Overview

Interchange design was a major consideration during the development of this criteria library. All standard slope criteria (including catchslope criteria) offer several features to aid in interchange design.

These features include the capability to fully implement shear point lines, the ability to resolve intersecting slopes between shape clusters or alignments, and gore areas.

The shearpoint feature is designed to coordinate shearing between alignment slopes when the individual alignment cross sections are segregated to individual cross section cells and/or different cross section files.

Demonstration:Assume an interchange where RampC and LoopC cross section cells are in file RPC.XSC, and the cross section cells of Service Road A are in file ServA.xsc. Also assume that the slopes between the ramp and the service road are to be sheared along a line element represented in a plan view DGN.

The problem facing the designer is how to easily compute the elevation along the shear line at which to tie the service road slopes - Since the elevation depends on where the ramp slopes were sheared, AND since the service road cross section lines rarely intersect the shear line at the same point as the ramp.

• In this example, the ramp/loop criteria is run first. The right side slope criteria of the ramp employs the shearpoint feature by variable definitions. The slopes are sheared to existing ground at the ShearPoint Line, and a text label is placed at the shearpoint.
• The engineer then uses the Geopak Profile Grade Report utility to generate the shearpoint chain/profile. By using the Search Text option and specifying the exact text used on the shearpoint label, a chain and profile can be stored along the ShearPoint line.
• The Service road criteria is run employing the shearpoint feature on the left side, and using the shearpoint chain/profile that was previously stored.

This methodology allows the ramp criteria run to store elevation information in the cross section file that can be used to generate a chain/profile. This chain/profile can then be used by the service road criteria to adjust slope values in order to shear the slopes at the exact elevation and offset.

The ShearPoint Line Element

The ShearPoint Line element is placed by the engineer in a plan view DGN file. It's location and the extent of it's use will be based on the judgement of the engineer. Typically, it is a good idea to initially run all interchange criteria without any special options and then plot slope stake lines. These preliminary slope stake lines can then be used as a guide in deciding where shearpoint lines are needed and their exact locations.

Once the shearpoint line elements are in place, some or all of the interchange criteria will need to re-run using the shearpoint features.

Running criteria on the "control" alignment.

The "control" alignment is the alignment that controls the profile of the shearpoint chain/profile. Therefore, the engineer must decide first which alignment will control ... because that alignment's criteria will need to be run first.

The criteria input will identify the ShearPoint line element via DEFINE_DGN statement and direct the criteria to use the shearpoint feature by defining variables as follows:

 DEFINE_DGN "SHEARPOINT LINE"\
     DGN = patterns.DGN\              
     type = line,line_string,curve,arc\
     lv = \
     co = \
     wt = 
DEFINE    "AD01( USE SHEARPOINT"     1
DEFINE    "AD01 SHEARPOINT NAME TEXT"    RPCLT

When the control alignment criteria run is complete, the shearline chain/profile is stored using the Geopak Profile Grade Report utility as illustrated below.

In the Store Text field, enter the text that was defined for the SHEARPOINT NAME TEXT. (shaded yellow in illustration). Enter the name of the chain and profile to be stored for the shearpoint line (shaded in blue).

The Geopak Profile Grade Report will search the cross section file for occurrences of the Store Text, and wherever found will add that shearpoint location to the chain/profile; station-offset and elevation.

Still using the above example; forcing the Service Rd criteria to tie slopes to the shearline chain/profile is simply a matter of defining the following variables for SIDE SLOPE LT.

DEFINE  "FD02 USE SHEARPOINT"               1
DEFINE  "FD02 USE SHEARPOINT PROFILE"       1
DEFINE  "FD02 SHEARPOINT PROFILE"           SP_RPC
DEFINE  "FD02 SHEARPOINT PROFILE CHAIN"     SP_RPC

• The shearline features of these criteria do not require that the criteria types match on left and right. I.E., you may use LDSS, FDSS, ADSS and CSLP without regard to what type was or will be used on the other alignment.
  
• Use of shearline features does not require the alignment cross sections be in separate cells or separate files. It only requires 2 separate runs, because the chain/profile must be stored in between runs.
  
• When using the shearline feature and the second alignment is outside the limits of the chain or profile, the slopes will be drawn normally according to the values of the defined variables.
  

The Resolve Intersecting Slopes feature is designed to determine whether or not there is an intersection between the side slopes of two alignments. If an intersection occurs, the criteria provides two options for resolving the intersection conflict.

Option 1: Both slopes are trimmed at the intersection point, as illustrated below. Notice that the trimmed portions of the slopes are still drawn in alternate colors and line styles. The intent here is to allow the engineer to see exactly where the default slopes would have fallen if not trimmed at intersection.

Option 2: Both slopes are sheared to the existing ground at the point of intersection. The purpose of this option is two-fold. It allows the engineer to separate the earthworks for the two alignments. It provides the option of storing the intersection point as a shearpoint, thereby making it possible to store a shearpoint chain/profile (see explanation above on shearpoint feature ).

DEFINE "FD01 RESOLVE INTERSECTING SLOPES"     1 (assumes FDSS used on left cluster)
DEFINE "LD01 RESOLVE INTERSECTING SLOPES"     1 (assumes LDSS used on right cluster)

To request the slope shear at the intersection, define the following variables.

"FD01 SHEAR AT SLOPE INTERSECT"         0
"FD01 SHEARPOINT NAME TEXT"	     RPCLT

The gore area is drawn as a straight line connection between the two clusters; finished and subgrade lines by including the file gore.cri. Because there are no defined variables used by gore.cri, there is only one version of the gore criteria: gore.cri

The gore criteria file must be called from the SIDE SLOPE LT statement of the cluster on the right side of the gore area.

Assume a section of gore area between mainline and rampC as illustrated below. The gore shown in red would have been drawn by input as follows:

CRITERIA FOR SHAPE CLUSTER
   SHAPE CLUSTER BASELINE = L
   SHAPE CLUSTER PROFILE = L
   SHAPE CLUSTER TIE = 10.5
 
SIDE SLOPE RT where (station >= 106+80) and (station <= 108+00)
include U:\tmplt01.cri    

CRITERIA FOR SHAPE CLUSTER
   SHAPE CLUSTER BASELINE = RPC
   SHAPE CLUSTER PROFILE = RPC
   SHAPE CLUSTER TIE = 0

SIDE SLOPE LT where (station >= 106+80) and (station <= 108+00)
include U:\tmplt01.cri
include U:\gore.cri