Retaining Wall Design

Retaining Wall Design

General Retaining Wall Design Custom DesignCrete, Inc in Crescent, PA Retaining wall design and wall type selection is driven by several factors. Vertical Stamping Photo Gallery Wall Textures These factors include: Cost Required wall height Ease and speed of construction Ground water conditions and soil characteristics. Other factors can include skilled labor and material availability, building codes, site accessibility, aesthetics, local building practice, etc. Ultimately, all retaining walls serve to hold back a vertical or near vertical face of soil that would, without adequate retention, cave, slump or slide to a more natural slope. In most states, retaining wall designs taller than about four feet must be designed by or approved by a qualified, licensed professional engineer. Additionally, it is important to check with and adhere to local building codes prior to any construction, even when walls are shorter than four feet. Retaining walls are, and should always be viewed as load bearing members first, and aesthetic groundscapes second. Designing any retaining wall requires a knowledge of lateral earth pressure. Once the lateral earth pressures are known, the wall is checked for stability. This includes checks for wall overturning, base sliding, and soil bearing capacity failures. After the wall is sized, each wall member is checked for adequate strength and steel reinforcing is determined. One of the most common and telling failures of retaining walls is the inevitable tilting, cracking and bowing of brick, timber and concrete block retaining walls built by homeowners, well meaning builders, and landscapers. These “problems” truly are failures, since the wall has not performed the task it was built to do, and that is to hold back the soil. The failures also clearly demonstrate the lack of knowledge or design that is required by a successful retaining wall design. By understanding how a wall works, and how it can fail, it is possible to engineer a retaining structure that will meet all foreseen environmental, structural and construction demands.
retaining wall design 1

Retaining Wall Design

8 Retaining Wall DesignsIf you’re looking to reshape the contours of a sloped property so you can have flat areas for patios and lawns, you’ll need a retaining wall. They may be landscaping workhorses, but retaining walls can be imaginative contributors to your curb appeal. Here are some great retaining wall designs.
retaining wall design 2

Retaining Wall Design

2 × Building It Right Building It Right Photo by Carolyn Bates Timber walls are only moderately challenging to build by yourself up to 4 feet high Poor drainage resulting in saturated soil and frost heaving is the main cause of failure. That’s why all good retaining walls begin with landscape fabric, backfill, and 4-inch perforated drainpipe. Digging details The depth you need to excavate depends on frost depth as well as the wall and soil type. Mortared or concrete walls in heavy-frost areas require footings dug below the frost line. Nonmortared walls should be built on a gravel-filled trench dug below frost line. If you live where it doesn’t freeze and your soil drains well, you may be able to just scrape away topsoil to form a base for nonmortared walls. Before adding gravel, lay down enough landscape fabric to contain the new gravel. Form the fabric into a large C shape, with the open mouth of the C facing downhill. The fabric should wrap around and create a border between the gravel and topsoil to keep sediment from clogging the gravel and drainpipe. Backfilling basics Replace native soil with 3/4-minus gravel (no stones under 3/4 inch in diameter) or “bank-run” gravel (washed stones 1/4 inch to 6 inches in diameter). Shovel at least a 4-inch layer of gravel onto the landscape fabric. Grade this layer so it slopes 1 inch for every 4 feet, allowing water to drain away. Then lay in 4-inch perforated PVC drainpipe at the base of the wall and cover it with gravel. Shovel in backfill as you build the wall, one tier at a time. Don’t add all the backfill at the end—it won’t compact thoroughly. Tamp down the gravel as you go with a heavy hand tamper. Behind the top tier of the wall add 6 inches of topsoil and lightly compact it. Battering and tiebacks All retaining walls should lean into the hill 1 inch for every 12 inches of height. Timber walls 4 feet or higher should be tied to the hillside with “deadmen” anchors (6-foot-long, T-shaped tiebacks buried in the hillside) attached to the wall every 8 feet, extending 6 feet back to a 2-foot-wide T-bar. Deadmen are not included in some interlocking-block systems if the design allows backfill to secure the blocks individually in place. Still others require geo-grid, weblike tiebacks that get buried in the backfill. Check the manufacturer’s literature. A final heads-up on masonry walls—concrete blocks chip and crack easily. Carefully inspect the blocks upon delivery, and don’t be shy about returning damaged blocks for credit.
retaining wall design 3

Retaining Wall Design

Building It Right Photo by Carolyn Bates Timber walls are only moderately challenging to build by yourself up to 4 feet high Poor drainage resulting in saturated soil and frost heaving is the main cause of failure. That’s why all good retaining walls begin with landscape fabric, backfill, and 4-inch perforated drainpipe. Digging details The depth you need to excavate depends on frost depth as well as the wall and soil type. Mortared or concrete walls in heavy-frost areas require footings dug below the frost line. Nonmortared walls should be built on a gravel-filled trench dug below frost line. If you live where it doesn’t freeze and your soil drains well, you may be able to just scrape away topsoil to form a base for nonmortared walls. Before adding gravel, lay down enough landscape fabric to contain the new gravel. Form the fabric into a large C shape, with the open mouth of the C facing downhill. The fabric should wrap around and create a border between the gravel and topsoil to keep sediment from clogging the gravel and drainpipe. Backfilling basics Replace native soil with 3/4-minus gravel (no stones under 3/4 inch in diameter) or “bank-run” gravel (washed stones 1/4 inch to 6 inches in diameter). Shovel at least a 4-inch layer of gravel onto the landscape fabric. Grade this layer so it slopes 1 inch for every 4 feet, allowing water to drain away. Then lay in 4-inch perforated PVC drainpipe at the base of the wall and cover it with gravel. Shovel in backfill as you build the wall, one tier at a time. Don’t add all the backfill at the end—it won’t compact thoroughly. Tamp down the gravel as you go with a heavy hand tamper. Behind the top tier of the wall add 6 inches of topsoil and lightly compact it. Battering and tiebacks All retaining walls should lean into the hill 1 inch for every 12 inches of height. Timber walls 4 feet or higher should be tied to the hillside with “deadmen” anchors (6-foot-long, T-shaped tiebacks buried in the hillside) attached to the wall every 8 feet, extending 6 feet back to a 2-foot-wide T-bar. Deadmen are not included in some interlocking-block systems if the design allows backfill to secure the blocks individually in place. Still others require geo-grid, weblike tiebacks that get buried in the backfill. Check the manufacturer’s literature. A final heads-up on masonry walls—concrete blocks chip and crack easily. Carefully inspect the blocks upon delivery, and don’t be shy about returning damaged blocks for credit.
retaining wall design 4

Retaining Wall Design

Poor drainage resulting in saturated soil and frost heaving is the main cause of failure. That’s why all good retaining walls begin with landscape fabric, backfill, and 4-inch perforated drainpipe. Digging details The depth you need to excavate depends on frost depth as well as the wall and soil type. Mortared or concrete walls in heavy-frost areas require footings dug below the frost line. Nonmortared walls should be built on a gravel-filled trench dug below frost line. If you live where it doesn’t freeze and your soil drains well, you may be able to just scrape away topsoil to form a base for nonmortared walls. Before adding gravel, lay down enough landscape fabric to contain the new gravel. Form the fabric into a large C shape, with the open mouth of the C facing downhill. The fabric should wrap around and create a border between the gravel and topsoil to keep sediment from clogging the gravel and drainpipe. Backfilling basics Replace native soil with 3/4-minus gravel (no stones under 3/4 inch in diameter) or “bank-run” gravel (washed stones 1/4 inch to 6 inches in diameter). Shovel at least a 4-inch layer of gravel onto the landscape fabric. Grade this layer so it slopes 1 inch for every 4 feet, allowing water to drain away. Then lay in 4-inch perforated PVC drainpipe at the base of the wall and cover it with gravel. Shovel in backfill as you build the wall, one tier at a time. Don’t add all the backfill at the end—it won’t compact thoroughly. Tamp down the gravel as you go with a heavy hand tamper. Behind the top tier of the wall add 6 inches of topsoil and lightly compact it. Battering and tiebacks All retaining walls should lean into the hill 1 inch for every 12 inches of height. Timber walls 4 feet or higher should be tied to the hillside with “deadmen” anchors (6-foot-long, T-shaped tiebacks buried in the hillside) attached to the wall every 8 feet, extending 6 feet back to a 2-foot-wide T-bar. Deadmen are not included in some interlocking-block systems if the design allows backfill to secure the blocks individually in place. Still others require geo-grid, weblike tiebacks that get buried in the backfill. Check the manufacturer’s literature. A final heads-up on masonry walls—concrete blocks chip and crack easily. Carefully inspect the blocks upon delivery, and don’t be shy about returning damaged blocks for credit.