Koshimizu, Satoru

Mori, Taiki

Samizo, Masahiko

English

Hydraulic Engineering Repository

Conference Paper, Published VersionKoshimizu, Satoru; Samizo, Masahiko; Mori, TaikiA Method to Extract Scoured Bridge PiersVerfügbar unter/Available at: https://hdl.handle.net/20.500.11970/100131Vorgeschlagene Zitierweise/Suggested citation:Koshimizu, Satoru; Samizo, Masahiko; Mori, Taiki (2008): A Method to Extract ScouredBridge Piers. In: Sekiguchi, Hideo (Hg.): Proceedings 4th International Conference on Scourand Erosion (ICSE-4). November 5-7, 2008, Tokyo, Japan. Tokyo: The JapaneseGeotechnical Society. S. 281-284.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.1  A Method to Extract Scoured Bridge Piers   Satoru KOSHIMIZU 1,  Masahiko SAMIZO 1,  Taiki MORI 2  1Member of JSCE, Railway Technical Research Institute (2-8-38 Hikari-cho, Kokubunji, Tokyo, 185-8540, Japan)  2Member of JSCE, West Japan Railway Company  (5-4-20, Nishinakajima, Yodogawa-ku, Osaka, 532-0011, Japan)       It is essential for the maintenance of railway facilities to prevent bridge piers from susceptible scouring under flooded conditions. In this paper, the authors have proposed a method to extract the bridge piers for inspection. Railway bridge inspectors apply the foregoing method when bridge inspections take place. The method considers a change in the river environment adjacent to the bridge and pertinent factors.     Key Words : scours, bridge piers, judgment for soundness     1. Introduction   It is important to prevent a disaster due to scouring around piers of Railway Bridge under flood conditions for the maintenance of railway structures. Therefore, it is necessary to extract the bridge piers where we are afraid of scouring from many bridges. Railway company must take sufficient measures when they find bridges are in danger. Japan Railways (JR) do "general inspections" in every two years, they examine the need of the repair. The JR performs "Individual inspection" later to bridge judged in danger by the general inspection. The inspector who belongs to the railway company does detailed bridge inspection, and the company maintains these bridges safely with this countermeasure. Railway Technical Research Institute (RTRI) made a graded table to extract bridges in danger whose level will be high. This graded table was developed for the general inspection. The inspector of the railway company does a general investigation by using this graded table. They can judge whether bridges are in the risk or not by this inspection. Therefore, they often use this graded table. The inspectors verify bridges judged in danger with general inspection with individual inspection. Not all bridges that are extracted with general inspection are dangerous. Thus, the inspector must extract bridges in danger by the individual inspection. It is insufficient to do a precise extraction as an actual problem only by the above the graded table made for the general inspection to do a precise extraction as an actual problem. Thus, detailed investigation is necessary. The individual conditions of the bridge influence each bridge in flood conditions. Therefore, the change in the river environment around the bridge should be considered. RTRI developed the way of extracting it including a change in a river environment. An inspector uses this way of extracting it at the time of the individual inspection.   2. The Method to Inspect Railroad Bridges  Railway Companies maintain structures to ensure demanded performance. They must secure bridges from scour around bridge piers. Thus, Railway company regularly checks the structures, and does detailed inspections if they are necessary in the period of structure use. They must repair the structure, if it is necessary as the result of this inspection. They make a record after repair. The following, the case of JR are mentioned. They do the general inspection concretely every two year through the period of the structure use. Bridges are investigated mainly with general inspections by the visual observation. As a result of the general inspection, they do separately an individual inspection to the necessary structures as detailed one. 281B-5 Fourth International Conference on Scour and Erosion 2008 2  Table 1 shows the relations between the degree of defects and standard soundness. Soundness is divided into A, B, C and S. A limited use and a countermeasure such as a repair are urgently necessary if the structure is judged as AA in the category of A. The structure grouped in A with general inspection needs an individual inspection. Inspectors judge the degree of soundness of the structure with an individual inspection again. Railway company takes the structure judged A1 with the individual inspection immediately. As for the structure judged A2 in the same way, they repair it in the necessary time. Because the structures judged as A1 or A2 had a defect when they are inspected, such a defect will be likely to be more dangerous in the future.    3. A Inspection Method of Extracting Bridges Caution Needed as to Scouring   RTRI made field investigations of 49 bridges in Aomori, Iwate, Miyagi and Niigata and Nagano Prefectures in Japan. The field investigation results are statistically analyzed. We analyzed the speed (cm/ Year) of local scouring as an objective variable in the quantification method, type I.                         The definition of objective variables is as the following.  Partial Scouring Speed:  The riverbed degradation speed around the most scoured pier per year      Table 1  Judgment Classification for Soundness1)   Soundness Adverse Effect Extent & degree of Defects Countermeasures AA Immediate Danger Serious nature Urgently A1 Possible Danger (Near future) Regressing, or Declining Performance Immediately A A2 Possible danger at a later date  Susceptible due to surroundings As required B A, If no action taken A, If no action taken Monitoring As required C Appropriate at present Slight Detailed Inspection at regular interval, if requiredS Sound Nothing Unnecessary    Fig. 1 Partial Scouring  Former RiverbedRiverbed at presentPartial Scouring 282 3 This element was made the objective variable  as follows:  1) It has five types of factors, which causes partial scouring under flood conditions due to sand bars, crank flow of channel, channel transition, riverbed configurations and structures.  2) We analyzed previous cases of scouring disasters, partial scouring around the pier causes the damage of the bridge as shown in the figure 1. We selected eight elements as an explanatory variable. The result is shown in Table 2. We presumed that the graded table can be used with individual inspection. A fundamental point added to the score point of each category which is applicable to every valuation item makes a total point. This total point is the degradation speed (cm/Year) of partial scouring. The key components that regress partial scouring are as follows:       Table 2  the Graded Table for the Estimation of the Scouring Speed   Items Category dm< 2 2<=dm< 30 30<=dm<100 100<=dm Average Grain Diameters   dm(mm) 0.0 9.2 5.5 -6.7 S<=50 50<S<=200 200<S<=1000 1000<S Drainage Area S(km2) -11.7 1.6 5.1 22.5 0 < r /B < ∞ ∞ (Straight) the Ratio between   Radius of Curvature and Channel Breadth      r /B 1.7 -2.0    Supercritical Subcritical Supercritical Flow or  Subcritical Flow 16.0 -5.1     No Yes Channel Constriction  -2.2 15.8     No Yes Sand bars -3.5 0.9     P<=0.1 0.1<P<=0.15 0.15<P Impediment Ratio of River Flow (by Piers) P -2.2 -0.7 4.7   N<=0.66 0.66<N Frequency of Exceeding the Average of Annual FloodsN (Times / Year) 2.5 -6.9    Fundamental Point 18.8  (cm / Year)   283 4 Pier Width  D Penetration Depth  Z Depth Ratio  = Penetration Depth / Pier Width= Z / D Riverbed Prime Elements:  2mm <= Average Grain Diameters < 100mm Drainage Area > 50 km2 Channel Constriction: Yes Impediment Ratio of River Flow > 0.15    4. Application to Inspections   JRs are engaging at the time of the inspection for the safety maintenance of the bridges and piers as follows: They survey a riverbed around the pier, measure the pier a depth ratio (penetration depth Z / pier width D ) , if the pier needs an inspection, and they grasp the regress of scouring at present by recording the measured value. It is necessary to evaluate the danger of scouring, thus to evaluate the past, present and a future condition from respective viewpoints. As for the past, it is possible to realize the occurrence conditions such as disaster records and the results of the previous inspections. In addition, it is fully understandable with riverbed inspections in view of the present conditions. The satisfactory evaluation will be thereby possible if the rate of pier scour is predicted appropriately in the future.  Thus, we evaluate actual piers as follows:  We evaluate it at the room time calculated from partial scouring speed (cm/year) based on present depth ratio (penetration depth Z / pier width D) that the danger of scouring disaster occurrence was measured as mentioned in the Figure 2. A room time is the period until the ratio is lower than a critical depth ratio. The pier whose room time is short is evaluated as a bridge which it often suffers scouring damage (see Figure 3). Here, the maximum scouring depth can be the maximum depth in the neighborhood of the pier, and it is estimated at Z=1.45D1). In addition, a critical depth ratio is the ratio with the root, which copes with this maximum scouring depth.    5. Conclusions   The conclusions of this paper as summarized are in the following:  1) We considered grasping of the bridge environments and the danger due to regress partial scouring based on the data as obtained at present.  2) We evaluate it at the room time calculated from partial scouring speed (cm/year) based on present depth ratio (penetration depth Z / pier width D) that the danger of scouring disaster occurrence was measured.  REFERENCES 1) Railway Technical Research Institute: “Maintenance Standards for Railway Structures and Commentary (foundations and retaining structures)”, Maruzen, 2007(in Japanese)      Fig. 2 Depth Ratio   Fig. 3 Evaluation Line  Inspection：Now Depth Ratio Now TimeCritical Depth Ratio Time Line of Partial Scouring Speed  Partial Scouring Speed = Slope Depth Ratio284

A Method to Extract Scoured Bridge Piers

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A Method to Extract Scoured Bridge Piers

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