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.
Result
—
Capacidade de estaca por cravação (Engineering News)
A carga admissível de uma estaca cravada pela fórmula dinâmica Engineering News Record é Q_adm = (W_r·h) ÷ (FS·(s + c)), a partir do peso do martelo W_r, da altura de queda h, da nega s (penetração permanente por golpe), de uma constante de perda c (≈ 0,0025 m para martelos de queda livre) e do fator de segurança FS (≈ 6). As fórmulas dinâmicas de cravação estimam a capacidade de uma estaca a partir da observação de quanto ela penetra a cada golpe do martelo durante a cravação — o princípio é intuitivo: quanto mais difícil de cravar (menor penetração por golpe, a 'nega'), maior a resistência do solo e, portanto, maior a capacidade. A energia do golpe (peso × altura) é igualada ao trabalho de penetração (resistência × deslocamento), com perdas. A 'nega' (s) é medida no campo durante a cravação (penetração média dos últimos golpes), tornando essas fórmulas um controle de execução valioso e barato — crava-se até a nega atingir o valor que corresponde à capacidade desejada. A fórmula Engineering News é a mais clássica (e conservadora, FS = 6). Modernamente, o controle dinâmico de alta deformação (PDA, com análise CAPWAP) substitui essas fórmulas empíricas com muito mais precisão, mas a nega ainda é usada no dia a dia da obra. Informe o peso do martelo, a altura de queda, a nega, a constante e o fator de segurança.
Related Tools
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.
Pile Structural Stress
Calculate the structural compression stress in a pile shaft, σ = Q ÷ (π·D²/4), from the applied load Q (kN) and the pile diameter D (m); the result is in MPa. Besides the SOIL having capacity to support the pile (geotechnical capacity), the pile itself, as a STRUCTURAL element (concrete, steel or timber), must resist the load without failing or deforming excessively — this is the pile's STRUCTURAL check. The shaft compression stress is simply the load over the cross-sectional area. It must be below the pile material's allowable stress: codes limit cast-in-place pile concrete working stress to conservative values (typically 5-8 MPa, less than the concrete strength, due to subsurface execution uncertainties — blind concreting, possible defects, eccentricities). This check often GOVERNS the minimum pile diameter (the pile may have ample geotechnical capacity, but structural stress limits the load). Pile design is always the SMALLER of geotechnical (soil) and structural (material) capacity — both must be checked. Enter the applied load and the pile diameter.
Pile Tip Resistance
Calculate a pile's tip resistance, Q_p = q_p·A_p, from the tip stress (bearing capacity) q_p (kPa) and the tip cross-sectional area A_p (m²). Tip resistance is the share of pile capacity from the BEARING of its base on a strong soil or rock layer — the pile acts as a column compressing the soil under its tip, mobilizing that soil's bearing capacity (like a shallow foundation, but at depth). The tip stress q_p is the soil's unit bearing capacity at the tip elevation, estimated by bearing-capacity theories (Terzaghi, Meyerhof, Vesic for piles), SPT correlations (q_p = K·N, with K depending on soil and pile type) or the CPT (cone) test. Times the tip area, it gives the force the tip supports. Tip resistance dominates in piles reaching a firm layer (end-bearing piles), and then the pile is very stiff (settles little). Large-diameter piles (caissons) have large tip areas and mobilize high tip resistance. This share adds to the side resistance for the total capacity. Enter the tip stress and the tip area.
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.