OPTIMAL SHAPES OF PARALLEL EAST WEST ORIENTED SINGLE-SPAN TUNNELS WITH RESPECT TO DIRECT LIGHT TRANSMISSIVITY

Existing single-span tunnels have semicircular or nearly semicircular cross-sections. However, there have been a few analytical investigations into the effects of the tunnel shape on light transmissivities which must be affected by and perhaps improved by changing tunnel shape. Assuming an infinitely large number of infinitely long, parallel, East-West (E-W) oriented, single span tunnels in middle latitude countries, shapes of tunnels which have the highest direct light transmissivities during cold seasons have been studied using numerical calculations. Results show that optimal tunnels have nonsymmetric cross-sections with steep south surfaces and direct light transmissivities in cold seasons can be improved by approximately 10% over semicircular cross-sections. Experimental results also point towards the benefits of using the optimal tunnels. It is expected that these improvements will bring about higher productivities or earlier harvests of the crops. © 1991 The British Society for Research in Agricultural Engineering.