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CHAPTER 6: DRAINAGE AND SLOPE PROTECTION

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florante valdez

on 25 November 2015

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Transcript of CHAPTER 6: DRAINAGE AND SLOPE PROTECTION

6-1 DRAINAGE
- is defined as the means of collecting, transporting and disposing of surface water originating in or near the right of way, or flowing in stream crossings or bordering the right of way.
END
CHAPTER 6:
DRAINAGE AND SLOPE PROTECTION
Surface drainage problems follow two basic considerations:
1. Hydraulic Design

2. Erosion Control

6-2 HYDROLOGY
- is branch of physical geography that deals with water of the earth.
The branch of hydrology that concern highway engineers is
PRECIPITATION.
Relationship and Effect of Hydraulic and Construction:
1. Usually, highway construction disrupt existing natural drainage pattern.
2. Construction operations may disturb the ground cover, and loosen the soil creating muddy stream as a result of erosion.
3. Erosions create debris that are carried downstream, and deposited at points where the velocity slackens.
4. Any changes in the land use may alter the historical run-off or un-gauged rural water shed.

Cardinal Rules on Drainage Design

1. As much as possible, any existing drainage system patterns and soil cover should not be disturbed.
2. Necessary changes in the drainage patterns should not in any manner bring velocities that may create new erosion problems.

The term economy in drainage system, simply mean; finding the solution to a problem that is cheapest in the long run under the following conditions:
1. Determine the estimated initial investment cost.
2. Consider the maintenance cost or outlay.
3. Consider anticipated loss and damage for each solution.

6-3 DRAINAGE ECONOMIC CONSIDERATIONS

Rain water flows laterally or obliquely on the surface of the road pavement under the influence of the cross section slope or super elevation in the pavement and shoulders.
If the water flow is controlled, then, the shoulder is in danger of erosion. However, the shoulder will have minimal erosion damage if it is already covered or protected by turf or grass.
6-4 DRAINING THE HIGHWAY

On city street, rain waters are guided by the road slope to the gutters and along with them the curb and inlets designed to limit the spread of water over the traffic lanes.
DRAINING THE URBAN STREET


MATERIAL REQUIREMENTS:
1. Corrugated Metal Units
2.Joint mortar mixture should be one part Portland cement and two parts fine aggregate (gravel) plus hydrated lime equal to 10% of the cement by weight.
3. Frames, gratings, covers and ladders rungs, should be assembled before shipment and may be reassembled readily in the same position when installed.
6-5 MANHOLES, INLETS AND CATCH BASIN
CONSTRUCTION REQUIREMENTS
1. Masonry shall fit nearly and tightly around the type.
2. When grade adjustment or existing structure is specified, the frames, covers and gratings are removed and then reset to the specified elevation.
3. Upon completion, each structure should be cleaned of any accumulation of silts, debris, or foreign matters of any kind until final acceptance of the work.

6-5 MANHOLES, INLETS AND CATCH BASIN
The purpose in designing a channel is to determine the cross section of the canal that will accommodate water flow smoothly and cheapest to construct and maintain.

1. Side slope with a ratio of 2:1 or even flatter is most acceptable, except on rock or harder materials where channels are lined.
2. The design of crown ditches, gutters, stream channels, and culverts flowing partially or fully, are based on the principles of flow in an open canal.
6-6 CHANNEL
The condition to various channel problems rest on the following distinctions:

1. Water flowing down a mild slope in an open canal is
Sub-critical flow
– exists when the depth of water in the channel is greater than the critical depth.

2. Water flowing on steep slope is in
Super critical flow
– exists when then depth is less than the critical level.

6-6 CHANNEL
1. Culvert is loaded vertically by the wheel load of vehicles; the earth fill covering the culvert; and the horizontal passive or active earth pressure.
2. The stress calculation for pipe culverts is based on the assumptions regarding the methods of under pipe support, soil support at its sides and loading distribution over it.
3. Corrugated metal pipes are more flexible that could tolerate greater deformations.
6-7 CULVERT
4. Highway engineers rarely make structural design for pipes and culvert because of the difficulties and uncertainties involved.
5. For concrete, vitrified clay and cast iron pipe, what is specified is the strength or class of pipe to be used in each condition.
6. It is now the practice of relying much on the recommendations of various manufacturers who prepared all the design data and computations etc.
7. Highway agency has standard drawing of various culvert design appropriate for the more common heights and widths of openings, heights of fill, including skew angles.

6-7 CULVERT
In order to safeguard the culvert and to prevent subsequent settlement in the roadway surface, standard procedures for culvert installations are given special attention particularly the bedding (footing) and backfilling.
1. Culverts are installed in the original bed of stream with their slope and flow line conforming to the natural channel or canal.
2. In mountainous or rolling terrain, departure form channel alignment, either upstream or downstream, may divert the current flow tom one side of the channel.

INSTALLATION OF CULVERTS
3. Culverts on skewed channel are relatively longer and costly.
4. Inverted siphons should be avoided whenever the water carries sediments of debris.
5. Stagnant water trapped inside the culverts sag is highly objectionable that must be avoided.
6. Most culverts start upstream with headwalls and terminate downstream with end wall.
7. Hydraulically, the headwalls and end walls functions separately but both retain the embankment and protect it from washout.

INSTALLATION OF CULVERTS
8. In most cases, cut-off wall is extended to the level of expected scour.
9. The use of small pipe as end wall and sometimes headwall is being discouraged because they hydraulically inefficient as entrances.
10. The L type headwall concrete create serious accident hazard, thus, gutter inlet with grate cover is recommended.
11. A wing type wall is recommended for large culverts. The flared U and warped walls are used on special applications.


INSTALLATION OF CULVERTS
Conduits are laid on bedding or footing that conforms to the following standard specifications:

1. Conduit bedding is classified into Class A, B, and C.
2. In laying culvert pipes, the requirement of class C bedding is applied if no bedding class is specified.
3. Class A bedding shall consist of a continuous concrete cradle conforming to the plan details.
4. Class B bedding is extended to a depth not less than 30% of the vertical outside diameter of the conduit pipe.


CONDUITS
5. The minimum thickness of the bedding materials beneath the pipe is 10 centimeters composed of sand passing a 95 mm sieve but not more than 10% passes .075 mm sieve.
6. The layer of bedding material is arrange and shaped to fit in the conduit for at least 15% of its total height.
7. When a bell and spigot type is used, the recesses in the bottom trench are shaped to accommodate the bell.
8. Class C bedding should be extended to a depth not less than 10% of its total height.


CONDUITS
1. Installation of conduit pipes should start at the downstream end of the conduit line.
2. The lower segment of the conduit pipe should be in contrast with the shape throughout its full length.
3. The lower segment of the conduit pipe should be in contact with the shape throughout its full length.
4. The bell or groove ends of rigid conduits and outside circumferential laps of flexible conduits are placed with longitudinal laps or seams at the side.


LAYING THE CONDUIT PIPE
5. Paved or partially lined conduit pipes are laid with the longitudinal centreline of the paved segment coincides with the flow line of water.

6. Elliptical and elliptically reinforced conduits are placed with the major axis within 5 degrees of a vertical plan through the longitudinal axis of the conduit.



LAYING THE CONDUIT PIPE
Rigid conduit pipes are the bell and spigot type, tongue and groove, or other types that may be specified.
1. In joining conduit pipes, the ends are fully entered into the inner surface evenly flushed. Joints are connected by:
a. Portland cement mortar or grout
b. Rubber gaskets
c. Oakum and mortar or joint compound
d. Plastic sealing compound
e. A combination of these types or any other as may be specified.

JOINING THE CONDUIT PIPES
2. Joint mortar for concrete pipes consists of 1 part by volume of Portland cement and 2 arts of approved sand with water necessary to obtain a refined consistency.
3. Mortar joint is made with excess mortar to form a continuous bead around the outside joint of the pipe and smoothly finished on the side.
4. Rubber gaskets are installed to form a flexible watertight seal.
5. Flexible conduits are firmly joined by coupling bands.


JOINING THE CONDUIT PIPES
Backfilling follows after the laying installation of conduit pipes under the following specifications:

1. Materials for backfill should be fine, readily compacted soil or granular material selected from approved sources.

2. Backfill materials should be free from stones that would be retained on 50 mm sieve, nor chunks of highly plastic clay and other objectionable materials.


BACKFILLING
3. At least 95% of the granular backfill materials pass the 12.5 mm sieve and not less than 95% of it is retained on a 4.75 mm sieve.

4. Oversized materials if present should be removed.

5. On top of the trench, backfill materials are placed at or near optimum moisture content and compacted in layers not exceeding 15 cm. (compacted) on both sides up to 30 centimeters above the top of the conduit.



BACKFILLING
BACKFILLING
6. For that portion above the trench on each side of the conduit pipe, the width of backfill is equal to twice the diameter of the conduit or 3.50 meters whichever is smaller.

7. After being bedded and backfilled, all conduits are protected by cover fill 1.00 meter high, before any heavy equipment is permitted to cross during the construction of the roadway.




6-8 DESIGN OF UNDERDRAIN

Underdrain is categorized under item 501 of DPWH Standard Specifications, which provides that:

“This item shall consist of constructing underdrain, using pipes and granular filler material underdrain pipe outlets and blind drains using granular material in accordance with the specifications and in reasonably close conformity with the lines and grades shown on the plans or as established by the engineer.”

6-9 DEBRIS CONTROL


Flood waters usually carry objectionable objects like brushes, banana trunks, tree branches, etc. These floating debris clogs culverts entrances and raise the headwater elevation overflowing the road and damaging adjoining properties.


6-10 THE LEGAL ASPECT OF DRAINAGE


Flood waters usually carry objectionable objects like brushes, banana trunks, tree branches, etc. These floating debris clogs culverts entrances and raise the headwater elevation overflowing the road and damaging adjoining properties.

6-10 THE LEGAL ASPECT OF DRAINAGE

Highway agency is illegally responsible for any damage to private property affected by the changes it makes in natural drainage within the limit that water must flow.


6-10 THE LEGAL ASPECT OF DRAINAGE


Damage claim against the Department could be established if:
1. When as a result of the agency’s project, the flow of several streams or creeks were concentrated into a single channel that resulted to erosion, silting or flooding of private property.


6-10 THE LEGAL ASPECT OF DRAINAGE


2. When due to poor design or inadequate maintenance, water backed against highway or embankment resulted to inundation of land or property or caused injury or death.



6-10 THE LEGAL ASPECT OF DRAINAGE


3. Liability however, is limited to damages in direct consequences of the improvement.
4. Engineering decisions if based on an accepted practice do not provide for a course of action.
6-11 ROADWAY DESIGN AND CONSTRUCTION FOR UNUSUAL SOIL CONDITIONS


Problems usually encountered in the design and constructions of roadways are:

1. The stability of fill and slope
2. The drainage

6-11 ROADWAY DESIGN AND CONSTRUCTION FOR UNUSUAL SOIL CONDITIONS

3. Capillarity and frost heave
6-11 ROADWAY DESIGN AND CONSTRUCTION FOR UNUSUAL SOIL CONDITIONS

4. Permafrost
6-11 ROADWAY DESIGN AND CONSTRUCTION FOR UNUSUAL SOIL CONDITIONS

5. Elasticity and rutting
6-12 STABILIZING THE UNSUPPORTED SLOPE
An existing earth slope that has been stable can experience significant movement called slope failure or landslide due to the following physical changes:

1. Changes in natural conditions
2. Changes induced by man

SLIDE
Slides refer to the occurrence where the moving mass is defined and separated from the underlying and adjacent earth by plane, comprising a number of adjacent planes where seepage results.
The seepage plane represents the continuous surface where the maximum shear strength of the earth material has been reached with the result that large displacement occurs.
SLIDE
SLIDE IS CLASSIFIED INTO FOUR:


1. Rotational slide – is associated with natural slopes and constructed embankment of homogenous materials possessing cohesion.
SLIDE IS CLASSIFIED INTO FOUR:

2. Translational slide – is associated with slope of layered materials where the mechanism of slippage occurs along a weak plane that possesses a downward dip and in cohesionless soil slopes where seepage occurs.
SLIDE IS CLASSIFIED INTO FOUR:


3. Block or wedge failure – refers to the displacement of an intact mass of soil due to the action of an adjacent zone of earth.
SLIDE IS CLASSIFIED INTO FOUR:
4. Flow and spread failure – is the most complex type of soil mass movement. Flow involves lateral movement of soil having a characteristic of viscous fluid, although the actual consistency of the moving mass may vary from very wet to dry..
6-13 IMPROVING THE STABILITY OF SLOPE
Slope areas that have experienced slides in the past should be considered likely to undergo further movement if loading condition changes.
6-13 RETAINING WALL
The practical use of gravity wall is controlled by height limitations. Thus, the required wall cross section increases significantly with tall heights due to the effect of the triangular soil pressure distributed behind the retaining wall.
EXCAVATION AND PLACING
The bed for riprap is excavated down the required depth properly compacted, trimmed and shaped. The riprap foundation is dug below the depth of scour. The toe trench is filled with stone of the same class as specified.
GROUTING
When grouted riprap is specified, stones are placed by hand or individually laid by machine. Spaces between stones are then filled with cement mortar sufficient enough to completely fill all the voids except the face surface of the stones left exposed.
1. Cement Grout is placed starting from the bottom to the top of the surface then swept with stiff broom. After grouting, the surface is cured like structural concrete for a period of at least 3 days after the installation.
2. Masonry stone is categorized under item 505 of the DPWH standard specifications. This item consists of stone masonry in minor structures, in headwalls for culverts and retaining walls at the toes of the slope.
MATERIAL REQUIREMENTS
1. The stone should be clean, hard and durable. Adobe stone shall not be used unless specified.

MATERIAL REQUIREMENTS
2. Stones shall have a thickness not less than 15 cm and width not less than 1 ½ times their respective width. Each stone shall be of good shape free of depressions and projections that might weaken or prevent it from being properly laid or bedded.
MATERIAL REQUIREMENTS
3. Stones are dressed to remove any thin or weak portions. Face stones are also dressed to provide bed and joint lines that do not vary more than 2 cm from the true lines and to ensure the meeting of bed and joint lines without the rounding of corners of the stone in excess of 3 centimetres in radius.
MATERIAL REQUIREMENTS
4. The bed surface of the face stone should be approximately normal to the face of the stones for about 8 cm and from this point may depart from a normal plane not to exceed 5 cm in 30 centimetres.
MATERIAL REQUIREMENTS
5. Face stones are pitched to line along the bed and joints. The minimum projection of rock faces beyond the pitch lines should not be more than 5 centimetres.
MORTAR REQUIREMENTS
1. Stone masonry mortar proportion is one part Portland cement and two parts cement by volume and sufficient water to make the mortar consistent to be handled easily and spread with a trowel.
MORTAR REQUIREMENTS
2. Mortar are mixed only in quantities required for immediate use. Mortar not used within 90 minutes after water has been added should be discarded.
MORTAR REQUIREMENTS
3. Re-tempering of mortar should not be allowed.
CONSTRUCTION REQUIREMENTS
1. The foundation bed where the masonry is to be placed should be firm and normal to the face of the wall. Large stones are used in the corners. Bunching of small stones of the same size should not be allowed.
CONSTRUCTION REQUIREMENTS
2. All stones should be cleaned and wetted before being set. The bed that will receive the stone should be cleaned and moistened before the mortar is spread.
CONSTRUCTION REQUIREMENTS
3. Stones are laid with their longest faces horizontal in full beds of mortar. Joints are flushed with mortar.
CONSTRUCTION REQUIREMENTS
4. Exposed face of individual stone should be parallel to the face of the wall in which the stones are set.
CONSTRUCTION REQUIREMENTS
5. Stones are handled carefully so as not to jar or displace the stones already set. Suitable equipment is required to set stones of larger size that cannot be handled by two men.
CONSTRUCTION REQUIREMENTS
6. The rolling or turning of stones on the walls should not be allowed. If the stone is loosened after the mortar has taken initial set, it should be removed, the mortar cleaned off and the stone re-laid with fresh concrete mortar.
BEADS AND JOINTS
1. Beads for face stones may vary from 2 cm to 5 cm in thickness. They should not extend in unbroken line through more than 5 stones.
BEADS AND JOINTS
2. Joints may vary from 2 to 5 centimetres in thickness. They should not extend in unbroken line through more than two stones. They may be at angle with the vertical from 0 degree to 45 degrees.
BEADS AND JOINTS
3. Face stone should bond to at least 15 cm longitudinally and 5 cm vertically. In no case should corners of four stones be adjacent to each other.
BEADS AND JOINTS
4. Cross beads for vertical face wall should be level, and for battered walls may vary from level to normal to the batter line of the face wall.
HEADERS
1. Headers should be distributed uniformly throughout the walls of the structures to form at least 1.5 of the exposed faces. It should extend from the front face of the wall intothe backing by 30 cm minimum.
HEADERS
2. When the wall thickness is 45 cm or less, the header should extend entirely from the front to the back face.
HEADERS
3. Backings are built chiefly of large stones. The individual stones of backing and hearting are well bonded with the face wall and with each other.
HEADERS
4. All openings and interstices in the backing are filled completely with cement mortar or with spall surrounded completely with mortar.
POINTING AND COPING
Cement mortar for joints on top of masonry surface are crowned slightly at the centre to provide drainage. If coping is required, it should be indicated in the plan.
POINTING AND COPING
Where coping is not required, the top of the wall is finished with stone wide enough to cover the top of the wall from 45 cm to 100 cm in length and of random heights of 15 cm. Stone is laid where the top course is an integral part of the wall.
POINTING AND COPING
The tops of the top course stone are pitched to line in both vertical and horizontal plane.
WEEPING HOLES
All walls and abutments should be provided with weep holes placed at the lowest point where free outlets for water can be obtained and spaced not more than 2 meters centre distance.
CLEANING AND CURING
Immediately after laying and while the mortar is still fresh, all face stones should be thoroughly cleaned of mortar stains and should be kept clean until the work is completed.
CLEANING AND CURING
If the weather is hot or dry, the masonry should be protected from the sun and kept wet for a period of at least 3 days after the completion.
ITEM 506: HAND LAID ROCK EMBANKMENT
MATERIAL REQUIREMENTS
Stones for laid rock embankment must be sound and durable furnished in a well balance range of sizes meeting the requirements as follows:
MATERIAL REQUIREMENTS
1. All stones should be more than 0.015 cubic meter in volume and not less than 75 percent of the total volume should consist of stones at 0.03 cubic meter in volume. Stones obtained from excavation performed under the contract may be used.
MATERIAL REQUIREMENTS
2. Adobe stone should not be used unless otherwise specified in the plan.
CONSTRUCTION REQUIREMENTS
1. Excavation shall be sufficient enough to expose the foundation bed. Stones are laid flat securely placed with their broken joint lined.
CONSTRUCTION REQUIREMENTS
2. The larger stone should be generally located in the lower portion of the structure and voids eliminated to possible extent.
CONSTRUCTION REQUIREMENTS
3. Spall smaller than the minimum stone size are used to check the larger stones solidly in portion to fill voids between the major stones laid in the embankment.
CONSTRUCTION REQUIREMENTS
4. The exposed face of the rock mass should be uniform without projections of more than 15 cm beyond the neat lines indicated on plans.
CONSTRUCTION REQUIREMENTS
5. Backfill adjacent to the hand laid rock embankment should be filled entirely with acceptable materials coming from the excavation items and compacted.
ITEM 5-7: SHEET PILES
This item consists of furnishing dividing and cutting off of sheet piling covered by the specifications.
MATERIAL REQUIREMENTS
1. TIMBER SHEET PILE may consist of any species that will satisfactorily stand driving. It is sawn or hewn with square corners free from worn holes, loose knots, wind shakes, decay or unsound portions or other defects that might impair its strength or tightness.
MATERIAL REQUIREMENTS
2. CONCRETE SHEET PILES. Concrete reinforcement and manufacture of concrete sheet piles should conform to the requirements of item 400 – Piling.
MATERIAL REQUIREMENTS
3. STEEL SHEET PILES should be of the type , weight and section modulus indicated on the plans or special provisions and conform to the requirements of item 400 – Piling.
ITEM 509: GABION
Gabion is a wire mesh supplied in various width and length that is in multiple of 2,3, or 4 times its width. The height is equal to 1.2 or 1.3 the horizontal width equal to 100 centimetres with a tolerance limit of 3%.
ITEM 509: GABION
The wire mesh is made of galvanized steel or plastic having a minimum size of 3.05 mm diameter. Its tensile strength should be in the range of 423.7 – 686 Mpa 60, 000 – 85, 000 psi.
ITEM 509: GABION
For galvanized wire mesh, the minimum zinc coating should be 22.7 grams per 0.0929 m2 (0.80 oz/sq. ft.) of uncoated wire surface as determined by tests conducted in accordance with AASHTO T-65.
CONSTRUCTION REQUIREMENTS
1. The wire mesh is twisted to form hexagonal opening of uniform sizes.
2. The mesh should be non-ravelling.
3. That the gabion sides, ends, lid and diaphragms can be assembled at the construction site into rectangular baskets of the specified sizes.
CONSTRUCTION REQUIREMENTS
4. That gabions could be divided equally by diaphragms of the same gauge as the body of the gabions into cells the length of which does not exceed the horizontal width.
CONSTRUCTION REQUIREMENTS
5. All perimeters of the edges of the mesh forming the gabion should be securely selvedge so that by tying the selvedge the joints should have at least the same strength as the body of the mesh.
CONSTRUCTION REQUIREMENTS
6. The tie and connection wire should be supplied in sufficient quantity to securely fasten all edges of the gabion and diaphragms.
6-15 HIGHWAY BRIDGES
Highway bridges are of two types:
1. Those that carry vehicular traffic and pedestrians over a large stream.
2. Those that separate traffic movements as interchanges and street pedestrians over or under crossings.

HYDRAULIC PROBLEMS
1. There must be available stream record that provides the usual method of estimating water discharges under the bridge.
HYDRAULIC PROBLEMS
2. Analysis of the channel relationship as to:
a. Peak Flow
b. Water way Opening
c. Water surface elevation at the structure and upstream and flow velocity.

HYDRAULIC PROBLEMS
3. The degree of contraction of the flowing water in the channel approach.

4. Final structure proportions and required channel modifications based on the studies.

HYDRAULIC PROBLEMS
5. Effect of bridge opening and approaches that might cause flood to adjacent properties. This is associated with hydraulic aspects of bridge design.
HYDRAULIC PROBLEMS
6. Economic, legal and social implications where cooperative planning with all affected groups and agencies is necessary.
HYDRAULIC PROBLEMS
7. Where the bridge is to rest on eroding streambed scouring is the primary concern. The problem of the designer is, if the design is over safe, it is over design, meaning the foundation becomes very costly.
HYDRAULIC PROBLEMS
But if scouring is underestimated, the foundation might be undermined which might result to total destruction of the entire bridge.
HYDRAULIC PROBLEMS
8. Recent findings showed that the latest scours is when the pier has less resistance to flow. Meaning, that the piers are aligned with the flow with the smallest cross section that is best where scouring is a problem.
HYDRAULIC PROBLEMS
Test results further show that, scouring increases with depth of flow and becomes a problem in streams with high ratio between flood and normal flow.
Highway bridges, designed to resist loads brought by:
1. The weight of the structure itself called dead load.

2. The weight and dynamic effect of moving load called “live load”.

3. The centrifugal forces developed by moving vehicles on curved structure.

4. The wind load and the stress brought about by:
a. Temperature change
b. Earth
c. Shrinkage
d. Buoyancy
e. Rib shortening
f. Erection
g. Current pressure
h. Earthquake

A bridge consist of substructure of abutments and piers that supports superstructures that carry the roadway between supports. The selection of the kind of bridge to be installed depends on the length of individual span as follows:
BRIDGE TYPES
1. Short span up to 18 meters

2. Bridge of large span

3. Span that exceeds 90 meters long steel trusses, arches of steel or reinforced concrete.


BRIDGE TYPES
BRIDGE TYPES

4. Span that exceed 150 are generally made of steel trusses, cabled-stayed or suspension bridge.
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