Load Tests
INTRODUCTON AND PURPOSE
This method statement is prepared for static axial compressive load test, on nominal diameters Ø800/880mm bored piles.
This method statement is also summarizes materials, machinery, equipment, plant, tools and instruments to be used, and defines the loading and unloading schedule and recording of the field data during the test.
This method statement is applicable for load testing of vertical reinforced concrete piles in maintained axial compression.
REFERENCE DOCUMENTS AND STANDARDS
The tests are going to be in accordance with:
ASTM D 1143 – 07 Standard Test Methods for Deep Foundations Under Static Axial Compressive Load.
CONSTRUCTION & PREPARATION OF TEST PILES AND TEMPORARY PILE CAPS
Top of the working pile should normally be cut down (trimmed off) to the design pile cut-off level. If the design pile cut-off level is too deep from the existing ground level, alternatively, soil above the pile cut-off level may first be disturbed to avoid its contribution to the axial geotechnical capacity of the pile, before construction of the temporary pile cap. (Excavating down to the pile cut-off level and backfilling without heavy compaction is sufficient to disturb the soil above the pile cut-off level.)
Irrespective of design pile cut-off levels, heads of the test piles shall be cut down to level of sound concrete and prepared to receive temporary pile caps.
A temporary reinforced concrete (RC) pile cap will be constructed on top of the test pile. Centre of the pile cap in plan shall be concentric with the vertical axis of the pile, and shall have a horizontal surface and this surface shall be specificially prepared flat for placing the steel test plates, loading and measuring equipment.
Size of the temporary RC pile cap should be large enough to accommodate the loading & measuring equipment and to distribute concentrated loads.
Height of the pile cap (ASTM D1143M-07 “5.4”) is 1.0 m to enable proper anchorage of starter bars from piles, fixing & overlapping of steel reinforcement, and placing of concrete in the pile cap.
A sufficient gap or clear space should be provided under and around the pile cap projecting beyond the test pile such that, no load will be transmitted to the ground from the pile cap at maximum expected settlement.
Pile caps should be reinforced to prevent damage from application of vertical concentrated loads. Vertical starter bars extending above the pile cut-off level should be embedded in and confined by the pile cap. Pile cut-off level should be about 100 mm above the soffit of pile cap.
Pile caps should be constructed using the same grades of concrete and reinforcement that is used in test piles. Sufficient time shall be allowed for maturing of concrete placed in the pile and the pile cap. Compressive strength of the concrete cast in piles and pile caps shall be determined prior to commencement of load testing. Piles shall be load tested once the pile concrete has attained (28 ) days compressive strength but not until at least (21) days elapsed after placing the concrete .Such a case will be verified by concrete samples taken during casting of bored pile.
EQUIPMENT FOR APPLYING LOADS
Axial compressive load test: The apparatus for applying compressive loads to the test pile is capable to transfer the load through the central longitudinal axis to minimize the eccentric loading. In addition a hinge is going to be used to prevent eccentric loading. A steel bearing plate is placed on the pile cap to form a base for placing the load transferring apparatus. A hydraulic jack is going to be used, which can hold the load constant as pile settlement occurs.
EQUIPMENT FOR MEASURING MOVEMENT
Axial compressive load test: Independent reference beams will be used to enable the measurement of the movement of the pile. Reference beams will be founded clear distance from the test pile of at least five times the diameter of the test pile(s) but not less than 2.5 m Reference beam supports will be firmly embedded in the ground and one end of it will have roller support to let horizontal movement with temperature change.
Dial gauges with 0.01 mm precision are mounted on the reference beams for manual reading and to perform the measurement of pile movement. Two dial gauges are going to be distributed around the pile head with equal distance and axis. Displacements will be calculated as the average of these dials gauges. One dial gauge is going to be placed to each reaction piles for measuring the displacements of the reaction piles.
DATA RECORDING
The load and settlement recording will be done manually from Manometer and Micrometer. The reading intervals (according to ASTM D1143M-07 “8.2.1.1 and 8.2.3”) are going to be; for any period when the load is constant, time and settlement shall be recorded immediately on reaching the load, at not more than 5 minute intervals up to 15 minutes, at approximately 15 minutes intervals up to 1 hour, at 30 minute intervals between 1 hour and 6 hours, and 1 hour intervals between 6 hours and 12 hours after the application of the increment of load.
REACTION SYSTEM
Load is going to be applied to the test pile by hydraulic jack acting against reaction piles. Where permissible area around test pile is determined sufficient reaction piles will be constructed by the permission of the Engineer. Reaction piles will have sufficient tension capacity for the forces to be mobilize during the test. Test system layout and section view are given in Fig.2-a and Fig 2-b, respectively.
As it can be seen from Fig.2-a, Fig 2-b. 2 unit reaction piles which have the same test pile diameter, will be constructed. Steel beams, which are going to be placed on the hydraulic jack, should be capable of bearing the incremental loads till the anticipated maximum test load.
PILE LOAD TESTING PROCEDURE
AXIAL STATIC COMPRESSIVE TEST LOADING PROCEDURE:
Unless failure occurs, the pile is going to be loaded up to the specified load level 1.5 DVL and 2 DVL. The allowable minimum pile capacity –Design Verification Load- is given at the table shown below:
Pile Diameter (mm) |
DVL |
1,5 DVL |
2,0 DVL |
Ø ... |
... kN |
... kN |
... kN |
Ø ... |
... kN |
... kN |
... kN |
The loading and unloading will be carried out according to ASTM D1143-07 “Standard Test Methods for Deep Foundations Under Static Axial Compressive Load” item 8.1.3 “Procedure B: Maintained Test”. A minimum load holding duration of 30 minutes is adopted to observe and evaluate the rate of axial movement. After 30 minutes, If the rate of axial movement does not exceed 0.25mm/hour then the load will be increased to the determined subsequent loading step. Otherwise, load will be remained up to the rate of axial movement will be determined less than 0.25mm/hour but not more than 2 hour. After applying the maximum load and reaching an overall test duration of at least 6 hour, unloading phase will be started and load will be removed in decrements of 25% of the maximum test load with 30 minutes between decrements.
TEST RESULTS
The results of tests, which are carried out according to ASTM standards will be submitted to Engineer with a report.
A full record of time, loads and settlements taken as specified above will be recorded in a pile load test data sheet and submitted to the Engineer within 24 hours of completion of the test.
The following will also be presented in graphical form after the completion of the proof load test:
- Set up design
- After static axial compressive load test:
Load plotted against pile head settlement
Load plotted against time
Pile head settlement plotted against time
Final Report of the axial load test will be submitted to the Engineer within six days after completion of the test.
SUPERVISION / MANPOWER AND SAFETY
The team for the load tests will be composed of ;
- Chief responsible engineer
- Assistant to chief engineer
Hydraulic cylinders and hydraulic pumps that are stable and safe for application of the maximum test load will be used.
The pile proof load test will be carried out only under the direction of an experienced and competent supervisor conversant with the test system, testing equipment and the test procedure. All personnel operating the test equipment shall be trained to use them.
The following safety rules are in addition to general safety requirements applicable to construction operations:
- All work areas, walkways, platforms, etc. shall be kept clear of scrap, debris, small tools, and accumulations of snow, ice, mud, grease, oil, or other slippery substances.
- All timbers, blocking and cribbing materials shall be of quality material and be in good serviceable condition with flat surfaces and with rounded edges
- Hydraulic jacks shall be equipped with spherical bearing plates or shall be in complete and firm contact with the bearing surfaces and shall be aligned so as to avoid eccentric loading.
- Loads shall not be hoisted, swung, or suspended over anyone and shall be controlled by tag lines
- The attachments of the test beam(s) or reaction frame to the anchor piles or other anchoring devices shall be designed and installed to transmit the required loads with an adequate factor of safety.
- All reaction loads shall be stable and balanced. Safety wedges shall be in place at all times to prevent the platform from tipping. During testing, movement of the reaction load or system should be monitored to detect impending unstable conditions. All test beam, reaction frames, platforms, and boxes shall be adequately supported at all times. Only authorized personnel shall be permitted within the immediate test area.
