Analysis of the Pile Load-Bearing Capacity

This mode enables you to determine the load-bearing capacity of end-bearing and friction piles subjected to a vertical compressive load, F_d, and a vertical uplift load, F_du. Driven, cast-in-place, drilled, and shell piles are considered according to the requirements of Section 4 of SNiP 2.02.03–85 (Section 7.2 of SP 50-102-2003 or SP 24.13330.2011, Section 8.1 of "Instruction Manual for Design and Engineering of Pile Foundations for Structures in the City of Moscow"), and requirements of Section 5 of "Guide to the design of pile foundations". When calculating the load-bearing capacity of piles, peculiarities of the design for seismic regions are taken into account (Section 11 of SNiP 2.02.03–85, Section 12 of SP 50-102-2003 or SP 24.13330.2011, and Section 12 of "Guide to the design of pile foundations"). If the selected design code is DBN B.2.1-10-2009, then the requirements of Sec. N.7 of Annex N of this DBN are taken into account.

The analysis takes into account that the pile may have a pedestal at its tip and that a soil plug may be left intact or fully removed from the shell pile when its hollow core is filled with concrete. The possibility of grading the adjacent area (by cutting, filling, or hydraulic filling) and the presence of excavation in the location of the pile installation are also taken into account. The service factors for the pile in soil, γ_с, under the tip of the pile, γ_сr, and on the side surface of the pile, γ_сr, are specified by the user (it is also possible to select their values from an available set).

Data Preparation

The General tab enables you to specify a pile type in the End-bearing piles or Friction piles groups. Depending on the pile type, the values of a safety factor for soil, γ_g, service factor for pile in soil, γ_с, and for soil under the pile tip, γ_сR, are selected from the drop-down lists. If the construction site is in a seismic region and a friction pile is specified, you should check a respective checkbox and use the drop-down lists which will appear to select a concrete class, design seismicity of the site, and the frequency of occurrence of seismic actions, and then specify in the table the values of design loads (M and Q) applied to the pile at the ground level in a special combination of loads taking into account the seismic action. No additional data is required for an end-bearing pile, and it suffices to check the checkbox to allow for the seismic region.

It should be noted that the current edition of SNiP II-7-81* "Construction in seismic regions" does not provide any information on the frequency of occurrence of earthquakes, although Table 12.1 of the code contains a reference to such data. The data should, probably, be taken from the older editions of SNiP II-7-81*.

The Structure tab is used, depending on the selected pile type, to define the cross-section of the pile and its sizes and to specify some additional data. For various types of end-bearing piles, these may include the depth of pile embedment in rock or, if the pile is hollow, the height of the filled part of the pile hollow core.

The additional data for friction piles also includes the depth of penetration of the pile tip, the depth of excavation, parameters of the site grading; for a pedestal pile, the data includes the diameter of the pedestal and the type of connection between the pile cap and the pile (either hinged or rigid).

When specifying sizes of the pile cross-section, you can save them under a unique name in the database (use the button ) or to retrieve from the database (use the button ). The section can be checked by clicking the Preview button.

The depth of penetration of the pile tip when there is no grading (as well as when grading the area by cutting, filling, or hydraulic filling up to 3 m) is measured from the ground level, and in the case of cutting, filling, or hydraulic filling from 3 to 10 m – from a certain level 3 m above the level of cutting or 3 m below the level of filling, hydraulic filling respectively.

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No grading and grading with h_p<3m	Grading by filling, or hydraulic filling (h_p>3m)	Grading by cutting (h_p>3m)

Soil properties are specified in the table of the respective tab. To enter the properties of a new soil layer (including the first one), click the Add button and a new row will be added to the table. Select a soil type from the list. If sand is selected, its type can be specified in the drop-down list of the Sand type column. Index of liquidity should be specified for clayey soils. To delete a row or several consecutive rows, select them (place the mouse pointer over the number of layer, click and hold the left mouse button, and drag the pointer across the numbers of other layers to be deleted) and click the Delete button.

Since at the analysis of the load-bearing capacity SNiP requires information on whether a layer of sand is dense, the soil table for sand requests information on the porosity index.

The conclusion on density is made on the basis of recommendations from Table 10 of Guide to SNiP.

If the friction pile is located in a seismic region, you have to specify additional information for sand soil: whether its layers are water-saturated or not (use the Water-saturated checkbox in the respective rows of the soil table).

The given soil pack can be checked by the Preview button .

Results of Analysis

The analysis is performed by clicking the Calculate button. Results of this calculation are displayed in the specified units of measurement in the tabular form on the Results tab and include the following values:

(a) for an end-bearing pile – load-bearing capacity of a pile subjected to vertical load, F_d;

(b) for a friction pile – load-bearing capacity of a pile subjected to vertical load, F_d, and load-bearing capacity of a pile subjected to uplift load, F_du. Moreover, diagrams of the relationship of F_d and F_du vs. the depth of penetration of the pile are built for friction piles.

A report is generated with the results of the analysis (use the Report button). The report will be opened automatically by an application associated with the format defined in the ZAPROS application settings.

Limitations

Driven piles with their tips resting on loose sand or clayey soils with the index of liquidity I_L > 0,6 are not considered.
The current version does not consider pyramidal, trapezoid, rhombic, cylinder, or screw-down piles.
Notes 4–7 to Table 1 (Table 7.1 of SP 50-102-2003 Table 7.2 of SP 24.13330.2011), notes 3–4 to Table 2 (Table 7.2 of SP 50-102-2003, Table 7.3 of SP 24.13330.2011), and notes to Table 7 of SNiP 2.02.03–85 (Table 7.7 SP 50-102-2003, table N.3.3 of DBN В.2.1-10-2009) are not implemented.
Negative soil friction forces on the side surface of the piles are not taken into account.

Load-Bearing Capacity of a Pile Based on the Resistance of the Shaft Material

The check of the load-bearing capacity of a pile based on the resistance of the shaft material should comply with Sections 3.7 and 3.8 of SNiP 2.02.03-85, KMK 2.02.03-98 (Sec. 7.1.8, 7.1.9 of SP 50-102-2003 or SP 24.13330.2011). Only the first paragraph of Sec. 3.7 is taken into consideration, and the length of the pile segment from the free-standing pile cap base to the planning level is taken as zero (l0=0).

The strength check of the pile material is performed in the Resistance of R/C Cross-Sections mode of ARBAT. ZAPROS sends to ARBAT the type of cross-section and the sizes of the pile together with the effective length and properties of heavy concrete taking into account a service factor that describes the effect of a particular piling method.

The following sequence of steps is recommended for this mode:

initialize the Load-Bearing Capacity of the Pile mode in ZAPROS;
enter the initial data and perform the analysis;
click the Save Data button in the Results tab for the analysis of the load-bearing capacity based on the material in ARBAT;
in the Additional Data dialog box, specify a method of piling and click OK;
in the dialog that opens, specify a directory and a filename (with the .sav extension) to save data necessary to check the load-bearing capacity;
start ARBAT and initialize the Resistance of R/C Cross-Sections mode;
select the Open item from the File menu and open the file previously generated and saved by ZAPROS;
add missing data necessary for the check of the pile cross-section (class of longitudinal and transverse reinforcement; thickness of the concrete cover; arrangement, diameter, and number of longitudinal rebars; diameter, spacing, and number of transverse rebars);
perform the analysis of the interaction curves.

The check of the pile shaft material is performed as for a reinforced concrete element according to requirements of SNiP or SP regulating the analysis of reinforced concrete structures (see Sec. 3.6 of SNiP 2.02.03-85, Sec. 7.1.7 of SP 50-102-2003 or SP 24.13330.2011).