Appendix C: Monumentation
Anchor: #i1005341Overview
Introduction
Appendix C provides the TxDOT-approved methods of setting monuments in various soil conditions.
Each disk has an assigned DHT number and may be ordered from TxDOT warehouses. The use of various settings and disks is determined by the district survey coordinator. Each district may have specific markers to fit particular area needs. DHT numbers for statewide distribution of disks will be given only to the standard disks listed here or new configurations approved by SCOS.
The following marker disks are depicted:
- ROW markers
- Survey Control Points, horizontal/vertical stations
- Bench marks
- Property corners
- Denial of access markers.
Markers and Methods
ROW Marker
This bronze Right-of-Way marker has remained unchanged for many years. Only slight changes to the embossed face of this disk will be noticed. The marker is a 4 inch domed-top disk with an open area for a punch mark. Usually, it is set in a poured concrete post and previously referred to as a Type II monument.
EXAMPLE:
Figure C-1. ROW Marker. DHT #3247. Marker, Survey, Bronze 4'', ROW.
Control Point Marker
Example:
This aluminum dome-top disk is pre-punched for setting as project control points. The triangle symbol has traditionally been used for horizontal control but this type of monument may also have an elevation value as well. There is a configuration for setting in rock and concrete and a configuration for use as a rebar cap. With the plastic spacer removed, the rebar cap can be driven onto a ¾ inch aluminum datum point rod section if preferred. Both configurations come with an imbedded magnet for aid in location with a magnetic detector.
Configuration A: DHT #164946. Marker, Survey, Control point, 3 ½'' alum for rock and concrete
Configuration B: DHT #164949. Marker, Survey, Control point, 3 ¼'' alum rebar cap
Figure C-2. Control Point Markers.
Bench Mark
This aluminum dome-top disk is intended for permanent elevation stations. The engraved mark is a standard notation for bench marks. The rock and existing concrete configuration can be mounted on a vertical surface if necessary.
EXAMPLE:
Configuration A: DHT # 164948. Marker, Survey, Bench Mark, 3 ½'' alum for rock or concrete
Configuration B: DHT # 164947. Marker, Survey, Bench Mark, 3 ¼'' alum cap for 5/8'' rebar
Figure C-3. Bench Mark Markers.
Property Corner Marker
This smaller 2'' diameter disk is used to mark the intersection of existing property lines with new ROW. If it must be set in rock or concrete, several grooves should be filed into the sides to give it more gripping power.
EXAMPLE:
Figure C-4. Property Corner Marker. DHT # 164950. Marker, survey, property corner, 2'' alum cap for 5/8'' rebar.
Denial of Access Marker
This 2'' diameter disk is used to mark points on the ROW line indicating control of access when a bronze ROW marker does not fall at the point. The face is flat and open for stamping pertinent information such as “beginning,” “ending” or an arrow indicating direction of denied access. It is to be driven onto a piece of rebar of appropriate length – usually 18''.
EXAMPLE:
Figure C-5. Denial of Access Marker. DHT # 165012. Marker, survey, denial of access, 2'' alum for 5/8'' rebar.
Rock Setting
A disk can be bonded into a drill hole in bedrock for a very stable setting. A similar setting in a large concrete structure can be used but is more subject to movement over long periods of time. Culvert headwalls are convenient for bench marks but make poor locations for static GPS occupations.
A two-part epoxy or other high strength cement is recommended. The stem hole can be drilled with a power hammer drill or a star drill can be used. A recess should be chiseled for the head. As depicted below by the dashed lines on the stem, any of the disks with ferrules or flare legs can be used.
Stability: Rock settings are very stable when in bedrock (NGS stability code A if in bedrock, otherwise B, or C)
Uses: Bench marks, project and secondary control points, property corners, ROW markers
EXAMPLE:
Figure C-6. Rock Setting.
Datum Point Rod
This is a very stable and secure configuration and should be used whenever possible for major project control points and TxDOT levels 1 and 2 GPS positions. A power driver should be used to drive the rod sections to refusal. However, with proper protection of the rod end, the rod can be hammered into the ground manually. This is similar to an NGS Class A rod mark but lacks the grease sleeve.
Stability: Very good (NGS stability code B)
Uses: Bench marks and control points
EXAMPLE:
Figure C-7. Datum Point Rod Setting.
Poured Concrete Setting
A disk placed in a freshly poured concrete post as shown in the following sketches will provide a stable setting. It should be reinforced with either 1/2'' or 5/8'' rebar as shown. This is the setting of the old Type II monuments. It should be used where it is important to hold the position well. It is shown here with the ROW marker but can also be used for control points and bench marks.
Stability: Good (NGS stability code C)
Uses: ROW markers, bench marks and control points
EXAMPLE:
Figure C-8. Poured Concrete Setting, Top View (M-92).
Figure C-9. Poured Concrete Setting, Cross Section (M-92).
Light Duty Setting
A cap type disk can be driven onto a length of 5/8'' rebar and set in the ground. This is a more economical setting where setting a more stable monument is not justified. A hole at least 12'' in rocky soil or 18'' in loose soil should be dug before driving the rod. The rod should be driven to refusal when practical. A 3/4'' aluminum sectional rod may be used if it is not known how much resistance will be met. The hole shall be filled flush to the surface with concrete. Consult the district survey coordinator to determine what circumstances are appropriate for setting this type of monument.
Stability: Poor (NGS stability code D)
Uses: For secondary survey control
EXAMPLE:
Figure C-10. Light Duty Setting.