Professional teams of builders and designers before starting construction always carry out certain preparatory work. Such works include static and dynamic testing of piles. They are carried out in order to have complete information about the soil, as well as in order to obtain the most complete information about the foundation and its behavior.
General information
Currently, static tests are designed for three types of support elements.
The first type of such elements includes field samples. These are products that are used in ordinary construction work. The dimensions of this product, the material, as well as the installation method, correspond to the actual conditions of development. Suppose, if a full-scale sample is installed to test bored piles, then the technology of its installation should be similar to elements from the same group.
The second type is a reference pile. Such elements are made of a composite metal rod, and in its shape it is similar to a conventional driven pile, the diameter of the rod of which is 114 mm. The assembly of the reference piles is carried out from different elements, and the final length is 12 m.
Pile probe. The diameter of this object is 127 mm, and it is also made of components. The length of this pile is 16 meters.
Stage for testing
GOST static test piles regulates the verification of objects at some stages.
The first stage at which it is necessary to conduct a static or dynamic check is the stage of research, as well as the implementation of design work. It is necessary to find out the size, cross-section, as well as determine the bearing capacity of the piles and compare it with the required design for a particular construction object. After testing at this stage, experts give a conclusion that all the calculations are consistent, or they are re-performed if something does not match.
The second stage, during which static tests of piles are carried out, is the immersion and extraction of the object. These actions allow you to compare the actual ability of the piles to withstand the load with its design data.
It is also important to note that the data obtained from the static tests of piles are more accurate than the data obtained from dynamic tests.
Test purpose
Field tests of piles are carried out in order to solve the following problems:
- Choose a suitable product design that is planned to be used at this building object, select the correct geometric dimensions for each object, and determine their ability to withstand the load.
- Also, static tests of piles are carried out in order to determine whether it is possible to immerse the object to the required depth, and in order to assess the uniformity of the soil in which the foundation will be installed.
- The last thing that tests are carried out for is to determine the amount of movement of the pile under load, which will be applied to it for a given period of time.
Test Methods
There are several methods for conducting static pile tests. These tests are carried out depending on the method of applying the load to the product. It is also important to note that the alternating load depends on the selected verification method, which will be applied to the tested object. The choice of application of the load is very important, since it will depend on what equipment will be needed for testing.
- For some tests, a special loading device is required, which most often is a hydraulic type jack or a platform with a load, the weight of which can be adjusted. Also, during static testing of piles in this way, it is allowed to use tension couplings or winches.
- In some cases, a prefabricated structure of materials such as metal beams and reinforced concrete slabs with anchors is used. This design is installed in such a way as to transfer all the weight to the test structure.
- There are also cases when it is necessary to use a special measuring device that controls the amount of pile immersion under load. This device is a group of measuring instruments that are combined into one set. The accuracy of measurements obtained in this way is provided up to 0.01 mm.
Test technology
The technology of static testing of piles begins with the fact that it is necessary to check the quality of the rod, as well as the place where the object will be installed. According to GOST, it is necessary to drive piles to the place that is characterized by the worst soil performance on the entire construction site. Also, according to the test technology, time is provided for the "rest" of the pile. That is, you need to give time to the object to stand after driving. Only in this case will objective results be obtained from testing the piles with a static load.
Test time
GOST also sets the amount of time that is required on a simple pile. The amount of time depends on the type of soil in which the object is installed.
- 1 day of downtime will be required if the object is mounted in dense soil, which is saturated with sand or clay, as well as for coarse soil;
- 3 days are allotted for simple piles in a completely sandy basis;
- 6 days of downtime will be required when installing piles in heterogeneous soil or clay;
- the greatest amount of time, that is, 10 days, will have to be spent if the pile is installed in a completely sandy and moist base.
However, it is fair to say that at present, the most optimal period of downtime is considered to be 6 days. Since it is heterogeneous soil that prevails throughout the Russian Federation. It is also important to note that the load on the pile according to GOST must be carried out in steps. You can proceed to the next load stage only when this stage has passed 100% stabilization.
Verification Methods
To date, three methods of static testing of piles are used. One of these methods involves the use of only its own weight. This method is used if the object is mounted in rather soft soil, the resistance of which is small. A platform with a load or a jack can also be used.
It is worth saying that the estimate for the static test of piles is made in advance. It is also important to know that the use of a hydraulic jack is considered the most common verification method. This method is most widely used, in particular because it requires a minimum amount of time to check, and is also the cheapest way to check. It can also be noted that static testing can be carried out not only in specially designated areas for this, but also directly at construction sites.
Test
In order to carry out the verification, experts hammer several test piles. The number and the place where objects are driven in are determined by the design organization, which follows GOST 5686 "Soils. Field test methods with piles." The load on the object is carried out gradually and proceeds to the next stage only after complete stabilization of the pile driving in the previous stage.
In order to measure the draft of the piles, which is being tested, set 4 indicators of the watch type, the scale division value of which is 0.01 mm. The reactive forces that load the pile are transferred to it from the beam system. Also, in order to register a possible pulling out of the anchor pile, two more dial-type indicators are installed on it, with a scale division price of also 0.01 mm. If we take into account the possible lengthening of the upper part of the reinforcing cage of the pile, the pulling out of the object should not exceed 2 mm.
Static testing of bored piles
The static verification method is an imitation of the operation of an object under load, which will be applied to it in the future. This verification method is considered the most correct and accurate when compared with dynamic tests, but at the same time it will cost more and take longer. The bearing capacity of the foundation is the ability to withstand loads, while maintaining the integrity of the structure.
In order to cope with the loads, the pile foundation must have a bearing capacity not less than the totality of all the loads exerted on it, as well as taking into account several correction factors. Static tests are designed specifically to determine the bearing capacity of a pile foundation.