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Transition curve 6°, Ls=90 m, chainage 13+700

Short answer

Δ = 40°, R = 286.48 m. Transition shift s = 1.178 m, total tangent Ts = 149.70 m, circular length Lc = 110.00 m. First two transition deflections at TS: 0°02′05″ and 0°08′37″; circular at SC: 0°58′11″ and 3°58′11″.

Two tangents T₁V and T₂V intersect at chainage of 13+700 km. The bearing of T₂V is 300°30' and T₁V is 80°30'. It is proposed to insert 6° circular curve with transition curve 90 m at each end. Calculate the first two deflection angle for setting out first transition and circular curve only at peg interval of 10 m on transition curve and 30 m at circular curve.

Deflection angle between the tangents

Bearing of T₁V (travelling towards V) =80∘30′= 80^\circ30'. Bearing of T₂V is observed from T₂ towards V, 300∘30′300^\circ30', so the forward direction of travel from V to T₂ is 300∘30′−180∘=120∘30′300^\circ30' - 180^\circ = 120^\circ30'.

Δ=120∘30′−80∘30′=40∘ (deflection to the right)\Delta = 120^\circ30' - 80^\circ30' = 40^\circ\ \text{(deflection to the right)}

Radius and transition elements

6° curve with a 30 m arc: R=1718.87/6=286.48R = 1718.87/6 = 286.48 m. Ls=90L_s = 90 m.

s=Ls224R=90224×286.48=1.178 mθs=Ls2R=9.000∘Ts=(R+s)tan⁡20∘+Ls2=149.70 mLc=R(Δ−2θs)=110.00 m\begin{aligned} s &= \frac{L_s^2}{24R} = \frac{90^2}{24\times 286.48} = 1.178\ \text{m}\\ \theta_s &= \frac{L_s}{2R} = 9.000^\circ\\ T_s &= (R+s)\tan 20^\circ + \frac{L_s}{2} = 149.70\ \text{m}\\ L_c &= R(\Delta-2\theta_s) = 110.00\ \text{m} \end{aligned}

Chainage of V =13700= 13700 m (13+700 km).

PointChainage (m)
TS = V − T_s13550.30
SC = TS + 9013640.30
CS = SC + L_c13750.30
ST = CS + 9013840.30

First two deflection angles

Transition curve (theodolite at TS), α=573 l2/(RLs)\alpha = 573\,l^2/(RL_s) minutes, points at multiples of 10 m:

Point (chainage, m)l (m)α (min)α
13560.009.702.09′0°02′05″
13570.0019.708.62′0°08′37″

Circular curve (theodolite at SC), δ=1718.87 c/R\delta = 1718.87\,c/R minutes, points at multiples of 30 m:

Point (chainage, m)Chord c (m)δCumulative
13650.009.700°58′11″0°58′11″
13680.0030.003°00′00″3°58′11″

Answer: transition: 0°02′05″ and 0°08′37″; circular: 0°58′11″ and 3°58′11″.

✓ Answer checked by Claude Opus 5.5 (high effort)

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