| Case Name |
The result which underdrain construction didn't achieve the purposes of the construction since it was remarkably different from the design. |
| Pictograph |
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| Date |
1995 |
| Place |
Fukushima Prefecture. |
| Location |
A road construction site. |
| Overview |
In the No.5 underdrain construction, the packing of the water stop joint had not completely been constructed on 23 underdrain joints within 24, and also on the other 1 place, it had been constructed only the part of the whole circumference.And the government subsidy considerable amount \ 2,630,500 which concerned this was considered unreasonable. |
| Incident |
No.5underdrain 49m long is consisted of 25 box culverts(1 unit 1m long, 24 units 2m long) by factory product of reinforced concrete structure whose width and height of inner cross section were both 1m installed in the lower of the embankment so that the water in the torrent which crosses with the road may flow.No.5 underdrain had been planned to be constructed as following according to the drawing and specification.
(a) lay and compact unscreened gravel as a base of the culvert over the ground at the 20cm thickness and after that, construct the basic concrete 10cm thick, and bed mortar 3cm thick.
(b) on the superscription base, found the culvert as following.
1 The binding material is applied to the groove established over whole circumference of the joint of the culvert, and fix the rubber packing ( width of 28 millimeters, thickness of 20 millimeters ) to it( of "the water stop joint" this part ).
2 couple the culvert by tightening 4 joints metal fitting of the outside edge, and install on the base described above in order to the bottom face become a smooth and uniform gradient.
3 fill the groove in inside and outside of the joint of the culvert with the mortar ( of "pointed joint" this part ).
The water stop joint of the superscription is for preventing that water leakage from the culvert and invasion water from the periphery draw the gravel of the periphery and produce cavity, and it brings about transformation of the culvert and road body. And the pointed joint inside the culvert is for increasing flow effect by smoothing the downward flow plane of the water.
Culverts were in conditions as follows, when it was examined.
(a) 25 culverts of 49m were in the differential settlement (largest 17.0 cm) over the whole, and the joint had opened 2.5 cm at largest, etc.. And the water was leaked in almost joint, and the water was invading from the periphery.
(b) within 24 joints of the culvert, the mortar of the pointed joint had come off all on 6 places, and the part had come off on 14 places, and it had been washed away.
(c) at 11 joints of the culvert, the highway embankment of the periphery was drawn, and the cavity ( depth largest 38 cm ) occured.
(d) in the basic concrete, the crack (width largest 1.0m) of 10 places overall widths had been generated. |
| Sequence |
3 underdrains and embankments of No.3, No.4, and No.5 were carried out at government subsidies \ 55,578,182 in order to construct the road of embankment structure as part of the road improvement project of No.400 national road. In the drawing and specification, the binding material would have been applied to the groove established over whole circumference of the joint of the culvert, and the packing made of the rubber would have been made ( "the water stop joint" ). the culvert of the No.5 underdrain construction was remarkably differing from the design of the construction in the water stop joint of the joint, and No.5 underdrain construction and embankment construction of the department besides didn't achieve the purposes of the construction, and the government subsidy considerable amount \ 6487,800 was considered unreasonable. |
| Cause |
Importance of the water stop joint and the pointed joint in the drawing and specification were not completely understood. And, what is called the omission only for reducing the workload can be considered to be the reason. |
| Countermeasures |
Sense of tension must be brought over whole industry by establishing the penal regulation, etc.. |
| Knowledge Comment |
Observe the drawing and specification! |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Regular Operation, Nonobservance of Procedure, Malfunction, Specifications Not Met, Possible Damage, Potential Hazard
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| Sources |
The 1995 fiscal year settlement inspection report ( Board of Audit ).
|
| Financial Cost |
Government subsidy delivery amount considered unreasonable : \ 6487,800. |
| Multimedia Files |
Fig2.The fifth culvert concept chart
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| Field |
Civil Engineering
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| Author |
YONEZAWA, Akio (The University of Tokyo)
KUNISHIMA, Masahiko (The University of Tokyo)
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