Terzaghi Rock Load Height
Estimate the rock load height over a tunnel crown by Terzaghi's classic method, Hp = Cf·(B + Ht), from the rock load factor Cf (depending on mass quality — ~0 for intact rock to >2 for heavily fractured or swelling rock), the width B and the height Ht of the excavation. Hp represents the loosened rock zone above the tunnel that effectively loads the support — Terzaghi proposed that, due to arching in the mass, only a fraction of the total overburden acts on the lining. This loosening-load model is the historic basis for rock tunnel support design. Multiplying Hp by the unit weight gives the support pressure. Enter the load factor, width and height.
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Altura de carga de rocha (Terzaghi)
Karl Terzaghi, o pai da mecânica dos solos, propôs em 1946 um dos primeiros métodos racionais para dimensionar o suporte de túneis em rocha: Hp = Cf·(B + Ht), onde Hp é a altura da zona de rocha solta que efetivamente carrega o suporte, Cf é um fator de carga de rocha tabelado conforme a qualidade do maciço (de ~0 para rocha sã e intacta a mais de 2 para rocha muito fraturada, esmagada ou expansiva), e B e Ht são a largura e a altura da escavação. A ideia genial por trás da fórmula é o efeito de arco: quando se escava um túnel, a rocha acima não desaba inteira sobre o suporte — ela forma um arco natural que transfere a carga para os lados, e apenas uma zona afrouxada de altura Hp, logo acima do teto, realmente pesa sobre o revestimento. Por isso, em túneis profundos, o suporte não precisa resistir a toda a coluna de recobrimento (que seria esmagadora), mas a uma fração dela. Esse conceito de carga afrouxada revolucionou o projeto de túneis e ainda hoje serve de referência e verificação, mesmo com os métodos modernos baseados em classificações geomecânicas (RMR de Bieniawski, sistema-Q de Barton). Multiplicando Hp pelo peso específico do maciço obtém-se a pressão de suporte. Informe o fator de carga, a largura e a altura do túnel.
Related Tools
Tunnel Support Pressure
Calculate the support pressure a tunnel lining must resist, pv = γ·Hp, from the rock mass unit weight γ (kN/m³) and the rock load height Hp (m) — typically from Terzaghi's method or geomechanical classifications (RMR, Q-system). Support pressure is the vertical stress the loosened rock zone exerts on the support (shotcrete, steel sets, final lining), and it drives the structural design of the lining. In shallow tunnels the load may be the full overburden; in deep tunnels, arching reduces it to a fraction. Estimating it correctly is decisive: underestimating leads to collapse, overestimating raises cost. Enter the unit weight and the rock load height.
Advance per Blast (Pull)
Calculate the effective advance per blast (pull) in drill-and-blast tunnelling, advance = L·η, from the drilled hole length L (m) and the blast efficiency η (0-1). Not all drilled depth converts to advance: part is lost because the hole bottoms do not always break fully, leaving a 'socket'. Typical efficiency is 85-95% — depending on the blast pattern, rock type and execution. Advance per blast, times the cycles per day, sets the rock face productivity. Maximizing it reduces cycles and schedule, but very long holes lose drilling accuracy and efficiency. Enter the drilled length and the blast efficiency.
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.