Gravity Retaining Wall Unit Installation

Gravity (PMB) Precast Modular Blocks (PMB) or Segmental Retaining Wall (SRW) systems are structures that use the MagnumStone™ unit weight combined with crushed clear gravel infill to resist the earth pressures behind and on top of the retaining wall. With MagnumStone’s gravity retaining wall extender units fortifying the base of the structure, gravity walls can be built taller with gravity extenders anchoring the base courses in 2ft. (0.6m) and 4ft. (1.2m) increments.

The 1” (25.4mm) / unit 2.4 degree batter or setback of the MagnumStone™ wall along with proper soil conditions below and behind the wall provide an excellent structural stability.

For walls 3.0ft (0.9m) and taller, it is strongly recommended that a qualified engineer be consulted. Some counties may require permits.

STEP

Lay First MagnumStone Blocks of Base Course

Quick Steps

Remove the Screed Pipes from the leveling pad.
Place a steel stake at both ends of the leveling pad to establish where the back of the first course of units will be.
Tightly secure a string line to the stakes at either end, which will provide guidance to line up the back of each MagnumStone® base unit in a straight line.
The distance of the string line between the steel stakes may vary due to heavy winds.
The MagnumStone blocks should begin at a fixed point in the retaining wall. This includes the lowest point of elevation, a 90-degree corner or an abutment to another structure.
Lift and place each MagnumStone base block on top of the leveling pad in a way that does not disturb the level gravel.
Each block should be placed in direct contact with adjacent blocks, pressed as tightly together as possible to ensure there are no gaps between the blocks.
The back of each block should align as tight as possible to the string line located along the back panel of the block.
Measure each block to confirm it is completely level from front-to-back and side-to-side.

STEP

Installing Extender Units to MagnumStone Block

Quick Steps

Place the tongue of the extender block inside the groove of the MagnumStone Base Block.
If extender-to-extender blocks are required, install them following the same process and ensure the blocks stay level.

STEP

Complete Full Base Course Installation

Quick Steps

Place the next MagnumStone retaining wall block on the levelling pad and ensure they are level and aligned front-to-back and side-to-side.
Complete the first course of the gravity retaining wall and all extender units outlined in the approved engineering design.
Compact in front and behind the base course blocks prior to adding backfill or another course on top, this will prevent the blocks from shifting as added weight is placed on top, such as drainage gravel or additional rows of MagnumStone blocks.

STEP

Drain Pipe Options and Uses for Gravity Retaining Wall

Quick Steps

Face of Wall Drain

Heel Drain

Toe Drain

Face of Wall Drain

Heel Drain

Toe Drain

STEP

Backfill the Retaining Wall’s Base Course

Quick Steps

At the discretion of the project engineer, impermeable materials can be placed and compacted at the toe of the wall. If this is specified, the amount of impermeable material should reach the desired height of the perforated drainpipe.
Backfill the MagnumStone blocks and extender units with layers of clear crush gravel (#57 Stone) or equivalent slightly above the units. Run a plate vibratory compactor over each layer of stones, allowing them to settle into the hollow cores and securely surround the gravity extender units.
Sweep any excess stones off the top of the units and blocks before beginning to place the next course of retaining wall blocks.

STEP

Installing Soil Separation Fabrics

Quick Steps

Install a soil separating fabric (Filter Fabrics) to separate the fines and compacted backfill material from the drainage aggregate.
The filter fabric can be installed directly behind the MagnumStone extender units. They can also be installed directly on top of the drainage gravel.

STEP

Complete Second Course Installation

Quick Steps

Make a mark at the center of each MagnumStone block on the base row, this will serve as a guideline of where the end of the block above will be placed in a bond pattern.
Lay the next row on a running bond pattern with the SecureLugs Connected in the hollow core below. The SecureLug Connection provides a strong block-to-block connection and alignment throughout building your retaining wall.
Continue to place the MagnumStone blocks on top of the retaining wall blocks below.
Ensure they are level front to back and side to side. Small adjustments may need to be made during the construction process.
Soil separation fabrics can be added wherever the backfill meets the drainage gravel to keep fines from migrating into the drainage zone.

STEP

Approved Backfill and Compaction for Second Course

Quick Steps

Compact the approved backfill materials in between the excavation cut zone and the back of the retaining wall blocks.
Ensure that it compacted in lifts of no more that 8″ and also compacted to 95% Standard Proctor Density. It is crucial that these areas do not have loose fill where settlement can occur.

STEP

Continue Installation of MagnumStone Gravity Wall

Quick Steps

Continue the installation of MagnumStone big block gravity retaining wall as per the design provided. Cross section drawings will show you where the units are placed in order of depth.

STEP

Top Block and Finishing Gravity Retaining Wall

Quick Steps

Install the top MagnumStone retaining wall units like the rest of the wall.
MagnumStone top units are manufactured with the back panel 8″ lower than the front face panel.
The clear crush drain gravel and backfill materials will be placed flush to the top of the MagnumStone top block’s back panel. There are times when more than 8″ of topsoil may be required.
This is the location that the soil separation fabric will lay to protect the hollow core and drainage channel of the block.