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Soil Testing with Bored Piles

Bearing capacity of piles or ability of pile to resist external loads can be determined by by tables and estimated dependences, according to dynamic tests, dynamic and static sounding, tests of reference and full-scale piles. The most authentic method is field tests of piles. Field tests of piles are carried out to purpose of monitor the compliance of their bearing capacity to the design loads accepted in the project of the pile base. Tests of bored piles for the indenting, pulling out and horizontal static loads are executed according to STB 2242 - "Soil. Methods of field tests" taking into account requirements of TKP 45 - 5.01-254 - "The bases and the bases of buildings and constructions. Basic provisions. Construction norms of design" or TKP 45-3.03-188 "Bridges and pipes. Construction norms of design of the bases".
The quantity of the tested piles in case of construction shall make:
- in case of test of piles the static indenting load to 0,5% of total quantity of piles on this object, but at least 2 pieces;
- in case of test of piles the static pulling-out or horizontal load - at least 2 pieces.
 

Measuring tools and equipment for test of piles

1. Hydraulic mobile pumping station;
2. Hydraulic mobile pumping station;
3. Deflectometers – 6 PAO units with price value division of 0,01 mm;
4. Gidroskan pessure gage or dynamometer;                     

Pile testing with static axial pressed and pullout loads           

Tests of bored piles are carried out to determine their bearing capacity on indentation (pullout) and find out dependency of soil displacement on loads. To load bored piles special equipment , which utilizes stop bar system as a hydraulic jack , is used. The installation diagram is provided in Figures 1-3.

 

Figure 1-installation diagram stand for the test pilings impressed loads

1-compelling pile; 2-anchor pile; 3-reference system with deflectometer;
4 - Hydraulic mobile pumping station with pressure gauge; 5-beam system 

Figure 2 - A general view of the test rig

Figure 3-installation diagram stand for testing pile pulling loads

Loading when testing a natural pile the pressing loading shall be brought to value in case of which the general draft of a pile constitutes at least 40 mm. When deepening the lower ends of natural piles in largely detrital, dense sandy and clay soil of a firm consistence loading shall be brought to the value provided by the program of testing, but one-and-a-half value of the bearing capability of the pile determined by calculation or the settlement resistance of a pile on material suffices.

Loading when testing soil the pulling-out loading in case of engineering testing for construction shall be brought to the value causing a pile exit from soil at least 25 mm.

Loading in case of control testing of a pile the pressing (pulling-out) loading in case of construction shall not exceed settlement load of the pile specified in the project of the pile base.

Unloading of the tested bored piles is made after achievement of the greatest loading by steps. Supervision over elastic movements at each step of loadings are made within 30 min. In case of complete unloading are observed within 1 hour.

Test of piles static horizontal loadings

Devices for measurement of horizontal movements of the tested pile establish in the planes parallel to the plane of action of force, not less than two: at the level of a surface of soil and at the level of the application of horizontal loading.

Loading of a pile static horizontal loading (figure 4) and removal of counting on devices is made according to requirements as for tests of a natural pile the pressing and pulling out loadings.

The figure 4 Scheme of Installation of the Stand for test of piles horizontal loadings

 

Take the speed of horizontal movement of a pile at each step of the application of horizontal loading which isn't exceeding 0,1 mm for the last 2 h supervision on the devices located at the level of the application of horizontal loading for criterion of conditional stabilization of deformation.

Loading at test of soil horizontal loading at engineering researches for construction has to be brought to the value causing horizontal movement of a pile not less than 40 mm at the level of the application of loading appointed by the program of tests. Loading at control test of a pile horizontal loading at construction shouldn't exceed settlement horizontal load of the pile specified in the project of the pile base.

Results of tests

Results of testing of soil a pile arrange in the form of schedules of dependence of deformation (draft, an exit, horizontal movement) a pile or its separate elements (the lower end and a trunk) from loading and measurement of deformation in time on loading steps.

The bearing capability of a pile and the greatest allowed load of a pile when testing is determined from STB 2242 and TKP 45-5.01-254.

Data for carrying out testing of bored piles a static load with technical characteristics of the equipment and devices and results of testing of piles are represented in a report form about testing of soil by piles.

Requirements to the program of field trials of soil piles

Requirements to the program of field trials of soil are established by piles in appendix A (STB 2242-2011)

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