Smoke layer thickness is a key parameter in tunnel fire research. In this paper, the effects of the dimensions of the tunnel cross-section and Heat Release Rate (HRR) in naturally ventilated short tunnel fires were studied. A series of numerical simulations with Fire Dynamics Simulator (FDS) were carried on, and some tunnel model experiments were conducted in a 1/10 scaled short tunnel model to verify the results of the numerical simulation. The thickness of smoke layer in the simulations and experiments was determined by the integral ratio method, which is more subjective and has been applied in FDS. The effects of different tunnel lengths and widths were studied. The results show that the smoke layer thickness increases with the increment of tunnel length, and conversely, with the increased tunnel width, the thickness decreases. The HRR is also a main factor influencing the smoke layer thickness, and with the increase in the HRR, the thickness increases. In addition, a prediction model of the smoke layer thickness was proposed, which presented a good agreement with the results of simulation and experiment.

烟层厚度是隧道火灾研究的关键参数。本文研究了自然通风短隧道火灾中隧道横截面尺寸和放热率（HRR）的影响。利用Fire Dynamics Simulator（FDS）进行了一系列数值模拟，并在1/10比例的短隧道模型中进行了一些隧道模型实验，以验证数值模拟的结果。在模拟和实验中，烟层的厚度是通过积分比法确定的，该方法较为主观，已在FDS中得到了应用。研究了不同隧道长度和宽度的影响。结果表明，烟层厚度随隧道长度的增加而增加，反之，随着隧道宽度的增加，烟层厚度减小。HRR也是影响烟层厚度的主要因素，并且随着HRR的增加，厚度也会增加。另外，提出了烟层厚度的预测模型，与模拟和实验结果吻合良好。