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HIGH CAPACITY CAST-IN-PLACE CONCRETE PILE LOAD TESTS AT CNRL’S OIL SAND PLANT NEAR FORT McMURRAY, ALBERTA Renato Clementino, Robin Tweedie, John Sobkowicz, Christopher Workman, Thurber Engineering Ltd., Edmonton/Calgary, Alberta, Canada Richard Sisson, CNRL, Calgary, Alberta, Canada ABSTRACT A comprehensive pile load test program was conducted in 2003 and 2004 at CNRL’s Horizon Oil Sands Plant site near Fort McMurray, Alberta, assess capacities for design of foundation piles. The program consisted of five piles tested in a static frame to vertical loads of up to 10 MN, two piles tested using Osterberg Cells at equivalent top-down loads of up to 22 MN, and four piles tested using the Statnamic method to loads of up to 16 MN. This paper describes the installation and instrumentation of the piles, presents the test results, compares these to historical design values, and discusses the results. RÉSUMÉ Afin de confirmer de plus grandes capacités pour des pieux forés de béton, la compagnie CNRL Des Sable Bitumineux, a commissionné un programme compréhensif d’essais de chargement de pieux à son nouveau chantier situé près de Fort McMurray en Alberta. Le programme d’essais inclut cinq pieux avec des charges statiques allant jusqu’à 10MN; deux pieux furent testés en utilisant des « cellulles d’Osterberg » avec des charges allant jusqu’à 22MN, et quatre pieux furent testés en utilisant la méthode « Statnamic » avec des charges allant jusqu’à 16MN. Cette étude décrit l’installation et l’instrumentation des pieux, présente les résultats et les compare à des valeurs historiquement utilisées et discute les résultats obtenus. 1. INTRODUCTION The CNRL Horizon Oil Sand Project is located 70 km north of Fort McMurray, Alberta. One of its major compo-nents is a large plant for the extraction and upgrading of bitumen from oil sand. Preliminary geotechnical investigations indicated that the plant site is underlain by a sequence of outwash sand, clay till, Clearwater Formation clay shale and McMurray Formation oil sand. The oil sand ranges from lean to rich bitumen content and is at suitable depth for construction of cast in place concrete pile foundations. Cast in place (CIP) concrete, belled, end bearing piles founded in oil sand have been used for support of heavily loaded structures at several existing oil sand plants in the Fort McMurray area. Traditionally, these piles were designed using end bearing support, had shaft diameters of 600 to 900 mm and bell diameters of 1500 mm to 2700 mm, and were founded at relatively shallow embedment depths of 1.5 m to 2 m into competent oil sand. Previous pile load tests on end bearing piles founded in oil sand have indicated relatively high end bearing capacity (Sharma, et. al., 1986). However, the friction capacity of piles within the oil sand has not been investigated and has frequently been ignored. A comprehensive pile load test program was carried out at the CNRL Horizon oil sand plant site to optimize the pile design and to quantify the end bearing and shaft friction parameters in the oil sand and overburden soils.
The pile load test program was conducted in two phases, as follows: The first phase was carried out in 2003 and consisted of static pile load tests (ASTM 1981) on two CIP concrete belled piles and one CIP concrete straight shaft pile. The load test frame capacity was 10 MN and the ultimate geotechnical capacity of these piles was not reached. To assess ultimate pile capacity, a second phase of testing was carried out in 2004. Higher load capacity was achieved through the use of Osterberg Cells (Osterberg 1998), which delivered an equivalent top-down load of up to 22 MN, and Statnamic tests (Middendorp, et. al. 1992), which had a dynamic test load of up to 16 MN. Two O-Cell tests and four Statnamic tests were performed during the Phase 2 program. In addition, two long-term (creep) tests were carried out during Phase 2 to assess potential creep characteristics of heavily loaded piles bearing in oil sand. One test was conducted on an existing Phase 1 straight shaft pile using a static test method, and the second creep test was performed with the Osterberg Cell (O-Cell). Load tests were also conducted on end bearing piles founded in Clearwater clay shale and on driven steel piles founded in clay shale and oil sand. However, this paper will describe only the results of the high capacity cast-in-place concrete pile tests founded in oil sand.
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2. STRATIGRAPHY
The soil conditions at the pile load test sites consists of outwash sand overlying glacial clay till, Clearwater Formation clay shale, and McMurray Formation oil sand. The depth to the oil sand stratum ranges from 7.5 m to 19.2 m at the test sites. A simplified stratigraphic profile at each of the test sites is shown in Figure 11. The bitumen content of the oil sand varies (Table 1). Standard Penetration Test N values are typically over 100. Results of triaxial compression tests on high quality cores by Thurber Eng. (Sharma, 1986) indicated peak friction angles of 50o on undisturbed cores, and peak friction angles of about 44o on gas expanded samples.
3. PILE LOAD TEST PROGRAM 3.1 Phase 1 – Static Load tests Static pile load tests were carried out on three CIP concrete piles founded in the McMurray Formation oil sand, including two belled piles (Site A and Site B) and one straight shaft pile (Site C). Table 1 provides a summary of the test pile characteristics. All the test piles had instrumentation installed within the pile consisting of embedded vibrating wire strain gauges in the shaft and load cells installed between the shaft and the bell or at the base of the shaft in the straight shaft pile. Figure 1 shows the bottom load cell attached to the pile’s cage before installation into the drilled shaft.
Table 1 – Phase 1 and 2 pile load test summary
SITE STRATIGRAPHY OIL
CONTENT*
PILE TYPE (CIP)**
PILE DEPTH
(m)
MAXIMUM POSSIBLE
APPL. LOAD (MN)
TYPE OF TEST
PHASE 1 TEST PILES
A 0 to 4.0 m - Clay Till 4.6 to 7.6 m - Clearwater > 7.6 m - Oil Sand
Lean Shaft 790 mm Base 990 mm
12.6 9 Static
B
0 to 4.0 m - Sand 4.0 to 7.8 m Clay 7.8 to 8.8 m - Sand > 8.8 m - McMurray Oil Sand
Rich Shaft
790-1370 mm Base 1490 mm
16.2 9 Static
C 0 to 4.5 m - Sand 4.5 to 7.5 m - Clay Till > 7.5 m - McMurray Oil Sand
Shaft lean to rich
Base rich
775-1100 mm straight shaft
14.2 10 Static
PHASE 2 TEST PILES
G 0 to 3.6m – Sand 3.6 to 8.0m - Clay Till >8.0 m – McMurray Oil Sand
Shaft lean to rich
Base rich 14.7
18MN (two 6MN O-cell)
Multi stage O-cell
H
0 to 1.3 m – Sand 1.3 to 5.3 m – Clay Till 5.3 to 9.2 m – Clearwater > 9.2 m McMurray Oil Sand
Shaft lean Base rich
15.9 22MN
(one 11MN O-cell)
Single stage (with creep)
O-cell
I
0 to 2.5m - Sand 2.5 to 7.9m - Clay Till 7.9 to 19.2m – Clearwater >19.2m – McMurray Oil Sand
Shaft lean to rich
Base lean 24.6 16MN Statnamic
J
0 to 5.4m – Sand 5.4 to 6.4m – Clay 6.4 to 8.4m – Clay Till > 8.4m - McMurray Oil Sand
Shaft rich Base rich
14.8 16MN Statnamic
K 0 to 6.0m - Sand 6.0 to 10.8m - Clay Till > 10.8m – McMurray Oil Sand
Shaft lean/rich Base rich
17.7 16MN Statnamic
L
0 to 3.5m – Sand 3.5 to 5.8m – Clay 5.8 to 8.0m – Clay Till 8.0 to 10.8m – Clearwater > 10.8m – McMurray Oil Sand
Shaft moderate to
rich Base rich
760-900mm straight shaft
16.9 16MN Statnamic
*Oil Content: Lean < 6%; Moderate 6-8% and Rich >8% **Shaft Diameter refers to nominal diameter. Actual shaft size increased due to casing requirements
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Figure 1 – bottom load cell. The test piles and anchor piles were installed by a con-ventional pile auger rig and temporary casing(s) were used where required to control sloughing and seepage during pile boring and belling. The reaction system consisted of four anchor piles and two reaction beams with a design load capacity of 10 MN. The area surrounding the test piles was hoarded and heated during each test, however due to the size of the test layout the anchor piles were outside the hoarding. A 10 MN (nominal) hydraulic jack was used to load the piles. Top of pile head deflections were monitored using two dial gauges. The test pile set up was in general accordance with ASTM D1143 (1981). Figure 2 shows a view of the outside setup of the reaction piles and hoarding.
Figure 2 – Outside view of the reaction system; 3.2 Phase 2 – Osterberg Cell and Statnamic Six test sites were chosen (noted as Sites G, H, I, J, K and L in Table 1) for the installation of the Phase 2 test piles. In addition, one existing test pile (Site C) from the previous Phase 1 was selected to perform the static long-term (creep) load test. Table 1 provides a summary of the test piles characteristics. 3.2.1 O-Cell Setup Two O-cell pile load tests were performed on straight shaft CIP concrete piles. The O-Cell test pile installations were supervised by personnel from Loadtest Inc., from
Gainesville, Florida, USA, who also carried out the pile load tests. The first test was performed on Site G, and the second test at Site H. The O-Cell pile test areas were hoarded and heated for the duration of both tests. The setup for both tests was similar and is as shown in Figure 3. Pile top movements were recoded using both a reference beam and a laser level. An estimation of the ultimate base capacity and shaft friction of the test piles was first made based on the results of the Phase 1 pile load test program, to enable selecting the optimum O-Cell position, i.e., the position where a balance of ultimate capacity above and below the O-Cell could be achieved. A multi-stage O-Cell test was carried out at Site G to provide information on the end bearing resistance and to separate the shaft friction component in oil sand and overburden soils.
Figure 3 – O-Cell typical setup. The multi-stage test consisted of two 6 MN O-Cells installed in the pile shaft. The first O-Cell was installed 0.6 m above the pile base and the second was installed 2.0 m above the first O-Cell. Figure 4 shows a schematic view of the multi-stage O-Cell test pile and soil profile and Figure 5 shows a photograph of the multi-stage O-Cells before installation. The results from the multi-stage test were used to estimate the optimum position for the single stage test carried out at Site H using an 11 MN O-Cell placed 2.0 m above the pile base. A long-term (creep) test was also carried out at this site. The load distribution along the shaft was assessed by vibrating wire strain gauge pairs installed at three different levels along the shafts of the test piles.
Test Pile
Laser level
Reference beam
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Figure 4 – Multi-stage O-cell layout.
Figure 5 – Multi-stage O-Cell prior installation.
3.2.2 Statnamic Setup Four Statnamic pile load tests were performed on CIP concrete straight shaft piles at Sites, I, J, K and L. The Statnamic tests were carried out by Applied Foundation Testing, Inc. (AFT) from Green Cove Spring, Florida, USA on behalf of Bermingham Foundation Solutions, from Hamilton, Ontario. The Statnamic equipment was mobilized from Florida and had a dynamic capacity of 16 MN. All Statnamic test piles had three levels of resistance strain gauges (three gauges per level) installed in the reinforcement cages. The dynamic load applied to the top of each pile was measured using a load cell positioned at the top of the pile. The pile deflections were obtained using three accelerometers mounted at the top of the pile. Figure 6 shows a general view of the Statnamic apparatus. 3.2.3 Static Creep Test A long-term static pile load test was performed on the existing test pile from Site C used during the Phase 1 program. The creep test was initially carried out with an applied load of 6 MN (design load), however some difficulties were experienced with the dial gauges setup after 3 weeks of testing. The gauge setup was improved and three new gauges were added. Once the gauges were re-set the pile load was increased to 7.5 MN (1.25 design load) and the creep was monitored for an additional 16 days.
Figure 6 – Statnamic – applying the load. 4. PILE LOAD TEST RESULTS Table 2 provides a summary of the pile load tests results, including the pile dimensions, maximum applied loads,
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measured settlements, and interpreted shaft friction and end bearing capacities based on the measurements from the shaft strain gauges and base load cells. Figure 9 shows the applied load vs pile top deflection for all the test piles. Also included in this plot are the two test pile results (SCL-TP1 and SCL-TP2) from Sharma (1986) for comparison. These previous test piles (Sharma 1986) were CIP belled concrete piles based in oil sand. SCL-TP1 was a 12.5 m long pile with a 660 mm diameter shaft and 914 mm diameter bell, embedded 1.5 m into oil sand. Pile SCL-TP2 was 12.5 m long with a 610 mm diameter shaft and 914 mm diameter bell, embedded 1.6 m into oil sand. When the test pile at Site B was loaded to about 7.2 MN, a popping noise was heard. The pile load was increased to 7.62 MN when it started to creep continuously. Heavy seepage was encountered during the drilling of this pile making it a very difficult to install all the instrumentation and pour the concrete into the pile in a satisfactory manner. It is believed, therefore, that this pile had a structural failure of the shaft rather then a geotechnical failure and this is supported by the strain gauge readings. The Statnamic test performed in the test pile on Site K recorded an excessive pile head displacement and shaft strain incompatibility, showing higher strain measurement in deeper strain gauges along the shaft. This strain incompatibility can only be caused by structural or geometric properties of the shaft. Hence, similarly to the pile on Site B, the test pile on Site K likely suffered a structural shaft failure. Exhuming the pile at Site B to confirm the structural failure was attempted, but found to be impractical. Figure 10, shows a typical pile shaft load distribution vs depth curve from strain gauge readings obtained from a static pile load test, Site C. Figure 11, provides a summary of the interpreted pile load distributions of each of the test piles based on the instru-mentation data. Figures 7 and 8 show, respectively, the results of the creep tests performed on the test pile on Site C, using the conventional static load frame, and on the test pile on Site H using the O-Cell.
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
1 10 100 1000 10000 100000
Time (minutes)
Dis
pla
ce
me
nt
(mm
)
Average South Gauge North Gauge Centre Gauge
Dial Gauge Locations
Figure 7 – Long term creep test – Site C
Figure 8 – Long-Term Creep Test – Site H The Site C pile was loaded to 7.5 MN and the load was held constant to monitor creep movement for a period of 16 days. The O-Cell in the test pile on Site H was held constant for a period of over 3 weeks at a load value of 2.4 MN. This load was estimated to represent the average shaft load in the lower two metres of pile in oil sand for a top loaded pile under an applied top-down load of 6 MN. 5. DISCUSSION The results of the pile load test program indicate that high capacities are obtained on straight shaft piles extending 6 m or more into oil sand. The major portion of the pile capacity is from shaft friction in the oil sand. As noted in Table 2, the mobilized shaft friction in oil sand ranges from 250 kPa to greater than 1000 kPa. The best information on the load transfer was obtained from the multi-stage O-Cell test, which indicated a mobilized shaft friction increasing from 550 kPa to over 1000 kPa, increasing with depth below the top of the oil sand. The load-settlement performance of the piles show that in general the deeper the pile is founded into oil sand the stiffer is the load-settlement response. For example Site A, which was a belled pile with the least oil sand penetration (5 m), represents the softest load-settlement response of all the test piles. Similarly the previous test piles reported by Sharma (SCL-TP1 and SCL-TP2), which had even less oil sand embedment, also show relatively soft responses compared to the straight shaft piles at this site. It is also apparent that greater pile capacity and settle-ment performance may be achieved by extending the pile shafts deeper into oil sand to engage greater shaft friction, rather than belling at minimum depth into oil sand (typically 1.5 m minimum penetration in oil sand).
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Table 2 – Summary of pile load test results.
LOAD METHOD STATIC O-CELL STATNAMIC
TEST PILE SITE A B C G H I J K L
Shaft (m) 3.6* 6* 6.3 5.9* 6.2 5.4 6.4 6.9 6.1 OIL SAND EMBEDMENT
Bell (m) 1* 1* N/A N/A N/A N/A N/A N/A N/A
SHAFT DIAMETER (m) 0.79 0.79 0.775 0.76 0.76 0.76 0.76 0.76 0.76
CASED SECTION SHAFT DIAM. (m)† N/A 0.92/1.37 0.95/1.10 0.90 0.90 0.90 0.90 0.90 0.90
CASED SHAFT LENGTH (m)† N/A 9.7 6.3 8.20 8.30 8.2 8.3 8.2 8.2
UNCASED SHAFT LENGTH (m) 10.4 1.5 6.0 6.50 7.6 16.4 6.5 9.5 8.7
TOTAL SHAFT AREA (m2) 25.8 42.2 35.72 38.80 41.71 62.50 39.08 45.78 44.06
BASE AREA (m2) 0.77 1.74 0.472 0.456 0.456 0.456 0.456 0.456 0.456
MAXIMUM APPLIED LOAD (MN) 8.99 7.62 10.06 15.3 12.0 14.64 12.25 11.12 12.87
PILE TOP DEFLEC. MAX. LOAD (mm) 34.5 15.2 18.1 52 34 21.0 17.8 232*** 18.3
ESTIMATED BASE LOAD (MN) 3.3 3.3 0.14 1.8 5.4 2.1 3.1 N/A 5.70
ESTIMATED SHAFT FRICTION (MN) 5.7 6.7 9.92 13.5 6.6 12.5 9.2 N/A 7.17
OIL SAND SIDE FRICTION (kPa) 255* N/A 410* 557-812 (1162)+ 315 463** 370**-610** N/A 254-422**
ESTIM. END BEARING STRESS (kPa) 4284 248 300 4081 12000 4647 6719 N/A 12500
* Excludes internal load cell length. ** Ultimate condition was not reached. *** Probably due to structural defect of the pile. + Ultimate value using a hyperbolic extrapolation. † Temporary casing was removed during pouring of concrete.
0 4 8 12 161 2 3 5 6 7 9 10 11 13 14 15 17 18Load (MN)
60
40
20
0
50
30
10
Dis
pla
cem
ent (
mm
)
SITE A (Static Test)
SITE B (Static Test)
SITE C (Static Test)
SCL-TP1 (Static Test)
SCL-TP2 (Static Test)
SITE G (O-Cell)
SITE H (O-Cell)
SITE I (Statnamic)
SITE J (Statnamic)
SITE K (Statnamic)
SITE L (Statnamic)
HyperbolicExtrapolation
Figure 9 – Load vs pile head displacement curve for all test piles.
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0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000Pile Shaft Load (kN)
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
De
pth
fro
m G
rou
nd
Su
rfa
ce (
m)
LOAD (kN)406
1219
2032
3251
3961
5994
8026
10058
TOP OF LOAD CELL (13.7m)
BOTTOM OF PILE (14.2m)
SAND
CLAY TILL
OILSAND
BASE LOAD141 kN
CASING 1
CASING 2
Sono tube (1.35m depth)
Figure 10 – Pile shaft load distribution vs depth for each load increment – test pile Site C
0 4 8 12 16
SITE GLOAD (MN)
25
20
15
10
5
0
22.5
17.5
12.5
7.5
2.5
DE
PT
H (
m)
0 4 8 12
SITE HLOAD (MN)
0 4 8 12 16
SITE ILOAD (MN)
0 4 8 12
SITE JLOAD (MN)
0 4 8 12
SITE LLOAD (MN)
0 4 8 12
SITE CLOAD (MN)
OIL SAND
OIL SAND
OIL SAND
OIL SAND
OIL SANDOIL SAND
CLAY SHALE
CLAY SHALE
SILTSTONE
CLAY TILL
CLAY TILL
SAND
SANDSANDSAND
CLAY TILL
SAND
SAND
35
CLAY
CLAY TILL
CLAY
CLAY TILLCLAY TILL
SH
AF
TF
RIC
TIO
N (
kP
a)
145
566
812*
60
246
315
57
337*
463*
88
370*
610*
61
254
422*
123
502*
681*
479*
SH
AF
TF
RIC
TIO
N (
kP
a)
SH
AF
TF
RIC
TIO
N (
kP
a)
SH
AF
TF
RIC
TIO
N (
kP
a)
SH
AF
TF
RIC
TIO
N (
kP
a)
SH
AF
TF
RIC
TIO
N (
kP
a)
*ULTIMATE SHAFT FRICTION WAS NOT REACHED
Figure 11 – Shaft load distribution. Figure 9 provides a summary of the load settlement curves for the test piles (Static Tests A, B and C; Osterberg Cell Tests G and H and Statnamic Tests I, J, K and L). All test piles were 760 mm nominal diameter straight shaft piles (with the exception of A and B which were belled piles) founded at depths of embedment of 5 to 6.9 m into oil sand with total depths ranging from 12.6 m to 24.6 m. The Phase 1 Static Test piles Sites A and B were loaded to 9 MN and the pile in Site C was loaded to 10 MN. The
phase two test piles were loaded to 12 MN to 15 MN for the Osterberg Piles (equivalent top down load) and 11 MN to 15 MN for the Statnamic Piles (equivalent static load). None of these piles reached ultimate capacity based on typical settlement criteria. For example, Poulos (2003) provides the simplest definition of ultimate capacity based on a pile settlement equal to 10 % of the base diameter (i.e., equivalent to 76 mm of deflection for the 760 mm diameter pile). The Statnamic piles had an estimated settlement of about 18 mm, and the Osterberg cell tests,
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having slightly softer response had a maximum deflection of 50 mm (Site G). The Static Pile Test A had a maximum settlement of 35 mm at 9 MN load. Various criteria were used to estimate the ultimate capacity. The Vander Veen (1953) method indicates that the ultimate capacity of Test Piles G and H (O-cell) are 17 MN and 18 MN respectively, and 16 MN for Test Pile C. Application of this approach to the Statnamic Tests indicates unreasonably high capacities of about 25 MN, and does not appear to be a suitable method for interpretation of the Statnamic pile test capacities. Based on the above estimated ultimate capacities of 16 MN to 18 MN, allowable capacities of up to 8 MN could be justified for these test piles using a minimum factor of safety of 2. Relatively large deflections would however be expected for such pile loads, in the range of 12 mm to 20 mm based on the pile load tests (with the exception of pile A). A typical pile capacity of 6 MN was recommended for these piles to limit pile design settlements to about 12 mm at design load. Comparison of the test pile results in Figure 9 indicates a similar load-settlement response between the Statnamic tests and the static tests, at least up to the recommended allowable pile load of 6 MN, and a slightly softer response for the O-Cell tests. The Statnamic tests indicate an interpreted top of pile deflection at 6 MN top load of 7 mm to 8 mm; the Static Load test 8 mm (test B and C); and the O-Cell tests 12 mm. It should be noted that both the O-Cell and the Statnamic test methods provide indirect measurement of top-down static loads and require interpretations to construct the load settlement curve. The O-cell test requires construc-tion of an “equivalent top down load settlement curve” which includes an interpreted settlement component to represent elastic pile shaft compression, which may be somewhat conservative. On the other hand, the Statnamic Test is of short duration and hence may provide a stiffer response even after appropriate correc-tion to the data. Considering these differences in test methods, the load-settlement response in the working range (6 MN) is remarkably similar for all test piles. The results are useful in estimating the likely settlement of production piles under various load conditions. Test Pile C was loaded to a maximum static load of 7500 kN for a period of 16 days and indicated no appreciable creep (Figure 7). Similarly, O-Cell test pile H was loaded for a period of 23 days and also indicated no appreciable creep in the bottom 2 m of the pile shaft and base, which were within oil sand (Figure 8). Ten additional pile load tests have since been conducted on 600 mm diameter production piles, with design loads of 2000 kN. Their performance falls within the range shown on Figure 9. The results of all these piles thus indicate a pile top settlement of about 2 mm per 1000 kN of vertical load.
To date, single CIP concrete piles with design loads of up to 16 MN (for a pile diameter of 1.5 m and a 9 m embed-ment into oil sand) have been installed at the CNRL plant site. 6. CONCLUSION The pile load test program demonstrated that high capacity can be achieved with straight shaft piles that extend 6 m or more into oil sand, with small settements. Piles may be designed using a combination of shaft friction and end bearing capacity. In many cases, end bearing capacity can be ignored, requiring less base preparation and inspection. Average allowable shaft friction values applied during design ranged from 100 kPa at the top of the oil sand increasing linearly to 500 kPa at a depth of 6 m, below which the allowable shaft friction remained constant. The authors believe that shaft frictions continue to increase below the 6 m penetration, but relying on such an increase was not justified on the basis of the testing programs. An allowable end bearing capacity of up to 1500 kPa was used for design of straight shaft, end bearing piles. 7. ACKNOWLEDGEMENTS The authors wish to acknowledge Canadian Natural Resources Ltd. personnel for their support throughout the project and for their permission to publish the results. The authors also acknowledge the contribution of LOADTEST, Inc, Applied Foundation Testing Ltd. and Berminghammer Foundation Equipment during the pile load test program. Thanks are also extended to Dr. Jack Clark for his valu-able input during the work. 8. REFERENCES ASTM D1143, 1981, Standard Test Method for Pile Under
Static Axial Compression Load, ASTM, Philadelphia, Pennsylvania, USA.
Middendrop, P., Bermingham, P., and Kuiper, B. 1992. Statnamic Load Testing of Foundation Pile. Proc. of the 4th Int. Conference on Application of Stress-Wave Theory to Piles, The Hague, 581-588.
Osterberg, J.O. 1998. The Osterberg Load Test Method for Drilled Shafts and Driven Piles – The First Ten Years. Prec. of the 7th Int. Conference on Pilling and Deep Foundations, Vienna, Austria. Published by Deep Foundations Institute.
Poulos, H.G. 2003. Pile Foundation Analysis and Design Seminar, Canadian Geotechnical Society, Toronto, Canada.
Sharma, H.D., Harris, M.C., Scott, J.D., and McAllister, K.W. 1986. Bearing Capacity of Bored Cast-in-Place Concrete Piles on Oil Sand. Journal of the Geotech-nical Engineering Division, ASCE, 112(12):1101-1116.
Vander Veen, C. 1953. The Bearing Capacity of a Pile. Proceedings of the 3rd ICSMFE, Zurich, Switzerland, vol 2, pp. 84-90.
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