Idea Transcript
APPENDIX 7 GEOTECHNICAL INVESTIGATION (DOUGLAS PARTNERS)
Report on Geotechnical Investigation Proposed Residential Development Lot 3 and Lot 15597 Wilkins Street Bellevue, WA
Prepared for Morefield Holdings
Project 82426.01 March 2015
Table of Contents Page
1.
Introduction ................................................................................................................... 1
2.
Site Description ............................................................................................................ 2
3.
Field Work Methods ...................................................................................................... 2
4.
Field Work Results........................................................................................................ 3 4.1
Ground Conditions ............................................................................................... 3
4.2
Groundwater ........................................................................................................ 3
4.3
Permeability Testing ............................................................................................ 4
5.
Laboratory Testing ........................................................................................................ 4
6.
Proposed Development ................................................................................................ 5
7.
Comments .................................................................................................................... 6 7.1
Suitability of the Site for Development ................................................................. 6
7.2
Site Classification ................................................................................................ 6
7.3
Site Preparation ................................................................................................... 7
7.4
Design Parameters for Earth Retaining Systems ............................................... 11
7.5
Foundation Design ............................................................................................ 12
7.6
Pavement Design Parameters ........................................................................... 13
7.7
Soil Permeability ................................................................................................ 14
8.
References ................................................................................................................. 14
9.
Limitations .................................................................................................................. 14
Appendix A:
About this Report
Appendix B:
Drawings
Appendix C:
Results of Field Work
Appendix D:
Geotechnical Laboratory Testing
Report on Geotechnical Investigation Lot 3 and Lot 15597 Wilkins Street, Bellevue, WA
Project 82426.01 March 2015
Page 1 of 15
Report on Geotechnical Investigation Proposed Residential Development Lot 3 and Lot 15597 Wilkins Street, Bellevue, WA
1.
Introduction
This report presents the results of a geotechnical investigation undertaken by Douglas Partners Pty Ltd (DP) for a proposed residential development located at Lot 3 and Lot 15597 Wilkins Street in Bellevue, Western Australia. The investigation was commissioned on 21 January 2015, by Mr Burditt Krost of Strategic Planning Institute P/L, and was undertaken in accordance with DP’s proposal dated 18 December 2014. It is understood that the site will be redeveloped with townhouses up to two storeys in height, apartment buildings up to three storeys in height and associated access roads and car parking areas. It is also understood that the existing Bellevue Primary School Building at the north eastern corner of the site, will form part of the proposed development. The objective of the geotechnical investigation was to assess the soil and groundwater conditions underlying the site and subsequently provide comments and recommendations on: •
The suitability of the site for the proposed development;
•
A description of the sub-surface conditions;
•
The likely site classification in accordance with the requirements of AS 2870-2011, and earthworks requirements to achieve Class A and Class S, where required;
•
Likely thickness of sand filling to achieve a targeted site classification;
•
Suitable site preparation and earthworks. Site preparation and earthworks requirements, likely excavation conditions, compaction, recommended batter slopes and suitable materials for structural filling;
•
Appropriate foundation system(s) for the proposed structures;
•
Recommended pavement design parameters including California bearing ratios;
•
Assessment of the permeability of the soils and comment on the suitability of stormwater disposal; and
•
The depth to groundwater, if encountered.
The investigation included the excavation of seven test pits, two in situ permeability tests and laboratory testing on selected samples.
Report on Geotechnical Investigation Lot 3 and Lot 15597 Wilkins Street, Bellevue, WA
Project 82426.01 March 2015
Page 2 of 15
2.
Site Description
The site comprises a trapezoidal shaped area of approximately 1.6 ha and is identified as Lot 3 and Lot 15597 Wilkins Street in Bellevue, Western Australia. It is bounded by Clayton Street to the north, Wilkins Street to the south, Pascoe Street to the east and Roe Highway on ramp to the west. At the time of the investigation, the site was operating as a tree nursery, however it is understood from Strategic Planning Institute P/L that it previously comprised Bellevue Primary School, with several single storey buildings still present in the eastern part of the site. Several asphalt paved areas were also present between the school buildings, and rows of potted plants were present across the open parts of the site. The natural vegetation across the site comprised short grass and trees approximately 10 m in height, generally located around the site boundaries. A stockpile of waste building materials was observed at the south western corner of the site. The site surface was relatively flat, with site levels generally sloping from RL 16.5 m AHD at the north eastern corner, to RL 16.1 m AHD at south western corner the of the site. The Perth 1:50 000 Environmental Geology sheet indicates that shallow sub surface conditions at the site consist of pebbly silt of alluvial origin of the Guildford Formation, and is described as brown silt, with common fine to coarse grained, subrounded laterite quartz sand and heavily weathered granite pebbles. Published ASS risk mapping indicates that the site is generally mapped as “no known risk of acid sulphate soils occurring within 3 m of natural soil surface”. However, areas of “high to moderate risk of acid sulphate soils occurring within 3 m of natural soil surface”, are shown approximately 200 m to the northeast and 400 m to the northwest of the site. The Perth Groundwater Atlas (2004) indicates that the groundwater was at a level of between RL 8 m AHD and RL 9 m AHD in May 2003, which is at least 7 m below the lowest site level. The above information from the Perth Groundwater Atlas (2004) should be treated with caution at this site.
3.
Field Work Methods
Field work was carried out on 11 February 2015 and comprised the excavation of seven test pits, two in situ permeability tests and dynamic penetrometer testing adjacent to each test pit location. The test pits (TP76 to TP82) were excavated to a maximum depth of 3.0 m using an 8 tonne excavator equipped with a 600 mm wide toothed bucket and were logged in general accordance with AS1726-1993 by a suitably experienced geotechnical engineer from DP. Soil samples were recovered from selected locations for subsequent laboratory testing. The DCP tests were carried out adjacent to the test pit locations and in accordance with AS 1289.6.3.2, to assess the in situ density of the shallow soils. Two in situ permeability tests were carried out using the constant head method at TP81 and TP82 at depths of 1.0 m and 0.3 m, respectively.
Report on Geotechnical Investigation Lot 3 and Lot 15597 Wilkins Street, Bellevue, WA
Project 82426.01 March 2015
Page 3 of 15
Test locations were determined using GPS coordinates and are marked on Drawing 1 in Appendix B. The surface elevations at each test location were surveyed by Strategic Planning Institute P/L, and are quoted in m AHD.
4.
Field Work Results
4.1
Ground Conditions
Detailed logs of the ground conditions and results of the field testing are presented in Appendix C, together with notes defining descriptive terms and classification methods. Ground conditions generally comprise stiff to very stiff cohesive materials of the Guildford Formation to a maximum test termination depth of 3.0 m at TP78. Topsoil approximately 0.12 m in thickness was recorded overlying the above materials at TP82, where vegetation was present (i.e. no topsoil was recorded in hardstanding or filling areas). Filling materials were generally poorly to well compacted and observed to contain varying amounts clay, gravel, bricks, concrete, wire, glass, pipes and wood. This layer was recorded overlying the Guildford Formation, to depths of between 0.4 m at TP79 and more than 1.2 m at TP81. Poorly compacted filling materials were recorded at TP76, TP78 and TP81. The depths below existing surface level and relative level to the base of the filling materials, is summarised in Table 1. Table 1: Summary of Depth to the Base of Filling and Approximate Relative Levels Test Location
Ground Surface Level [1] (m AHD)
Depth to Base of Filling (m)
Level to Base of Filling [1] (m AHD)
TP76
16.50
0.50
16.00
TP77
16.20
0.70
15.50
TP78
16.40
0.60
15.80
TP79
16.20
0.40
15.80
TP80
16.10
0.60
15.50
TP81
16.10
Notes:
[2]
>1.2
[2]