JPH06299566A - Water-gathering and drainage member, underground drainage structure and construction method thereof - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a drainage structure with an excellent collection and drainage function with a simple configuration. [Structure] A drainage pipe 21 is projected laterally and a water collecting slit and a water collecting hole are formed in the upper part. A member having a V-shaped vertical cross section and a U-shaped horizontal cross section, and a large number of water collection holes are formed. The horizontal drain 51 which can close the front side of the U-shaped member constitutes the collecting and draining pipe 11 made of hard polyvinyl chloride. On the other hand, perlite is stored as a lightweight aggregate 73 in a bag-shaped material 72 made of non-woven fabric to form a water collecting / filtering member 71, and the water collecting / filtering member is filled in a U-shaped member, and then a horizontal lid 51 is attached. To form the water collection and drainage member 61. The drainage member 61 is attached to the retaining wall when constructing the drainage structure. In this case,
The drainage pipe 21 is inserted into the water outlet pipe that penetrates through the retaining wall, and the side wall 33 of the U-shaped member is fixed to the rear face of the retaining wall by bonding with a double-sided tape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drainage structure for collecting and draining water in the ground in order to prevent an increase in earth pressure inside a retaining wall, a water collecting and draining member therefor, and the water collecting and draining member. Concerning the construction method of the drainage structure used.

[0002]

2. Description of the Related Art Conventionally, as the drainage structure, a drainage pipe having a large number of water collection holes formed in its peripheral wall is driven into the ground and is buried at an angle, or a stratum excavation part (formed by excavating the stratum is formed. The drainage pipe is laid in the
It is known that the collection and drainage pipes are covered with a point pressure finish by filling them with stones, a fiber composite material and the like.

[0003]

However, in the above-mentioned water collection and drainage pipe, the water collection holes form silt, sediment, etc. (hereinafter,
(These are collectively referred to as silt), which easily causes clogging, and there is a problem that the water collecting function deteriorates in a short period of time. Further, in the one filled with the crushed stone or the like, the silt or the like is easily clogged in the voids between the fillers such as the crushed stone, and the water collecting function of the packed bed deteriorates in a short period of time, which makes it difficult for water to flow into the collecting and draining pipe, There is a problem that the soil pressure rises and the packed bed changes into a plate shape to stop the flow of water, so that not only the collecting and draining function deteriorates but also the packed bed does not function as a buffer layer. Furthermore, recently, the amount of crushed stones supplied has decreased, and the crushed stones have a large specific gravity, which makes filling work troublesome.

The present invention is intended to solve the above problems, and a first object thereof is to provide a drainage structure having an excellent drainage / collection function. A second object of the present invention is to provide a simple construction method for the water draining structure. A third object of the present invention is to provide a water collecting and draining member suitable for carrying out the above construction method.

[0005]

According to a first aspect of the present invention, there is provided a water collecting and draining member, wherein a water collecting hole is formed in at least an upper wall of a short pipe having a substantially V-shaped vertical cross section, and the central pipe of the short pipe is bent. A drainage port is laterally opened in the curved portion to form a drainage pipe, and the short pipe is filled with a lightweight aggregate.

According to a second aspect of the present invention, there is provided the drainage and drainage member according to the first aspect.
In the water collecting / draining member described in the item (1), the water collecting / filtering member in which a lightweight aggregate is housed in a porous sheet material is filled in the short pipe of the water collecting / draining pipe.

According to a third aspect of the present invention, there is provided the drainage and drainage member according to the first aspect.
Alternatively, in the water collection and drainage member described in 2, a water collecting hole is formed in an upper wall of a central bent portion of a short pipe having a substantially V-shaped vertical cross section and a quadrangular horizontal cross section in a direction orthogonal to an axis of the short pipe. A mountain-shaped plate is provided directly above the water collecting hole, and a water collecting slit is formed by the gap between the plate and the upper wall of the central bent portion, and the central bent portion of the short pipe is formed. It is characterized in that drainage pipes are horizontally connected to form a drainage pipe.

According to a fourth aspect of the present invention, there is provided the drainage and drainage member according to the third aspect.
In the water collecting and draining member according to the item (1), the short pipe has a U-shaped member with a lateral cross-sectional shape in which the side wall outer surface is fixed to the retaining wall back surface and both axial end portions are completely open. A tubular body having a rectangular cross-section, the drain pipe being connected to the short pipe through the side wall of the U-shaped member, The lid is characterized by having a water collection hole.

According to a fifth aspect of the present invention, there is provided the drainage and drainage member according to the third aspect.
In the water collection and drainage member according to claim 1, the short pipe is a member having a U-shaped cross section in which a plurality of slits or through holes are provided on both end faces in the axial direction with the side wall outer surface as a fixed surface to the retaining wall back surface, A tubular body having a rectangular cross-sectional shape, which comprises a lateral lid fixed to the end surface facing the side wall of the U-shaped member, and the drain pipe is connected to the short pipe through the side wall of the U-shaped member. A water collecting hole is formed in the lateral lid.

According to a sixth aspect of the present invention, there is provided a drainage and drainage member according to the fourth aspect.
Alternatively, in the water collection and drainage member described in the item 5, the water collection and drainage pipe is made of hard polyvinyl chloride, the porous sheet-like material is a non-woven fabric, and the lightweight aggregate is pearlite.

According to a seventh aspect of the water draining structure of the present invention, a filling portion of lightweight aggregate is formed in a formation excavating portion formed inside a retaining wall, and water in the underground is drained through the filling portion. A structure for draining water from the ground to drain water, wherein a large number of water derivation channels are provided in the retaining wall in a downward gradient from the rear surface side to the front surface side of the retaining wall and in the thickness direction of the retaining wall. The drainage and drainage member according to claim 4, 5 or 6 is formed in the retaining wall, the drainage pipe is inserted into the water outlet channel from the rear side of the retaining wall, and the side wall of the U-shaped member is formed. It is characterized by being attached by fixing it to the back of the retaining wall.

The method for constructing the underground drainage structure according to claim 8 is the method for constructing the underground drainage structure according to claim 7, wherein a plurality of water outlet pipes are provided on the retaining wall. It is inclined and penetrated in the thickness direction, and the drainage pipe according to claim 4, 5 or 6 is inserted into the retaining wall, the drainage pipe is inserted into the water outlet pipe from the rear side of the retaining wall, and the U-shape is formed. It is characterized in that after attaching the side wall of the member by adhering it to the rear surface of the retaining wall, lightweight aggregate, crushed stone, crushed stone, etc. are backfilled in the excavated formation formed inside the retaining wall.

[0013]

In the water collecting and draining member according to the first or second aspect of the present invention, the water collecting and draining member is fixed to the retaining wall, the drain port is communicated with the water outlet passage provided in the retaining wall, and the ground excavation portion is backfilled with, for example, crushed stone. Form a drainage structure. Therefore, the construction of the drainage structure can be performed very easily. In these drainage structures, the water in the ground flows down the crushed stone layer and then flows into the lightweight aggregate through the water collection holes or into the water collection / filtration member through the water collection holes. The filtered water thereby flows into the water outlet passage from the drain port and is discharged. In this case, since the water collection and drainage member was constructed by filling the lightweight aggregate, the flow of silt into the voids between the fillers and the adhesion of the silt to the fillers are prevented, so that an excellent drainage and drainage function is achieved for a long time. Is maintained.

In the water collecting and draining member according to the third aspect, the drainage pipe is inserted into the water outlet passage provided in the retaining wall to fix the drainage member. In this drainage structure, the water in the ground flows down the crushed stone layer, then flows into the packed bed of lightweight aggregate through the water collecting slit and then the water collecting hole, and the filtered water by this flows out from the drain pipe. It flows into the road and is discharged. In this case, since the water flows into the filling layer of the lightweight aggregate through the water collecting slit, the effect of preventing clogging of the water collecting holes by the silt is improved as compared with the water collecting and draining member according to the first or second aspect.

In the water collecting and draining member according to the fourth aspect, the U-shaped member is filled with the lightweight aggregate, and then the lateral lid is fixed to form the pipe body, and the drainage flow passage is provided in the retaining wall. While inserting the pipe, the side wall of the U-shaped member is fixed to the rear surface of the retaining wall by adhesion or the like, and the ground excavation portion is backfilled with, for example, crushed stone to form a drainage structure. In this drainage structure, the water in the ground flows down the crushed stone layer, and then partly through the water collecting slit and then the water collecting hole, partly through the openings at both ends of the short pipe, and partly Through the water collecting holes of the lateral lid, the water flows into the packed bed of the lightweight aggregate, and the filtered water thereby flows from the drain pipe into the water outlet passage and is discharged.
In this case, since a large number of water inflow passages to the water collection and drainage pipe are formed in a large area, the use efficiency of the lightweight aggregate is improved.

In the drainage structure using the water collecting and draining member according to the fifth aspect, after the water in the ground flows down the crushed stone layer, a part of the water flows through the water collecting slit and then the water collecting hole, and part of the water. Through slits or through holes at both ends of the short pipe, part of them flows into the packed bed of lightweight aggregate through the water collection holes of the horizontal lid, and the filtered water thereby flows from the drain pipe into the water discharge passage. And then discharged. In this case, since a large number of water inflow passages to the water collection and drainage pipe are formed in a large area, the use efficiency of the lightweight aggregate is improved.

In the drainage / collection member according to claim 6,
Since the water collection and drainage pipe is made of hard polyvinyl chloride, it has excellent corrosion resistance, and since perlite is used as a lightweight aggregate, it is safer to handle the water collection and drainage member and construct the water drainage structure in combination with the weight reduction of the water collection and drainage pipe.・ Easy to carry out, and perlite also provides water purification. Also,
Since the non-woven fabric is used as the porous sheet-shaped material, it is possible to construct a drainage structure having an excellent water-passing function and silt intrusion preventing function.

In the underground drainage structure according to claim 7,
The drainage pipe of the collecting / draining member according to claim 4, 5 or 6 is inserted into a water outlet passage provided in the retaining wall from the rear surface side of the retaining wall, and the side wall of the U-shaped member is rear surface of the retaining wall. Since the drainage / drainage member is attached by fixing the drainage / drainage member to the drainage / drainage member, the drainage structure can be constructed safely, simply, and quickly. can get.

In the method for constructing a drainage structure in the ground according to claim 8, the drainage pipe is formed from the rear surface side of the retaining wall by using the water collecting and draining member according to claim 4, 5 or 6. Since the water collecting / draining member is attached by inserting the side wall of the U-shaped member and adhering the side wall of the U-shaped member to the rear surface of the retaining wall, the water drainage structure according to claim 7 can be implemented more simply and quickly. In particular, by using the one as described in claim 6 as the water collecting / draining member, the handling of the water collecting / draining member and the construction of the drainage structure can be performed more safely and easily.

[0020]

The present invention will now be described in more detail with reference to the embodiments shown in the drawings. Example 1 A drainage pipe 1 shown in FIGS.
1 is a U-shaped member 3 shown in FIG.
1 (the cross-sectional shape is U-shaped), and a horizontal lid 51 shown in FIGS.
The water collecting and draining member 61 shown in FIGS. 7 to 9 is composed of the water collecting and draining pipe 11 and the water collecting / filtering member 71 shown in FIG.

As shown in FIGS. 2 to 4, the U-shaped member 31 includes a short tubular body having a V-shaped vertical cross section and a quadrangular horizontal cross section, including its axis. The U-shaped member 31 has a shape obtained by dividing it in a plane.
4 is formed with an opening 32 that is completely open. In addition, the outer surface 34 of the side wall 33 has a retaining wall 81 shown in FIG.
As the surface to be fixed to the back surface 82, the both ends in the axial direction are completely opened to form the openings 35 and 36. Further U-shaped member 3
1, a slit-shaped water collecting hole 38 is formed in the central bent portion of the upper wall 37 in a direction orthogonal to the axis of the member 31, and an inverted V-shaped cross section is formed at the upper end of the inner surface of the side wall 33. The plate 22 is laterally projected, and the tip of the plate 22 is extended to the tip of the upper wall 37 and positioned directly above the water collecting hole 38 to form the water collecting slit 39. The drain pipe 21 is
The side wall 33 is protruded by laterally butting and adhering to the lower portion of the outer surface of the side wall 33 so as to communicate with the inside of the U-shaped member 31. In addition,
Reference numeral 40 denotes a lower wall, and 41 denotes a perforated plate (may be a net body) inserted and arranged in a through hole formed in the side wall 33.

As shown in FIGS. 5 and 6, the lateral lid 51 has a plate body having a shape and size capable of closing the entire opening 32 of the U-shaped member 31 and the entire tip of the plate 22. The holes 52 are formed, and the outer edge portions are adhered to the end surfaces of the upper wall 37 and the lower wall 40 and the end surface of the plate 22 so that they can be fixed to the U-shaped member 31. The structure of the water collection and drainage pipe 11 configured by fixing the lateral lid 51 is as shown in FIGS.

The water collection / drainage member 61 comprises a water collection / drainage pipe 11 and a water collection / filtration member 71 shown in FIG. In this case, the water collecting / filtering member 71 is configured such that the lightweight aggregate 73 is housed in the bag-shaped material 72 made of a porous sheet-shaped material, and the light-weight aggregate 73 is opened in the U-shaped member 31 as shown in FIG. After filling through 32, the horizontal lid 51 is fixed and the water collecting and draining member 61 having the structure shown in FIGS.

Next, the construction of the water draining structure will be described together with its construction method. First, as shown in FIG. 11, an excavation part 83 is formed by excavating a stratum near a back surface 82 of a retaining wall 81 provided on the ground 91, and a large number of water outlet pipes 84 are provided on the retaining wall 81. 7 is arranged while penetrating in the thickness direction of the retaining wall 81 with a downward slope from the back surface 82 side toward the front surface 85 side.
A collecting / draining member 61 shown in is prepared. Next, the drainage pipe 21 of the water collection and drainage member 61 is inserted into the water outlet pipe 84, and the outer surface 34 of the side wall 33 is adhered to the back surface 82 with a double-sided tape (not shown). Finally, the excavated portion 83 is backfilled with, for example, crushed stone 92, and the construction of the drainage structure of FIG. 11 is completed. In addition, in FIG. 11, 93 is a drainage pit.

In the above drainage structure, the water in the ground is crushed stone 9
After flowing down the two layers, a part of the water flows through the water collecting slit 39,
A part is through the water collecting hole 52 of the horizontal lid 51, and a part is the opening 3
5 and the opening 36, respectively, and flows into the water collection / drainage pipe 11 and thus into the water collection / filtration member 71, and the filtered water thereby flows through the pores of the perforated plate 41 from the water drainage pipe 21 to the water discharge pipe 84. Into the drainage pit 93.
The perforated plate 41 is for preventing the lightweight aggregate 73 from flowing into the drain pipe 21 even when the bag-shaped material 72 is damaged.

As a constituent material of the drainage pipe 21, the U-shaped member 31, and the lateral lid 51 which are the constituent members of the collecting and draining pipe 11, a plastic material is preferable, and a rigid polyvinyl chloride is particularly preferable. A metallic material may be used if desired. As the porous sheet material forming the bag-like material 72, a net / woven fabric / knitting made of non-woven fabric, synthetic fiber or natural fiber, punched plastic sheet (including plastic film), or the like is used. . As the lightweight aggregate 73, perlite, pumice stone, lapilli, coal shell, rice husk and the like, as well as a porous lightweight aggregate obtained by expanding an expansive natural inorganic material by heating to a high temperature, etc., are arbitrarily selected. Can be used. In this case, it is particularly preferable to use hard polyvinyl chloride as a constituent material of the drainage pipe 11 and non-woven fabric as a porous sheet-like material, respectively, and to obtain water having excellent functions such as collecting and draining, buffering, preventing earth pressure rise, and water purification. It becomes possible to construct the punching structure easily, quickly and inexpensively.

As the short tube having a substantially V-shaped vertical cross section, a U-shaped tube or an arc-shaped tube may be used in addition to the V-shaped tube as in the above embodiment. Also,
The cross-sectional shape may be circular or semi-cylindrical.
As the mountain-shaped plate, an inverted U-shaped plate or a semi-circular plate can be used in addition to the inverted V-shaped plate. In the above-described embodiment, the water collecting / filtering member 71 is filled in the U-shaped member 31, but the lightweight aggregate 73 may be directly filled in the U-shaped member 31 without using the bag-shaped material 72. However, an annular plate body may be used instead of the lateral lid 51, and the opening 32 of the U-shaped member 31 may be substantially entirely opened. If the water collecting / filtering member 71 fits compactly in the U-shaped member 31, the lid 51 may be omitted if desired. Drainage member 6 for retaining wall 81
When attaching 1, the outer peripheral surface of the drainage pipe 21 may be adhered to the inner peripheral surface of the water outlet pipe 84, or the water outlet pipe 6 may be attached.
It is also possible to provide a flange at the tip end of No. 1 so as to project from the back surface 82 of the retaining wall, form the side wall 33 of the water collection and drainage pipe 11 also as a flange, and connect these flanges by adhesion or bolting. When projecting the drainage pipe 21 on the side wall 33, a screw hole may be formed in the side wall 33 and the drainage pipe 21 may be screwed into the screw hole. Instead of providing the perforated plate 41. , Drain pipe 2
It is also possible to provide a perforated plate or a net at the tip of 1.
Furthermore, in the U-shaped member 31, as shown in FIG. 10, a plurality of flat plates 42 may be provided at both ends in the axial direction to form the slit 43 for water passage (claim 5).

[0028]

As is apparent from the above description, according to the collecting / draining member of the first or second aspect, the collecting / draining member is fixed to the retaining wall, and its drain port is provided in the water outlet passage provided in the retaining wall. To communicate,
Since the water excavation structure is configured by backfilling, for example, crushed stones in the formation excavation portion, there is an effect that the construction of the water expulsion structure can be performed very easily. Further, according to this drainage structure, since the water collecting and draining member is configured by filling the lightweight aggregate, it is possible to prevent the inflow of silt into the voids between the fillers and the adhesion of the silt to the fillers for a long period of time. , The excellent drainage function is maintained and the rise of earth pressure is prevented. According to the water collecting and draining member of the third aspect, the drainage pipe is inserted into the water outlet passage provided in the retaining wall to fix the water collecting and draining member, so that the construction of the water draining structure is extremely simple. There is an effect that can be done. And according to this drainage structure, since water flows into the filling layer of the lightweight aggregate through the water collecting slit and then the water collecting hole, the water collecting hole of the silt has This has the effect of further improving the effect of preventing clogging. According to the drainage and drainage member of claims 4 and 5,
Since the lightweight aggregate is filled through the front opening of the U-shaped member, the filling operation becomes extremely simple. Further, since a large number of inflow channels of water to the lightweight aggregate filling layer are formed in the collecting and draining pipe and have a large area, the use efficiency of the lightweight aggregate filling layer is improved. According to the drainage / drainage member of claim 6, since the drainage / drainage pipe is made of hard polyvinyl chloride, the drainage / drainage pipe is inexpensive and has a high corrosion resistance. Since perlite is used as the lightweight aggregate, the collection / drainage pipe is lightened together. The drainage member can be handled and the drainage structure can be constructed more safely and easily, and the water purification function can be obtained with pearlite. Also, since nonwoven fabric is used as the porous sheet material, it has a water-passing function. Also, there is an effect that it is possible to construct a drainage structure having an excellent silt intrusion prevention function. According to the underground water drainage structure of claim 7, since the water collecting and draining member of claim 4, 5 or 6 is used, construction of the water drainage structure can be carried out safely, simply and quickly. Claims 4, 5 or 6
There is an effect that the collecting and draining action of the collecting and draining member described in (3) is obtained. According to the method for constructing a drainage structure in the ground according to claim 8, the drainage pipe is inserted into the water outlet pipe from the back side of the retaining wall by using the water collection and drainage member according to claim 4, 5 or 6. In addition, the side wall of the U-shaped member is attached to the rear surface of the retaining wall to attach the water collecting / draining member. Therefore, there is an effect that the water draining structure according to claim 7 can be implemented simply and quickly.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a front view of a water collection and drainage pipe.

FIG. 2 is a plan view of FIG.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a front view of a U-shaped member that constitutes the water collection and drainage pipe of FIG. 1.

5 is a front view of a lateral lid that constitutes the water collection and drainage pipe of FIG. 1. FIG.

FIG. 6 is a plan view of FIG.

7 is a front view of a water collection and drainage member configured using the water collection and drainage pipe of FIG. 1. FIG.

FIG. 8 is a sectional view taken along line BB in FIG.

FIG. 9 is a front view showing a configuration procedure of the water collecting and draining member of FIG. 7 before fixing the lateral lid.

FIG. 10 shows another embodiment of the water collection and drainage pipe and is a front view of a U-shaped member constituting the water collection and drainage pipe.

11 is a vertical cross-sectional view of a drainage structure constructed using the water collecting and draining member of FIG.

[Explanation of symbols]

 11 Drainage Pipe 21 Drainage Pipe 22 Plate 31 U-Shaped Member 32 Opening Part 33 Side Wall 34 Outer Surface 35, 36 Opening 37 Upper Wall 38 Water Collection Hole 39 Water Collection Slit 40 Lower Wall 41 Perforated Plate 42 Flat Plate 43 Slit 51 Horizontal Lid 52 Water collection hole 61 Water collection / drainage member 71 Water collection / filtration member 72 Bag-like material 73 Lightweight aggregate 81 Retaining wall 82 Back surface 83 Excavation section 84 Water outlet pipe 85 Surface 91 Ground stone 92 Crushed stone 93 Drainage pit

Claims (8)

[Claims] 1. A water collecting and draining pipe having a water collecting hole formed in at least an upper wall of a short pipe having a substantially V-shaped vertical cross section, and a drain port being laterally opened at a central bent portion of the short pipe. A water collecting and draining member, characterized in that the short pipe is filled with a lightweight aggregate. 2. The water collection and drainage according to claim 1, wherein the water collection and drainage pipe is filled with a water collection and filtration member in which a lightweight aggregate is contained in a porous sheet material. Element. 3. A water collecting hole is formed in an upper wall of a central bent portion of a short pipe having a substantially V-shaped vertical cross section and a quadrangular horizontal cross section in a direction orthogonal to an axis of the short pipe. A mountain-shaped plate is provided directly above the water collecting hole, and a water collecting slit is formed by a gap between the plate and the upper wall of the central bent portion, and a drain pipe is laterally provided at the central bent portion of the short pipe. The water collection and drainage member according to claim 1 or 2, wherein the water collection and drainage pipes are connected to each other. 4. A member having a U-shaped cross section with the outer surface of the side wall fixed to the rear surface of the retaining wall and both ends in the axial direction being completely open, and the side wall of the U-shaped member. A tubular body having a rectangular cross-section, the drainage pipe being connected to the short pipe through the side wall of the U-shaped member, and The water collection and drainage member according to claim 3, wherein the water collection hole is opened. 5. A member having a U-shaped cross section in which the outer surface of the side wall is fixed to the rear surface of the retaining wall and a plurality of slits or through holes are provided on both end surfaces in the axial direction of the short pipe, and the U-shaped member. A tubular body having a rectangular cross-section, the drain pipe being connected to the short pipe through the side wall of the U-shaped member, The water collection and drainage member according to claim 3, wherein a water collection hole is formed in the lid. 6. The collecting and draining pipe is made of rigid polyvinyl chloride, and the porous sheet-like material is a non-woven fabric,
The drainage / drainage member according to claim 4 or 5, wherein the lightweight aggregate is perlite. 7. An underground drainage structure in which a filling portion of lightweight aggregate is formed in a formation excavation portion formed inside a retaining wall, and water in the underground is drained through the filling portion. A plurality of water derivation flow paths are formed in the retaining wall in a downward gradient from the rear surface side to the front surface side of the retaining wall and penetrate in the thickness direction of the retaining wall. The drainage and drainage member according to claim 1 is attached to the retaining wall by inserting the drainage pipe into the water outlet channel from the rear side of the retaining wall and fixing the side wall of the U-shaped member to the rear side of the retaining wall. Characteristic underground drainage structure. 8. The method for constructing the underground water drainage structure according to claim 7, wherein a plurality of water outlet pipes are arranged on the retaining wall so as to be inclined and penetrate in the thickness direction, Or after attaching the drainage / drainage member described in 6 to the retaining wall by inserting the drainage pipe into the water outlet pipe from the rear surface side of the retaining wall and adhering the side wall of the U-shaped member to the rear surface of the retaining wall. , A method of constructing a drainage structure in the ground, which is characterized by backfilling lightweight aggregate, crushed stone, rubble, etc., in a geological excavation portion formed inside a retaining wall.