Q Bank for Civil Engineer LDCE Exam - Write Short Notes (7)

Q.No. 6. Short Notes

1. What are the main cause of crushing of PRC sleeper in washable aprons and what are the remedial measures?

2. Railway affecting works.

3. Distressed bridges and schedule of inspection by official.

4. Vulnerable location & monsoon precautions.

a)Why the concrete sleeper damage The washable aprons are constructed on the concrete raft. The PRC sleepers placed on the raft and after palcing of sleeper the crib is casted one bitumen sheet also provided under the sleepers at both ends for facilitating the elastic medium between sleeper and raft. Now during casting of crib the concrete as well as cement sullary flows under the middle of sleeper which give the rigid support to the sleeper resulting to this the sleeper becomes centre rigid and ends on elastic support due to this uneven base the sleeper sheared while wheel load comes on the sleeper . A another cause of damage of sleeper in washable apron is regularly falling of water, and human waste from the coaches which eroded the sleeper surface and sleeper become to start damage. As explained earlier that the ends of sleeper rests on the bitumen felt to provide elastic medium between raft and bottom of sleeper. But due to vibrations of moving trains if a small Qty. of water percolate from side of sleeper on the bitumen pad. The bitumen felt starts damage and lost its elastic property. This is the main cause of damage of concrete sleeper. During construction of washable apron it should be ensured that the placing of bitumen pad to done on quite smooth surface and water should not percolate. The side drain also to be made with proper slope so that water can not stagnate in drain. This stagnated water may become a source of percolation inside the bottom of sleeper. 

(b) Railway affecting works: 

 Railway affecting works are those, the construction, design, maintenance or operation of which may cause serious damage or breaches or flooding of railway line or bridges. Some of the examples are: 

I. Irrigation and water supply tanks or reservoirs 

II. Canals in embankment and river bunds 

III. Road embankment with inadequate waterway for drainage situated situated upstream or downstream of railway line. 

IV. Temporary channels cut for irrigation or other purpose from beds of active river V. Other work, which alter or impede the natural course of flood or cause increase of flow such as new irrigation projects, new townships, large/scale deforestation etc. 

(C) Definition of distressed bridge:- A distressed bridge is one which shows some physical deterioration of its physical condition, indicating the need for rehabilitation through special repairs strengthening or rebuilding (including replacement of griders). 

Classification of distressed bridges

Category-i: Those requiring rehabilitation to be done immediately, say within a year’s time. Category-ii: those requiring to be kept under observation and to be taken up for rehabilitation on a programme basis. Signs of distress for Group I bridges:* 

I. Foundation: Settlement of foundations, deep scour around pipers/abutment, 

II. Piers and abutment: Crushing of masonry, tilled piers and abutment, wide cracks in abutment/piers, crushing of masonry. 

III. Bed block and bearings: shaken/displaced/cracked bed blocks, cracks or any other distress in bearings, 

IV. Arches: Diagonal cracks in arches, transverse in cracks arches, distortion of arch, displacement of brick/stone from arch ring, V. Misc.: Progressive loss in camber of prestressed concrete/steel girders, wide cracks in Reinforced Cement Concrete/prestressed concrete members. Crack/heavy corrosion in load bearing members of steel girders, weak/corroded weak/corroded/cracked piles, particularly cast iron crew pipe, snapping of rivets. Sings of distress for Group II bridges

 I. Abutments, piers, wing wall and return walls: cracks in return walls/wing walls, slight tilting/buging of masonry in return wall/wing walls, perceivable deterioration of stone/brick masonry,

 II. Arches: wide longitudinal cracks in arches, abutments and piers, cracks/lean/bulge in parapet walls of an arch, bulging or separation of spandrel from arch barrel, 

 III. Misc.: Spelling of concrete in beams and slabs, loose rivets above 20% at any point, observations of any excessive vibration in part of the bridge. 

 Category Inspection by Periodicity I. 

(a) Inspector (concerned) Once in a month 

(b) AEN or ABE Once in two months 

(c) DEN or Sr. 

DEN Once in three month II. 

(a) Inspector (concerned Once in three months 

(b) AEN or ABE Once in six months 

(c) DEN or Sr. DEN Once in a year

(d) Venerable location: Venerable locations are those spots in the track gridges etc where there is possibility of failure exists due to the constructional as well as natural conditions. These locations are listed and keep in the office. These location should be inspected quickly. In case of extreme whather condition these locations should be watched regularly to check out any damage. 

Mansoon precaution:- 

 I. Location and quantity of reserve stock of pitching stone, boulder and other monsoon reserves should be fixed and ensure the stock, as per requirement. 

II. Arrangements should be made to stock them before the onset of monsoon at locations specified in stacks or in loaded wagons. 

III. Reserve stock should not be used except in emergency; where it is used, it should be recouped. 

IV. The “Reserve” for use in bridge should be stacked at suitable locations above the HGL close to the bridge and the protection works. 

V. The annual return of pitching stone, boulder and monsoon reserve should be submitted. It should be accompanied by a statement of training woks added or abandoned during the year with recommendation for reduction or increase to the reserve”. 

VI. Permanent remedial measures should be taken as soon as possible in very case and recurring expenditure avoided or minimized.