# Stone Masonry Guardwall

+-----------------------------------------------------------------------+
| **Design and Construction Notes for Aesthetic Barriers**              |
+-----------------------------------------------------------------------+
| **Stone Masonry Guardwall (May 15, 2002)**                            |
|                                                                       |
| 1.  The stone masonry guardwall has been crash tested and meets the   |
|     requirements of NCHRP Report 350. This rough-faced barrier system |
|     is approved for design speed of 100 km/h or less. A smooth-faced  |
|     wall with smaller projections and shallower raked joints and beds |
|     is also approved.                                                 |
|                                                                       |
| 2.  The crash tested rough stone masonry guardwall used               |
|     specifications that defined the maximum projections up to 38 mm   |
|     beyond the neat line, 50 mm deep raked joints, and beds 50-75 mm  |
|     thick. Based on aesthetics and available stone, specifications    |
|     for the guardwall may be revised to specify any smoother stone    |
|     face, such as class A or B masonry. Stone faces with critical     |
|     dimensions greater than those listed above are not considered     |
|     crashworthy.                                                      |
|                                                                       |
| 3.  Numerous designs for the stone masonry guardwall and its          |
|     terminals have been reviewed and tested during the development of |
|     this system. One of the critical dimensions is the 500 mm between |
|     the ground line and the top of the corewall. Federal Lands        |
|     Highway Standard Drawings for berms, turn-down terminals, and     |
|     back-slope anchored terminals reflect the best compromise of      |
|     safety, aesthetics, and ease of construction. Prior designs are   |
|     not to be used. Due to the possible effect on the crashworthiness |
|     of the guardwall, any modifications to Federal Lands Highway      |
|     Standards for the stone masonry guardwall must be approved by the |
|     Federal Lands Highway Office.                                     |
|                                                                       |
| 4.  The grading in front of the guardwall and terminals must be at a  |
|     slope of 1:10 or flatter for the guardwall to be effective.       |
|                                                                       |
| 5.  The maximum dynamic deflection of the stone masonry guardwall is  |
|     0 m for design speeds of 100 km/h or less.                        |
|                                                                       |
| 6.  During construction, care should be taken to avoid large rock     |
|     projections oriented toward oncoming traffic. Such projections    |
|     have a tendency to snag a vehicle resulting in greater vehicle    |
|     and occupant injury. The recommended orientation for the          |
|     projections is away from oncoming traffic, so that the vehicle    |
|     can ride over the projections.                                    |
|                                                                       |
| 7.  The stone masonry guardwall can be used as a median barrier as    |
|     long as both sides of the guardwall have a vertical face.         |
|                                                                       |
| 8.  The Federal Highway Administration has approved the back-slope    |
|     anchored terminal based on other terminal tests. The Federal      |
|     Lands Highway Office has standard drawings designed specifically  |
|     for the stone masonry guardwall and my use drawings designed for  |
|     a berm Buried terminal (BT), a back-slope anchored terminal       |
|     (BAT), and a stand alone terminal (SAT) (turn-down), and may be   |
|     used:                                                             |
|                                                                       |
|     a.  The stone masonry guardwall terminal sections were designed   |
|         specifically for use with an earth berm in a median. The      |
|         steep 1:4.5 tapers on these terminal sections necessitate the |
|         use of a 600 mm earth berm. The sideslopes on the earth berm  |
|         should be 1:4 or flatter and the approach slope should be     |
|         1:20 or flatter. The approach slope for opposing traffic may  |
|         be steepened to a maximum of 1:6 if there is inadequate room  |
|         for the 1:20 slope. However, in no case should the 1:20       |
|         approach slope be steepened. The preferred design is to place |
|         the approach end of this configuration outside the clear      |
|         zone.                                                         |
|                                                                       |
|     b.  Where there is a back-slope to tie to, the preferred terminal |
|         is the back-slope anchored terminal (BAT). Special            |
|         consideration will be needed to maintain drainage, because    |
|         this terminal will not accommodate a drainage ditch.          |
|                                                                       |
|     c.  For roadside applications where there is adequate room, and   |
|         no back-slope to tie to, the preferred terminal is the buried |
|         terminal (BT) with an earth berm. Due to the steep 1:4.5 top  |
|         tapers, the earth berm must have a 600 mm earth berm          |
|         specified instead of the standard 450 mm berm. The terminal   |
|         section should be located outside the clear zone, but if this |
|         is impractical it should be flared as far from the roadway as |
|         possible. The earth berm should be oriented approximately     |
|         parallel to the roadway. It is intended that each berm will   |
|         be stacked to fit its particular location. For safety,        |
|         aesthetics, and maintenance considerations, it is desirable   |
|         to flatten the slopes of the berm as much as possible. A 1:3  |
|         sideslope on the berm facing the roadway is considered        |
|         minimally acceptable. It is also desirable to increase the    |
|         height of the berm, but the 1:20 approach slope must be       |
|         maintained..                                                  |
|                                                                       |
|     d.  Where it is not possible to construct an earth berm or tie to |
|         a backslope, the guardwall may be terminated using the SAT    |
|         (turned-down) without an earth berm. Crash tests on similar   |
|         turn-down designs have demonstrated the potential for this    |
|         type terminal to launch a vehicle or produce a rollover.      |
|         However, this terminal is superior to leaving the exposed     |
|         guardrail end that could snag or even penetrate a vehicle.    |
|         The widened shoulder area and guardrail flare aids is         |
|         providing stability for a vehicle riding up on the terminal.  |
|         Stone masonry terminals may only be used without an earth     |
|         berm if they are located outside the clear zone.              |
|                                                                       |
| 9.  The nature of the stone masonry guardwall provides that,          |
|     typically, no transition is required to bridge rails. Care should |
|     be exercised not to create possible snagging points were the      |
|     barrier connects to the bridge rail, even on trailing bridge rail |
|     ends.                                                             |
+-----------------------------------------------------------------------+