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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Capacidade de grupo de estacas
A capacidade de carga de um grupo de estacas é Q_g = η·N·Q_est, a partir da eficiência do grupo η, do número de estacas N e da capacidade de carga de uma estaca isolada Q_est. A capacidade de um grupo (estacas cravadas próximas sob um bloco de coroamento que distribui a carga do pilar entre elas) é a capacidade individual de cada estaca, multiplicada pelo número de estacas, ajustada pela eficiência do grupo (η ≤ 1, que desconta a interferência entre estacas vizinhas, calculada por Converse-Labarre). Em solos argilosos e estacas de atrito, a eficiência é menor que 1 (as estacas 'competem' pelo mesmo solo, e o grupo pode até romper como um bloco maciço — a 'ruptura em bloco', que deve ser verificada à parte). Em areias e estacas cravadas, a cravação adensa o solo e a eficiência pode chegar perto de ou ultrapassar 1. A capacidade do grupo é o que de fato sustenta a carga do pilar acima do bloco, e deve ser maior que essa carga com o fator de segurança adequado. Esse cálculo, junto com a verificação do recalque do grupo (que pode ser maior que o de uma estaca isolada, pois o bulbo de tensão do grupo é mais profundo), define o projeto de uma fundação em grupo de estacas. Informe a eficiência, o número de estacas e a capacidade individual.
Related Tools
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.
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.