The pile-strip foundation is a dependable option for creating a strong foundation for any kind of building, particularly in regions with difficult soil conditions. This kind of foundation combines the even load distribution offered by strip foundations with the stability of pile foundations. In construction, it’s frequently employed to support buildings on unevenly bearing soil.
In order to calculate a pile-strip foundation, one must make sure the strips evenly distribute the load from the structure and comprehend how the piles and soil interact. In order to avoid settlement problems and guarantee the building’s structural integrity over time, this calculation process is essential.
The bearing capacity of the soil, the depth and spacing between the piles, and the size and reinforcement of the concrete strips are important variables in the computation. To calculate these parameters, engineers utilize precise formulas that take into account various factors like the weight of the building, the compressibility of the soil, and environmental factors like the levels of the water table.
An extensive site investigation is the first step in the design process, which aims to evaluate the properties of the soil and identify the best kind of foundation. The foundation’s behavior under various load scenarios is then predicted by engineers using mathematical formulas and models, ensuring that the structure complies with building codes and safety requirements.
Initial data
Geological surveys of the site must be carried out before planning any kind of foundation.
Details required to determine the foundation’s parameters include:
- soil type;
- physical and mechanical properties of soil;
- the presence of layers in the soil prone to buoyancy, weathering pockets;
- depth of seasonal freezing;
- ground water level;
- possibility of erosion of layers near the foundation, etc.d.
The study’s findings will enable us to assess the site’s bearing capacity and, consequently, determine the quantity of supporting components and the foundation’s supporting area.
The total loads brought on by the design structure’s pressure on the ground also have an impact on the parameter values. In addition, the weight of the payload and snow load is considered, along with the walls, ceilings, and roofs.
The regulatory documentation for pile-grillage foundation construction lays out the requirements for performing calculations:
- SP 63.13330.2018;
- SNiP 3.03.01-87;
- SNiP 2.02.03-85.
How many piles are needed??
The position of the solid bearing layer in the soil and the line of seasonal soil freezing are used to calculate the depth of the piles. The following formula determines the value of the soil freezing current if it is less than 2.5 m below the surface:
- M_t – sum of average monthly negative temperatures for the entire winter;
- d_0 – coefficient taking into account the type of soil on the site.
| Soil type | Meaning |
| Clay, loam | 0.23 |
| Sandy loam, fine and silty sand | 0.28 |
| Gravelly sand, medium and large coarse | 0.30 |
| Coarse rock | 0.34 |
The pile is buried 30 cm below freezing to prevent frost heaving forces from affecting the foundation.
The strip grillage may be buried, hung over the space, or lie on the ground.
In the latter instance, the pile’s height is determined by the following elements:
- amount of precipitation;
- snow level;
- depths of underground sources;
- likelihood of flooding;
- room temperature.
If the structure is intended to be built on dense soil, the base’s minimum height is 20 cm. If not, select a height between 35 and 45 cm while assessing the supporting structure’s load-bearing capacity in relation to potential deformations.
To do this, use the following formula to determine the amount of deformation F:
- a is a coefficient that depends on the quality of concrete (selected from 1 to 0.8 depending on the severity and granularity);
- Rbt – concrete strength class;
- u – perimeter of the supporting structure;
- h – pile height.
The height of the supporting elements is appropriately chosen if the result is higher than the design loads on the earth. If not, you should reevaluate the parameter value.
SNiP 2.02.03-85 provides a description of how to calculate the deformation of a pile-screw foundation for punching.
In a base like this, the typical step between supports is between 1.5 and 2.5 meters. Where design loads are predominant, load-bearing elements are found beneath the intersection points of load-bearing walls and at the corners of the structure.
Based on the total weight of the structure and one pile’s bearing capacity, the number of supports is calculated. If necessary, the permissible load of the foundation can be increased by decreasing the step between the load-bearing elements.
For stability and durability in building construction, knowing how to calculate a pile-strip foundation is essential. The subtleties of this foundation type are examined in this article, which offers helpful insights into the important calculations and factors to take into account. It seeks to provide builders and renovators with the fundamental knowledge required to confidently implement pile-strip foundations in construction projects by demystifying the calculation process in plain terms.
How to calculate the amount of tape?
The width of the tape should be selected within the range of 40 to 60 cm when building brick and cinder block homes. Given that 10 cm is set aside for submerging the pile in the tape, the height of the grillage in this instance should not be less than 45 cm.
Engineering calculations are used to calculate the stability of the structure to different deformations that may occur during installation and operation in order to determine the grillage parameters. As a result, determining the grillage in accordance with the guidelines given in SNiP is a labor-intensive and meticulous task best left to experts.
A simplified formula can be applied to the construction of private housing:
- B – the minimum possible width of the grillage (taken to be 20 cm greater than the thickness of the supports and should not be less than the width of the load-bearing walls);
- M – total loads of the design structure (without the weight of the foundation);
- L – grillage perimeter;
- R– permissible soil load at the surface.
Calculation of draft
It is necessary to compare the stress under the sole (p) with the allowable soil load (R) prior to determining the draft. If the requirement is satisfied, you can compute the settlement using the layer-by-layer summation method and the linear model.
Determine the natural pressure diagrams’ ordinates for the top soil layer:
- γ_n is a coefficient depending on the type of soil;
- h_n- layer height;
- n – layer serial number.
| Coefficient value for different types of soil, kN/m 3 | |
| compacted embankment | 17 |
| Packed sandy loam | 21 |
| Medium sand | 18.9 |
| Soil oversaturated with moisture | 10.25 |
| Tight plastic loam | 19.1 |
Finding the parameter value for each layer after that and adding it to the fundamental formula Q_(n-1) is the next step.
Stabilized settlement is calculated using the following formula:
- β – coefficient accepted on the basis of specified conditions according to regulatory documentation;
- E – soil deformation modulus (determined based on survey results).
Further information about the calculations can be found in the guidelines for designing foundations for civil buildings, which can be downloaded from the link, and in document SP 24.13330.2011.
Calculation using programs
It is clear from the above that performing calculations on your own is quite challenging.
In actuality, you can make use of internet resources:
| Factor | Description |
| Soil Type | Determine soil characteristics including bearing capacity and settlement rates. |
| Load Calculation | Calculate loads from the structure to determine the required foundation capacity. |
| Pile Spacing | Decide on the distance between piles based on load distribution and soil conditions. |
| Foundation Depth | Calculate the depth required for the pile and strip foundation based on soil stability and load requirements. |
| Design Factors | Consider factors like safety margins, environmental conditions, and building codes in the design process. |
To guarantee the stability and durability of any structure, it is essential to comprehend the intricacies involved in calculating a pile-strip foundation. Engineers can determine the best design for this kind of foundation by carefully taking into account variables like soil type, building loads, and environmental conditions.
Determining the soil’s bearing capacity is a crucial step in this computation process. In order to determine how much weight the soil can support, this entails analyzing soil samples and applying empirical formulas or geotechnical engineering principles. Engineers can choose the right pile and strip dimensions to distribute the building’s weight evenly by precisely measuring this capacity.
Taking into consideration settlement and maintaining consistency throughout the foundation are additional crucial factors. Differential settlement, in which some areas of the structure sink more than others, can be caused by variations in the composition of the soil. Engineers work to reduce these risks as much as possible through careful planning and precise calculations, which improves the building’s stability and safety.
Furthermore, local building codes and safety requirements are frequently taken into account in the formulas used to calculate pile-strip foundations. These rules make sure that buildings follow the law’s construction practices guidelines in addition to meeting structural requirements.
To sum up, understanding how to perform pile-strip foundation calculations requires a combination of theoretical knowledge and real-world experience. Engineers are able to design foundations that will give buildings strong support and longevity for the duration of their intended lives by using exact formulas and taking into consideration a variety of site-specific factors.
