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Best Practices for Segmental Retaining Walls Best Practices


The intent of this material is to communicate the best practices for design of Segmental Retaining Walls (SRW) as determined by Allan Block Corporation based on 25 plus years of research, design and field experience. This is not meant to be a final authority as each project has its own set of unique situations.

The local engineer of record must use their best engineering judgment to account for those situations that present themselves and provide a safe and efficient design for the customer. At no time does the contractor or local building official have the authority to override the approved plans and specifications provided from the local engineer of record.

It is the recommendation of Allan Block Corporation that the local engineer of record work for and be paid by the project owner. It has been determined that the local engineer of record should be the Project Site Civil Engineer as they are best suited to take responsibility for the design, and how it affects the site, whether they do the design in-house or use an outside consultant to do the design for the project.

The Project Site Civil Engineer has control of several of the overall aspects of the project and therefore is most able to properly handle the integration and communication required to ensure the performance of the wall complies with the needs of the site. For wall design applications that are outside of the experience level of the Project Site Civil Engineer, a wall designer with the appropriate knowledge and experience should be contracted with by the Project Site Civil Engineer. It is recommended that the wall contractor not be responsible for securing the engineering.

last updated: 1/14/2022

Chapter 3: Typical Water Management

typical water management

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Click on the topics below to view more information on the best practices for Allan Block segmental retaining wall design for residental and commercial applications.

Design Guidelines Item: The term, "owner" refers to the property owner or their designated representative.

3.1    Identifying Potential Water Sources

3.1    Identify localized water sources such as storm drains and drop structures. Consult with Project Site Civil Engineer to ensure that water will not be introduced into the reinforced mass. Consider excess irrigation or natural groundwater sources.

  1. Utilize Water Management Section 3 in the Allan Block Spec Book.
    1. Surface drainage
      1. Must drain away from the top and bottom of the wall.
      2. water management site plan

        Figure 3-1: Surface Water Management

      3. Slopes above walls should have swales placed above so water is not allowed to flow over the top of the wall.
      4. During construction, Surface water must not be allowed to pond or be trapped in the area above the wall or at the toe of the wall. Surface water must be directed away from partially constructed walls at the end of each day’s construction.
      5. Provisions, such as check valves, to prevent flooding from broken lines or heads must be put in place to stop over irrigation above walls.
  2. Additional wall rock should be added around all storm drains and drop structures to aid in draining any areas of the pipe that may leak.
  3. If there are any utilities within the reinforcement zone, place gravel around them to generate good compaction levels.

3.2    Blanket and Chimney Drains

3.2   Use a combination of blanket and chimney drains.

  1. If site soils are used that do not have granular characteristics, a chimney and blanket drain should be considered to ensure the infill mass stays as dry as possible. Unless otherwise directed by the geotechnical engineer, a blanket and chimney drain should be used when infill soils have a less than 30 degree friction angle when determined without the use of cohesion.
  2. If migrating subsurface water is on the site a chimney and blanket drain should be used.
  3. See Allan Block Chimney and Blanket Drain detail.
  4. Drain material to be consistent with wall rock material. For more information on wall rock material see Chapter 2 Typical Wall Construction.
  5. Manufactured chimney and blanket drains to be approved by the geotechnical and/or the local engineer of record prior to use.

3.3    Venting of Drain Pipes

3.3    Location, type, and venting of drain pipes.

  1. Utilize Water Management Sections 1.4 and 1.5 in the Allan Block Spec Book.
  2. 10 cm perforated flexible drain pipe or rigid perforated pipes are recommended.
  3. When a rigid perforated pipe is used, it should be placed with holes down.
  4. All drain pipes must exit to daylight or be connected to an underground drainage system. Use Allan Block Alternate Drain detail for examples of venting to daylight.
    1. It is recommended that a minimum 1% gradient be maintained on the placement of the pipe with outlets on 15 m centers, or 30 m centers if the pipe is crowned between the outlets.
    2. It is recommended that all pipe outlets be configured to be protected from crushing or plugging from other means.
  5. For terraced applications, the toe and heel drains shall be routed as to not exit on the lower terraces. Drainpipes shall be extended to provide a path for water to be channeled away from the wall structure. Pipes at exit locations shall be marked to facilitate identification of where water is draining from.
  6. Drain pipes exiting to daylight through the wall should be installed with rodent screen to prevent nesting within the pipe. Cut adjoining block to allow for installation of a manufactured drain cover. Alternatively, Wall Drain Pro could be used without the requirement of cutting block. See more information here on Wall Drain Pro.

3.4    Above Grade Water Management

3.4    Above grade water management plan and finishing of the compacted soil mass.

  1. Surface water that cannot be diverted from the wall must be collected with surface drainage swales and drained laterally in order to disperse the water around the wall structure. Construction of a typical swale system shall be in accordance with Drawing No. 2.0. See also Chapter 12 for further discussion on above wall considerations.