Construction risk evaluation of pipe jacking method in subway tunnel based on projection pursuit method

The pipe jacking for subway tunnel construction effectively minimizes impacts on urban environment, traffic and facilities, and reduces noise. However, it alters stratum stress and causes soil loss, potentially leading to tunnel collapse and surface settlement with high construction risks. To predict risks, they are classified into four levels: Ⅰ (no risk), Ⅱ (low risk), Ⅲ (high risk), Ⅳ (very high surface settlement risk). A risk evaluation index system considering engineering geology and construction factors is established. Using projection pursuit method, the optimal projection direction a=[0.345,0.425,0.285,0.225,0.235,0.245,0.395,0.544] (as index weights) is obtained via accelerated genetic algorithm, forming the risk evaluation model. Results show construction factors have greater weights than engineering geology among primary indices; top three secondary indices are construction downtime, soil conditions, and axis deviation. This indicates reasonable construction is crucial, good geology aids safety, and surface settlement risk is high during construction. The early warning results align with on-site conditions, verifying the model’s effectiveness.