Combined Approved Plans RAL21/0003

                Total Concept Homes                                                                             20332-001-Rev1
                                                                                                                 22 March 2021

                Table 3: Retaining Wall Design Parameters
                                                                                 Lateral earth pressure coefficients
                                          Unit       Friction
                  Retained material     weight        angle
                                                                           Ka                    Ko
                                        (kN/m3)     (Degrees)                                                          Kp
                                                                    (Cantilever wall)    (Non-yielding wall)


                  Stiff to Very Stiff
                                           18           26                0.39                  0.56                   2.56
                  Natural Clays


                  Weathered Phyllite
                                           21           35                0.27                  0.43                   3.69
                  Rock



                These parameters do not include allowance for surcharge above the wall, or additional loads imposed by
                sloping ground.
                Subsurface drainage must be installed behind any retaining walls in order to prevent the development of
                hydrostatic pressure (e.g. slotted ‘aggi’ pipe wrapped in filter ‘sock’ placed in gravel backfill).

                4.5     Drainage
                Adequate site drainage should be installed to ensure that stormwater runoff is directed away from the
                building walls and footings (e.g. swales in landscaped areas or grated drains across pavements up slope of
                structures including retaining walls for the driveway). Diversion drainage should be installed above the crest
                of all cut/fill batters, and toe of all cut batters. Uncontrolled flow of stormwater over embankment batters (e.g.
                from gutter overflow during high intensity storms, or if formal arrangements are not in place for the retaining
                wall on the neighbouring property to the south-west) has the potential to saturate and weaken the
                embankment materials, potentially leading to slumping failure. Future building and landscaping must be
                carried out to maintain good drainage.

                Subsurface drainage must be installed behind any retaining walls in order to prevent the development of
                hydrostatic pressure (e.g. slotted ‘aggi’ pipe wrapped in filter ‘sock’ placed in gravel backfill).

                All excess stormwater collected on site must be directed by pipes to the legal point of discharge, at least 5 m
                down slope from the proposed or existing structures. Surface dissipation, such as a rock weir or similar,
                must be installed at the stormwater outlet(s) to minimse the risk of soil erosion at the discharge point..
                Subsurface disposal of stormwater must not be undertaken.



                5.0       SUMMARY & CONCLUSIONS
                Based on the findings of our assessment we consider that there would be a Low Risk of slope instability
                impacting the proposed development. This advice is subject to implementation of the recommendations
                given in this report.




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Document Set ID: 21426326
Version: 1, Version Date: 24/03/2021