JP2007169927A - Earthquake resisting manhole structure and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple manhole structure made considerably resistant to an earthquake to protect a manhole installed or planned to be installed in the ground liable to cause liquefaction by the earthquake or the like, from damage caused by the liquefaction of the ground. <P>SOLUTION: This earthquake resisting manhole structure is constructed by extending a base course material supporting floor plate almost horizontally from a position, higher than the mean annual highest underground water level of the manhole installed ground, of the external wall surface of a manhole structure in the manhole installed at a connection place of an underground buried pipe, and laying a stabilizing base course material on the base course supporting floor plate, and manufactured so that the total of the weight of the manhole structure including the base course supporting floor plate, and the total weight of a base course and the stabilizing base course material supported to the base course material supporting floor plate, is larger than buoyancy by muddy water which the manhole structure is predicted to receive when sediment below the mean annual highest underwater level of the manhole installed ground changes into liquefying muddy water. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improved structure for making a manhole earthquake-proof at a connection position of an underground underground pipe, and in particular, an earthquake-proof structure for preventing a manhole from rising and moving due to liquefaction of the ground when an earthquake occurs. About.

  Various underground pipelines such as water supply, sewerage, city gas, electric power, and communication are often buried in the underground such as roads. Manholes installed at the connection positions of these pipelines are subject to earth pressure. It is usually constructed of tough materials that can withstand. However, it is difficult to expect that the geology of the ground is constant and uniform within the range where the pipe is buried, and the density of the earth and sand filled around the buried structure may be uneven. Especially in places with high groundwater levels, there is a risk of ground liquefaction when an earthquake occurs. If this happens, the manhole provided on the spot will rise, move, or fall down, causing a failure to disconnect the pipeline, leading to the failure of the lifeline function.

  Therefore, in order to avoid the occurrence of the above-mentioned obstacles, measures such as driving a long pile reaching the underground rock and fixing the manhole to this can be considered, but the manhole is a road where various pipes are embedded It is often installed in the basement of the city, and there is a drawback that not only construction is difficult, but also the construction cost increases.

  Therefore, the present invention is a simple manhole that is greatly earthquake-resistant to protect manholes that are installed or planned to be liquefied by earthquakes or the like from damage caused by liquefaction of the ground. The present invention proposes a structure, and further intends to provide a method for reliably manufacturing the above-mentioned earthquake-proof manhole structure.

  The seismic manhole structure of the present invention is for manholes installed at underground underground pipe connections, for supporting roadbed materials in a substantially horizontal direction from a position higher than the average annual maximum groundwater level of the manhole installation ground on the outer wall surface of the manhole structure. The floor board is extended, and the stabilized roadbed material is laid on the roadbed material supporting floorboard.

  Further, in such a seismic manhole structure of the present invention, the weight of the manhole structure including the roadbed material support floor plate, the total weight of the stabilized roadbed material and the roadbed supported by the roadbed material support floor plate, Is greater than the buoyancy due to the mud that is expected to be received by the manhole structure when the sediment below the average annual maximum groundwater level of the manhole installation ground changes to liquefied mud, However, the destruction of the manhole structure can be surely prevented.

  Furthermore, in the seismic manhole structure of the present invention, the stabilized roadbed material is preferably a material obtained by stabilizing a high specific gravity aggregate such as earth or sand or gravel using a debris binder such as cement, May be used in combination with those previously molded into an appropriate shape such as a brick shape or a block shape, or after preparing an agglomerated roadbed material composition by mixing aggregate and binder at the construction site. It can also be laid on a floor board and condensed to form a stabilized roadbed material.

  Further, the seismic manhole structure of the present invention is a roadbed material extending in a substantially horizontal direction from a position higher than the average annual maximum groundwater level of the manhole installation ground on the outer wall surface of the manhole structure in the manhole connecting the underground pipe. Stabilized roadbed material is laid on the supporting floorboard, and the total weight W0 (tf) of the manhole structure including the floorboard supporting floorboard and the total weight Wb (tf) of the stabilized roadbed material and roadbed The total weight Ws (tf) of the buoyancy is set to be larger than the buoyancy value Wf (tf) obtained by multiplying the immersion volume V0 (m3) of the liquefied mud water estimated from the external dimensions of the manhole structure by the density of the mud Therefore, it can be reliably manufactured.

  The seismic-proof manhole structure of the present invention is a manhole connecting underground pipes, and the floor plate for supporting roadbed material extends substantially horizontally from a position higher than the average annual maximum groundwater level of the manhole installation ground on the outer wall surface of the manhole structure. In addition, since the stabilized roadbed material is laid on the floorboard for supporting the roadbed material, even if the entire ground liquefies due to the occurrence of an earthquake, the upper part of the manhole structure in the earthquake-resistant manhole of the present invention, etc. The weight of the floor plate for supporting the roadbed material extending horizontally from the floor, the weight of the stabilized roadbed material laid on the floorboard, and the roadbed around the manhole laid on the stabilized roadbed material The weight of the pavement, etc., and the weight of the manhole structure are combined together to act as a stabilizing weight for the manhole structure, so that the manhole structure can be effectively prevented from rising, moving, and falling. It is.

Hereinafter, the earthquake-resistant manhole structure of the present invention and the manufacturing method thereof will be described with reference to the drawings.
In FIG. 3, 1 is a conventional manhole structure provided at the middle point of the sewer pipe 2, etc. This manhole structure 1 is used for manhole installation by driving a sheet pile C or the like into the ground G from the ground surface. In addition, a foundation B with a crushed stone layer Ba and a concrete layer Bb formed thereon is formed, and a bottom plate 1a, a pipe mounting wall cylinder 1b, a straight wall cylinder 1c, and a lower slant wall cylinder 1d are drilled. The lower adjustment ring 1e, the upper slant wall cylinder 1f, and the upper adjustment ring 1g are sequentially stacked and joined with cement mortar, etc., and a lid mounting frame 1h is provided, and the lid 1i is detachably fitted. It will be. In a manhole having such a general structure, earth and sand obtained when excavating a vertical hole are often used for backfilling the surroundings, and the upper surface of the lid 1i is provided so as to substantially coincide with the ground GL. As the groundwater level is high, water easily flows around the manhole. When the earthquake occurs and the earth and sand containing water liquefies, the entire manhole is lifted by the buoyancy of the generated mud and connected to the sewer pipe 2. In addition to being destroyed, in some cases there was a danger of falling.

  Therefore, when there is a plan to install a seismic manhole, it is better to first investigate the ground of the planned manhole installation site and examine the suitability of the plan with reference to the situation of annual fluctuations in the groundwater level. As a result of a preliminary survey on the manhole installation site, if it is found that the groundwater level may rise and reach the manhole installation location, and if the ground around the manhole is likely to liquefy, the manhole equipped with an earthquake resistant structure It is recommended to consider the installation. However, if either of the above conditions is missing, that is, if the groundwater level is sufficiently low, or if the ground is stable against earthquakes and there is no concern about liquefaction, the conventional general manhole structure is used. Installation is considered sufficient.

By the way, in order to judge whether the geology of the manhole installation site is likely to be liquefied, after conducting a geological survey including a soil test, it is described in, for example, the road bridge specifications. In addition, the following three conditions are evaluated. When all three conditions are satisfied, it can be said that the soil is easily liquefied.
(1) Alluvial sandy soil.
(2) The content (FC) of soil particles (fine particles) having a particle size of 75 μm or less is 35 w% or less, or the plasticity index (Ip) is 15 or less.
(3) In the particle size distribution, the central particle size at 50 w% position is 10 mm or less, and the particle size at 10 w% position is 1 mm or less.
Therefore, based on the above criteria, when it is determined that the ground of the planned installation site is highly liquefiable, the groundwater level is within the vicinity of the planned manhole installation location and within 10m underground It should be considered that manholes with a conventional structure are likely to be greatly affected by the liquefaction of the ground due to earthquakes and the like.

  Thus, when the policy of installing the manhole having the seismic resistance manhole structure of the present invention is determined, the data of the groundwater level investigated previously, the data of soil liquefaction and the distribution range of the soil, In consideration of the above, select the manhole structure of the desired form, select the fluidization prevention treated soil that fills it as backfill soil, and what kind of aggregate and what kind of treated material or condensing material respectively In addition to deciding what form to use, the policy of adopting the seismic resistance manhole structure of the present invention is decided, and the roadbed material support floor board extending from the outer wall surface of the manhole structure is extended. Work to design the location and shape of the installation and the properties and quantity of the stabilized roadbed material to be laid on the roadbed material support floor plate, and estimate the amount of use of these anti-fluidized soil and stabilized roadbed material Preparatory work and there is a need of Unado.

  After the preliminary investigation and preparatory work as described above, manhole installation work with the earthquake-resistant manhole structure of the present invention is possible, but the purpose of the work is not just new installation, repair of existing manholes, Or it may be a modification. In that case, it would be in order to remove or abolish existing manholes only when remodeling is not economical and to consider establishing new manholes. Therefore, in the following, an existing manhole for the middle of the sewage pipe 2 buried under the road passing through the soft ground G is remodeled into a manhole having the seismic resistance manhole structure of the present invention as shown in FIG. The procedure for providing the earthquake-resistant manhole structure of the present invention will be specifically described by taking construction as an example, but the technical idea disclosed here is a manhole equipped with the earthquake-resistant manhole structure of the present invention as a new manhole facility. It is added that it can be applied in the same way when installed.

  First, for the manhole having the same basic structure as the conventional manhole structure 1, the groundwater level of the ground G on which it is installed is measured, and the water level of the nearest waterway and the waterway are communicated. The normal groundwater level of the ground G is about 2.7m deep from the road surface, that is, the level near the axis of the sewer pipe 2 connected to the manhole structure 1 If there is a change in the water level of the above-mentioned waterway and the water level of the above-mentioned channel, it will be found that the change will be delayed, and if a heavy rainfall continues, the ground near the manhole will increase as the river level rises. It can be expected that the groundwater level in G will rise and reach a depth of 2m to 1.5m. In addition, as a result of separately investigating the soil soil, there is a silty soil layer mixed with gravel that contains a relatively large amount of fine particles in the vicinity of the depth where the sewer pipe 2 is buried, and the risk of liquid is particularly high Although it cannot be said, it is judged that the state is in need of vigilance.

  Further, the structure of the manhole structure 1 is scrutinized to confirm that it is a manhole structure 1 having the same basic structure as shown in FIG. A plan for the remodeling work according to the present invention in which a part of the structural member at a high position is removed and a roadbed material supporting floor board 3 as shown in FIG. It was decided to arrange for structural member design and procurement. However, the other manhole members are installed on the ground G, which has been known to be soft for a long time, and they are specially reinforced including the crushed stone layer Ba and the concrete layer Bb of the foundation B. It was determined that there was no need to add, and it was determined that there was no particular defect in the connection structure between the manhole structure 1 and the sewer pipe 2 as well as the manhole structure 1 itself, and it was decided to use it as it is.

  Furthermore, as a result of the survey of the shape of the manhole structure 1, the lower 2.0m length is a concrete cylinder with an outer diameter of 1400mm and an inner diameter of 1200mm. It turned out that it corresponds to. Therefore, using the specifications of No. 2 manhole, the total weight and apparent volume of the hollow manhole structure 1 including the bottom plate with a thickness of about 15 cm are obtained. The total height is 3.55 m and the cross-sectional area is 1.54. The length of the m2 straight tube portion was 2.0 m, the total weight was about 3.87 tf, and the apparent volume was 4.37 m3. Therefore, normally the groundwater level is about 2.7m, that is, 0.85m from the bottom of the manhole structure 1 is immersed in the groundwater (specific gravity 1.0), and the buoyancy of about 1,31tf is applied. Ascending to 1.5 m, manhole structure 1 will be immersed in groundwater by 2.05 m from the bottom, increasing buoyancy to 3.16 tf. However, since the total weight of the manhole structure 1 is about 3.87 tf as described above, the weight of the manhole structure 1 is 0.51 tf greater than the buoyancy of groundwater, and it is considered that a stable state can be maintained.

Therefore, if an earthquake occurs when the groundwater level rises to 1.5 m, there is a possibility that up to 2.05 m from the bottom of the manhole structure 1 is immersed in the liquefied mud. And the specific gravity of muddy water is 1.4
Assuming that the buoyancy increases to 4.42 tf for the total weight of the manhole structure 1 of about 3.87 tf, a load of at least 0.55 tf is applied to the manhole structure 1 in order not to float the manhole structure 1. There is a need. Therefore, if the seismic structure of the present invention is to be introduced into a manhole, the roadbed material supporting floor plate 3 is placed in a horizontal direction above the manhole structure 1 at a height above 1.5 m below the groundwater level. It may be modified so that a load of 0.55 tf or more is applied to the manhole structure 1.

  By the way, the base plate 3 for supporting the roadbed material is for stably supporting the stable roadbed material in an amount laid on the upper surface in order to prevent the manhole structure 1 from rising, and is reinforced with, for example, a reinforcing bar. It is preferably formed of a tough and heavy material such as a concrete board. Moreover, the shape does not need to be fixed in particular, For example, it can also be set as the shape extended long in the embedding direction of the sewer pipe 2, and you may select suitably according to the condition of the installation place of a manhole. Furthermore, the mounting position of the road base material support floor plate 3 can be fixed at a position close to the upper portion of the manhole structure 1 and not in contact with groundwater, for example, a position where the lower adjustment ring 1e is assembled or a higher position. Preferably, it is configured. Therefore, for example, a fitting hole 3a is provided in the center of the road base material support floor plate 3, and the portion where the diameter of the upper part of the manhole structure 1 is narrowed is coupled so as to penetrate the fitting hole 3a. Alternatively, the bottom adjustment ring 1e at the top of the manhole structure 1 is removed and replaced with a combination of another short lower adjustment ring 1e1, 1e2 and the fitting hole 3a, etc. 3 can be bonded to the manhole structure 1 and fixed with cement mortar or the like.

  Such a roadbed material supporting floor plate 3 may be a perforated concrete plate reinforced with a reinforcing bar or the like, but has a strength and durability capable of supporting a load necessary to suppress the floating of the manhole structure 1. Any suitable one can be used without any particular limitation. For example, as shown in FIG. 2, a 2.0 m × 2.2 m × 0.1 m square-recessed perforated concrete plate with a hole diameter of 0.90 m If the specific gravity of the concrete board is estimated to be about 2.4, the weight is calculated as 0.90 tf, which is the above-mentioned insufficient load when the manhole structure 1 is immersed in muddy water up to 1.5 m underground. A load sufficient to exceed 0.55 tf is applied.

  Therefore, we have reached the stage where we can start work to make existing manholes earthquake resistant, so we will explain the remodeling work according to the figure. In the first step of remodeling the conventional manhole shown in FIG. 3, the above-mentioned road base material supporting floor plate 3 made of a perforated concrete plate having a rectangular shape with a size of 2.0 m × 2.2 m × 0.1 m is prepared. In order to form a working space for attaching the roadbed material support floor plate 3 to the manhole structure 1, for example, a sheet pile C is driven into the ground G around the existing manhole, Remove the pavement part of the road to the extent expected for the remodeling work, and excavate and remove the soil around the manhole. Then, in the second step, as shown in FIG. 5, members (such as the lower adjustment ring 1e) that are not necessary for remodeling the manhole structure 1 and all the members that are assembled above it are removed. In order to backfill below the position where the floor plate 3 for supporting the roadbed material is attached, a lower 1 adjustment ring 1e1 as a minimum additional member is attached to the remaining manhole structure 1 from which the upper member is removed, The member 1e1 is joined and fixed with cement mortar or the like.

  Next, as the third step after such work, the first filling work is performed as shown in FIG. 6, and this work is to refill the excavation space up to the position immediately below the position where the road base material support floor plate 3 is attached. It is. As the backfilling soil at this time, it is desirable to use earth or sand that has been subjected to fluidization prevention treatment on the generated earth and sand at the time of excavation work, or stabilized ground material, etc. It is desirable to make the gap remaining between the upper surface of the 1 backfill soil layer Ga and the lower surface of the roadbed material supporting floor plate 3 attached later as small as possible.

  In the fourth step after the first filling operation is finished, an earthquake resistant structure is introduced into the manhole structure 1, but in this step, as shown in FIG. 7, the bottom one adjustment attached in the second step is performed. On the ring 1e1, the base plate 3 for supporting the roadbed material necessary as a modified structure and the lower 2 adjustment ring 1e2 for replenishment necessary for matching the position of the manhole cover 1i with the road surface are assembled. The upper inclined wall cylinder 1f, the upper adjustment ring 1g, and the lid mounting frame 1h that have been removed and attached are sequentially reattached, and each member is joined with cement mortar, etc. Finally, the lid 1i is restored to its original position, and the top of the lid mounting frame 1h. On top of that, the modified manhole structure 1 is completed. Compared to the modified manhole structure 1 before the modification, the lower adjustment ring 1e before the modification is replaced with the assembly of the lower 1 adjustment ring 1e1, the road base material support floor 3 and the lower 2 adjustment ring 1e2. The other shapes, dimensions, functions, etc. are just the same.

  As described above, in the fifth step after the remodeling work of the manhole structure 1 is completed, as shown in FIG. 8, the work excavation hole, which is the last work, is backfilled and the wall support of the sheet pile C and the like is supported. In this second filling operation, as the backfilling soil used for backfilling the excavation space, as in the first filling operation, soil and crushed stone subjected to fluidization prevention treatment are used. In addition, it is desirable to use the stabilized roadbed material similar to the material of the roadbed in the surrounding roads to fill the space around and above the roadbed material support floor plate 3 and proceed with the laying while uniformly compacting.

  It is often the case that the manhole installation location is under the road, and it is not only undesirable that the manhole installation location is different from the surrounding roadbed in the structure and strength, but it is also a defect that impairs the fracture strength of the roadbed. If the part is left, it will lead to the destabilization of the manhole levitation prevention load supported by the floor plate 3 for supporting the roadbed material, and thus increasing the resistance of the roadbed in the vicinity exceeded expectations. Even if liquefaction of the ground occurs, it works as an anti-floating force against manholes, which has the effect of further increasing the safety factor.

  In the fifth step of the present invention, the above-mentioned stabilized roadbed material is used to backfill the excavation space from the roadbed material supporting floor plate 3 to the ground surface GL. In this case, the structure of the ground before excavation is performed. In particular, it is preferable to restore the roadbed structure and the pavement structure at the manhole installation location. Therefore, except for the asphalt pavement part that consists of two layers, for example, the base layer and the surface layer, provided on the ground surface, the roadbed part below it is highly stable so that it is generally constructed according to road standards. Since it is desirable to form a crushed stone layer with a thickness of about 20 to 40 cm, the second backfill soil layer Gb formed of earth and sand or crushed stone subjected to fluidization prevention treatment is used for the roadbed in the above road structure. It may be limited below the work part. And the improvement work for earthquake resistance of the manhole of the present invention is completed only after the roadbed of the road is constructed on the second backfill soil layer Gb and further paved.

  The seismic-resistant manhole structure of the present invention as described in detail above is configured such that a roadbed material supporting floor plate 3 extending in the horizontal direction supports the stabilized roadbed material at an upper position where it does not contact the groundwater of the manhole structure 1. Since it acts as a load to prevent the manhole structure 1 from rising, it has become possible to prevent the manhole from falling or moving due to liquefaction of earth and sand due to an earthquake or the like. Therefore, not only when manholes are newly installed, it has become easy to retrofit existing manholes and introduce earthquake-resistant structures, so manholes built in areas where the ground tends to liquefy Can be made earthquake resistant in a short time.

It is a longitudinal cross-sectional view which shows the earthquake resistant manhole structure of this invention. It is a top view of the example of the floor board for a roadbed material support used for the earthquake resistant manhole structure of this invention. It is a longitudinal cross-sectional view which shows the installation state of the conventional non-earthquakeproof manhole structure. It is a longitudinal cross-sectional view explaining the 1st process of the seismic retrofit construction of the conventional manhole structure. It is a longitudinal cross-sectional view explaining the 2nd process of the seismic retrofit construction of the conventional manhole structure. It is a longitudinal cross-sectional view explaining the 3rd process of the seismic retrofit construction of the conventional manhole structure. It is a longitudinal cross-sectional view explaining the 4th process of the seismic retrofit construction of the conventional manhole structure. It is a longitudinal cross-sectional view explaining the 5th process of the seismic retrofit construction of the conventional manhole structure.

Explanation of symbols

B foundation Ba crushed stone layer Bb concrete layer C sheet pile G ground Ga primary backfill soil layer Gb second backfill soil layer GL ground surface 1 manhole structure 1a bottom plate 1b pipe mounting wall cylinder 1c straight wall cylinder 1d lower slant wall cylinder 1e Lower adjustment ring 1e1 Lower 1 adjustment ring 1e2 Lower 2 adjustment ring 1f Upper slant wall cylinder 1g Upper adjustment ring 1h Lid installation frame 1i Lid 2 Sewer pipe 3 Roadbed material support floor plate 3a Fitting hole

Claims (4)

  In the manhole to be installed at the connection site of the underground underground pipe, a roadbed material support floor board is extended substantially horizontally from a position higher than the average annual maximum groundwater level of the manhole installation ground on the outer wall surface of the manhole structure. A seismic manhole structure, characterized in that a stabilized roadbed material is laid on a floorboard for supporting materials.   The sum of the weight of the manhole structure including the roadbed material support floor plate and the total weight of the stabilized roadbed material and the roadbed supported by the roadbed material support floor plate is the average annual maximum groundwater level of the manhole installation ground. The seismic proof manhole structure according to claim 1, wherein the buoyancy due to the muddy water predicted to be received by the manhole structure when the soil below is changed to liquefied muddy water.   The earthquake-resistant manhole structure according to claim 1 or 2, wherein the stabilized roadbed material is obtained by stabilizing high-specific gravity aggregate such as earth or sand or gravel using a debris binder such as cement.   In the manhole connecting the underground pipe, the stabilized roadbed material is laid on the floorboard for the roadbed material that extends in the horizontal direction from a position higher than the average annual maximum groundwater level of the manhole ground on the outer wall surface of the manhole structure. The total weight Ws (tf) of the total weight W0 (tf) of the manhole structure including the floor plate for supporting the roadbed material and the total weight Wb (tf) of the stabilized roadbed material and the roadbed is expressed as the manhole. Manufacture of earthquake-resistant manhole structure, characterized in that it is larger than the buoyancy value Wf (tf) obtained by multiplying the immersion volume V0 (m3) by liquefied mud water predicted from the external dimensions of the structure and the density of the mud water Law.

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