In the method for the stabilization of stream bed of the present invention using the above-described unit blocks (100), several unit blocks (100) are linked in a two-dimensional

direction by means of their iron loop (104) to form a block mat (200) having a predetermined size (area) and several block mats are prepared by the same procedure as described above.

At this time, the interlocking between unit blocks is achieved by using a U bolt (110). Of course, other similar interlocking means can be employed. Figure 2 represents an interlocking mode in which 9 unit blocks (100) are interlocked together. The number of unit blocks (100) to be interlocked can be changed and thus 12,15, 16 or more unit blocks can be linked together to form a block mat structure (200), depending on the construction working plan considering the flow velocity or scour status at the construction area.

Thus prepared block mats (200) are paved in a single layer or multilayer on the stream bed in the vicinity of the foundation of a submerged structure (300) (for example, bridge pier and/or abutment). A block mat structure (200) having a weight of several tens tons is lifted by a specially designed crane having a lifting frame apparatus and then positioned under water. Said lifting frame apparatus and a method of constructing concrete block using the same are specifically described in USP 6,293, 730.

Before the above block mat structures (200) are paved on a stream bed, it is preferable to previously pave base mat (400) made of an engineering fiber on the overall construction area of the stream bed to avoid a local sinking of the soft ground owing to the weight of the block mat (200) itself. When the water is very deep, the base mat (400) is attached under the block mat structure (200), which is then dropped and positioned.

Block mat structures (200) are positioned adjacently together (for example, with a distance between block mats of 30 cm 10 cm), but they are not interlocked together.

Meanwhile, Figure 4 shows a change of a stream bed in the vicinity of the foundation of a bridge pier when the flow amount is increased (at a flood state) after block mats are paved as represented in Figure 3.

As represented in Figure 4, when the flow amount and velocity of a river or a stream

are increased at a flood state, local scours then happen at the front end of the upstream flow and at the rear end of the downstream flow. However, since unit blocks (100) are interlocked together by iron loops (104) to form a block mat structure (200), which is flexible due to their weight. When a local scour happens, unit blocks (100) bend down along to the inclined surface of a local scour hole generated. As such, an enlargement or spread of the local scour into the inside of the foundation of a bridge pier is avoided.

Figure 5 shows a change of a stream bed in the vicinity of the foundation of a bridge pier when the flow amount is decreasingly recovered to the original state (at a normal state) after a flood state of Figure 4 has passed.

As represented in Figure 5, a reduction of the flow amount and velocity is accompanied with a deposition of sand and gravels into local scour holes which have been generated at said front end and said rear end, and an insertion thereof into the space between the unit blocks of said block mats (200). Said deposition and insertion will make the ground of the stream bed firm and solid. As a normal state and a flood state are repeated, the ground of the stream bed is further stabilized against scour and any local scour can be avoided.

Meanwhile, comparing the unit block and the block mats of the present invention with the conventionally used stones or gravels in terms of the construction concerns such as coefficient of roughness, the coefficient of roughness of stones or a mesh bag of stones is 0. 033-0. 036 and that of the block of the present invention is 0. 018-0. 031. Therefore, it is concluded that the drainage of the block of the present invention is much more stable than that of the mesh bag of stones.

Comparing the hydrographic characteristic of stones or gravels, the tolerated shear stress for the block is calculated to about 10 times more than that of stones having a diameter of 10-30 cm. Therefore, it is confirmed that the flow resistance for the block is more

stable than that for the stones.

In addition, the blocks may be used as a"wear". In such case, since the flow parameters tend to have a regular relation with the water depths of upstream and downstream areas, a"wear"for a concrete-integrated structure can be effectively used in the measurement of the flow amount.

In the above, embodiments in which the method of the present invention is applied to stream bed in the vicinity of the foundations of a bridge pier and/or an abutment are illustrated, but the present invention is not limited only to such applications and can also be applied to the constructions of a debris barrier and a fire prevention dam as shown in Figures 6 and 7, respectively.

Figures 6 and 7 show a debris barrier and a fire prevention dam, respectively, which are constructed according to the method of the present invention. Figure 6 is a front view of a debris barrier and Figure 7 is a sectional view of a fire prevention dam.

As represented in Figures 6 and 7, when the method of the present invention is applied to the construction of a debris barrier or a fire prevention dam, the block mats (200) are basically on the ground of stream bed, as in the construction for the stabilizing stream bed in the vicinity of bridge. Further, since they should have a function to reserve water as a dam, the block mats (200) having various size are prepared and then laminated in a multilayer. When the block mats (200) are laminated in a multilayer, an upper unit block and a lower unit block are positioned so that their protrusion part (101) and the concave groove part (102) formed on each unit block are matched together. The reference number 600 described in Figures 6 and 7 represents a mat for restoring water.

INDUSTRIAL APPLICABILITY The method for the construction of an anti-scour protection of a bridge and for the

stabilization of stream bed in a river or a stream which uses block mats according to the present invention can improve a resistance to a descending stream at an upstream region of a pier and to a turbulent stream at a downstream region of a pier, prevent the ground of stream bed from being locally scoured by the stream because of the flexibility of the block mat due to the weight of each of the unit blocks interlocked with each other by means of U-type bolts, and to stabilize the ground of stream bed, and stabilize the ground of stream bed, since gravels and sand fill the spaces between the unit blocks to make them firm after several repetitions of a flood state and a normal state.

The present invention can also be applied to a constructions for preventing of scour and erosion, a construction for resisting of dropping water, a breakwater, etc. in a river, a seaside and a port, and various other fields including an erosion control work. etc.