1-22276-01 site plan

Project No. 1-22276                                                                                                                     Page | 30
February, 2020
Ref: 1-22276, 2020-02-28, BR VER 2
Wessel Petroleum Pty Ltd – GEOTECHNICAL INVESTIGATION - Proposed Service Station Reconstruction, 52-54 Mary Street and Weyba Road,
Noosaville




TABLE 7                RETAINING WALL DESIGN PARAMETERS (Unfactored)
                                                              Long Term                Earth Pressure Coefficient(1)
                                     Bulk Density
            Material                                         Drained Shear                    Flat Top Slope                         Passive Kp
                                       (kN/m3)
                                                               Angle (o)                 Ka               Ko
SP/SM
- Loose(2)                                  18                       28                    0.36                   0.53                 2.76
- Medium Dense(3)                           19                       33                    0.29                   0.49                 3.39
- Dense/Very Dense                          20                       38                    0.24                   0.38                 4.20
Clays
- Firm(2)                                  16.5                      23                    0.43                   0.61                 2.33
- Stiff(3)                                  18                       25                    0.41                   0.58                 2.46
- Very Stiff                                19                       25                    0.41                   0.58                 2.46
- Hard                                      20                       25                    0.41                   0.58                 2.46
Gravel(4)                                  19.0                      35                    0.27                   0.43                 3.69
Notes:-
1. These values of earth pressure co-efficient ignore the effects of wall friction.
2. Also refers to uncontrolled fill for the material type.
3. Also refers to controlled fill for the material type.
4. Infers granular free draining material placed behind the retaining wall as a drainage layer.
5. If fill is compacted against the retaining wall, the actual earth pressure could exceed the vertical pressure, (ie. Ka
    >1.0).
6. These values do not account for a backslope.

Resisting forces to sliding and rotation are provided by the shear resistance at the concrete
footing/soil or rock interface and the passive soil resistance in front of the footing or shear key,
for which the following design parameters are presented:-

          i)      Base friction for walls without a key may be taken as tan (2/3 Ø). If the wall has a
                  shallow base key the shearing resistance may be based on tan Ø. Refer to Table 7
                  for shear angle.
         ii)      Soil density as in Table 7.
         iii)     The passive pressure coefficient Kp as in Table 7.
         iv)      Base bearing capacity as in Table 4.

               6.6.3   Resistance to Lateral Forces

Retaining walls can be designed to resist lateral pressure distribution in several ways ie.:-

              Passive resistance at the toe of the wall
              Passive resistance at the key of the wall
              Frictional resistance due to the weight of the wall
              Propping off existing structures

As the resistance can be affected by various parameters, Soil Surveys Engineering should be
contacted once a general wall geometry has been identified to provide further comment.

               6.6.4   Construction Considerations

With all retaining walls, it is essential that adequate drainage be provided behind the wall. Any
backfill placed behind the wall should be loose granular material. The backfill should not be
heavily compacted since research has shown that compaction can raise the earth pressure to
above the 'at rest' pressure.

The placement of a filter fabric between the retained soil and the drainage material (e.g.
granular backfill) for protection against silting of the drainage material is recommended. The



                                                                                                            SOIL SURVEYS