Referenced Document - OPW20-0037

Mr Andrew Jensen                                                                                     20013-001-Rev0
                                                                                                     4 February 2020

4.2     Earthworks
No further cut or filling should be carried out on site unless reviewed by Tectonic.
Permanent batter slopes should be constructed at a maximum grade of 1V:2H in natural soil, fill and
weathered rock (may be steeper in rock subject to inspection and confirmation by Tectonic). Permanent soil
or fill batters will require erosion protection (e.g. revegetation or surface protection).

Steeper batters such as the embankment on the western side of the top of the driveway should be re-profiled
at 1V:2H, or alternatively should be retained by engineer designed retaining walls (ref. Section 4.3 below).


4.3     Retaining Structures
Retaining structures must be founded as described in Section 4.4 below. Retaining structures greater than
1 m high will require engineer design and certification of construction.

We suggest the following parameters may be adopted for retaining wall design:
 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)


 Gravelly Silty Clays      19           25                0.40                   0.57                2.46


 Weathered Rock            21           36                0.26                   0.41                3.85

 Fill                       *            *                 *                       *                   *
*Depends on type of fill used, and level/quality of compaction

These parameters do not include allowance for surcharge above the wall, or additional loads imposed by
sloping ground.



4.4     Footing Design
Footings should penetrate through any fill, and residual soils, to found a minimum of 300 mm into weathered
rock. Footings so founded may be designed using an allowable bearing capacity of 250 kPa. Where
weathered rock is exposed in the southern, cut side of the building pad it may be possible to use normally
dimensioned high level footings to achieve this. However, to penetrate through the deeper fill on the northern
side of the building pad deeper footings such as bored piers or similar will be required.

The above footing advice would also apply to future construction adjacent to the house (e.g. a swimming
pool).

All footings should found such that they are not adversely affected by any adjacent excavations, batter
slopes, trenches, or retaining walls that are not designed to support building loads. Footings should found at
least below a plane extending 1 m horizontally from the base of trenches/batter slopes/excavations/retaining
walls, then rising up at 1V:1H, as illustrated in Text Figure 11 overleaf.




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