Study On Ventilation Characteristics And Key Technologies Of Long Tunnels And Complicated Underground Engineering In The Construction Stage

Construction ventilation is an important factor affecting the construction schedule of long tunnels and large complicated underground caverns group, especially under complex conditions such as high temperature and humidity, high altitude areas, gas tunnels and multiple working faces of inclined shafts with steep slope. The optimization of ventilation techniques in construction stage is an important subject worth studying. To achieve a reasonable ventilation design, advanced theoretical methods are required to calculate and analyze the ventilation process. Ventilation characteristics and key parameters of long tunnels and large complicated underground cavern groups in construction stage are studied applying theoretical methods and technologies of many disciplines such as tunnel and underground engineering, system engineering, computational fluid dynamics, network graph science and software engineering. Ventilation technologies of practical project in construction stage are optimized on the basis of theoretical analysis, numerical simulation and field test. The forced ventilation, together with other ventilation methods, is utilized to further study ventilation technologies in multiple working faces of inclined shafts with ventilation clapboard, multi-stage combined ventilation of ultra-long tunnel excavated by TBM and large complicated underground cavern groups. The main work done and achievements are as follows:Through field testing on single head forced ventilation with flexible air duct in tunnel construction stage under different initial air quantity, the relationship between initial air quantity(Q0) and influence coefficient of air leakage rate(KQ) is obtained.According to simulated experiment, the local pressure loss of air duct and air leakage rate per one hundred meters are measured under different wind velocities and bending angles to obtain the influence coefficient of air leakage rate affected by the bending angle.The calculation results of measured meteorological data at high altitude show that the influence of humidity on the calculation deviation of air density is about 0.3%, which can be neglected. The concentration distribution of harmful gas differs in tunnels of different altitude. With the increase of altitude, the concentration distribution of harmful gas conforms to exponential form. The correction factor of harmful gas(Kh) and correction factor of dust concentration(Kd) at different altitudes(h) are figured out.Energy equation model is established to calculate the temperature distribution of tunnel by numerical simulation. Temperature in tunnel (t) decreases with the increase of air quantity(Q) and conforms to negative power function. The calculation formula of temperature in tunnel(t) and temperature of fresh air supplied by duct(ti) is obtained.Field test of ventilation is carried out in No.1 inclined shaft of Changhongling tunnel and No.7 inclined shaft of Guanjiao tunnel. The results show that leakage rate of clapboard is within 4% and the average coefficient of friction is about 0.02. Numerical simulation is conducted to research ventilation efficiency with wind-chamber, and it is found that the length of wind-chamber is the most important factor affecting the ventilation efficiency of clapboard joint wind-chamber. The calculation formulas of influence coefficient of length(Ka), influence coefficient of width(Kh) and influence coefficient of height(Kc) are obtained. The results show that the average increment of air quantity in the entrance direction is 29.2% and that of exit direction is 19.9% by comparing air quantities before and after applying wind-chamber ventilation technology in No.1 inclined shaft construction area of Changhongling tunnel.Ventilation schemes of Zhongtianshan tunnel excavated by TBM are optimized by theoretical analysis, numerical simulation, and field test. Ventilation model of ultra-long distance excavated by TBM is established including multi-stage joint ventilation scheme, foul air reflux controlling methods, fans controlling strategy and so on. The relationship between ventilation length and energy consumption of ultra-long tunnel at different stages is analyzed. The results show that ventilation resistance in tunnel increases with the increase of excavation distance, and more fan power is required. The relationship between the two ones is linear. The power consumption under the double lines air supplying is higher than that of single line air supplying.The network ventilation technology of large complicated underground cavern groups in construction stage is optimized relying on the underground caverns of Wanhua Industrial Park, Yantai. Network ventilation software is applied to adjust branch air pressure and air quantity, thus controlling the entire ventilation network. Automatic controlling and regulating systems are applied to monitor the environmental indicators of the working faces. The rotational speed of fans is regulated automatically by frequency convert system to regulate the fans flow. When the balance of ventilation network is broken, air quantity reallocation is automatically calculated by network ventilation calculation program. In this way, the new balance of ventilation network is established to meet the requirement of air quantity at different working faces and the effect of energy-saving is achieved.