T&P in Civil Engineering

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CEA&RC was established in 2011 as a nonprofit Education society at Panchkula (near Chandigarh). The society is being sponsored and supported by various construction companies, educational institutes and individual professionals. CEA&RC is managed by Governing body comprising of entrepreneur of Construction Company, Qualified & experienced Civil engineers, Educationists and workers. CEA&RC lead by an eminent civil engineer with experience of more than 30 years in construction & consultancy field in India and abroad. The Chairman of the Society Mr. Inderjit Ghai is owner of a well-established Engineering Consultancy organization “Consulting Engineers Associates” Approved by Ministry of Road Transportation and Highways (MORT&H). This consulting organization has been providing consultancy in the field of highway, bridges and infrastructure development projects since 2000.

Introduction

The specifications, standards and other details for any particular item/material/subject is provided in different codes of IRC/IRC:SP/Manuals /IS MoRT&H Specification Book/ Circulars/ Standard Documents & Guidelines issued by MoRT&H,/NHAI or other Authorities from time to time.

It is mentioned in the RFP document/Contract agreement that the work will be executed as per applicable Manual which further refer to many other codes.

All the documents are interdependent i.e. cross reference is very commonly given among themselves.

Thereafter, selective revisions/Amendments/Additions are done to a particular Clause/item in a particular code without clarification regarding their effects among the other dependent documents.

The Actual Practice being followed at Site in certain cases are not the same as mentioned in their applicable documents referred above. Theory (even among different documents) & practice may lead to disputes, which subsequently has many more issues and ultimately causing a financial loss to the Nation.

There is ambiguity in the THEORY part and actual PRACTICE being followed.

With aim to compile these issues (item wise) in a comparable tabular form and bring it to the notice of all concerned Authorities (IRC, IS, Consultants, Contractors and others) so that they may decide the course of action to sort out these discrepancies/ contradictions, Civil Engineers Association & Research Center (CEAR&C) has decided to form a Platform in the name of THEORY & PRACTICE (T&P).

The details of specific issues will be collected by T&P ‘MANCH’. It will be compiled in in a tabular form, views will be collected from the concerned persons. The identity of the person giving views will not be disclosed without the consent of the person.

Under this Platform ‘THEORY & PRACTICE (T&P)’ we shall endeavor to bring out the cases where Theory derived from relevant standard documents mismatches not only among their different applicable sources themselves but with the Practice actually being followed at site and in turn bring them to some logical conclusion.

No changes are ever made without raising issues among concerned intellectual people and by doing so we intend to bring out changes in due course of time for the betterment of entire system and in turn our Nation as a whole.

T&P-CASE-2021-01 (Highway Drainage)

Discrepancies in Number of Drainage Spouts to be provided on Structures and Disposal of Storm Water

Reference Standard Codes/Documents:-

IRC:SP:42-2014 (Guidelines on Road Drainage)

IRC:SP:50-2013 (Guidelines on Urban Drainage)

IRC:SP:84-2019 (Manual of Specifications and Standards for Four Laning of Highways)

IRC:SP:90-2010 (Manual for Grade Separators and Elevated Structures)

Standard Plans For Highway Bridges Plans Drawings (MOST) [Drawing No. SD/210]

1.1.1 Number of drainage spouts/spacing of drainage spouts

1.1.1 (i) Theory:- As per IRC:SP:84-2019 & IRC:SP:90-2010, typically water spouts are provided at the kerbs at the rate of 1 No. per 12 sqm of the surface in level portions and 1 No. per 15 sqm of the surface area on gradients. Which means that for a 2 lane structure (12m wide) drainage spout is to be provided at every 1 meter all along at-level length portion of the structure and at every 1.25 meter at sloping length portion of the structure.

1.1.1 (ii) Practice:- The general Practice in field, is to provide drainage spouts at the rate of 1 No. per 36 sqm (staggered) as per Standard Plans For Highway Bridges Plans Drawings (MOST) Drg. No. SD/210.

1.1.2 Disposal of Rain Water from Structure

1.1.2 (i) Theory:- As per IRC:SP:50-2013, the rain water on flyover, which has to be above road is drained through either down take pipes or pipes embedded in the piers into series of network of rainwater harvesting system of the area and overflow can then be directed to the drains.

As per IRC:SP:84-2019, drainage spouts be connected to horizontal and vertical pipe system such that the water from the structure does not fall on the road, does not stagnate over the road or at entry and exit points of grade separated structure and is discharged into the draining system of the area.

1.1.2 (ii) Practice:- Generally the Rain water from structure is taken down through down take pipes & left on the road surface as it is.

In RCC portion or stilted portion at level & sloping sometimes drainage pipes are taken down up to level of road (at grade) and sometimes drainage spout is not provided with down-take pipe and water falls freely on the service road from height of the structure.

The approximate cost of a single drainage spout with pipe is Rs 4000.

The cost of carrying out drainage work as per IRC:SP:84-2019 comes out to be approx. Rs 1 crore per structure which is rarely provided in field and water is allowed to flow on road.

Suggestions:-

1. The mismatch needs to be addressed.

2. The CPWD manual has certain guidelines regarding drainage spouts, which may be referred to in this regard .

3. Refer Manual on Storm Water Drainage Systems - 2019:-

https://drive.google.com/file/d/1Mr1wLglMIizq3PQxw0z2Q4ddVSZUJeny/view?usp=sharing

4. Design of Bridge Deck Drainage Document:- https://rosap.ntl.bts.gov/view/dot/745/dot_745_DS1.pdf?

5. Refer Deck Drainage Document:-

https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/maintenance/str/bi/reference-manual/chapter-10-deck-drainage.pdf?sfvrsn=f4f8a4d7_0

Comparison of IRC:SP:42-2014, IRC:SP:50-2013, IRC:SP:84-2019, IRC:SP:90-2010 & Standard Plans For Highway Bridges Plans Drawings (MOST):-

Detailed references of IRC:SP:42-2014, IRC:SP:50-2013, IRC:SP:84-2019, IRC:SP:90-2010 & Standard Plans For Highway Bridges Plans Drawings (MOST)

As per IRC:SP:50-2013

3.2.5 Bridge deck drainage

Bridge deck drainage will be relatively less efficient than road way drainage due to flatter cross slopes, gutters collect large amount of debris and drainage spouts are less hydraulically efficient and more easily clogged by silt and debris. Because of the difficulties in providing for and maintaining adequate deck draining systems, side drain flow from road ways shall be intercepted before it reaches the bridge. For similar reasons, zero gradients and sag vertical curves shall be avoided on bridges. Additionally, runoff from bridge decks shall be collected immediately through drainage sprouts with gratings after it flows into the subsequent pavement section where larger grates and inlet structures limiting to shy distance shall cater for effective end point drainage. Splashing of collected water on vehicles moving on the bridge will result in reduced visibility and cause accidents. Each pier shall have a drainage disposal pipe designed for the area of disposal for immediate discharge of rain water from bridge deck.

9 STORM WATER DRAINAGE OF SPECIAL LOCATIONS

The special locations in urban scenario for drainage will normally be:

9.1 Flyovers and bridges

9.2 Drainage at foot of flyovers

9.3 Vehicular subways

9.4 Rotaries

9.5 Retail outlets

9.6 Drains underneath the carriageway

9.7 Intersection

9.1 Drainage of Flyovers and Bridges

The entire rain water on the carriage way of flyover shall be drained though efficient piping network of rainwater of the area. Caution shall be exercised not to allow straight drop of water from flyover to road surface below, which results in disruption of traffic and damage to road pavement. The rain water on flyover, which has to be above road is drained through either down take pipes or pipes embedded in the piers into series of network of rainwater harvesting system of the area and overflow can then be directed to the drains. All such disposal systems shall blend well and aesthetically pleasing.

9.2 Drainage at Foot of Flyovers

The longitudinal gradient of ramp of flyovers is usually upto 3 percent or even more and the cross slope will be about 2 percent. The majority of rain water flows rapidly in longitudinal direction rather than cross slope resulting in very large quantity of water reaching the valley curve area where it meets ground level road. This junction shall be provided with finger plate drain across the pavement. The valley junction shall be engineered in such a way, that even below road pavement shall have downward longitudinal gradient towards valley junction, so that entire rain water from flyover can be efficiently discharged into the drain at the edge. Then it can be directed to nearby stormwater management facility and overflow can be directed to the main drain which will stop the water from flowing directly to the road.

9.3 Vehicular Subways

Drainage of vehicular subways shall be efficiently planned at its conception stage itself. Most preferable system of drainage shall be by gravity. Entire surface drain of subway shall be taken to a lowest level and a suitable grating provided across full width of road. A typical subway drainage is shown in Photo 9.3 (a) & Fig. 9.3 (b). The grating shall have a disposal chamber which will collect the stormwater and dispose it to the nearby stormwater management facility like detention, retention ponds or open ground and overflow can be directly connected to the main drain. The lead off drain shall be preferably pipe drains with manholes at a maximum spacing of 30 m. In case of larger subways, two inlets can be provided at both ends of

box-approach ramp junctions. The gratings shall be at least 1 0 m away from the deck to minimize ascending water during rains in the box portion.

As per IRC:SP:84-2019

6.8.2.2 Efficient drainage of the deck structure shall be ensured by providing a suitably designed drainage arrangement consisting of drainage spouts connected to horizontal and vertical pipe system such that the water from the structure does not fall on the road, does not stagnate over the road or at entry and exit points of grade separated structure and is discharged into the draining system of the area. Care must be taken that the pipes are taken down in such a way that they are aesthetically pleasing.

6.8.2.3 Typically water spouts are provided at the kerbs at the rate of 1 No. per 12 sqm of the surface in level portions and 1 No. per 15 sqm of the surface area on gradients. Water spouts are connected to runner pipe of suitable diameter (minimum 100 mm) on either side of roadway and taken down by downtake pipes at pier & abutment locations.

As per IRC:SP:42-2014

9.5 Bridge Drainage

Bridge drainage is important from two aspects, first is drainage and other is road safety. It is important to provide the effective drainage of runoff on bridges to avoid flooding of deck, which may leads to traffic safety hazards and can severely limit the life span of concrete deck. The uncontrolled flows of water, will lead to corrosion of concrete and steel surfaces below deck level.

Considering drainage aspect, it is enough if all the water that is precipitated on the bridge in design rainfall is drained away quickly without allowing the traffic to stop. Particularly if the bridge is located in a valley curve or in a valley on the road, the surface water from the adjoining stretches of road are likely to flow to it and cause ponding which may stop the traffic at least for a short duration

9.6 Design Consideration

The drainage system for bridges are design as Open Drainage system, i.e. allowing the free fall of water when bridges pass through the water way i.e. River, Creek, Nallah etc. and Closed drainage system in which proper channelized Pipe conduit system are provided to take the water to main drain applicable for Grade separator, side walk and rail road right of way beneath the bridges. Designer shall suitably select the appropriate drainage system

based on the project characteristics.

The design of a drain should be such that its inlet is large enough to admit lot of water easily. It is to be remembered that due to the grill on top, the effective area of inlet is reduced to half. Moreover, the velocity of water entering the drain is low. Hence the opening should be flared to at least twice the size of the pipe. The type design of the MORTH in which the opening at top is 30 cm X 30 cm for a 15 cm dia drain is good from this angle.

In case of wider bridges, the numbers of drainage spouts will have to be increased to match the increased area to be drained. In very wide bridges of 4x4 divided carriageways with a central divider, it may be better to provide a crown in each carriageway and camber in both direction and then to provide drainage spouts along both edges of each carriageway.

Deck Slab Drainage Inlet: To ensure effective drainage of the bridge deck a minimum cross slope of 1 percent and a minimum longitudinal grade of 0.5 percent should be provided with a gutter grading at 1 percent. The collected runoff water shall be taken by pipes through the deck at regular interval. Grating the inlet points are necessary aids for achieving the efficient drainage.

Drainage is especially important in the case of earth-filled arch spans and obligatory span as inadequate drainage would saturate the earth filling and decrease the load bearing capacity of the structure. Special drains will also be necessary at natural low spots of piers of arch bridges to tap accumulated water and allow it to flow out.

9.7 Sloping Ramps of Bridges and Flyovers

In case of sloping ramps of bridges or flyovers, it is often said that due to the steep longitudinal slope, it is no use providing drainage spouts on the ramps, which creates pool of water at the start of bridge approach. Considering the situation such as, a driver of a smaller car trying to go up an approach ramp of a flyover or bridge in heavy rains faces a daunting situation with a heavy stream of rainwater rushing towards him through which he has to drive his car. An example of this is shown in Photo 9.1. So whatever 10 or 20 percent water that can be taken out by drains on sides will be a big help.

In case of curved bridges (and roads too) due to super elevation, water tends to accumulate near the central median, forming a small pond. A fast vehicle coming round the bend suddenly sees the pond. Then either there will be a big splash or the vehicle will swerve suddenly to avoid the pond. These possibilities both create an accident situation. Cross drains provided at the valley curve covered with robust steel grating will help in disposing of surface water.

9.8 Spacing of Drainage Spout

In the olden days the standard practice was to provide drainage spouts at a spacing of 3 m on both edges of a two lane bridge. But the inlets were of the same diameter as the drain pipes.

Some of these used to get choked due to debris or garbage fully or partly. Sometimes during renewal of road surface, some of them used to get closed also. Design must cater to all such contingencies. The drain openings should be in the deck slab. In case of submersible bridges the discontinuous kerb provides ample drainage facilities.

In a segmental construction, it is easier to provide a drain hole in each segment instead of providing the drains at odd spacing which will result in some of the segments with drain holes and some without drains. Hence it is suggested to provide the drain hole in each segment.

9.9 Disposal of Drain Water

The water coming out of the spout can fall into the river or creek below. But the outlet should be shaped so that it does not fall on the superstructure. It could be pointed away from the bridge. There was a trend to provide long down take pipes to ensure that the water discharged does not splash on to sides of main beams. But when it is raining heavily the entire surroundings are wet and moist. Hence long down take pipes are not favoured.

In case of a flyover or approach viaduct of a bridge or flyover, if there is movement or existence of other traffic or people below on at grade roads, the water coming out of drainage spouts must be collected and led away. Such a collector system must be of large diameter, there must be enough elbow plugs provided to facilitate frequent cleaning to prevent clogging. The down take pipe if taken through the body of the solid pier (Plioto 9.2) must be large enough to avoid choking. Ultimately the water must be led to the city drainage system. Anti-theft measures must be in place to prevent vandalism or thefts of pipes. Small things but they can be very damaging if not corrected.

9.10 Maintenance of Drainage System

It is very important to maintain the drainage system in good working order. This mainly consists of looking at all the drainage inlets frequently to see that they are not choked or clogged. The elbow plugs must be opened and the pipes cleared of any material like paper, plastic etc. which might have got lodged in the pipes. Any piece of pipe which might have got damaged or taken away must be replaced forthwith. This aspect must be checked during the pre-monsoon inspection of bridge structures and corrected wherever necessary.

The cost of drainage spouts as compared to that of the bridge is minuscule. The public judges the work not by the strength of concrete but by the alignment of parapet, the condition of road surface, the expansion joints and the efficiency of drainage system. Hence it is not prudent to try to economize on it at the cost of a water free bridge.

As per IRC:SP:90-2010

14 DRAINAGE OF ROADWAY

14.1 Effective drainage shall be provided both longitudinally and transversely particularly in heavy rainfall areas. The transverse drainage shall be secured by means of suitable camber in the roadway surface. Longitudinal drainage shall be secured by means of scuppers, inlets, or other suitable means of sufficient size and numbers to drain the run-off efficiently.

14.2 Typically, water spouts are provided at the kerbs at the rate of 1 No. per 12 sqm of the surface in level portions and 1 No. per 15 sqm of the surface area on gradients. Water spouts are connected to runner pipe of suitable diameter (minimum 100 mm) on either side of roadway and taken down by downtake pipes at pier & abutment locations.

14.3 Drainage fixtures and downspouts, if provided, shall be of rigid, corrosion resistant material not less than 100 mm as the least dimension and shall be provided with suitable cleanout fixtures.

14.4 The arrangement of floor drains shall be such as to prevent the splashing discharge of drainage water against any portion of the structure. Overhanging portions of concrete floors shall be provided with drip moulds.

14.5 Catch water drains are necessary at the end of viaduct portion so that water coming from span does not over saturate and affect the earthen embankment. Similar catch water drains should be at the end of gradient so that water coming from flyover is properly let out to nearest drain.

14.6 An integrated drainage plan for the water coming from the deck of structures, local catchment area of the project and all other sources should be prepared so that no water falls on any surface of the structures, or remain standing or flowing over the level roads. All the water is collected through sumps and finally discharged into the local drainage systems i.e., storm water pipes etc either by gravity through connecting drains or by pumping into the existing outgoing drains.

14.7 The rainwater from the deck of the structures usually does not flow transversely but flows on the high gradient slopes of the road or approaches and is collected in the valley curve portion. As such attention is to be paid to get this large quantity of water drained out fast without accumulating there causing problems for traffic low resulting in traffic jams. The draining out systems should be designed with greater margins so as to avoid this problem, at least for grade separators inside the cities or inhabited areas.