Study on leakage and diffusion law of buried gas pipeline in tunnel

Objective After the leakage of the buried gas pipeline in the tunnel, it is easy for the gas to accumulate and reach the minimum explosion limit concentration, resulting in explosion danger. Thus, it is necessary to study the continuous diffusion of gas in soil and air environment after pipeline leakage.

Methods The gas concentration is monitored continuously by theoretical analysis and numerical simulation.

Results (1) At 10 min, 20 min, 30 min and 40 min after the occurrence of small hole leakage, the maximum diffusion radius of the isoline with the volume fraction of CH₄ of 0.05 in the soil was 0.9 m, 1.15 m, 1.25 m and 1.30 m, respectively while the maximum diffusion radius of CH₄ was between 10 m and 15 m; (2) CH₄ concentration in the soil tends to be stable after the leakage for about 5 min; (3) The variation of CH₄ volume fraction in the air area with time can be divided into three stages: rapid growth, slow growth and steady state. When the leakage lasted for 60 min, the 6 m-long area at the top of the tunnel was in the range of explosion concentration limit.

Conclusions After the leakage of buried gas pipeline in the tunnel, the diffusion radius of gas in the soil should not exceed 15 m. The relatively closed environment in tunnel makes the 6 m-long area at the top of the tunnel within the limit concentration of explosion, which needs to be controlled.