HomeMy WebLinkAboutMiscellaneous - Exception (473)Guidelines for the Design and Installation of Impervious Barriers
'impervious Barrier with Retaining Wall:
An impervious barrier, as an integral part of a retaining wall, is required when both the
horizontal distance between the edges of the two inch layer of washed peastone and the adjacent
side slope can not be met and the side slope is steeper than 3:1 (310 CMR 15. 255(2)) . The
criteria listed in this guidance for impervious barriers shall also apply to impervious barriers
using retaining walls.
The following conditions also apply to retaining walls used only for structural purposes:
1. Materials used shall be structurally sound, non -degradable and waterproof.
The structure shall have no weep holes when used as an impervious barrier.
2. It shall be designed by a Massachusetts Registered. Professional
Engineer, consistent with the provisions in 310 CMR 15.255(2)(b).
3. The horizontal distance from the edge of the SAS to the retaining wall shall
be measured from the SAS to the closest edge of the footing if a footing is used.
4. In accordance with 310 CMR 15.255(2)(d), a Massachusetts Registered
Professional Engineer shall design and inspect the installation and
construction of the impervious barrier using a retaining wall or a retaining
wall, and shall certify, in writing, that the structure has been constructed
according to the approved design. The written certification shall be submitted
to the approving authority prior to the issuance of the Certificate of
Compliance.
Slope w/out
retaining %
wall --
(steeper %
than 3:1)
15' minimum*
...........................................................
Top Elevation of SAS
Fill
Finished Grade
>>`
Soil Absorption System
% - ....... ..
. .. ..
. . . .'.'.'.'.' . . . . . . . . • . . • . . • • • • • • •
'
Naturally Occurring
% . . Pervious Material
.... ... .
% .. '
Finished.,.
.'.'.'.'..'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.. . . . . . .
Grade:::::;:::::::::::::;:::::::::::::::::::;:::::::;;::::;:::::::•::::;:.:
*impervious barrier necessary if less than 15'
Figure 2: Typical Retaining Wall without Impervious Barrier