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A Case Study on Renewal Strategies Concerning Lost
Technologies in Construction of Rubber Gates

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Tomoji Takatsu1,a, Kohei Nagano1,b, Shuji Takasu1,cJapan Dam Engineering Center, 2-9-7 Ikenohata, Taito-ku, Tokyo, JAPANatakatsu@jdec.or.jp, b nagano@jdec.or.jp, c takasu@jdec.or.jp
Abstract

Rubber gates, which have advantage over steel gates with hydraulic lifting when installing across rivers,
have been installed in Japanese rivers since the end of 1960s. The number of rubber gates in Japan goesaround 4,000. As many of them are over 20 years old, Japan needs to generate some plans to renew them
despite appropriate maintenance of them. On the other hand, the number of installing rubber gates has been
decreasing since the 1990s, this fact prevents handing down the know-how of production to younger
generations. It is one of the main causes for technologies to be lost. We may call those the Lost
Technologies. Therefore, the authors have conducted simulation studies for the repair/renewal of rubber
gates, with the assumption that the technologies to produce them are lost, by decreasing the number of
construction works of rubber gates. Although the results come from these simulation studies, the authors
guess the study results shall be used as references for actual renewal works.
Keywords: renewal, rubber gate, lost technologies

1.

INTRODUCTION

Rubber gates, which have advantages over steel gates with hydraulic lifting in installing across rivers andwhose sample is shown in Figure 1, have been installed since the end of 1960s. Many of these are currently over
20 years old. In Japan, we have created several technical standards on construction, maintenance and renewal of
rubber gates. Furthermore, Japan has been able to install gates across wide rivers using these standards
developed in Japan, specifically for the construction of large gates. Over 4,000 rubber gates have installed bythese standards. Rubber gates, which are raised up during ordinary times to maintain water level and lowered
during floods to let the water flow, are essential for irrigation in Japan. Rubber gates need to be repaired andreplaced due to deterioration of their material, even if they are maintained properly. In addition, there areexamples when rubber gates have been repaired or replaced. This implies that Japan needs to prepare forrepairing and replacing rubber gates. In Japan, we can repair and replace rubber gates using technologies of
constructing new ones. That said, construction technologies are also required for repairing and replacing thedamaged rubber gates.
On the other hand, the number of rubber gates construction works in Japan has been decreasing since the1990s. This trend can be seen on Figure 1.
Rubber gates over 20 years old

Photo of rubber gate
Change in the number of constructions
Figure 1. Change in the number of rubber gates constructed in Japan and a sample of rubber gate
This implies that rubber gates construction technologies are hardly handed down to future generations. It isnatural that constructors withdraw from the business in case that demand has decreased. If the construction
technologies were lost, Japan would not be able to construct nor maintain rubber gates. In Japan, we strongly
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5 Asia‐Pacific Group International Symposium on Dams (APG 2019)need to keep construction technologies available. Furthermore, Japan needs to hand down these technologies tofuture generations. The reason why the authors generated this case study is because maintaining, repairing andreplacing infrastructure all depend on the Public Accounting Law. The strategies for maintaining, repairing andreplacing are as follows:1)
Repairing needs to be on/by same material
2)
Replacing needs to be on/by same structure
In this paper, the authors assume that some technologies are lost, therefore not viable options for rubber gates.

2.

RUBBER GATES IN JAPANIn Japan, rubber gates have been installed in severe environmental conditions. For example, rivers havehigh velocity water flow, massive rolling stones, flood/drift woods and so on. Moreover, they are destructive
attackers. These come from the followings:
1) Rivers have steep incline: as Japan has lots of mountains despite its narrow land, the rivers need to carrywater from high to low through a short distance.
2) Mountains with massive trees and rocks: since Japan's mountains are steep and covered with lots of trees,
river water goes down to its estuary with flood/drift woods and rocks.
The sample photos in Figure 2 show rolling stones (on the left) and flood/drift woods (on the right). The
diameters of rolling stones with sharp edges are over 20 cm. The length of flood/drift woods is over 5 m. So
they have enough potential to damage rubber gates.

3m
Samples of rolling stones
Samples of flood/drift woods
Figure 2. Samples of flood/drift woods on rivers
Let us return to the original issue. As the above damaging objects seriously endanger the rubber gatesinstalled across rivers, they need to be protected from them. The representative techniques for rubber gate
protection are as follows:
1) Outer protection layer with ceramics chips: since ceramics are abrasion proof, damages hardly reach therubber layers.
2) Thick rubber (more than twice as thick as ordinary rubber): this gains time for damage to reach inner layers.
3) Outer protector by harder material: since ceramics are abrasion proof, damages hardly reach the rubber
layers.
4) Cushioning material in bag for impact: cushions are able to absorb energy that could damage the rubber.
5) Cushioning material on river bed: cushions are able to absorb energy that could damage the rubber.
Technologies applied with ceramics are easily lost due to their peculiarity. This is because very few suppliers
have the ability to apply technologies with ceramics. Two types of technologies are needed to use this material.
One is to manufacture chips with small diameter. The other is to rub chips. Since the need for thick rubber isdecreasing due to a decrease in the number of installing rubber gates, the technology for manufacturing these isalso easily lost. Outer protectors cannot protect the entire surface of rubber gates, so their effect is not enough.
The comparison of these protection techniques is given in Table 1.
In this paper, the authors focus on the technique of protecting rubber bags from damaging objects on
the outer protection layer with ceramics chips. The reason is that we have a sample case of a 35 m long and 4 mhigh renewal rubber gate with ceramics chips layer. Figure 3 shows the surface of outer protection layer within
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5 Asia‐Pacific Group International Symposium on Dams (APG 2019)the ceramics chips. The rectangular shapes that can be recognized on the photo are the exposed ceramic chips.
The chips have a diameter of 1 mm and a length of 5 mm. Rubber bags are protected by these ceramic chips that
contact the damaging objects in the river water. This depends on the abrasion resistance of ceramics. This
protection technique has the advantage that the rubber bag thickness does not increase much. The rubber withceramics chips is manufactured as shown in Figure 4.
Table 1. Comparison of Countermeasure/Protection Options

5mm

Figure 3. Surface of outer protection layer with ceramics chips

OutsideCeramics Chips

Protection Layer
Reinforcing Layer
X4
Inner Layer
InsideFigure 4. Structure of the rubber with ceramics chips
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5 Asia‐Pacific Group International Symposium on Dams (APG 2019)3.

INSPECTIONS

Rubber gates need to be inspected with designated technical standards. Table 2 shows the inspection
guideline given in one of them. Members are classified as rubber bag, Fixture and Aspect. Inspection intervals
are classified as Annual, Monthly and Special Inspection. For special inspection, almost all functions of therubber gates are stopped. This means the gates can be inspected in more detail than during a routine inspection.
Overhauling the gates is a good time to perform special inspection. Visual inspection is mainly used as aroutine inspection, yearly and/or monthly.
Table 2. Inspection Guideline

MemberSpotAbrasion

Item/Measured Variable

Interval

MethodAbrasion Loss compared with
Planned Value

AnnualVisual inspection
MeasureAnnualVisual inspection
MeasureOuter
Layer Deterioration Separation and Crack related to
RubberDamageexposed Texture in Outer Layer
Bag
Separation and Crack
CreaseJoint
Convex Ballooning
Separation by Hands
Air Leakage
Bolt
Deformation
Fixture Anchor
Corrosion
Fastener
Abrasion
Loose Bolt

AnnualMonthly

Visual inspection
MeasureManipulate
Hammering test
Visual inspection

SpecialVisual inspection
Inspection
Hammring test

Air Leakage Detection by
Bubbles to clarify it

Silt Accretion

Upper Side of Fin
Silt Accretion
Air Leakage
Figure 5. Representative damages near fins
A few representative damages are shown as follows. Firstly, Figure 5 shows silt accretion and air
leakage, which appear near fins controlling gates’ vibration. These damages come from cracks and/or
separations of joints and/or layers. Mainly rolling stones in river water generate the cracks.
Secondly, convex ballooning is illustrated in Figure 6 that gives a sample of growth process on convex
one for 4 months. The damages of convex one occur due to two causes. The first is penetrating water between
the outer and inner layers. The second one is air leakage from crack on inner layer that is very much dangerous.
The illustration of gap on embedding rubbers is shown in Figure 7. Table 3 lists up the damages and theirestimated causes, and summarizes information from technical standards.
Finally, Figure 5 shows the flowchart and criteria of inspection, coming from technical standards. From
inspection results, the engineers on site need to judge soundness, follow-up observation, emergency repair,permanent repair, and/or renewal. That is, the inspection results should serve as feedback for any next action.
Moreover, inspection engineers need to have acquired judgment ability.
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Existing Convex Ballooning (Start of observation)
Convex Ballooning (After 1 year)
Convex Ballooning (After 1 year and 4 months)

Figure 6. Growth process on convex ballooning
SecondLayer ofReinforced
TextureJoint
EmbeddingRubberGap

Delaminationof Embedding
RubberInner Rubber
Maximum Tension
Third Layer of Reinforced Texture
Sample case of the gap on joint
Illustration of the gap
Figure 7. Illustration of gap on embedding rubbers

Damages

Table 3. Damages and their estimated causes
Estimated Causes

Air Leakage on Rubber Bag Crack by Rolling Stones or Separation of Joint
Rubber Bag Burst

Crack, Over Pressure or Degradation on Joint

Air Leakage on Fixture

Failed Construction of Sealing, Packing and Fixture Bolt
Degradation of Sealing
Gap and/or Crack on Rubber Bag due to Vibration and/or Over Tension

Shallow Crack

Degradation of Rubber Bag

Deep Crack

Separation on ill-bonding part or Degradation of bonding

Convex Ballooning in Outer Air Leakage from crack on inner layer, this is very much dengerous
and/or Inner Layer
Pooling water between outer layer and inner layer

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Rubber Bags・Metal Fittings

Inspection

Sound
〇

Damage△Grave Damage
×Continuous
Observation△２

Inspection

Emergency Repair△１△３Distinguish repair andrenewal and decisionof the method.

Permanent Repair△１

ActionRenewal×
Production of
Rubber Bags

Routine of Inspection
Broken Line: Process with history of inspection
Inspection Result

Action×

RenewalIf repair is difficult, permanent repair cannot ensure original
reliability, or economic advantage, renewal is selected.

△１

Emergency
Repair andPermanent
RepairEmergency repair cannot ensure the original reliability. Permanent
repair is selected, if it has economically advantage.
Renewal is selected and it is determined ×, if the selection ofrenewal has economically advantage.

△２

Emergency
RepairEmergency repair can ensure the original reliability.
It is determined as △ 1 when the damage scale is large.

△３

Follow-up
Observation

Although there is damage and deterioration, reliability is
maintained. Depending on the progress of the defect, it may be
determined as △2.

△

〇

Sound

Criteria

No defects are found in the rubber bag and fixing bracket.

Figure 8. Flowchart and criteria of inspection

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4.

REPAIR AND RENEWAL

When the inspections in the previous section give results which are neither sound nor follow-up
observations, those gates must be repaired or renewed. Firstly, let us consider the case of replacing. The authors
assumed that protective layer rubber bag with the ceramics chips cannot be manufactured due to their peculiarity.
In fact, the author recognizes the case that the manufacturer withdraws. Then, we must select an alternativetechnology from Table 1. Options 3 and 5 in Table 1 are not effective enough. Moreover, the authors assumed
that Options 2 and 4 cannot be sufficiently procured. Only by making these assumptions were the authors able tonegate all five options. Consequently, none of the five options has both abrasion resistance and availability. At
this point, repairs are not possible due to unavailability of ceramics. Therefore, this is no longer repair, but
renewal with a different type of gate. The candidates for gate types are steel flap gate with single/double rubber
bladders and steel flap gate with hydraulic cylinders.
The authors then compared these three candidates. The allowed water level in target river caused theconstraint of gate height to be 4 m. With this constraint, the height of riverbed becomes higher than the present
height when selecting steel flap gate with single/double rubber bladders. This is the reason why steel flap gateswith height more than 2.5 m for single rubber bladder, or 3 m for double ones, cannot be installed. Table 4shows their comparison, while Figure 9 shows sample pictures of them. Since a lift-up is needed in case of asteel flap gate with single/double rubber bladders, more detailed planning is needed. Moreover, gate owners
need to have a good relationship with the authorities in order to carry out this project. The necessary level ofriverbed must be negotiated with the authorities. The reason is that the level is determined by technical standard
and contracted between the authority and the gate keeper. In conclusion, detailed planning and negotiations are
essential. The sample case which the authors have is redesigning now.
The above process is summarized in Figure 10.
Table 4. Comparison of rubber bladders and hydraulic cylinders

Rubber Gate

Steel Flap Gatewith Rubber Bladders

Steel Flap Gatewith Hydraulic Cylinders

Figure 9. Samples of rubber gate and steel flap gate with rubber bladders and hydraulic cylinders

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Figure 10. Flowchart for maintenance of rubber gates with lost technologies

5.

CONCLUSIONSJapan has created several original engineering standards for rubber gates in severe conditions. Thesestandards have been established not only for the construction of rubber gates, but also for their maintenance andrenewal. Moreover, no major accidents have occurred on rubber gates constructed on the basis of the establishedstandards. Finally, all of these have realized the construction of large scale rubber gates instead of steel flap
gates. This implies that Japanese civil engineers have improved rubber gates to fit the Japanese environment.
Moreover, rubber gates have taken essential role in river management of Japan.
Based on the above achievements in the field of rubber gates, the authors have reached the following
conclusions in their case study:1) Necessity keeps technologies sound: this generally implies that construction works help handing down tofuture generations technologies to build infrastructure.
2) Alternative elemental technologies are not always available: some key technologies for repair and/or
renewal of infrastructure have not been handed down to future generations.
3) Gate type has to be changed under certain circumstances: some technologies to construct a particular
structure have become lost technologies, e.g. the technology to build the Great Buddha of Todaiji Temple inJapan.
Though the authors have obtained valuable results for the renewal of rubber gates, further
investigations must still be done on actual rubber gates. Therefore, the remaining issues are as follows:
1) We must collect more renewal examples: the number of construction examples owned by authors iscurrently too small.
2) We must generate standards for renewal of rubber gates: we are not able to apply/share the stored
knowledge if it is not standardized.
3) We must renew more rubber gates using the standard: it is necessary to improve the standard when we findsome improvement points.

REFERENCE
S. Takasu, T. Takatsu and K. Nagano (2019),“Examination on Renewal Plan of Rubber Gate,” Annual Report2019 of Dam Engineering Research Institute, Japan Dam Engineering Center, pp. 4-19 – 4-27 (in Japanese).

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