Derek Booth Consultancy t/a DBCON
Corner of Spa Road and Rotokawa Street
PO Box 1123
TAUPO 3351
Ph.: 0800 232266
www.dbcon.co.nz
Date: 31 January 2014
Our Job Ref: 140605
CAMBRIDGE PARK SUBDIVISION
Lot 202
3886 – 3910 CAMBRIDGE ROAD
CAMBRIDGE
REPORT ON SUBDIVISION EARTHWORKS AND
RECOMMENDATIONS FOR BUILDING DEVELOPEMENT
Lots 1 – 10
Prepared by:
James Dunning
____________________________
Engineering Technician
Peer Reviewed by:
Michael Richardson
____________________________
Chartered Professional Engineer
CPENG – 1005467
1.0
Background
The Cambridge Park Subdivision is the development of cultivated and/or pastoral land for
residential development. The subdivision is accessed off Cambridge Road via an existing
round a bout. The fully developed subdivision will consist of 210 residential lots. This report
covers Lot 202, consisting of 10 residential lots.
The land form upon which Lot 202 is located was generally fairly flat and so only minor
earthworks were undertaken during the construction of the subdivision.
2.0
Geological Description of the Land
Geologically, the landform on which the Cambridge Park residential development is located is
an old river terrace. The soils underlying the subdivision consist of the Hinuera Formation, ie
alluvial sediments (pumiceous sand, silt and gravel) which were deposited by the Waikato
River over thousands of years.
3.0
Subdivision Earthworks
In general terms, earthworks undertaken during the construction of the subdivision consisted
of minor cuts and fills to form a near level site for the lots.
In detail, the earthworks undertaken as part of construction of the subdivision development
consisted of the following:
Placement of controlled fill to a maximum depth of 1.4m but generally 0.2m to 0.8m on
all or parts of lots 1 to 10 (as shown in Appendix B) to infill shallow depressions to
create level lots.
Cuts to a maximum depth of 0.5m on all or parts of lots 2 to 10 (as shown in Appendix
B) to create level lots. The excavated material was used as the controlled fill in the low
lying areas noted above.
Excavations to form the road network and the trenches in which the, power, water, gas
and sewerage services are located.
All controlled filling undertaken by the developer was completed in accordance with NZS
4431:1989 "Earth Fill for Residential Development". All vegetation, topsoil and near surface
organic soils were removed from the areas to be filled prior to the controlled fill being placed.
4.0
Ground Conditions
Ground conditions across the Cambridge Park Subdivision were investigated during May
2014 by hand augered drill holes with accompanying Scala Penetrometer tests to a depth of
approximately 2.0m below ground level on each of the 10 lots. Logs of the materials
encountered in the drill holes and the soil strengths are attached in Appendix A.
Based on the auger hole results and our experience with similar sub soils in the area,
subsurface conditions on the lots in Lot 202 of Cambridge Park generally consist of 0.1m to
0.3m of dark brown silt (topsoil) overlying alternating layers of silt, sandy silt and gravelly
sands to a depth of at least 2.0m below ground level.
The soil densities are generally slightly loose near the surface and increasing with depth. As a
general rule, the near surface silt layers were looser than the underlying gravelly sand layers
as inferred from the Scala Penetrometer soil test data.
The soils strength tests on the lots indicate that the soils generally have sufficient density to
provide the required 300 kPa ultimate foundation bearing capacity for standard residential
development in accordance with NZS 3604:2011, but the depth to 300kPa (ultimate bearing
capacity) ground varied from a depth of 0.2m to 0.9m. Static groundwater level (the ground
water table) was not encountered to a depth of at least 2m below ground level at the date of
testing (May 2014).
5.0
Building Development Recommendations
Based on the results to date and subject to the recommendations in this report, the lots in
Cambridge Park Lot 202 Subdivision are considered suitable for residential development in
accordance with NZS 3604:2011 "Timber Framed Buildings': However, due to the near surface
soils being loose in some areas, excavations to remove the loose soils followed by the
placement of controlled fill will be required where the near surface soils are not able to
provide an ultimate foundation bearing pressure of 300 kPa.
To provide guidance on the soil strengths and foundation systems recommended for each lot
in Cambridge Park Lot 202, the following table has been prepared.
The foundation recommendations detailed in the attached table are based on the assumption
that the foundations for the proposed dwellings on each lot will be formed at a minimum
depth of 0.3m below current ground level. If basement type foundations are proposed (which
is very unlikely on this subdivision due to the near level topography), then additional soil
tests will need to be carried out to confirm that the required 300 kPa ultimate bearing
pressure is available at the underside of the basement foundations.
5.1
Cambridge Park Lot 202 Foundation Recommendations
The augered holes and Scala Penetrometer tests undertaken to date indicate that the soils on
lots 1 to 10 from a depth of approximately 0.9m below ground level are generally adequate
for 300 kPa ultimate bearing.
It is all possible that on some lots excavations to depths greater the values tabulated below
may be required under the load bearing footing lines to remove isolated soft pockets of soil.
The foundation system recommended for each lot is based on one soil test completed near the
centre of each lot. Whilst we believe these tests to provide a good representation of the soils
found on the lots, it may necessitate further soil testing being required prior to commencing
the foundation works for a proposed dwelling.
In addition, excavations to form the foundation sand pads that are undertaken in wet weather
may result in excavation depths exceeding the depths noted below if the silty and sandy
subgrade soils are softened by rainwater ponding on the sites.
Foundation Recommendations for Lot 202 Of Cambridge Park Subdivision
Depth to 300 kPa
Lot No. Ultimate bearing
capacity
1
0.3m
2
0.3m
3
0.3m
4
0.9m
5
0.3m
6
0.3m
7
0.3m
8
0.5m
9
0.7m
10
0.3m
Recommended Foundation System
NZS3604 foundations
NZS3604 foundations
NZS3604 foundations
NZS3604 foundations on compacted sand pad
NZS3604 foundations
NZS3604 foundations
NZS3604 foundations
NZS3604 foundations on compacted sand pad
NZS3604 foundations on compacted sand pad
NZS3604 foundations
Minimum Foundation
Excavation Depth Below
Finished Ground Level
0.3m
0.3m
0.3m
0.6m
0.3m
0.3m
0.3m
0.5m
0.6m
0.3m
Notes:
1. The foundation recommendations above have been specified assuming all topsoil and organic
2.
3.
material is removed. And these foundations are based on no further modification of the soils below
the topsoil depth as specified in right hand column.
Any foundation designs other than that specified above will be required to have a Chartered
Engineer confirm the design.
Any compacted backfilling of lots to achieve the desired finish floor level shall be compacted to a
minimum 300kPa Ultimate bearing pressure.
5.2
Cambridge Park Stage Lot 202 Storm water Recommendations
The hand augered percolation tests located approximately at the centre of each lot,
confirm that the gravelly sand sub soils are relatively free draining soils. Only lots 2 to
8 were able to be drilled to a depth suitable to carry out a percolation test.
The percolation tests completed at the test locations indicate that the soils are suitable
for the on-site disposal of storm water and percolation rates of between 310 mm/hr to
420 mm/hr were achieved.
Preliminary recommendations for soak holes on the property were determined based
on the following design parameters:
Depth to the ground water table exceeds 3m
Design soakage rate =310 mm/hr
For the house sites, the design storm event is a 10 year return period, 1 hour
duration
The assumed impermeable area on each lot (house, driveway etc.) has been
assumed to be 300 m2
Using the above parameters, we have calculated the following will be required:
For the lots, we would recommend a one 14m long x 1m wide x 2m deep soak
trench (soakage trench shape can be altered providing overall volume is
obtained)will be require to process the design 10 year storm.
Due to not being able to conduct a percolation test on every lot we would recommend a
percolation tests and design be carried out for each lot prior to construction on site.
For storm events exceeding the design 10 year period noted above, a designated
overland flow path will need to be provided to ensure that storm water can be safely
discharged to the street.
6.0
Conclusion
Based on the investigations undertaken to date and subject to the development
recommendations contained in this report, the land designated as the Cambridge Park
Subdivision (Lot 202) is considered suitable for residential development in accordance with
NZS 3604:2011. The following recommendations are given to guide building construction on
the lots, but additional detailed soils investigations on each lot are recommended prior to
designing the appropriate foundation system.
6.1
6.2
For lots 1 to 10 an ultimate foundation bearing pressure of 300 kPa is available
at a depth of between 0.3m and 0.7m below ground level. A standard concrete
slab (NZS3604) foundations supported on a sand pad can be used to support
the proposed houses on these lots.
Specific hand auger and Scala Penetrometer tests are recommended on all lots
prior to development to confirm the foundation recommendations provided
above are appropriate.
A Statement of Professional Opinion as to the Suitability of Land for Building Construction (i.e.
the NZS 4404:2004 Schedule 2A Certificate for the Cambridge Park Lot 202 Subdivision) is
attached.
7.0
Limitations
The recommendations and options contained in this report are based on data from the field
investigations described above. Inferences about the nature and continuity of ground
conditions away from test locations are considered reasonable, but cannot be guaranteed.
During development of the lots, a person competent to assess should examine ground
conditions exposed in foundation excavations and cuttings to confirm whether the conditions
are compatible with the assumptions made in this report. In all circumstances, if ground
conditions differ from those described in this report the matter should be referred to a
geotechnical engineer. This professional opinion does not remove the requirement for the
normal inspection and verification of foundation conditions for all buildings constructed on
the lots. This report has been prepared for the particular project described in the owner's
brief to us. No responsibility is accepted for the use of any part of this report in other contexts
or for any other purposes.
NZS 4404: 2010
SCHEDULE2A
STATEMENT OF PROFESSIONAL OPINION AS TO
SUITABILITY OF LAND FOR BUILDING CONSTRUCTION
Development Cambridge Park Subdivision Lot 202
Developer Cambridge Park Ltd
Location 3886 – 3910 Cambridge, Cambridge
I, Michael Richardson
(Full Name)
of DBCON, PO Box 1123, Taupo
Hereby confirm that:
1.0
2.0
3.0
I am a geo-professional as defined in clause 1.2.2 of NZS 4404:2010 and was retained by the developer as the geoprofessional on the above development.
The extent of my inspections during construction, and the results of all tests carried out are described in my geotechnical
completion report dated 11 June 2014.
In my professional opinion, not to be construed as a guarantee, I consider that (delete as appropriate):
a.
The earth fills shown on the attached Cambridge Environmental Plan No. 3707-2-02 have been placed in
compliance with the requirements of the Waipa District Council and my specification.
b.
The completed works give due regard to land slope and foundation stability considerations.
c.
The original ground not affected by filling is suitable for the erection thereon of buildings designed according to
NZS 3604 provided that:
i.
Those lots where the ultimate bearing pressure is less than 300 kPa can have the proposed houses
supported on either a stiffened floor slab (if a minimum of 225 kPa is available) or a Raft Style floor
slab (if a minimum of 150 kPa is available)
ii.
For the balance of the lots an ultimate foundation bearing pressure of 300 kPa is available at a depth of
0.3m below ground level. A standard concrete slab foundation supported on a sand pad can be used to
support the proposed houses on these lots.
iii.
Specific hand auger and Scala Penetrometer tests are recommended on all lots prior to development
to confirm the foundation recommendations provided above are appropriate
d.
The filled ground is suitable for the erection thereon of buildings designed according to NZS 3604 provided that:
i.
Those lots where the ultimate bearing pressure is less than 300 kPa can have the proposed houses
supported on either a stiffened floor slab (if a minimum of 225 kPa is available) or a Raft style floor slab
(if a minimum of 150 kPa is available)
ii.
For the balance of the lots an ultimate foundation bearing pressure of 300 kPa is available at a depth of
0.3m below ground level. A standard concrete slab foundation supported on a sand pad can be used to
support the proposed houses on these lots
iii.
Specific hand auger and Scala Penetrometer tests are recommended on all lots prior to development
to confirm the foundation recommendations provided above are appropriate
e.
The original ground not affected by filling and the filled ground are not subject to erosion, subsidence or slippage
in accordance with the provisions of section 106 of the Resource Management Act 1991 provided that:
i.
Those lots where the ultimate bearing pressure is less than 300 kPa can have the proposed houses
supported on either a stiffened floor slab (if a minimum of 225 kPa is available) or a Raft style floor slab
(if a minimum of 150 kPa is available).
ii.
For the balance of the lots an ultimate foundation bearing pressure of 300 kPa is available at a depth of
0.3m below ground level. A standard concrete slab foundation supported on a sand pad can be used to
support the proposed houses on these lots
iii.
Specific hand auger and Scala Penetrometer tests are recommended on all lots prior to development
to confirm the foundation recommendations provided above are appropriate
NOTE: The sub-clauses in clause 3 may be deleted or added to as appropriate.
4.0
5.0
This professional opinion is furnished to the TA and the developer for their purposes alone on the express condition that it
will not be relied upon by any other person and does not remove the necessity for the normal inspection of foundation
conditions at the time of erection of any dwelling.
This certificate shall be read in conjunction with my geotechnical report referred to in clause 2 above and shall not be
copied or reproduced except in conjunction with the full geotechnical completion report.
Signed……………………………………………………………..
Michael Richardson
Chartered Professional Engineer
CPEng 1005467
……………………………………………………………………..
(Name, title and professional qualifications)
Date……………………………………………11 June 2014
APPENDIX A
TEST RESULTS
Project
Job ref
Cambridge Park Subivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Scala
(blows/100mm)
revision
sheet no
jmd
1
Element
Date
Fax: 07 3782800
www.dbcon.co.nz
Depth
140605
Lot 1
May-14
Soil Description
Percolation Test
100
0
200
4
300
4
10
50
400
500
20
EOB
SANDY LOAM, light brown, some gravel, damp
15
20
UNABLE TO EXTRACT, gravel
30
TOPSOIL, some fine gravel
600
Time (min)
Drop (mm)
5
650
25
700
800
35
900
1000
40
45
1100
50
1200
55
1300
60
1400
1500
Soakage rate
(mm/hr) =
1600
0
1700
Average (last 6 results)
1800
1900
2000
0.00
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 Weather was overcast but warm
2 No Ground water was detected
3
4
5
mm/5mins
Project
Job ref
140605
Cambridge Park Subivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Fax: 07 3782800
www.dbcon.co.nz
Scala
Depth
(blows/100mm)
revision
sheet no
jmd
2
Element
Date
Lot 2
Soil Description
May-14
Sample / Temperature
100
0
Time (min)
200
4
5
505
300
6
10
145
400
11
15
80
500
13
20
65
600
25
55
700
30
50
800
35
40
900
40
35
1000
45
30
TOPSOIL, some fine gravel
SAND, coarse, light grey, some fine gravel, damp
1100
Drop (mm)
50
30
1200
55
25
1300
60
20
Soakage rate
(mm/hr) =
360
1400
1500
1600
UNABLE TO EXTRACT, gravel
1700
Average (last 6 results)
1800
1900
30.00
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 Weather was overcast but warm
2 No Ground water was detected
3
4
5
mm/5mins
Project
Job ref
Cambridge Park Subivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Fax: 07 3782800
www.dbcon.co.nz
Scala
Depth
(blows/100mm)
100
0
200
3
300
20
140605
revision
sheet no
jmd
3
Element
Date
May-14
Lot 3
Soil Description
TOPSOIL
Sample / Temperature
Time (min)
Drop (mm)
5
710
10
140
400
15
90
500
20
70
600
25
40
700
30
35
800
35
30
40
30
1000
45
25
1100
50
25
1200
55
25
1300
60
20
Soakage rate
(mm/hr) =
310
SAND, coarse, mottled light brown/light grey, some fine gravel, damp
900
1400
1500
UNABLE TO EXTRACT, gravel
1600
1700
Average (last 6 results)
1800
1900
25.83
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 Weather was overcast but warm
2 No Ground water was detected
3
4
5
mm/5mins
Project
Job ref
Cambridge Park Subivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Fax: 07 3782800
www.dbcon.co.nz
Scala
Depth
(blows/100mm)
140605
revision
sheet no
jmd
4
Element
Date
May-14
Lot 4
Soil Description
Sample / Temperature
100
0
Time (min)
Drop (mm)
200
4
5
410
300
6
10
95
400
4
15
80
500
5
20
60
600
3
25
55
700
3
30
50
TOPSOIL, some fine gravel
SILTY LOAM, light brown, some fine gravel
800
3
35
50
900
20
40
40
1000
45
35
1100
50
30
1200
55
30
60
25
Soakage rate
(mm/hr) =
420
SAND, coarse, mottled light brown/light grey, some fine gravel, damp
1300
1400
1500
1600
1700
UNABLE TO EXTRACT, gravel
1800
1900
Average (last 6 results)
35.00
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 Weather was overcast but warm
2 No Ground water was detected
3
4
5
mm/5mins
Project
Job ref
140605
Cambridge Park Subivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Fax: 07 3782800
www.dbcon.co.nz
Scala
Depth
(blows/100mm)
100
0
200
4
300
6
400
5
500
4
600
20
revision
sheet no
jmd
5
Element
Date
May-14
Lot 5
Soil Description
Sample / Temperature
Time (min)
TOPSOIL, some fine gravel
Drop (mm)
5
290
10
125
SILTY LOAM, light brown
15
95
SILTY LOAM, light brown, some fine gravel
20
50
25
50
700
30
40
800
35
30
900
40
30
1000
45
30
SAND, light brown, some gravel, damp
1100
50
25
1200
55
25
1300
60
20
Soakage rate
(mm/hr) =
320
1400
1500
UNABLE TO EXTRACT, gravel
1600
1700
Average (last 6 results)
1800
1900
26.67
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 0
2 No Ground water was detected
3
4
5
mm/5mins
Project
Job ref
Cambridge Park Subivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Fax: 07 3782800
www.dbcon.co.nz
Scala
Depth
(blows/100mm)
100
0
200
4
300
4
400
20
140605
revision
sheet no
jmd
6
Element
Date
Lot 6
Soil Description
May-14
Sample / Temperature
Time (min)
TOPSOIL, some fine gravel
SANDY LOAM, light brown, some fine gravel
Drop (mm)
5
460
10
110
15
90
500
20
85
600
25
70
700
30
50
800
35
40
900
40
35
45
30
1100
50
30
1200
55
25
1300
60
25
Soakage rate
(mm/hr) =
370
SAND, light brown, some gravel, damp
1000
1400
UNABLE TO EXTRACT, gravel
1500
1600
1700
Average (last 6 results)
1800
1900
30.83
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 0
2 No Ground water was detected
3
4
5
mm/5mins
Project
Job ref
Cambridge Park Subivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Fax: 07 3782800
www.dbcon.co.nz
Scala
Depth
(blows/100mm)
100
0
200
5
300
8
400
20
140605
revision
sheet no
jmd
7
Element
Date
May-14
Lot 7
Soil Description
Sample / Temperature
Time (min)
TOPSOIL, some fine gravel
SANDY LOAM, light brown, some fine gravel
Drop (mm)
5
500
10
120
15
75
500
20
60
600
25
50
700
30
40
800
35
40
900
40
35
45
30
1100
50
30
1200
55
25
1300
60
20
Soakage rate
(mm/hr) =
360
SAND, light brown, some gravel, damp
1000
1400
1500
UNABLE TO EXTRACT, gravel
1600
1700
Average (last 6 results)
1800
1900
30.00
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 0
2 No Ground water was detected
3
4
5
mm/5mins
Project
Job ref
Cambridge Park Subdivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Scala
(blows/100mm)
revision
sheet no
jmd
8
Element
Date
Fax: 07 3782800
www.dbcon.co.nz
Depth
140605
Lot 8
May-14
Soil Description
Percolation Test
100
0
Time (min)
200
3
5
535
300
4
10
225
400
500
3
5
15
20
150
75
TOPSOIL, some fine gravel
Drop (mm)
600
7
25
50
700
14
30
40
800
20
35
40
40
45
35
30
1100
50
25
1200
55
20
60
20
Soakage rate
(mm/hr) =
340
900
1000
SAND, coarse, light grey, some gravel, damp
UNABLE TO EXTRACT, gravel
1300
1400
1500
1600
1700
Average (last 6 results)
1800
1900
2000
28.33
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 Weather was overcast but warm
2 No Ground water was detected
3
4
5
mm/5mins
Project
Job ref
140605
Cambridge Park Subdivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Fax: 07 3782800
www.dbcon.co.nz
Scala
Depth
(blows/100mm)
revision
sheet no
jmd
9
Element
Date
Lot 9
Soil Description
May-14
Sample / Temperature
100
0
TOPSOIL
Time (min)
200
4
SILTY LOAM, light brown
5
755
300
2
10
115
400
1
15
40
500
2
20
40
600
1
25
35
700
8
800
20
SILTY LOAM, light brown, some fine gravel
SAND, coarse, light grey, some fine gravel, damp
900
Drop (mm)
30
35
40
1000
UNABLE TO EXTRACT, gravel
45
1100
50
1200
55
1300
60
1400
1500
Soakage rate
(mm/hr) =
1600
0
1700
Average (last 6 results)
1800
1900
0.00
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 Weather was overcast but warm
2 No Ground water was detected
3
4
5
mm/5mins
Project
Job ref
Cambridge Park Subdivision
Drawing ref
calculations by
P.O Box 1123, Taupo
Phone: 07 3785067
Fax: 07 3782800
www.dbcon.co.nz
Scala
Depth
(blows/100mm)
100
0
200
5
300
6
400
8
500
20
600
sheet no
10
Element
Date
May-14
Lot 10
Soil Description
TOPSOIL
SANDY LOAM, mottled light brown/light grey, some fine gravel
Sample / Temperature
Time (min)
Drop (mm)
5
605
10
105
15
80
20
UNABLE TO EXTRACT, gravel
800
revision
jmd
SILTY LOAM, light brown, some fine gravel
700
140605
25
30
35
900
40
1000
45
1100
50
1200
55
1300
60
1400
1500
Soakage rate
(mm/hr) =
1600
0
1700
Average (last 6 results)
1800
1900
0.00
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
Notes:
1 Weather was overcast but warm
2 No Ground water was detected
3
4
5
mm/5mins
Soil Investigation Results
25
20
Test Location 1
Test Location 2
Blows per 100mm
15
Test Location 3
Test Location 4
Test Location 5
Test Location 6
10
Test Location 7
300 kPa
150 kPa
5
0
100
300
500
700
900
1100
1300
1500
1700
1900
Depth (mm)
2100
2300
2500
2700
2900
Soil Investigation Results
25
20
Test Location 8
Blows per 100mm
15
Test Location 9
Test Location 10
10
300 kPa
150 kPa
5
0
100
300
500
700
900
1100
1300
1500
1700
1900
Depth (mm)
2100
2300
2500
2700
2900
APPENDIX B
PLANS