Any tests of soil with piles can be carried out at various stages of construction - both during the survey and before the design, during the process of submerging the elements, during the acceptance of submerged piles.
There are several purposes of testing soil with piles static load, they will depend directly on the stage:
- At the survey stage, any static load test is usually performed to select the desired length, diameter of the pile cross-section, correct evaluation of the bearing capacity.
- During the immersion of test elements and their extraction, the main goal of static tests will be to determine the correspondence of their actual bearing capacity and to correctly compare it with the calculated one, the one that is adopted in the design.
That is, any test with a static load is performed in order to determine if there is a correspondence between the readings of the actual bearing capacity of such piles with the design load. The data obtained during static tests usually differ substantially in their accuracy and reliability, in contrast to dynamic tests. But at the same time, static ones are more complex, expensive and labor-intensive than dynamic ones, and therefore are often assigned for the construction of more complex, large objects with a huge foundation.
When choosing a test procedure for static loads, as well as the number and evaluation of the results achieved by a static load, the following points should be considered:
- the number and data obtained with such checks are characterized with a high degree of accuracy by the bearing capacity for indenting the test element as compared to the obtained dynamic load test data or the ground sounding method;
- the increase in the time interval of the static load (duration and number of tests) for the newly tested pile leads to an increase in displacements, but has almost no effect on the magnitude of this ultimate load;
- the obtained data on the test results of some single elements that are in the bush characterize, with a normal degree of approximation, the maximum load during operation as part of the foundation, but can not be directly applied in estimating the values or horizontal displacement of the foundation as a whole;
- the very limit position of the pile according to its condition (ultimate resistance on the ground) is characterized by the beginning of the priority of the movements of the tested pile with a constant step of increasing the load applied to it.
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What is necessary for a successful test under static loads?
Perform a static test of all piles on indenting and pulling loads, necessarily using a special installation.
Often it includes the following elements:
- loading devices: jacks or platforms with a load, the mass of which can be arbitrarily changed;
- support structure consisting of reinforced concrete, metal trusses, having anchor piles, which will transfer the load to the test element;
- device for measuring the value of the draft of the pile under load (there should be a measurement accuracy of approximately 0.01 mm), which includes several special measuring instruments that are qualitatively integrated into the whole system.
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Technology of static testing of piles
The process of static testing of piles always begins with the determination of the number of test piles, the future locations of their piling. And only after that in some certain places some test piles are dipped. All tests during piling and acceptance are performed on piles that are located in places with the worst ground conditions for this facility or which have given the greatest failure when driving.
Tests of the soil with a static load should be started after resting. For those piles that are loaded in other ways, the beginning of the tests is determined by the program of such tests, but not earlier than one day after the dive. During the tests, the beginning of the tests is given by filling (boring) piles before the concrete reaches 80% strength. The testing of thawed soils with a static pressing load is performed uniformly, without any impacts, by load stages, the value and quantity of which is established by the test program. When all lower ends of similar field piles are buried into large clastic soils, dense sands and clay soils of solid consistency, the first 3 load steps are assumed to be equal to 1/5 of the total load.
Before carrying out any static tests, carefully plan the surface of the selected soil around the most experienced pile. The loading object must be mounted so as to provide a precisely central application of strictly vertical loading. The test pile must necessarily have the required strength of the material, which will ensure that all the required characteristics and features of the bearing capacity of the ground are obtained. And, if necessary, the pile head is strengthened by means of an outer cage. Immediately before the test, the elements should stand for a while. This is done in order to restore all the structural bonds in the ground and, accordingly, the test pile showed the most real result. Time-rest before all tests in accordance with GOST is:
- rest 1 day - when under the edge of the piles there are coarse clastic soils or dense sands;
- rest 3 days - the period calculated for sandy soils;
- rest 6 days - for clay soil and dissimilar soils;
- rest 10 days - for sand, saturated with water.
Often rest should be 6-7 days from the time of driving.
The tested piles are loaded with steps, it is possible to proceed to the next stage of loading after a special special stabilization of the draft at the previous stages.
In order to measure the sludge of the tested piles, hourly-type indicators are installed that have a division price of 0.01 mm. The emerging reactive forces that occur when any test piles are being loaded are transmitted directly through the beam system directly to the anchor piles. To record the possible pulling and dropping of the anchor elements by statistical load, 2 dial-type indicators with a division of 0.01 mm are set for each element. Taking into account the possible elongation of the top of the reinforcing cage, any pulling of the anchor piles at the time of testing should not exceed 0.2 cm.
Before all loads, take zero counts and the number of all available devices. And at each stage, before the static load, the samples for all available devices are also taken. For the criterion of some conditional stabilization of the strain before loading, the rate of settling piles at this stage of loading is usually taken to be greater than 0.1 mm for the last 60 or 120 minutes of observations. And for a particular value of the ultimate resistance of the test elements, a load is applied to the statistical load, under which the loading of the elements is already terminated.
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Methods of statistical testing
The correct choice of the necessary equipment and tools for static testing directly depends on the adopted method of loading. In modern construction, the following methods of loading are distinguished:
- stowing of the taken cargo on the platform, which is installed on the pile;
- use of tension couplings and winches;
- the use of all efforts of hydraulic jacks;
- use only own weight.
A method of static testing with the use of hydraulic jacks is quite widespread: it is considered to be the least laborious and the cheapest.
Calculation of the bearing capacity of the pile types incorporated in the project is based on the results of preliminary engineering and geological surveys. Field tests are performed to determine the actual load capacity, the optimal type, the size and the pile step, which can be static or dynamic.
Static Load Testing
Field testing and processing of survey materials are carried out in accordance with GOST 5686-2012 "Soils. Methods of field tests with piles ", JV 24.13330.2011" Pile foundations "updated version of SNiP 2.02.03-85 and according to the test program developed by our specialists and coordinated with the customer. The result of the tests is a report provided with graphs of the dependence of the pile load on the loading and deformation measurement in time on the loading stages, indicating the actual bearing capacity of each of the tested piles in accordance with GOST 5686-20125 and JV 24.13330.2011.
Static tests of 2016/17
| № | Type of work | An object | date | A photo |
|---|---|---|---|---|
| 1 | Static test for pile pressing with piles 300x300 mm, dl. 7,00 m, the load is 52 tons. | "Fencing center for training sessions" at the address: Moscow region, Khimki, Novogorsk microdistrict | 02.2016 | |
| 2 | Static test for punching of piles with piles Ø 250 mm, dl. 13.50 m, for a load of 37 tons. | "The warehouse base, located at the address" Moscow region, Ramensky district, p. Bykovo Str. Collective farm, section 16/3 | 02.2016 |  |
| 3 | Static test for punching of piles with piles Ø 350 mm, dl. 12.75 m, the load is 38 tons. | The pile for the foundations of the new warehouse block of JSC "NIKIET" at the address: Moscow, 2nd Irtysh passage | 05.2016 |  |
| 4 | Carrying out a static test (drilling pile piles Ø 200mm) | Strengthening the foundations of the building located at: Moscow, 1-st Truchenikov Lane. | 06.2016 |  |
| 5 | Static test for indenting piles with piles Ø 219 mm, dl. from 8.5 m - to 15.75 for a load of 18 tons to 78 tons. | Reconstruction and restoration with the adaptation for modern use of the object "Polytechnical Museum" at the address: Moscow, Central Administrative District | 07.2016 |  |
| 6 | "Construction of an individual house" at the address: DNP "Bear Lake" near the village of Kuzmenki, Shchelkovo district. | 08.2016 |  |
|
| 7 | Static test for punching of piles with piles Ø 250 mm, dl. 8.70 m, the load of 22.4 tons. | "Reconstruction and technical re-equipment of the laboratory-constructive building (LCC) of JSC" State Machine-Building Design Bureau "Vympel" them. I.I. Toropov "at the address: Moscow, Volokolamskoe highway. | 08.2016 |  |
| 8 | Static test for punching piles with piles Ø 273mm, dl. 5.60 m, the load is 24 tons. | "Construction of an annex of the sports hall to the building of the UDO school" Christian School named after Hingson "Moscow, Novocheremushkinskaya str., 39, building 3 | 09.2016 |  |
| 9 | Static test for indentation of soil with a screw pile shaft Ø 159mm, blade 550 mm long. 4.00 m and 1.61 m, the load is 14.4 tons. | Modernization of the shopping and entertainment center "MEGA" (reconstruction of individual zones). Moscow Region, Khimki, Microdistrict IKEA, building. No. 2, with regard to adjusting the pavilion structures in the axes 22a-24a / L-O1 | 09.2016 |  |
| 10 | Static test for punching piles with piles Ø 159 mm, dl. 6.35 per load of 10 tons. | The device of pile foundations under supports of awnings on the station. Oranienbaum of the Oktyabrskaya Railway. | 04.2017 |  |
| 11 | Static test for punching of piles with piles Ø 250 mm, dl. 15.00 m, the load of 22 tons. | "Reconstruction of a multifunctional public cultural center" at: Moscow, Bolshoy Kiselniy per., D.11 page 4 | 04.2017 |  |
| 12 | Static test for punching piles with piles Ø 800mm, dl. 7.00 m, the load of 64 tons. | Pig breeding complex with a completed cycle of 270 pigs per year "and" Slaughterhouse with refrigerators "in the Bezhetsk district of the Tver region | 04.2017 |  |
| 13 | Static test for punching piles with piles Ø 400mm, dl. 8.00 m, the load is 39 tons. | Reconstruction of real estate objects (building of the production building and structures) "at the address: Moscow region, Egorievsk, Kasimovs'ke shosse, 34 | 05.2017 |  |
Main technological nuances
1)
The work is started after the designers determine the number and location of the test piles. Among the few immersed test piles for testing, those that have the lowest failure rates or those located in areas with the most difficult ground conditions are selected for the test. 
2) Before the tests begin, the piles are allowed to settle, which provides an opportunity to restore structural bonds in the ground. The period of "rest" of piles varies from 1 to 10 days, depending on the type of soil. For Moscow and the Moscow region, this period is usually 6 days.
3) Static load tests are carried out using a special installation, which includes a loading device, a supporting structure and a measuring instrument system. During the tests, the impact on the pile is affected by the load of a certain mass (in most cases - 1/10 of the design load). Each subsequent load stage is performed exclusively after the stabilization of the precipitate at the previous stage, i.e. if the value of the draft did not exceed 0.1 mm in the last 30 minutes.
The essence of dynamic tests is to identify the connection between the generated hammer energy in the process of pile driving and the amount of its immersion in the ground. The failure of the pile decreases as the resistance of the soil increases and upon completion of the tests the final failure value is calculated. The final calculation of the load-bearing capacity of the pile requires consideration of a number of attendant factors, including the characteristics of the equipment (using the same types of equipment as for basic pile work).
Tests with dynamic loads are mobile enough and less costly in comparison with static loads, but in many cases do not provide proper accuracy of indications.
If the construction will be conducted on clay and sandy soils, then pre-test the soil with piles. This is necessary to determine the physico-mechanical properties of soils, their bearing capacity and resistivity, as well as to identify their deformation characteristics. The documents regulating such tests are GOST 20276-85, GOST 21719-80, GOST 23741-79, GOST 20069-81.
If it is impossible for any reasons to use heavy equipment on the construction site to drive piles, the company "BURINZHSTROY" offers to use technology devices for microspoons - effective, reliable and affordable. By the same method, the existing foundations can be strengthened - along with technologies
Long before the construction of the capital construction began, a whole complex of measures is being implemented to ensure the correct choice and further calculations of structural elements, in particular, foundations. Testing of piles is carried out at the stage of engineering surveys and control checks during the construction period. In the process of work, the bearing capacity and possible deformations are determined, after which the data are compared with the design parameters specified in the design documentation. If necessary, the type and dimensions of the piles are corrected, as well as the technologies for their penetration.
General Provisions
Field tests of piles are carried out before the beginning of their mass installation. The main document regulating the order of work is GOST 5686-2012. He is referred to SNiP and SP, which determine the correctness of calculations and the construction of pile foundations.It should be noted that this state standard does not cover soil rocks:
- large-fragmented, containing more than 40% volumetric inclusions;
- swelling or saline, if required to soak for testing.
The GOST in question has nothing to do with the studies conducted to determine the endurance of piles in the event of seismic or atypical dynamic loads appearing during the operation of the facility.
The soil is tested by piles:
- the natural, not differing from usual on the size, a material and a design;
- standard, representing a composite shell of metal d = 114mm, buried by the clogging method;
- probes - in the form of metal piles d = 127 mm with pointed tips and friction clutches.
The corresponding SNiP and GOST allow dynamic and static variants of soil testing with piles. In the process of testing, the inhomogeneity of the pile sinking is determined, as well as the dependence of their movements on time factors and loads. The sites and the number of test points are determined by the project taking into account the most characteristic places of the built-up area.
The technical task for conducting the test works is a specially designed field test program.
Features of dynamic tests
Dynamic loads are understood as the impact of impacts or vibrations on the driven pile. This method is cheaper and simpler than the static version of the test, but it is not suitable for screw and bored piles.
It should be noted that dynamic tests of piles are performed after their penetration and "rest", the duration of which depends on ground conditions and is assigned by the field test program. When driving, according to SNiP, the equipment to be used in basic work should be used. Research determines the indicators:
- bearing capacity - according to the failure accepted, averaged taking into account the values of the pile immersion after one stroke or minute vibration;
- homogeneity of soil layers - by resistance to penetration;
- the possibility of submersion to the design depth.
The results are entered into the test of piles by dynamic loading, and estimates are made to establish the cost of work.
Features of static tests
The test is performed using dents or pulling loads, as well as horizontal forces. As stated in SNiP, tests of driven piles can only be carried out after their "rest", and bored or injection piles - not before the acquisition of 80% strength concrete.
In the case of testing the pile structure with punching forces, the impact on it is performed evenly and unstressed, but stepwise. This condition applies to both loading and unloading piles. All results are recorded in the relevant journal.
For control tests of driven and bored piles, the principle of the wave theory of impact is used, which consists in applying a sharp powerful thrust with a hammer in the direction of the vertical axis, which helps determine the resistance of the ground and simulate the draft of the foundation trunk.
Static tests of piles for pulling loads are not used for concrete, screw, bored, composite and broadened down piles. Horizontal forces are applied at least in two points, fixing possible deviations of the pile pillar. The loads in this case are taken not according to the SNiP tables, but according to the calculated indices specified in the design documentation.
What is included in the field test program
Based on a certain list of documents, various characteristics and requirements, a soil testing program is prepared with piles. GOST specifies that at the stage of engineering surveys should be taken into account:
- the results of similar studies conducted earlier for nearby buildings;
- forecast of a possible change in hydrogeological conditions;
- design features of the projected facility;
- design load on the structure of the foundation;
- design marks of the bottom of the grillage and the level of planning of the territory;
- assumed displacement of foundation structures taking into account operating conditions.
The program for control tests of soils with piles is made, relying on accepted in the design documentation:
- types and dimensions of piles;
- options for immersing structures;
- estimated forces and loads;
- ground conditions of the site.
The number of regulated GOST points of the program includes:
- the number of structures to be inspected;
- test points in the plan;
- maximum loads, minimum movements and deformations;
- methods and depth of immersion, including design failure;
- duration of "rest" or set of strength for bored piles;
- schemes of test installations, the direction and nature of the loads.
One of the GOST applications indicates the required number of points to be examined. With dynamic test methods - up to 1% of all piles, but more than six pieces. With indenting static forces - up to 0.5%, but more than two units, and with pulling forces - more than 2% or three piles. Similar requirements are advanced by the SNiP.
The composition of the soil test program should include a feasibility study (feasibility study), confirming or refuting the meaning of the research.
Estimate
Based on the main list of works, an estimate is compiled, in which a detailed list of the activities to be carried out with a calculation of their cost is listed. It includes:
- tariff for transportation of equipment;
- cost of machine shifts for the period of work;
- prices for forced simple during the installation and dismantling of mechanisms;
- payment of the test piles;
- additional costs, including fuel costs and depreciation.
According to the data of specialized companies, the cost of a dynamic test, confirmed by a laboratory conclusion, can be at least 8 thousand rubles. for one pile, and static - more than 40 thousand rubles.
According to the requirements of GOST 5686 "Soils. Methods of field testing with piles, SNiP 2.02.03-85 "Pile foundations" , SP 50-102-2003 "Design and construction of pile foundations", "Pile test programs", piles are tested in two main methods:
- static testing of piles
our company conducts both tests, although the second is much cheaper and technically easier. It should, however, be noted that the testing of piles by the second method is not applied to plastic clay soils, as well as on loose soils in the form of construction debris or household dumps.
Testing of piles: why it is necessary
Field tests of piles are made:
- to determine the required type and dimensions, as well as the bearing capacity of the piles
- to verify the real possibility of piling the piles to the design depth and to assess the degree of homogeneity of the soils, for which the soil is tested with piles
- to establish the dependence of the draft of piles in the ground on the applied loads and over time
In this way, the bearing capacity of the piles is checked for design design loads.
Static tests of piles - what you need for this
To conduct static tests of piles on indenting and pulling loads, a special installation is required, which consists of:
- device to ensure load on the pile (this can be a platform with a calibrated load or using a jack). Tests with vertical static loads are also called die tests.
- Support structure, through which loads will be transmitted to the pile (a system of metal (reinforced) beams or trusses with anchor piles) measuring devices that fix the degree of movement of the pile during testing with a measurement accuracy of 0.01 mm.
See also:
The process of static testing of piles
When testing a pile with a static method, it is loaded with steps, the weight of which is calculated depending on the design load on the pile (usually not more than 1/10). At the same time, the load is the next step after stabilization of the draft at the previous stage.
Before loading the test pile, a zero mark is set on all measuring instruments. Indications are also taken from all instruments at each loading stage.
Conditional stabilization of the pile is determined by the following criterion: at this stage of loading, the rate of settling of the pile does not exceed 0.1 mm. During the last 30 minutes of observation. 
The value of the partial limit resistance is the load at which further loading of the pile is stopped.
We produce by any method. As we have already mentioned, the price for static testing is much higher, besides they require additional equipment. However, as mentioned above, in some cases it is simply impossible to do without static tests.
Static testing of bored piles
The static test technology (pictured below) shows the actual state of the permissible loads on the test piles.
The test procedure is quite simple, but it requires labor, time and special equipment. The principle is simple - you need to press the test pile with enough force to let it fall down. In this case it is required to press, and not to drop something from above, as in dynamic tests. In this case, special stands are built over the pile being tested.
Stand for static testing of piles and soils
These stands load a certain weight and observe the draft of the pile. Tests stop after the pile has settled more than the required level. However, there is a simpler and cheaper way - to use a hydraulic jack. It is necessary to press down, accordingly the question is solved by installing additional piles near the subject (usually near one line).
Such piles are called anchor piles. On top of the anchor piles is installed a metal beam, welded to them. It is in this obstacle that a hydraulic jack with a manometer will be installed.
The tested pile is clogged slightly below the anchor to mount the jack on it. The pressure is fed gradually in stages under constant control. Testing stops either according to the gauge (usually 20-30% more than the planned load), or if the pile does not withstand the load and plunges down. Static tests have a high cost, are spent about a day, but at the same time are the most accurate among all similar. According to the SNiP, up to 1% of the total number of installed piles are subjected to static tests.
To calculate the cost, estimates are used and, at the end of the tests, a test report is issued.
Standards, rules and standards of testing.
The current test standard is GOST 5682 2012. The standard applies to methods of field testing of soil with piles (standard, full, pile-probes), which are carried out during engineering surveys during the construction period. It also extends to the control tests of various piles.
The building rules and norms of SP No. 50-¬102-¬2003, SNIP No. 2.02.03-¬85 apply to the survey of foundations, the survey of foundations and the design of pile foundations of reconstructed and erected buildings and structures.
Design organizations in the development of the design part of the documentation using pile foundations calculate the bearing capacity of the pile based on engineering and geological survey data.
To obtain the actual value of the load-bearing capacity of the pile, before the start of mass piling, Test piles, after obtaining the test result of which, the designer decides on the confirmation of the lengths taken by the project of the number of piles, or makes changes to the design of the pile field, varying the length, or the step of the piles.
Rest piles before testing
Prior to testing, the piles must be stabilized in order to restore structural bonds in the ground and, accordingly, the pile showed real results. Time so-called. "rest" piles before testing in accordance with GOST is:
1 day - if there are coarse clastic soils under the tip of the pile, or dense sands
3 days - for sandy soils
6 days - for clay and dissimilar soils
10 days for water-saturated sands
For Moscow and Moscow region in 95% of cases, the time for "resting" of the pile takes 6 days from the moment of blockage.
Dynamic testing of piles
The essence of the dynamic test is the measurement of failure (pile settling) when the diesel hammer is dropped onto the head of the pile already immersed in the design mark. This type of test can be used for any types of driven piles. It is also possible to test the carrying capacity of clogged pipes (tongue).
Diesel hammer, without fuel supply, that is, "idle" is discharged from a certain height (for the hammers used by our company with an impact part of 2.5 tons, the discharge height is 1.8 meters). Further, the laboratory assistant measures the draft of the pile with the help of a special gauge device, or an ordinary level gauge. If the draft is too small, the value of precipitation (failure) is recorded with 10 blank shocks. Based on the results obtained, the laboratory calculates the bearing capacity of the pile and issues a report of the established form with all schedules and calculations.
Advantages of dynamic tests:
In the low cost price
The time taken for the test is no more than 20 minutes (by the end of the day you can get a report)
Sufficiently accurate load-bearing capacity
Usually, the designer assigns dynamic tests to 1% of the total number of piles.
An example of a report on dynamic testing of piles.
Static testing of piles
The essence of the static test of the pile is to "load" the clogged pile from above and track its draft with a stepwise increase in load. There are several options for how to apply pressure to the pile. You can build a special stand and, for example, a crane, add concrete blocks from above. But it is much easier to create a system using anchor piles. It is this testing system that our company applies to every facility. Pay attention to the photo below. In the middle, a small blue device is a hydraulic jack. It stands between the test pile and a large metal beam. With increasing pressure, the jack leaning against the beam (or the beam system) presses on our test pile with a given load. In turn, the beam is attached to the so-called. "anchor" piles, for which the head of the anchor piles are broken, and the reinforcement of the piles is welded to the beam. Anchor piles, depending on the estimated load can be from 2 to 6 pieces. The jack is equipped with a manometer. The pile is loaded with steps. The precipitation indices at each stage are fixed. If the sediment exceeds a certain value, the tests are terminated and the test readings are recorded in the previous stage.
The main advantage of static testing is that the test simulates the real work of the pile in the foundation. But the cost of such a test is approximately 10 times greater in comparison with the "dynamics".
On average, the cost of testing piles with a dynamic load is 6 thousand rubles, static cost - 60 thousand.