Review

Slip restoration

Job description

Landscape Retaining Walls (Below 1.5m)

Napier

The proposed remediation design is intended to remediate the slope to a more suitable angle and secure the soils to the face to reduce the risk of future surficial failures, encourage vegetation and protect against the effects of any future minor failures should they occur. The solution incorporates the use of either Mac Mat R3 or Duramat RF4 along with minor earthworks. The location of the indented area of coverage is indicated in Figure 5 (although we understand the proposed solution may be extended further across the slope). A Design Sketch is included in (Figure 6) and the assumed construction sequence and design details are detailed below. The construction sequence is anticipated to comprise:  Removal of the existing hedge,  Removal of any loose colluvium and stock piling of any competent rocks (under the direction of the design engineer),  Replacement of the rock with some small drainage gravel added to fill larger voids to an angle of approximately 40° (final angle to be confirmed by geotechnical engineer).  Trimming of the steeper portion of the slope back to the shallowest grade possible (ensuring the slope crest does not encroach within 0.8m of the site boundary as this distance is required for the Geo-Mat Trench and its minimum required offset from the slope crest). Any cutting back of the steeper upper slope must be confirmed with the engineer PRIOR to being undertaken.  Excavation of the trenches to install the Geo-Mat, the upper trench shall extend a minimum of 0.5m below ground or 0.2m into the top of the completely to highly weathered rock (whichever is deeper with the final depth to be confirmed by the engineer) the bottom trench shall extend to a minimum depth of 0.5m. - Note: You may want to consider using the upper trench as the footing for the new fence.  Installation of the Bidim A19 filter cloth (or approved equivalent) over the drainage rock / gravel along the base of the bottom trench then running up the back side of the retaining wall.  Topsoil (~100 – 150mm) placed over the Bidim A19 filter fabric. Cover with grass seed but do not plant vegetation yet.  Install the Geo-Mat (Mac Mat R or Duramat RF). The Geo-Mat shall be pinned to the base of the upper trench and then laid down the slope. Pinning using asymmetric steel 600mm / 100mm long legs (10mm 3 --- (Geofabrics - MacMat R Information Page) 4 --- / (Cirtex - Duraforce RF Information Page) Project Reference: --- Thompson Road, Napier Document ID: --- Professional Engineering Services -7- Project Reference: --- Thompson Road, Napier Document ID: --- minimum diameter) shall be undertaken at ~1.0m intervals in a staggered (triangular) pattern. The Mat shall also be pinned in the base of the lower trench. In areas of completely to highly weathered rock you may need to drill pilot holes slightly smally than the pin diameter to fully embed the pins. All other aspects of the installation shall be undertaken in accordance with the manufacturer’s installation guidelines.  The upper trench may be backfilled with well compacted residual soil or clean fill (only 100mm topsoil at surface), otherwise it may be backfilled with concrete as part of the fence foundations. This may however carry some risk of any movement of the reinforcement possibly causing some deflection of the fence in future.  The bottom trench shall be inspected by the geotechnical engineer to consider if there is adequate drainage behind the existing wall. If not, then a novacoil pipe shall be installed at the base of the trench out letting to a suitable location on site where it can drain from the site. This will likely require a small hole to be made in the retaining wall. The bottom trench shall be back filled with lightly compacted drainage aggregate such as AP20-40 with a low percentage of fines.  Vegetation may be added but only young plants are likely suitable as the root ball will need to fit through