Civil Engineering Construction I (CBE5031)

Transcription

1 Civil Engineering Construction I (CBE5031) Pile Test 1

2 Ch. 2B Quality Control of Piles As the design and construction of buildings become more complex, it is necessary to exercise closer supervision during construction to ensure quality of the building works. The foundation of a building is a fundamental structural element which supports the whole building. 2

3 Ch. 2B Quality Control of Piles As the foundation, when constructed, is buried in the ground, its built quality is not readily visible There is a need to enhance the supervision of foundation works during construction and testing of the completed works in order to ensure that the quality of the foundation works is up to standard. 3

4 2b.1. Pre drilling for piles founded on rock For piles founded on rock, sufficient pre drilling should be carried out before the installation works, such that the quality of the founding rock can be identified and the appropriate founding levels can be determined. The pre drilling should be sunk to at least 5m below the tentative founding rock levels of the piles. 4

5 2b.1. Pre drilling for piles founded on rock Pre drilling should be carried out for each of the large diameter bored piles, barrettes and the like. For minipiles, socketted steel H piles and similar small diameter bored piles, founding on rock, the number of pre drill boreholes required should be such that the pile tip of every such pile should be within 5 metres from a pre drill hole, or at a larger distance from it as decided by the Engineer. 5

6 2b.2 Determination of the Settlement of the Piles by Load Test Pile Loading Test Setup 6

7 2b.2 Determination of the Settlement of the Piles by Load Test Hydraulic Jack Kentledge 7

8 2b.2.1 Procedure of Load Test (Extraction from General Specification for Civil Engineering Works 2006) a. Working piles shall be tested to not less than 1.8 times working load. b. Test loads shall be applied and removed in three stages as stated in Table 1. c. The test loads shall be applied in increments, and removed in decrements, of 25% of the working load. Increments of load shall not be applied until the rate of settlement of the pile is less than 0.1 mm in 20 minutes. 8

9 2b.2.1 Procedure of Load Test d) The full test loads for Stage I shall be applied in increments and shall then be maintained for at least 24 hours after the rate of settlement has reduced to less than 0.1 mm per hour. The test loads shall be removed in decrements and the recovery of the pile determined before loading is resumed. e) The procedure stated in (d) shall be repeated for Stage II loading. f) The procedure stated in (d) shall be repeated for Stage III loading. 9

10 2b.2.1 Procedure of Load Test g) The settlement of the pile shall be measured at hourly intervals. The settlement of the pile under each increment and decrement of loading shall be measured. The exact times at which increments are applied and decrements are removed shall be recorded. h) The level of the reference beam shall be checked at regular intervals agreed by the Engineer during the test. Table 1 Test loading stages Stage Test load I 25%ofmax.testload II 50% of max. test load III 100% of max. test load 10

11 2b.2.2 Compliance criteria of load tests on piles (Remark: Buildings Department and Architectural Services Department have a different pile loading test procedure and compliance criteria. Please refer to the relevant technical documents which are available form the websites of the government departments.) 1. The settlement at any load shall be less than twice the settlement at 90% of that load (Brinch Hansen's criteria). 2. Under working load the gross pile head settlement shall not exceed 20 mm for buildings and 10 mm for other structures. 11

12 2b.3. Proof drilling 2b.3.1 For Large diameter bored piles Proof drilling shall be carried out on every largediameter bored pile to check the condition at the concrete/rock interface. A base coring tube of at least 150 mm diameter shall be left at about 1 m above the founding level of the pile. The core drilling shall be carried out to 1 m below the concrete/rock interface. 12

13 2b.3For minipiles and socketted steel H piles Proof drilling shall be carried out to verify the adequacy of the socketted length of minipiles and socketted steel H piles The depths of the proof drill holes shall be at least 5 metres below the founding levels of the adjoining piles. 13

14 2b.4Testing of concrete core from piles Concrete cores shall be 100 mm diameter. Each concrete core from a pile shall be inspected for evidence of segregation of the constituents and for the presence of voids. Specimens selected from each core shall be tested to determine the compressive strength. The concrete core shall be considered as non compliant if it exhibits honeycombing which means interconnected voids arising from, for example, inadequate compaction or lack of mortar. 14

15 2b.4Testing of concrete core from piles For any set of cores representing a test location, the average estimated equivalent cube strength shall be at least 85% of the specified grade strength. Each individual estimated equivalent cube strength shall be at least 75% of the specified grade strength. 15

16 2b.5. Sonic Test on bored pile Prior to concreting, three to four mild steel tubes of not less than 50 mm internal diameter are fixed to reinforcement cage of the cast insitu pile. The tubes shall be watertight, parallel to the axis of the pile and extend the full depth of the pile. Testing is carried out by lowering a pair of sensor probes (a transmitter and a receiver) to the bottom of the tubes. The tubes are filled with water/jelly prior to testing to provide acoustic coupling The probes are maintained at the same elevation and simultaneously raised slowly (20cm/s). The propagation of sonic signals between the tubes is recorded. 16

17 2b.5. Sonic Test on bored pile The test is repeated for each pair of tubes, i.e. three runs for a pile with three tubes and six runs for a pile with four tubes. 17

18 2b.6. Reference R.Chudley, 1985, Construction Technology Vol, 3 &4, Longman S.A.R. Jufri & R.J. Wellman, 1991, Civil Engineering Construction IV, Vol 2 & 3, Hong Kong Polytechnic R. Holmes, 1983, Introduction to Civil Engineering Construction, College of Estate Management M.J. Turner, 1997, Integrity testing in Piling Practice, Construction Industry Research and Information Association 18