LondonBoulder Installation Overview
Escavation / Base Preparation
LondonBoulder recommends that wall elevations be set using a laser level and stakes prior to excavation. This will greatly enhance the efficiency and accuracy of the entire project.
Foundation soil shall be excavated to the lines and grades of the construction drawings and as required for base course installation. Use caution to ensure that the foundation is not disturbed beyond the indicated depths. As shown in Figure A, base trench shall be excavated to a minimum of 60“ wide and 6“ deep for the LB42 Units. Use compacted backfill material to fill over-excavated areas. It is permissible to use a layer of non-woven landscape fabric along the three sides of the trench to maintain a barrier between the surrounding foundation and the base material to be put down later.
Using granular, inorganic material such as crushed road base material, crushed stone, or recycled concrete, place the base leveling pad in the excavated trench such that it maintains a width of 60“ and a minimum depth of 6“ after compaction. Compaction should meet or exceed 95% Standard Proctor and should be achieved through the use of a mechanical plate compactor.
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Concrete may be substituted for the granular base material. Granular base material may also be top-dressed with a minimum 3“ thick layer of lean and unreinforced concrete. Reinforced footings must be placed below the frost line.
Final base must be uniform, level, and well compacted to provide the best possibility for a smooth, hassle-free wall installation. Achieving this standard in the base will also help to limit the number of future repairs that may be necessary due to sections of sagging wall and other base-related failures.
Level compacted base material from side to side and front to back.
A drainage pipe should be installed in all walls. The drainage collection pipe should daylight into a storm sewer manhole or to a sloped area lower than the pipes behind the walls. The main collection drainpipe just behind the block facing shall be a minimum of 4″ in diameter.
Setting the First Course
Always start the base course at the lowest elevation of the wall, if possible. In the case of a base elevation that varies, refer to Figure C. LondonBoulder recommends a two block overlap when stepping up from one course to the next.
Place the first course of LondonBoulders directly on the leveling base pad, check to ensure that they are properly aligned and leveled. The bottom surface of each unit should be in full contact with the base. If units have lugs, removing them may be preferred prior to placing as base course. Adjacent units should be in contact with one another at the front face if constructing a retaining wall, and along all inside edges if constructing a partition wall (this is accomplished by reversing every other trapezoidal unit inside the two end units).
Alignment of a straight wall may be best achieved by using a string line or laser level on the machined edge of the blocks. If building a convex or concave wall, it may be helpful to run a radius string from an established center point. See Figure B for minimum radius information.
Place perforated or slotted PVC or corrugated HDPE pipe behind the course providing the optimal drainage of LondonBoulder units. LondonBoulder recommends that the drain pipe be at least 4″ in diameter and surrounded by a minimum of 1 foot of drainage stone. In special situations where water and drainage play a bigger role in the design, “weep holes”, larger drainage stone, larger drain pipe with sock, and/or filter fabric behind the drainage stone may be warranted. Contact a P.E. for recommendations and details.
All drainage material in the drainfield and infill soils within 3 feet of the wall must be properly compacted. Use appropriate compaction equipment for the soils.
Compact in maximum 6" lifts – i.e. compaction should occur a minimum of 2 times with each course of LondonBoulder
Place drainage aggregate behind and up to the height of the LondonBoulder wall. Drainage aggregate shall be placed to a minimum thickness of 12" measured from the back of the LondonBoulder unit. Reference photo to the right.
If installing a retaining wall, it is likely that there will be triangular voids between each LondonBoulder that are caused by the trapezoidal shape of the units. (Note that this void will not be present if installing a partition wall). Fill this void with 3/4″ – 1 1/2″ crushed rock or as specified on your project.
Large rock and fat clay soils should generally be avoided as backfill material unless approved by a qualified engineer. In addition, soils that are excessively wet, dry, frozen, or inundated with debris should not be used.
If required, install geotextile filter fabric between the compacted backfill material and compacted infill soil.
If using geogrid reinforcement, be sure to avoid using compacting equipment directly on geogrid. Place the next 6″ lift of soil on top of the grid before compacting.
Installing Sucessive Courses
Ensure the drainage aggregate is level with, or slightly below the top of the LondonBoulder unit.
Clean all excess material from the top of the units as well as any debris that may have fallen into the channels that run parallel across the top of each LondonBoulder. Even a small stone can create unevenness or a wobble.
Place the next row of LondonBoulder units with the seams offset from the seams of the units below.
If installing a 6″ setback place the lugs to engage the back edge of the units below. 2″ and 0″ setback LondonBoulders are manufactured for the lugs to set into the channel of the unit below.
Set up a string line horizontally down the wall to ensure wall straightness. Adjust units as needed to form straight lines and smooth curves. Make sure to check each block to certify that it is level from front to back and side to side. Adjust if necessary. Qualified geogrid material can be used as a shim to make minor corrections in level.
Place drainage aggregate and infill soil as stated previously.
Repeat these steps until the wall reaches its final height.
* NOTE for partition walls:
If installing a partition wall, a definite pattern must be used. This requires that the installer adhere to a specific set of wall lengths as determined by full-unit increments. All partition walls should have a base course consisting of full and full-corner LondonBoulder units. The second course will consist of full units encased by a half-corner block on one end and a 2/3-corner block on the other. All subsequent rows will repeat the pattern created by the first two courses. Please contact your LondonBoulder salesperson with any questions.