Why Grade? Because the Best Can Do This?

Important Note: Notice the graceful transition from the building pad to the public walk in the right of way.

Extremely thoughtful & skilled work demonstrated in setting the building pad elevation.

1Tuesday, October 26, 2010

But Why Roads?

To get you from the grace & comfort of home here....

To Here

Road design is complicated technically and specialist road engineers and high end software are involved

LA’s work with Engineers in Corridor Planning & Scenic Byway Design

Generally LA’s design minor drives & and almost always in conjunction with a qualified engineer

Basic Geometry of a Simple Circular Curve

Two fundamental elements are the curve that connects two tangents

Tangents are straight lines

The radius of the Curve is the same radius as the radius of the circle that the Curve is a portion of

Curve RadiusTangent

Tangent

Types of Circular Curves: Reverse Curve

Reverse Curve: Two curves moving in opposite direction linked by a tangent

Note: The radii of the two curves need not be the same

The radius of any curve must meet the minimum dimension for the design speed of the road being designed

Tangent Linking Curves

Curve Radii for Design Speeds

Note, higher design speeds require larger minimum radii for safety

Your assignment is a simple two lane drive with an intentionally slow design speed

Types of Circular Curves: Compound Curves

Compound Curves: A single continuous flowing curve with two (or more) radii

Note how the Center of Curve (O) falls on the radius of the larger radius curve

Note that the difference in radii between the two curves should not be more than 50%

Nautilus

Growth in a compound curve the radii of which are in proportion to one another using the golden ratio

Types of Circular Curves: Broken Back Curves

Broken Back Curves: Two curves moving in the same direction separated generally by a short tangent

Can be awkward to maneuver through, breaks rhythm of movement. can present sight line problems, only for very slow speeds

Circular Curve Elements: Point of Curvature (PC)

The Point of Curvature (PC) is the point where the curve begins at the end of the entering tangent

Circular Curve Elements: Point of Tangency (PT)

The Point of Tangency (PT) is the point where the curve ends at the outgoing tangent

Note: Stationing is a standard means of horizontally locating critical points along the centerline of a road’s horizontal profile

We will use stationing for this assignment

Entering Tangent

Circular Curve Elements: Point of Intersection (PI)

The Point of Intersection (PI) is the point where the extension of the entering and exiting tangents intersect

Important Note: The tangent line between the PC & PI will always be the same length as the tangent line between the PI and the PT

Exiting Tangent

Radii Characteristics

Important Notes: Other than for Compound Curves, the dimension of the radius for any specific curve remains constant

The radius of a curve is described by a line perpendicular to the entering tangent and the outgoing tangent at the PC & PT respectively

The Center of Curve (0)

The Center of Curve (O) is the point created by the intersection of the radius lines extended down perpendicular from the tangents at the PC & PT.

You insert your compass point in O to ‘swing’ your radius

Tangents Entering & Leaving the Curve

For our assignment we will consider the first entering tangent the first tangent entering the first curve from the left of the sheet ~ Point A

Tangent Entering the curve

Tangent Leaving the curve

Included Angle (I)

The Included Angel I (I) is the angle created by the intersection of the extended tangents

Note: I also is equal to the angle described by the intersection of radii extended from the PC & PT

Straight Curb ~ No Gutter Pan

Typical Section of a Straight Curb w/o gutter pan.

Road surface abuts vertical face of the curb.

Poured in Place Concrete Curbs w/Gutter Pan

Note direction horizontal face of gutter pan slopes. This gutter pan slopes away from the curb

Gutter pan sloped either toward curb or away from curb depending on drainage needs. The lower gutter pan slopes to the curb

Which of these would we use for our road project & why?

Drain Inlet

Drain Inlets have only an outlet pipe. They have no inlet pipe.

Drain Inlets have no Sump below the outlet pipe

Note “Bumble Bee” Grate

Catch Basin (CB) Characteristics

Note Sump: Volume of space below pipes entering & leaving for debris & sediment to settle & Collect

Note Pipe entering & leaving.

Catch Basins have a pipe in & out

For our project, the outlet pipe shall have an invert@ the CB 2” lower than the invert of the pipe coming into the CB where it enters

Catch Basin Installation

Note Concrete Structure on Top of CB below with Iron Inlet secured in concrete

CB & Inlet installed prior to placement of road compacted aggregate sub-base and finish surface

CB Inlet must be precisely set to proper Rim Elevation as indicated on Grading & Drainage Plan

Culvert Basics

Invert Elevation (INV. IN, INV. OUT.) Invert refers to the Elevation of the Bottom of the Pipe

Culvert Basics

INV. EL @ CL of road must be 2’-3” above top of pipe directly below it to achieve a minimum of 2 FT of cover over the top of the pipe.

Culvert Basics

Note interaction of contours with head wall

Culvert Basics

Note drafting of head wall beyond in concept section

Note interaction of contours with head wall

Culvert Basics

Note location of Catch Basins or either side of road against the curb

Culvert Basics

Note longitudinal flow pattern of road

Culvert Basics

Note flow pattern resulting from cross slope from crown of road to face of curb

Culvert Basics

Note flow pattern resulting from cross slope from crown of road to face of curb

Note flow pattern from low point on road center line to the catch basins

Gentle Swale Flowing to Culvert w/Headwall

This Culvert Runs beneath the entry drive to this park

It likely connects with what appears to be a ‘natural’ vegetated swale on the other side of the road

Note the simple yet elegant curved headwall

Contract Document Plan & Section of Culvert Outlet

Note washed cobble at outlet to absorb energy of water flow at outlet to prevent erosion

Note reinforcing filter fabric beneath end of pipe and cobble to prevent erosion

• Note slope on pipe. Our culvert pipe shall have a minimum slope of 1% & maximum slope of 2%

Concept Alternate Outlet for Culvert

Prepared Soil & Root Zone for bio-physical treatment of pollutants in runoff

Reinforcing Stone inter-planted w/flowering plants

Scarify subsoil to promote infiltration

Concept Culvert Outlet Plan

Concept Plant of Culvert Outlet

Cobble 4” to 8” dia. to absorb energy of outflow and not get washed away

Head Wall & Larger Scale Culvert Pipe

Note Contours on Headwall

Note Contours on Side Slope of swale, 3:1 max, 4:1 a better maximum side slope

Note Swale Signature at bottom of swale

Note Culvert is beneath road & top of pipe has soil cover

Note Swale Signature at bottom of swale

Culvert Outlet w/No Reinforcement of Land Surface

This condition on a slope will eventually lead to accelerating erosion of the slope which will continue until actions arrest and repair the damage made

The Immediate Process ~ Stay Tuned for Step 2

Analyze existing conditions, vegetation, natural features, views, built structures, topography, high points, low points, water conveyance patterns etc.

Read & understand the structure of the existing land form. What does it suggest for a road alignment.

Rough out a free hand alignment with design speed criteria in mind for minimum radii

Begin to formalize horizontal curve layout geometry

Engage the iterative process and be willing to explore & change options

Draft the preferred option with the curb line, the shoulders and walk

Why Grade? Because the Best Can Do This? · Poured in Place Concrete Curbs w/Gutter Pan Note...

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