Pile Group Capacity
Calculate a pile group's bearing capacity, Q_g = η·N·Q_pile, from the group efficiency η, the number of piles N and the single isolated pile capacity Q_pile (kN). A pile group's capacity (piles driven close under a cap that distributes the column load among them) is each pile's individual capacity, times the pile count, adjusted by the group EFFICIENCY (η ≤ 1, discounting the interference between neighbors, computed by Converse-Labarre or other formulas). In clayey soils and friction piles, efficiency is below 1 (piles 'compete' for the same soil, and the group may even fail as a solid block — 'block failure', checked separately). In sands and driven piles, driving densifies the soil and efficiency can approach or exceed 1. The group capacity is what actually supports the column load above the cap, and must exceed it with the proper safety factor. This calculation, with the group settlement check (which can exceed a single pile's, since the group stress bulb is deeper), defines the design of a pile-group foundation. Enter the efficiency, the pile count and the individual capacity.
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Pile group capacity
The load capacity of a pile group is Q_g = η·N·Q_pile, obtained from the group efficiency η, the number of piles N and the load capacity of a single isolated pile Q_pile. The capacity of a group (piles driven close together beneath a pile cap that spreads the column load among them) is the individual capacity of each pile, multiplied by the number of piles, adjusted by the group efficiency (η ≤ 1, which discounts the interference between neighbouring piles, computed with the Converse-Labarre formula). In clayey soils with friction piles, efficiency drops below 1 (the piles 'compete' for the same soil, and the group may even fail as a single massive block — 'block failure', which has to be checked separately). In sands with driven piles, driving densifies the soil and efficiency can approach or even exceed 1. The group capacity is what actually carries the column load above the cap, and it must exceed that load with an adequate factor of safety. This calculation, together with the check of group settlement (which can be larger than that of a single pile, since the stress bulb of the group reaches much deeper), defines the design of a pile group foundation. Enter the efficiency, the number of piles and the individual capacity.
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Pile Group Efficiency (Converse-Labarre)
Calculate a pile group's efficiency by the Converse-Labarre formula, η = 1 − (θ/90)·[(m−1)·n + (n−1)·m] ÷ (m·n), from the pile diameter D and spacing s (with θ = arctan(D/s), in degrees), and the number of piles per row m and per column n. When several piles are driven close together (forming a group under a cap), the group capacity is NOT simply the sum of individual capacities — there is INTERFERENCE between the stress bulbs of neighboring piles in the soil, which overlap. The efficiency η (less than 1) measures this loss: the CLOSER the piles (smaller spacing s relative to diameter D), the greater the overlap and the lower the efficiency. The Converse-Labarre formula, empirical and widely used, quantifies this reduction as a function of group geometry (pile count and spacing). So codes require a minimum pile spacing (typically 2.5-3 diameters) to limit efficiency loss. Efficiency times pile count times individual capacity gives the group capacity. This effect is more pronounced in friction piles in clay; in end-bearing piles in sand, the group may even have efficiency above 1 (driving densifies the sand). Enter the diameter, spacing and pile count per row and column.
Field Efficiency
Calculate the field efficiency of a mechanized operation, Ef = (effective capacity ÷ theoretical capacity) × 100%, dividing the effective field capacity (area actually worked per hour) by the theoretical capacity (the one obtained with no time losses). The result, in %, measures how much of the time the machine actually works, as opposed to headland turns, refills, adjustments, travel and overlaps. Simple operations in large fields have high efficiency (80-90%); complex operations in small, irregular fields, low (60-70%). Improving field efficiency (larger fields, fewer stops) reduces costs. Enter the effective and theoretical capacities.
Pile Allowable Load
Calculate a pile's allowable (working) load, Q_adm = Q_ult ÷ FS, from the ultimate bearing capacity Q_ult (kN) and the global safety factor FS. The allowable load is the maximum load that can be applied to the pile in service with adequate safety — obtained by dividing the ultimate capacity (the load that would cause FAILURE of the pile-soil system) by a safety factor covering uncertainties. The pile-foundation safety factor is typically HIGH (FS = 2.0-2.5 for ultimate capacity, higher if based only on theoretical formulas without a load test), reflecting the great uncertainty in determining soil capacity (unseen, heterogeneous and poorly known) and the severity of a foundation failure (which can collapse the whole structure). Codes often require different partial factors for tip and friction (which have different uncertainties), or limit-state methods. The allowable load sets how many piles are needed for the column loads: number of piles = column load ÷ allowable load. Load tests (measuring real field capacity) allow reducing the safety factor and optimizing design. Enter the ultimate capacity and the safety factor.
Pile Bearing Capacity
Calculate a pile's ultimate bearing capacity, Q_ult = Q_p + Q_l, summing the point (tip) resistance Q_p (kN) and the side (skin friction) resistance Q_l (kN). The pile is the DEEP foundation element used when surface soil lacks capacity for the structure's loads — it transfers loads to deeper, stronger subsoil layers. This transfer occurs by TWO mechanisms acting at once: TIP resistance (the pile bears on a firm layer at its base, like a column, mobilizing the soil resistance under the tip) and SIDE resistance (friction and adhesion between the pile's lateral surface and surrounding soil, along its whole length). Their proportion defines the behavior: END-bearing piles (crossing soft soil to bear on rock or firm soil) work mainly by the tip; FLOATING or friction piles (driven in homogeneous soil, no firm layer) work mainly by side friction. The ultimate capacity, divided by a safety factor (typically 2), gives the design allowable load. Determining Q_p and Q_l — by theoretical formulas, SPT-based semi-empirical methods (Aoki-Velloso, Décourt-Quaresma) or load tests — is the central deep-foundation design calculation. Enter the tip resistance and the side resistance.
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Compute resource utilization (CPU, machine, person) — busy time / total available time. Shows efficiency and idle time.
Pile Capacity by Driving (Engineering News)
Estimate a driven pile's allowable load by the Engineering News Record dynamic driving formula, Q_adm = (W_r·h) ÷ (FS·(s + c)), from the hammer weight W_r (kN), the drop height h (m), the set s (permanent penetration per blow, m), a loss constant c (m, ≈ 0.0025 m for drop hammers) and the safety factor FS (≈ 6 in this formula). DYNAMIC driving formulas estimate a pile's capacity from observing how much it PENETRATES per hammer blow during driving — the principle is intuitive: the HARDER to drive (smaller penetration per blow, the 'set'), the GREATER the soil resistance and thus the pile capacity. The blow energy (weight × drop height) is equated to the penetration work (resistance × displacement), with losses. The 'set' (s) is measured in the field during driving (average penetration of the last blows), making these formulas a valuable, cheap EXECUTION CONTROL — driving continues until the set reaches the value matching the desired capacity. The Engineering News formula is the most classic (and conservative, with FS = 6). Modern high-strain dynamic monitoring (PDA, with CAPWAP analysis) replaces these empirical formulas far more accurately, but the set is still used daily on site. Enter the hammer weight, drop height, set, constant and safety factor.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.