地下互通工程中通常在隧道分岔节点采取集中重点排烟形式，多隧道区段共用1台排烟风机集中排烟，形成单侧集中排烟模式。受地形制约，地下互通工程隧道存在纵向坡度，火灾工况下隧道内部受冷热空气密度差诱导形成烟囱效应，显著改变烟气纵向流动规律，加大单侧集中排烟难度。以排烟阀对称开启下单侧集中排烟模式为研究对象，采用全尺寸数值模拟方法，系统分析坡度、排烟量和火源功率对烟气蔓延距离的影响规律，并建立相应的预测模型。研究结果表明： 1)火源上游烟气蔓延距离随排烟量增大或坡度减小而缩短，呈非线性关系； 火源下游烟气蔓延距离随排烟量增大而减小。坡度相同时，火源功率增大需匹配更大的排烟量以控制上游烟气。2)通过量纲分析，构建涵盖坡度、排烟量及火源功率的量纲为一蔓延距离预测模型，烟气蔓延距离受火源功率、坡度及排烟量等参数影响。3)在火源上游，火源功率增大提供的额外浮力驱动力与烟囱效应所带来的驱动力相互叠加增强； 在火源下游，火源功率增大带来的额外浮力驱动力与烟囱效应所带来的驱动力相互抵消减弱。因此，下游量纲为一蔓延距离预测模型中的火源功率指数远低于上游量纲为一的烟气蔓延距离预测模型中的火源功率指数。

Centralized dedicated smoke extraction is commonly adopted at the tunnel bifurcation nodes of underground interchange projects. Multiple tunnel sections share one exhaust fan, forming a unilateral centralized smoke-exhaust mode. Constrained by terrain conditions, the tunnels of underground interchanges form longitudinal gradients. Under fire conditions, the density difference between the hot flue gas and ambient air induces the chimney effect inside tunnels, substantially changing the longitudinal flow characteristics of smoke and increasing the difficulty of smoke control for unilateral centralized exhaust. This study investigates a unilateral centralized smoke-exhaust mode with symmetric openings of smoke-exhaust valves. The influences of longitudinal gradient, exhaust flow rate, and heat release rate (HRR) on the smoke-spread distance are systematically analyzed through full-scale numerical simulations, and corresponding predictive models are established. Three results emerged from the study are as follows: (1) The upstream smoke-spread distance decreases nonlinearly with increasing exhaust flow rate or decreasing longitudinal gradient, whereas the downstream smoke-spread distance decreases with increasing exhaust flow rate. At the same longitudinal gradient, a higher HRR requires a larger exhaust flow rate to control the upstream smoke spread. (2) A dimensionless prediction model of smoke-spread distance, derived through a dimensional analysis, is established. The smoke-spread distance depends on the HRR, longitudinal gradient, and exhaust flow rate. (3) The additional buoyancy-driven force caused by the increased HRR superimposes and reciprocally reinforces the driving force induced by the chimney effect in the upstream region, and counteracts and weakens the driving force in the downstream region. Therefore, the exponent of HRR is much smaller in the downstream dimensionless prediction model of smoke-spread distance than in the counterpart upstream model.