Underground Systems: Hydraulic Design 1. Drainage Structures A.Sanitary Structures B.Storm Sewers C.Culverts 2. Manning Equation A.Nomograph B.Roughness

CONCRETE INDUSTRY MANAGEMENT TECHNOLOGY

Underground Systems: Hydraulic Design1. Drainage Structures

A. Sanitary StructuresB. Storm SewersC. Culverts

2. Manning Equation A. NomographB. Roughness Coefficient, n

3.Hydrological PrinciplesA. PrecipitationB. Runoff

1. Climatic2. Topographic

C. Rational Method

CONCRETE APPLICATIONS I

CIMT 210


1. Drainage Structures

A. Sanitary SewersThe pipes in a sanitary sewer system must be Strong and durable to resist the abrasive and Corrosive properties of the wastewater.

They must also be able to withstand stresses Caused by soil backfill material

Reinforced Concrete Pipe (RCP) are suitableFor larger sewer systems

RCP is available in diameters up to about 20 ft.(6m) and in lengths up to 25 ft. (8m)

RCP can suffer from crown corrosion due tohydrogen sulfide gas


A. Sanitary Sewers Manholes are located over the pipe centerline

under the following circumstances:

1. When there is a change in pipe diameter2. Change in pipe slope3. Change in direction of pipe4. At all intersections5. At intervals not exceeding 400 ft. (150 m)

Concrete Pipe

Septic Sewage

Crown Corrosion

H2S

Invert



A. Sanitary Sewer

Design

1. Slope of the sewer should follow the slope of the grade

2. Mannings Nomograph is used to determine the smallest standard pipe diameter that will carry the design flow.

3. For that diameter and slope, the velocity is checked.

4.Once the pipe diameter and slopes have been established , the invert elevations of the pipe can be determined and the proposed sewer can be drawn on the profile



A 120 –m reach of sewer is to be designedwith a flow capacity of 100 L/s. The streetelevation at the upper manhole is 90.00m andand at the lower manhole is 87.60 m,as shown. Determine an appropriate pipe diameter and slope for this reach, and establishthe pipe invert elevations at the upper and lowermanholes. Assume a minimum earth coverof 2m above the crown of the pipe.

Ground

1. Drainage StructuresA. Sanitary Sewer


1. WhitetoppingC. Advantages

Applicable where the depths of potholes are less than 50 mm (2 inches).

If rut or pothole depths are deeper, the potholesare filled or the surface is milled.

All three types of rigid pavement (JPCP, JRCPand CRCP) have been successfully used asClassical whitetopping (McGhee, 1994).

The chief advantage of classical whitetopping is that it requires minimal surface preparation

Minimum overlay thicknesses tend to be in the 125 - 175 mm (5 - 7 inch) range, which is quite thick and possibly unsuitable in situations where a specific elevation must be maintained such as in curbed areas or under bridges.


1. WhitetoppingD. Design

The design procedure contained in the 1993 AASHTO Guide is virtually identical to the AASHTO empirical design for new rigid pavements with one exception:

The effective modulus of subgrade reaction (k) is determined based on the existing flexible pavement resilent modulus.

Although perfectly acceptable, this methodgives little credit to the existing pavement's remaining strength.


1. WhitetoppingD. Design

The design procedure contained in the 1993 AASHTO Guide is virtually identical to the AASHTO empirical design for new rigid pavements with one exception:

The effective modulus of subgrade reaction (k) is determined based on the existing flexible pavement resilent modulus.

Although perfectly acceptable, this methodgives little credit to the existing pavement's remaining strength.


A. History

Ultra-Thin Whitetopping "UTW"Emerges

Term was needed to differentiate this new technology from classical whitetopping. Threefeatures differentiated the whitetopping of asphalt: (1.) The concrete overlay was substantially thinner (2.) Bond between the concrete overlay and the underlying asphalt created composite action. (3.) Short joint spacing significantly improved overlay performance.

2. Ultra-Thin Whitetopping


2. Ultra-Thin WhitetoppingA. History

“Ultra-thin whitetopping." requires bonding a relatively thin layer of concrete to the underlying asphalt

Over 200 ultra-thin whitetopping sections have been built, primarily on low-volume roadways.


2. Ultra-Thin WhitetoppingB. Bond and ThicknessThe concrete overlay and the underlying asphalt act as a composite section rather than two independent layers.

Significantly reduces the load-induced stresses The concrete overlay can be significantly thinner for the same loading as compared to a no bond to the underlying asphalt.


B. ThicknessUTW defined as: "A concrete overlay 50 mm to 100 mm thick with closely spaced joints bonded to an existing asphalt pavement."



2. Ultra-Thin WhitetoppingC. Joint Spacing

Joints are typically design much closer thanfor typical new-construction rigid pavement.The closer joint spacing, on the order of 1 - 4 m (3.3 - 13.1 ft.), does the following :

Reduces the moment arm of the appliedwheel load and minimizes the stresses due to bending.

Reduces the curling and warping stresses by reducing the size of the slab that can curl or warp.

Because of the short joint spacing, the overlaid PCC slabs transfer load to the underlying flexible pavement by deflecting downward as a unitrather than bending


2. Ultra-Thin WhitetoppingC. Joint Spacing

Figure : Shorter joint spacing reduces slab-bending. Wheel loads cause bending in concrete pavements with conventional joint spacing. In UTW, shorter joint spacing ca sues more transfer of wheel loads to the underlying asphalt through deflection.


D. Construction

Constructing UTW Overlays Proper construction of ultra-thin whitetopping consists of four fundamental steps:

1. Prepare the asphalt surface by milling and cleaning, or water or abrasive blasting.

2. Place, finish, texture, and cure using conventional techniques and materials.

3. Saw joints to prevent cracking.

4. Open to traffic. A clean surface is required for proper bond.



D. Construction

Milling the surface followed by cleaning improves bond because it exposes more of the aggregate of the asphalt pavement.

The milling creates a rough surface the alsoenhances the bond between the two layers.

If milling is not done, water or abrasive blastingshould be used to clean the asphalt surface.



D. Construction

When water blasting is used, the surface must be allowed to air dry before the concrete is placed.

Once a surface is cleaned it is important to keep it clean until the concrete overlay is placed. Dust, dirt and debris that falls or blows onto the asphalt surface must be removed.

If the surface is cleaned on the day prior to paving,air cleaning may be required on the day of pavingto remove dirt and dust.



D. Construction

If traffic is allowed on the milled surface, thesurface must be recleaned prior to paving.

Paving UTW is no different from paving anyother concrete pavement.

Conventional slip-form and fixed-form pavers, as well as small equipment - such as vibrating screeds –



D. Construction

Typical concrete finishing and texturing procedures are appropriate for ultra-thinwhitetopping.

Proper curing is critical to avoiding shrinkagecracking in the concrete overlay and to prevent debonding between the asphalt and concrete.



D. Construction

Because the overlay is a thin concrete slab,it has high surface area to volume ratio and can lose water rapidly due to evaporation.

Curing compound should be applied at twicethe normal rate.

Care must be used during application in order to avoid spraying curing compound on a prepared asphalt surface, which will decrease bonding.

Joints should be sawed with lightweight saws as early as possible to control cracking.



D. Construction

Saw-cut depth should be 1/4 - 1/3 of overlaythickness.

Typically, the joints are not sealed. They haveperformed well without sealant because theshort joint spacing minimizes joint movement.

Performance to date shows no benefit from sealant use.


Documents

Underground Systems: Hydraulic Design 1. Drainage Structures A.Sanitary Structures B.Storm Sewers C.Culverts 2. Manning Equation A.Nomograph B.Roughness