§ 11.3.3. General Requirements

Retaining walls, regardless of type or height, must be designed by engineers licensed in the State of Texas, using current industry standards and accepted engineering practices. Retaining walls, regardless of type, must be constructed of materials meeting City of Austin Standards and Standard Specifications , where applicable, or ASTM or AASHTO materials and test specifications. Walls for which there are no published, nationally recognized, design criteria or for which there are no ASTM or AASHTO materials or test specifications will not be permitted.

Conditional or incomplete designs will not be accepted for city review. All aspects of design must be addressed and clearly conveyed in the drawings and specifications.

Tiered walls and back-to-back walls will be permitted only under special circumstances and only with the approval of the Director.

Retaining walls must be designed for external and internal stability. The design must include, as necessary, the effects of water or wastewater line breaks, the effects of inundation and rapid drawdown resulting from flooding or stormwater detention or retention, including hydrostatic pressures, internal erosion, and alteration of engineering characteristics and behavior of foundation and backfill materials. The walls must be designed to support, where applicable, surcharge loads from traffic or structures and lateral loads from nearby guardrail or street light footings. Wall design must consider scour at the base, where appropriate.

Walls consisting of pre-cast segmental units, whether these units are facing or structural elements, must have a coping or capstone at the top of the wall. The coping may be pre-cast or cast in place. The coping or capstone must extend above the adjacent ground at least 4 inches (100 millimeters). If cast in place, the coping must be reinforced and must have control and expansion joints to accommodate differential movements in the wall. Pre-cast coping and capstone must be affixed to the upper layer of segmental wall by using epoxy, non-shrink grout or other methods or material as recommended by the manufacturer, appropriate for the material and installation.

Walls constructed using flexible facing elements, such as welded or woven wire, will be permitted only in drainage channel applications not affecting or related to roadway embankment. Metal prefabricated modular walls will not be permitted.

Where retaining walls are used as the exterior walls in stormwater retention structures, the walls must be cast-in-place reinforced concrete made watertight by using water stops in joints and using underdrains behind the walls, as necessary. Where retaining walls are used as the exterior walls in stormwater detention structures and the walls are not watertight, then the walls must be designed to provide free drainage of the backfill following drawdown.