The static load test method is recognized as the most direct and reliable test method for detecting the bearing capacity of foundation piles and foundations. It refers to applying vertical pressure, vertical pulling force or horizontal thrust on the pile foundation or foundation step by step or cyclically, observing the Settlement, uplift displacement or horizontal displacement of the top of the foundation over time to determine the test method of vertical compressive bearing capacity, vertical anti-pulling bearing capacity and horizontal bearing capacity of the corresponding pile foundation or foundation.
However, in actual engineering, the selection and installation of datum piles and beams are often overlooked by the inspectors, which ultimately leads to problems such as inaccurate displacement testing and increased stability time. Let's learn about the selection and installation of datum piles and beams in the displacement measuring device.
Datum pile: Datum pile is a concept in surveying, also called datum point. It is mainly used to erect a datum beam in static load test. The reference pile should meet the requirements of reliability and stability.
Reference beam: In the static load test, the displacement sensor for testing displacement is generally installed on the reference beam through a magnetic meter base. The reference beam should have sufficient rigidity, I-beam should be used, and the high-span ratio should not be less than 1/40. In actual engineering, scaffold steel pipe, I-beam, triangular truss, channel steel and other members are commonly used as reference beams.
"Technical Specifications for Construction Foundation Pile Inspection" (JGJ 106-2014)
4.2.4
3 The reference beam shall have sufficient rigidity, one end of the beam shall be fixed on the reference pile, and the other end shall be simply supported on the reference pile.
4 Fixtures and reference beams for fixing and supporting displacement gauges (percentage meters) shall not be affected by temperature, vibration and other external factors; when the reference beams are exposed to sunlight, blocking measures shall be taken.
4.2.6 The center distance between the test pile, anchor pile (the edge of the supporting platform of the weighted platform) and the reference pile shall comply with the requirements in Table 4.2.6.
Table 4.2.6 The center distance between the test pile, anchor pile (or the edge of the supporting platform of the weighted platform) and the reference pile.
Note:
D is the design diameter or side width of the test pile, anchor pile or ground anchor, whichever is greater;
The values in parentheses can be used when the pile center design of the multi-row pile foundation is less than 4D or the foundation soil within the influence range of 2 times to 3 times the width of the supporting platform pier has been reinforced;
When the test pile and the anchor pile are bottom-expanded piles or multi-disc installations, the center distance between the test pile and the anchor pile should not be less than 2 times the diameter of the enlarged end. When the stacking weight of the ballast platform on the soft soil site is large, it is advisable to increase the distance between the edge of the pier and the center of the reference pile and the center of the test pile, and observe the vertical displacement of the foundation pile during the test.
"Technical Specifications for Construction Foundation Pile Inspection" (JGJ 340-2015)
The specification puts forward specific requirements on the installation position of the reference pile, the length of the foundation pile quasi-beam, the installation method, and the control of external influence factors that may affect the test, mainly to ensure that the reference beam and the reference pile are not deformed by the material during the test , And the influence of external factors to ensure that the displacement test data in the static load test is correct, true, and reliable.
Small-tonnage static load demonstration experiment. The reference pile is driven into the ground 1m by using steel pipes. The reference beam is hollow square steel with a length of 8m. It is erected parallel to the direction of the pier. The reference pile is erected with a beam. Simply supported on the beam, the choice of foundation pile and foundation pile setting is relatively standard.
Note:
1 is the test pile center;
2 is the reference pile center;
3 is the edge of the supporting platform of the weighted platform, satisfying ≥4(3)D and >2.0m, one end is fixed and one end is simply supported.
On-site test at a construction site, the reference pile and the reference beam are all made of square steel into a triangular truss, and the length is 5m. During installation, one end rests on the foundation pile, and the other end is fixed on the reference pile with screws, so that one end is fixed and one end is simply supported. Requirements. However, due to site constraints, the distance between the edge of the pier and the center of the test pile and the distance between the foundation pile and the edge of the pier did not meet the requirements of the code.
a foundation test, a steel tube welded truss method is used as the reference beam. One end is simply supported and the other end is fixed by fasteners to meet the requirements of the specification.
Example of non-standard installation
