terra mdc limited - waitaki district...the site lies within an area where seismic shaking 4 from an...
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Page | 1
4 April 2016
Terra MDC Limited
1/326 Moray Place
Dunedin 9016
New Zealand
Ph/Fax: +64 (0) 3 477 0090
Mob: +64 (0) 220 737 480
E-mail: [email protected]
Web: www.TerraMDC.co.nz
For Attention: Mike Forgie Project Reference: 201603114
Waitaki District Council
c/o Forgie Hollows & Associates (Oamaru) Ltd
P O Box 32
Oamaru 9444
Dear Mike, RE: Geotechnical Assessment of Land for the proposed new
Cultural and Arts Facilities at 9 Thames Street Oamaru
This report has been prepared as a preliminary geotechnical assessment of the above property and
provides a summary of the likely ground conditions and a preliminary geotechnical hazard assessment.
It is understood that Waitaki District Council (WDC) wish to develop the existing building and the rear
car-parking area into a new Cultural and Arts Facility. This will involve a new three storey building to be
formed, which you have advised will cover most of the rear car-parking area (refer MacKenzie Architects
concept drawing for the basement layout 855/D201Feb2016).
The data provided and the findings of this report are based upon a site walkover completed on 9th March
2016 by the undersigned, along with reference made to the Otago Regional Council (ORC), WDC’s
District Plan information and the Geological and Nuclear Sciences (GNS) databases.
Five Scala penetrometers (SP01 - SP05) and three test pits (TP01 – TP03) were excavated at the
proposed site and these along with a number of photos taken during the site visit are attached for your
reference. It is considered that the ground investigation and initial geotechnical design assumptions will
be required to be verified by a suitably experienced engineer during foundation construction to confirm
the observations and conclusions made in this assessment. Further investigations including deeper
drilling may be required dependent upon the final building layout and design.
Observations around the Property and Immediate Environs
The site fronts onto Thames St, with the rear carpark accessed via a driveway from Humber St which
winds around a landscaped area. It is zoned in Business Area ‘H’ (BH) as determined from the WDC
Zones Map 76, with a total area of 1012 m2. The building on the site is deemed to be a heritage building
(H29). It is currently owned by the WDC and used as an art gallery. The neighbouring site to the north
is also listed as a heritage building (H38) and is owned by ANZ bank, while the southern site is owned
and operated by the Steam Café. Property information1 for 9 Thames Street Oamaru:
• Land Zone = BUS H
• Legal Description = SEC 1 BLK IV OAMARU TOWN
• Area = 0.1012ha
1 Property and Rates information provided by WDC: http://www.waitaki.govt.nz
Page | 2
The WDC water services map indicates a 150mm diameter sewer pipe bisecting the southern corners
of the site and a 150mm diameter stormwater pipe crossing alongside the drive way on the eastern
corner of the site. Initial ground scanning by local contractor Whitestone also indicated other old cables
or metallic pipes are buried within the site.
Review of Geological Hazards and Other Information
The bedrock geology of the area, as recorded on the GNS Geology Webmaps2, is noted to be in the
late Pleistocene Sediments Group. These are described as gravels, sand and silt of low river terraces
with patchy loess cover in places. A geological boundary is located approximately 50m to the south of
the site, where the shallow bedrock geology is noted to be in the Waiareka Volcanics Alma group. These
are described as agglomerated tuffs, basaltic dikes, sills and pillow lava.
The test pit and Scala testing indicated a soils strata comprising:
• 0.1m to 0.5m = Topsoil with many roots and tree stumps in landscape areas (made ground) or,
• 0.2m to 0.3m (SP04 only) = angular fine to coarse gravels in car-parking area (made ground)
• 0.5m to 3.2m = Soft to firm silt with traces of fine sand (loess)
• 3.2m to 3.5m = Medium dense to dense sandy gravel with occasional cobbles (alluvium).
Ground water was not encountered, with the soils typically dry in the upper 1.0m, i.e. desiccated and
thereafter the soil is damp with increasing depth below this crusted layer. There is some variation within
the soils with localised softer soil strata encountered at depth below 1.0m. The nearby Oamaru Creek
was flowing at relatively low levels at time of investigation, however it is considered this water level
would interconnect to the sandy gravel stratum encountered beneath the site.
The ORC Hazards3 database makes note of a flood hazard area around the Oamaru Creek which
approaches to within 100m of the site. It is noted the site is approximately 5m above the watercourse.
The ORC Hazards database also notes that the site lies on an area with low susceptibility to liquefaction
during an expected shaking intensity of 1:100 year earthquake. The nearest fault to the site is the
Awamoa Creek Fault which is approximately 2.6km away, this fault is determined to be currently
inactive. The nearest active fault is the Stone Wall Fault which is approximately 32km from the site.
The site lies within an area where seismic shaking4 from an Alpine Fault Magnitude 8.0 (1:100 year)
event can expect Modified Mercalli Intensity (MMI) of 6. The requirements of NZSL 1170 ‘Structural
Design Actions’ would prevail in any structural design. The site lies within what is determined as Class
‘C’ – Shallow Stiff Soils, per NZS: 1170 - Part 5.
The site does not lie within any mapped active alluvial fan hazard zone or active land slide zone.
Discussion and Conclusions:
The shallow soils strata underlying the site is assessed as approximately 3.0m to 3.5m thick layer of
firm (or compact) silty loessial soil overlying typically medium dense to dense sandy gravel. There are
some variable thickness of made ground overlying this soil strata, either a loose topsoil in the
landscaped areas or a medium dense to dense angular gravel which formed the car-parking surface.
It is considered that the upper 1.0m to 1.2m of soils strata is an unsuitable stratum for bearing any new
building foundations upon. Localised ‘soft spots’ may also be encountered at greater depths which
would also need to be removed and replaced with engineering fill. It is considered a suitable strip
foundation stratum may be achieved for any new building development at depths below 1.0m to 1.2m
where an allowable bearing capacity >100kPa may be inferred from the Scala Penetrometer test results
i.e. on ‘good ground’ per NZS: 3604 ‘Timber Framed Buildings’. However as the proposed building is a
multi-storey structure with a complex layout it is considered likely that there will be specific foundation
2 GNS website: http://data.gns.cri.nz/geology 3 ORC website: http://hazards.orc.govt.nz/Exponare/ORCWebMaps-advanced-1280x994.aspx 4 Opus – Seismic Risk in Otago Region, May 2005
Page | 3
design and detailing required. This will likely necessitate specific rafted or strip foundations or even
deeper foundations to be formed down into the sandy gravel stratum, the latter which could be
undertaken more efficiently with bored cast insitu or driven piles. Consideration to gross and differential
settlement along with design loads for bearing shall need to be included in overall foundation design.
The soils are typically damp at 1.0m depth and greater, however the underlying ground water table was
not encountered. It is considered the water table would be coincident with the sandy gravels and will
likely be interconnected to the nearby Oamaru Creek. Appropriate drainage will be required including
replacement of the existing building stormwater and potentially sewer drainage. It is noted the soils
closest to the existing building are typically softer than further out into the car parking area and it is
considered this is likely due to leaking stormwater drainage.
The difficulties associated with deep excavations will need to be considered if deep foundations and
excavations for a basement or retaining walls are required. Underpinning or staging of excavations at
the existing building or boundary walls of adjacent properties may be required, such that there is no
potential for destabilising or undermining of the existing buildings foundations.
Where driven piling is adopted there must be consideration given as to what the effects of the
construction vibrations will have on the existing building and adjacent structures.
Deep excavations will require to consider and plan appropriately for the temporary control and
management of groundwater ingress, including discharges if pumping is required. New storm water
drainage and any structural back of wall drainage plus any new foul piped outfalls should be integrated
to tie into existing piped services.
The site is not considered to be prone to significant damage from potential land hazards, including
liquefaction or land sliding. There should be some consideration given to the potential for flooding
hazard from the nearby Oamaru Creek. Suitable topographical survey should be undertaken at the site
with a level check made on relative levels to the nearby Oamaru Creek at the bed and the top of the
bank of the watercourse.
It is likely that the new development will extensively disturb or remove the existing landscaping and as
such new landform will be made. This may require alterations to the current driveway and retaining
walls dependant on final design and geometrics of the building floor levels and driveway and accesses.
It may be necessary to undertake further specific investigation to establish with a higher degree of
accuracy the ground and groundwater conditions as a detailed design evolves, this may involve deeper
rotary or cone penetrometer (CPT) drilling.
Appropriate drainage and new landscaping should be designed to accommodate the layout and
infrastructure associated with the new house. As a minimum, any soils left exposed by the works should
be covered with a topsoil and grassed or re-vegetated to promote good erosion control.
I trust the above information and recommendations are sufficient that your proposed planning and
funding application for the new development may continue as per envisaged.
Yours sincerely,
James Molloy
For Terra MDC Ltd
Enclosures: • Plates 1 to 6 of Site Reconnaissance and Investigation
• Site Investigation Location Plan
• Test Pit and Scala Penetrometer logs
Page | 4
Plate 1: Looking across carparking area toward Steam Café, with existing building to the rear right.
Plate 2: Test pit TP01 being excavated to rear of building.
Page | 5
Plate 3: Existing stormwater piped drainage from building to outfall along northern boundary of the site.
Plate 4: Test pit TP01 arisings, noting thick layer of topsoil in upper strata of excavation.
Page | 6
Plate 5: Excavation and arisings from Test Pit TP02.
Page | 7
Plate 6: Excavation and arisings for Test Pit TP03.
OF
Key
Scala Penetrometer
Test Pit
Refer to test pit and scala logs for ground information
1SHEET 1
SKETCH SHEET
PROJECT: WDC Cultural and Art facilities CLIENT: Waitaki District Council
DATE: 09/03/16SKETCH BY: Regan LordPROJECT No: 201603114
SUBJECT: Site Investigation Location Plan
SP03
TP01
SP02
SP04
SP05
SP01
TP03
TP02
Scala
Pen
etr
om
ete
r T
est
Resu
lts
Pro
ject:
T
este
d:
Jam
es M
ollo
y
Jo
b N
um
ber:
Ch
ecked
:Jam
es M
ollo
y
Lo
cati
on
:
Date
:
Cli
en
t :
Refu
sal =
12 >
10 o
r 1 >
50
Test
Location:
SP
01
Test
Location:
SP
02
Test
Location:
SP
03
Test
Location:
SP
04
SP
04
Depth
No.
Equiv
.Q
a
Depth
No.
Equiv
.Q
a
Depth
No.
Equiv
.Q
a
Depth
No.
Equiv
.Q
a
(mm
)B
low
sC
BR
%(k
Pa)
(mm
)B
low
sC
BR
%(k
Pa)
(mm
)B
low
sC
BR
%(k
Pa)
(mm
)B
low
sC
BR
%(k
Pa)
00
#N
/A0
0#N
/A0
0#N
/A0
0#N
/A
100
00
#N
/A100
00
#N
/A100
36
100
100
14
33
310
200
00
#N
/A200
00
#N
/A200
613
175
200
14
33
310
300
00
#N
/A300
12
25
300
715
190
300
920
235
400
00
#N
/A400
36
100
400
920
235
400
715
190
500
12
25
500
510
160
500
11
25
270
500
715
190
600
12
25
600
715
190
600
920
235
600
715
190
700
24
70
700
11
25
270
700
10
23
260
700
920
235
800
36
100
800
12
28
280
800
818
210
800
715
190
900
48
130
900
12
28
280
900
920
235
900
818
210
1000
36
100
1000
12
28
280
1000
715
190
1000
613
175
1100
510
160
1100
#N
/A1100
818
210
1100
920
235
1200
48
130
1200
#N
/A1200
818
210
1200
12
28
280
1300
48
130
1300
#N
/A1300
715
190
1300
12
28
280
1400
818
210
1400
#N
/A1400
613
175
1400
13
31
290
1500
818
210
1500
#N
/A1500
48
130
1500
#N
/A
1600
510
160
1600
#N
/A1600
48
130
1600
#N
/A
1700
818
210
1700
#N
/A1700
48
130
1700
#N
/A
1800
11
25
270
1800
#N
/A1800
36
100
1800
#N
/A
1900
510
160
1900
#N
/A1900
48
130
1900
#N
/A
2000
613
175
2000
#N
/A2000
48
130
2000
#N
/A
2100
510
160
2100
#N
/A2100
48
130
2100
#N
/A
2200
715
190
2200
#N
/A2200
48
130
2200
#N
/A
2300
715
190
2300
#N
/A2300
613
175
2300
#N
/A
2400
920
235
2400
#N
/A2400
613
175
2400
#N
/A
2500
10
23
260
2500
#N
/A2500
613
175
2500
#N
/A
2600
12
28
280
2600
#N
/A2600
613
175
2600
#N
/A
2700
12
28
280
2700
#N
/A2700
613
175
2700
#N
/A
2800
12
28
280
2800
#N
/A2800
715
190
2800
#N
/A
2900
13
31
290
2900
#N
/A2900
613
175
2900
#N
/A
3000
#N
/A3000
#N
/A3000
#N
/A3000
#N
/A
Re
co
rde
d
Blo
ws
10
0m
m
Blo
ws /
10
0m
m
Qa
(kP
a)
- fro
m
ch
art
Re
co
rde
d
Blo
ws
10
0m
m
Blo
ws /
10
0m
m
Qa
(kP
a)
- fro
m
ch
art
11
00
.00
25
11
9.0
92
70
25
0.0
07
01
28
.33
28
0
33
3.3
31
00
13
7.6
92
90
42
5.0
01
30
14
7.1
43
10
52
0.0
01
60
15
6.6
73
25
61
6.6
71
75
16
6.2
53
40
71
4.2
91
90
17
5.8
83
55
81
2.5
02
10
18
5.5
63
70
91
1.1
12
35
19
5.2
63
80
10
10
.00
26
02
05
.00
39
0
Note
: C
BR
% a
nd A
llow
able
Bearing C
apacity a
re a
corr
ela
tion
take fro
m M
.J. S
TO
CK
WE
LL (
1977),
'Dete
rmin
ation o
f allo
wable
bearing p
ressure
under
sm
all
str
uctu
res'
Cultura
l fa
cilt
ies d
evelo
pm
ent
201603114
As p
er
site location p
lan
9/0
3/2
016
Waitaki D
istr
ic C
ouncil
0
50
0
10
00
15
00
20
00
25
00
30
00
35
00
40
00
05
10
15
20
Depth (mm)
Blo
w C
ou
nt
Sca
la B
low
Co
un
t w
ith
Incr
ea
sin
g D
ep
th
Te
st L
oca
tio
n:
SP
01
Te
st L
oca
tio
n:
SP
02
Te
st L
oca
tio
n:
SP
03
Te
st L
oca
tio
n:
SP
04
0
50
0
10
00
15
00
20
00
25
00
30
00
35
00
40
00
01
00
20
03
00
40
0
Depth (mm)
Be
ari
ng
Ca
pa
city
Qa
(k
Pa
)
All
ow
ab
le B
ea
rin
g P
ress
ure
(kP
a)w
ith
In
cre
asi
ng
De
pth
Te
st L
oca
tio
n:
SP
01
Te
st L
oca
tio
n:
SP
02
Te
st L
oca
tio
n:
SP
03
Te
st L
oca
tio
n:
SP
04
Re
f @
0.9
m
Re
f @
1.4
m
Prin
t D
ate
: 1
4/0
3/2
01
6
1/2
Scala
Pen
etr
om
ete
r T
est
Resu
lts
Pro
ject:
T
este
d:
Jam
es M
ollo
y
Jo
b N
um
ber:
Ch
ecked
:Jam
es M
ollo
y
Lo
cati
on
:
Date
:
Cli
en
t :
Refu
sal =
12 >
10 o
r 1 >
50
Test
Location:
SP
05
Test
Location:
Test
Location:
SP
03
Test
Location:
Depth
No.
Equiv
.Q
a
Depth
No.
Equiv
.Q
a
Depth
No.
Equiv
.Q
a
Depth
No.
Equiv
.Q
a
(mm
)B
low
sC
BR
%(k
Pa)
(mm
)B
low
sC
BR
%(k
Pa)
(mm
)B
low
sC
BR
%(k
Pa)
(mm
)B
low
sC
BR
%(k
Pa)
00
#N
/A0
0#N
/A0
0#N
/A0
0#N
/A
100
00
#N
/A100
#N
/A100
#N
/A100
#N
/A
200
00
#N
/A200
#N
/A200
#N
/A200
#N
/A
300
00
#N
/A300
#N
/A300
#N
/A300
#N
/A
400
12
25
400
#N
/A400
#N
/A400
#N
/A
500
36
100
500
#N
/A500
#N
/A500
#N
/A
600
24
70
600
#N
/A600
#N
/A600
#N
/A
700
24
70
700
#N
/A700
#N
/A700
#N
/A
800
48
130
800
#N
/A800
#N
/A800
#N
/A
900
36
100
900
#N
/A900
#N
/A900
#N
/A
1000
36
100
1000
#N
/A1000
#N
/A1000
#N
/A
1100
24
70
1100
#N
/A1100
#N
/A1100
#N
/A
1200
24
70
1200
#N
/A1200
#N
/A1200
#N
/A
1300
24
70
1300
#N
/A1300
#N
/A1300
#N
/A
1400
36
100
1400
#N
/A1400
#N
/A1400
#N
/A
1500
510
160
1500
#N
/A1500
#N
/A1500
#N
/A
1600
48
130
1600
#N
/A1600
#N
/A1600
#N
/A
1700
48
130
1700
#N
/A1700
#N
/A1700
#N
/A
1800
48
130
1800
#N
/A1800
#N
/A1800
#N
/A
1900
510
160
1900
#N
/A1900
#N
/A1900
#N
/A
2000
48
130
2000
#N
/A2000
#N
/A2000
#N
/A
2100
715
190
2100
#N
/A2100
#N
/A2100
#N
/A
2200
715
190
2200
#N
/A2200
#N
/A2200
#N
/A
2300
715
190
2300
#N
/A2300
#N
/A2300
#N
/A
2400
715
190
2400
#N
/A2400
#N
/A2400
#N
/A
2500
715
190
2500
#N
/A2500
#N
/A2500
#N
/A
2600
715
190
2600
#N
/A2600
#N
/A2600
#N
/A
2700
715
190
2700
#N
/A2700
#N
/A2700
#N
/A
2800
10
23
260
2800
#N
/A2800
#N
/A2800
#N
/A
2900
14
33
310
2900
#N
/A2900
#N
/A2900
#N
/A
3000
#N
/A3000
#N
/A3000
#N
/A3000
#N
/A
Re
co
rde
d
Blo
ws
10
0m
m
Blo
ws /
10
0m
m
Qa
(kP
a)
- fro
m
ch
art
Re
co
rde
d
Blo
ws
10
0m
m
Blo
ws /
10
0m
m
Qa
(kP
a)
- fro
m
ch
art
11
00
.00
25
11
9.0
92
70
25
0.0
07
01
28
.33
28
0
33
3.3
31
00
13
7.6
92
90
42
5.0
01
30
14
7.1
43
10
52
0.0
01
60
15
6.6
73
25
61
6.6
71
75
16
6.2
53
40
71
4.2
91
90
17
5.8
83
55
81
2.5
02
10
18
5.5
63
70
91
1.1
12
35
19
5.2
63
80
10
10
.00
26
02
05
.00
39
0
Cultura
l fa
cilt
ies d
evelo
pm
ent
201603114
As p
er
site location p
lan
9/0
3/2
016
Waitaki D
istr
ic C
ouncil
Note
: C
BR
% a
nd A
llow
able
Bearing C
apacity a
re a
corr
ela
tion
take fro
m M
.J. S
TO
CK
WE
LL (
1977),
'Dete
rmin
ation o
f allo
wable
bearing p
ressure
under
sm
all
str
uctu
res'
0
50
0
10
00
15
00
20
00
25
00
30
00
35
00
40
00
05
10
15
20
Depth (mm)
Blo
w C
ou
nt
Sca
la B
low
Co
un
t w
ith
Incr
ea
sin
g D
ep
th
Te
st L
oca
tio
n:
SP
05
Te
st L
oca
tio
n:
Te
st L
oca
tio
n:
SP
03
Te
st L
oca
tio
n:
0
50
0
10
00
15
00
20
00
25
00
30
00
35
00
40
00
01
00
20
03
00
40
0
Depth (mm)
Be
ari
ng
Ca
pa
city
Qa
(k
Pa
)
All
ow
ab
le B
ea
rin
g P
ress
ure
(kP
a)w
ith
In
cre
asi
ng
De
pth
Te
st L
oca
tio
n:
SP
05
Te
st L
oca
tio
n:
Te
st L
oca
tio
n:
SP
03
Te
st L
oca
tio
n:
Prin
t D
ate
: 1
4/0
3/2
01
6
2/2
1
TPLOG.PUB
Site Investigation
Test Pit Log
Contract Title: WDC cultural facilities redevelopment Client: Waitaki District Council Contract No.: 201603114 Weather: Overcast Date: 09/03/16 Logged By: James Molloy Excavator: 14 tonne digger
Dark brown topsoil, soft with bark chippings ~ 50-100mm. Many tree roots with the occasional stumps.
Yellow brown SILT with traces of sand. Soft with low plasticity and in damp condition. Occasional roots in upper 1.0m. (Loess) (damage 4” clay pipe at back of test pit damaged during excavation)
HSV at 0.8m 135/120/105
Hard digging
Yellow brown clayey, fine to coarse gravel, much medium to coarse sand and occasional cobbles. Medi-um dense, damp to moist. (Alluvium)
End of Test Pit at 3.5m
Note: 4” pipe repaired and back filled with arisings. Possible softened ground due to poor drainage of water off building.
4 Photos, hole stable., slight belling of hole in the gravel layer.
Water @ Depth Soils Description
1.0m
2.0m
1.5m
TRIAL PIT No. TP01
0.5m
2.5m
3.0m
0.0m - 0.5m
0.5m - 3.2m
3.5m
4.0m
3.2m - 3.5m
2
TPLOG.PUB
Site Investigation
Test Pit Log
Contract Title: WDC cultural facilities redevelopment Client: Waitaki District Council Contract No.: 201603114 Weather: Overcast Date: 09/03/16 Logged By: James Molloy Excavator: 14 tonne digger
Dark brown topsoil, soft with bark chippings ~ 50-100mm in dry condition. Many tree roots with the occasional stumps.
Yellow brown SILT with traces of sand. Soft with low plasticity and in dry condition. Occasional roots in upper 1.0m. (Loess).
HSV at 0.6m 100/100/105
Becoming firm to stiff at 1.0m
Hard digging.
End of Test Pit at 1.8m
Note: 3 Photos, hole stable and dry
Water @ Depth Soils Description
1.0m
2.0m
1.5m
TRIAL PIT No. TP02
0.5m
2.5m
3.0m
0.0m - 0.3m
0.3m - 1.8m
3.5m
4.0m
3
TPLOG.PUB
Site Investigation
Test Pit Log
Contract Title: WDC cultural facilities redevelopment Client: Waitaki District Council Contract No.: 201603114 Weather: Overcast Date: 09/03/16 Logged By: James Molloy Excavator: 14 tonne digger
Dark brown topsoil, soft with bark chippings ~ 50-100mm in dry condition. Many tree roots with the occasional stumps.
Yellow brown SILT with traces of sand. Soft with low plasticity and in dry condition from 0.1 - 1.2m turning slightly damp until 2.3m. Occasional roots in upper 1.0m. (Loess)
End of Test Pit at 2.3m
Note: 3 Photos, hole stable and dry
Water @ Depth Soils Description
1.0m
2.0m
1.5m
TRIAL PIT No. TP03
0.5m
2.5m
3.0m
0.0m - 0.1m
0.1m - 2.3m
3.5m
4.0m