Method for determining bearing capacity of piles in subsidence soils
By driving a composite pile with extended testing and soil soaking, the method addresses inaccuracies and high costs in existing pile capacity determination, achieving precise results efficiently.
Patent Information
- Authority / Receiving Office
- RU · RU
- Patent Type
- Patents
- Current Assignee / Owner
- БУЛАНКИН НИКОЛАЙ ФЕДОРОВИЧ
- Filing Date
- 2024-05-29
- Publication Date
- 2026-07-07
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
Existing methods for determining the bearing capacity of piles in subsidence soils are inaccurate and costly, particularly when groundwater levels are at the lower boundary of subsidence soils, and traditional testing methods distort results due to pile flexibility and require expensive soil soaking processes.
A method involving driving a composite pile through a casing pipe to the design depth with a specific extension above the subsidence layer, testing with both pressing and pulling loads, and soaking the soil to determine the pile's bearing capacity accurately, eliminating the need for large-diameter casing and costly soil soaking.
This method reduces costs and labor while increasing the accuracy of bearing capacity determination by testing a single pile under various conditions, ensuring precise results without the need for extensive soil preparation.
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Abstract
Description
[0001] The invention relates to the field of construction, in particular to determining the bearing capacity of a pile in subsidence soils.
[0002] A method for determining the bearing capacity of a pile by calculation is known.
[0003] According to this method, the bearing capacity of a pile is determined as the sum of the bearing capacity of the pile tip and the friction of the soil along the lateral surface of the pile, while the characteristics of the soils are taken as negative when they are soaked; the friction force is determined by the characteristics of the soil in their natural state (clauses 9.5, 9.9 of SP 24.13330.2021).
[0004] However, the result of such a calculation is approximate and rarely coincides with the results obtained during static tests of piles.
[0005] Another method for determining the bearing capacity of piles in type II soils is known, based on the results of static tests for subsidence. The pile being tested is inserted through a casing pipe with a diameter greater than the pile's cross-section and, without touching the pile's edges, is subjected to compressive loads. In this case, the upper part of the pile is within the subsidence limits of soils with natural moisture content, and the groundwater level is at the lower boundary of the subsidence layer (clause 9.11 of SP 24.13330.2021).
[0006] Disadvantages of the above methods:
[0007] - sites with such soil conditions that the groundwater level is at the lower boundary of subsidence soils are a special case, which is practically very rare; artificially raising the groundwater level without soaking subsidence soils is an expensive undertaking, since soaking the soils through drainage wells with casing pipes, water metering wells, again with pipes, require significant expenditure;
[0008] - the option of casing the well with a pipe with a diameter larger than the cross-section of the pile, driving the test pile into it and loading it with a jack to the load specified by GOST 5686 will not be possible due to the flexibility of the piles and, therefore, the result will be distorted.
[0009] The objective of the invention is to reduce the cost and labor costs in determining the bearing capacity of a pile in subsidence soils, as well as to increase the accuracy of its determination.
[0010] To solve the problem in the known method of determining the bearing capacity of a pile in subsidence soils, which includes driving the test pile to the design depth in soils of natural moisture through a casing pipe with a diameter greater than the cross-section of the pile, length h sl (the thickness of the subsidence layer), while the groundwater level should be at the lower boundary of the subsidence soils (if necessary, maintain this level), determine the bearing capacity of a pile of length l св = lhsl , where l is the length of the pile in the ground, m, h sl - thickness of subsidence layer, m.
[0011] A pile driven through a casing pipe is tested with pressing loads, maintaining the groundwater level at the lower boundary of the subsidence soils, and the second pile is tested with pulling loads to determine the force of negative friction.
[0012] The second test pile is driven into the ground to the depth of the subsidence layer h sl .
[0013] In the proposed method, one test pile is driven into soil of natural moisture to the design depth. The pile length is l св equal to the pile penetration depth l plus Δl = 0.5÷1.0 m (the pile’s elevation above the design elevation for installing the pile pulling device).
[0014] Fig. 1 shows the test pile in the ground. The pile is composite with a cross-section equal to the cross-section of the design piles, consisting of an upper section 1 of length l св equal to the thickness of the subsidence layer h slplus 0.5÷1.0 m; length of the lower section 2 (l н.с. ) is equal to the total length of the pile l св minus the length of the upper section l в.с. .
[0015] Fig. 2 shows a joint of a composite pile 3, consisting of a rod 4 with an anchor plate 5, concreted in the lower end of the upper section and a tubular sleeve 6 with an anchor plate 7, concreted in the head of the lower section of the pile (there may be several lower sections).
[0016] When joining pile sections, rod 4 enters sleeve 6 and the joint fixes the pile sections from horizontal displacement, but does not prevent the sections from moving from vertical displacements.
[0017] After the pile being tested has been driven in and “rested,” the upper section is tested with pull-out loads until the pile extends at least 40 mm, then the soil on top is soaked to a moisture content of S r ≥ 0.8.
[0018] After the soil has been soaked, the upper section is tested with pressing loads until settlement occurs, at which point the ends of the pile sections are in close contact, and testing of the entire pile is continued until loads are applied in accordance with GOST 5686.
[0019] Bearing capacity of pile kN, is determined by the formula:
[0020] ,
[0021] where - bearing capacity of a pile of length l, kN;
[0022] - the bearing capacity of the upper section of the pile based on the results of tests with compressive loads in water-saturated soils, kN.
[0023] Example of the method implementation
[0024] On a construction site composed of the following soils:
[0025] Engineering-geological element-1 - hard subsidence loam, 10.0 m thick; subsidence due to the soil's own weight is 12.5 cm;
[0026] Engineering-geological element-2 - loam with sandy loam interlayers, solid, non-subsiding, 8.0 m thick;
[0027] The composite pile is driven with a tubular diesel hammer of the SP-78 brand with a striking part weight of 3.5 m to failure S a =0.2 cm / impact.
[0028] Characteristics of the composite pile: length 19.0 m (upper section 11.0 m long; lower section 8.0 m long), section 300x300 mm, concrete class B25, immersion depth 18.0 m.
[0029] The maximum load during the pull-out test of the upper section of the pile in soils of natural moisture content was 400.0 kN. The bearing capacity of the pile with the working condition factor γ с =1.0 was: F d =360.0 kH.
[0030] Then soak the soil to a moisture level of S r ≥ 0.8 and perform a test of the upper section of the pile with pressing loads until the settlement at which the ends of the pile sections are in tight contact.
[0031] The bearing capacity of the upper section of the pile during pressing was 250.0 kN in water-saturated soils.
[0032] Perform pile length / indentation load test.
[0033] The bearing capacity of a pile of length I when pressed in was 1200.0 kN in water-saturated soils.
[0034] The bearing capacity of a pile of length l was: F d =l200.0-250.0=950.0 KH.
[0035] Negative friction force with working conditions coefficient γ с =1.2 was: P n =1.2⋅360.0=432.0 kN.
[0036] The bearing capacity of the pile, taking into account the force of negative friction, was: F d =1200.0-432.0=768.0 kH.
[0037] Design calculated load on a pile with soil safety factor γ c,g =1.2 was: N=F d / γ c,g =768.0 / l.2=640.0 kH.
[0038] The above example shows the advantage of the invention:
[0039] - only one pile is tested instead of two;
[0040] - costs are reduced by eliminating the need for a large diameter casing well;
[0041] - the process of soil soaking is simplified.
Claims
1. A method for determining the bearing capacity of piles in subsidence soils and a device for implementing it, including static tests with pull-out loads of a pile driven to a depth equal to the thickness of the subsidence layer, and tests of another pile driven to the design elevation through a cased borehole with a diameter greater than the cross-section of the pile, to a depth equal to the thickness of the subsidence layer h sl , wherein the groundwater level must be at the lower boundary of the subsidence layer, characterized in that one pile is tested without isolating it from the subsidence soil and without soaking the soil by raising the groundwater to the lower boundary of the subsidence layer, while the pile is composite with a length of l св , with cross-sectional dimensions equal to the cross-sectional dimensions of the design pile, consisting of an upper section of length l в.с. , equal to the thickness of the subsidence layer h slplus 0.5÷1.0 m (for installation of the pile pulling device) and the lower section, length l н.с . which is equal to the total length of the pile l св minus the length of the upper section l в.с. .
2. The method according to paragraph 1, characterized in that after driving the test pile to the design level and allowing it to “rest”, the upper section is tested with pull-out loads until the pile extends at least 40 mm, the force of negative friction is determined based on the test results, and then the soil is soaked using the traditional method (through pits and drainage wells filled with crushed stone).
3. The method according to paragraph 1, characterized in that after water saturation, the upper section is tested with compressive loads until settlement occurs, at which the end of the upper section rests against the end of the lower section. The bearing capacity of the upper section of the pile is determined based on the test results.
4. The method according to paragraph 1, characterized in that after testing the pile of length l св pressing loads to determine Bearing capacity of piles in water-saturated soils kN, is determined by the formula: , Where - bearing capacity of a pile of length l св , kN; - bearing capacity of the upper section of a pile of length l в.с. , kN.
5. A device for implementing the method of paragraph 1, characterized in that the pile joint consists of a rod with an anchor plate concreted into the lower end of the upper section and a tubular sleeve with an anchor plate concreted into the head of the lower section. During joining, the rod enters the sleeve; the joint secures the sections from horizontal displacement, but does not impede movement of the sections from vertical displacement.