20090528113051.pdfKA No. 092-09020
March 10, 2009
Page 2 of 4
Landscaping Walls
Landscaping walls, constructed with modular blocks, may be used to help reduce the amount of slope
areas exposed to erosion. 'Tile following recorruriendations are for walls 4 feet in height or less, with
level backslope conditions. A system of tiered walls, each tip to 4 feet in height is acceptable if the tipper
wall is located at least 4 feet behind tile lower wall. The same recommendations for drainage and
embedment apply to the upper wall. Walls greater than 4 1cct in height or with sloping bacicfill require
geogrid reinforcement and specialized design.
Modular block landscaping walls should be constructed with the following coils iderations:
0 Embedment of at least I foot into inedium dense or firmer, native soils
• Structural fill backfill placed and compacted onto level bench areas to at least 95 percent of the
modified proctor (ASTM D -I 557), in 8 inch thick loose lifts, (maximum)
• Drainage systems including clean, open graded crushed rock placed in the block cells and
extending at least 12 inches behind the back ofthe wall, extending to finish grade
• A 4 inch diameter performed pipe placed at the base of the drainage area behind the wall, sloped
to drain from behind the wall (toward the NW property corner or a storm system),
The area below the wall should be a level area. If sloping conditions exist, we should re-evaluate the
wall system and provide additional recommendations, if necessary. A leveling pad of clean angular rock
should be constructed below the base blocks to, provide a more level area for wall construction.
We recommend that the areas where walls are proposed be benched and terraced as necessary to provide
level areas oil which to place structural fill. We recommend that cuts made at the base of steep slope
areas, for the construction of landscaping walls, be limited to 2 feet in height. A generalized cross
section of typical grading is attached it) Figure 1.
For the purpose of drainage directly behind the wall, a well graded clean crushed rock with as particle size
of V2, to, of inches should be placed for a minimum horizontal distance of at least feet. A perforated 4 inch
diameter drainpipe should be: placed along the back portion of the wall, at its base, extending to an
appropriate Outlet. Runoff from these drains should not be allowed to flow directly onto steep slope
areas without velocity controls, such as rock pads,
The, finish grade following construction of landscaping walls should be level with the top of the wall,
These walls are not structurally designed, and therefore cannot take additional surcharges.
Structural Fill and Testing
All material proposed for use as Structural fill should consist of a non -expansive, non -deleterious,
granular material containing no more than 3 percent organics and the soil should be approved by the
geotechnical engineer prior to placement. The fill should be placed in horizontal lifts not exceeding 12
inches loose thicluiess, moisture conditioned as necessary and compacted to a minimum of 95 percent of
Krazan & Associates, [tic.
offices Serving The Western United SWICS
KA No. 092-09020
March 10, 2009
Page 3 of 4
the maximum dry density based on ASTM Test Method D1557. In place density tests should be
performed to verify suitable moisture contents andadequate compaction.
If fill is, placed during wet weather, we reconmiend the use of a free draining select structural fill.
Imported structural fill material should consist of well -graded gravel or a sand and gravel mixture with a
maximum grain size of 3 inches and less than 5 percent fines. If the proposed structural fill material
contains more than 10 percent fines, the geotechnical engineer should evaluate the fill material prior to
placement. All structural fill material should be submitted for approval to the geotechnical engineer at
least 48 hours prior to delivery to the site,
Drainage
A minimum 4 inch diameter perforated PVC pipe should be placed at the base of the wall or walls and
sloped to drain to the NW property comer This pipe May be place(]
below the bottom of the embedded block in order to intercept some of the shallow groundwater observed
in the area. The drain pipe should be backfilled with clean rock at least I inch in diameter.
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Specific recommendations for and design of storm, water disposal systems or septic disposal systems are
beyond the scope of our services and should be prepared by other consultants that are familiar with
design and discharge requirements. We can provide specific recommendations for groundwater/spring
seepage mitigation upon request.
Erosion and Sediinent Control
Erosion and sediment control (ESQ is used to minimize the transportation of sediment to wetlands,
streams, takes, drainage systems, and adjacent properties. Erosion and sediment control measures should
be taken and these measures should be in general accordance with local regulations. As a minimum, the
following basic recommendations should be incorporated into the design of the erosion and sediment
control features of the site:
Phase the soil, foundation, utility, and other work, requiring excavation or the disturbance of the
site soils, to take place during the dry season (generally May through September). Flowever,
provided precautions are taken using Best Management Practices (BMP's), grading activities call
be undertaken during the wet season (generally October tlu-ough April), but it should also be
known that this may increase the overall cost of the project,
2) All site work should be completed and stabilized as quickly as possible.
3) Additional perimeter erosion and sediment control features may be required to reduce the
possibility of sediment entering the surface water. This may include additional silt fences, silt
fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration
systems.
4) Any rLU10ff generated by dewatering discharge should be treated through construction of a
sediment trap if there is sufficient space. If space is limited other filtration methods will need to
be incorporated.
Krazan & Associates, Inc.
Offices Serving Thc Wcqtern United States