| Study on the change of seepage field was very important to ensure the safe construction and normal service of river tunnels.The seepage field of tunnels at the bottom of river included the key factors such as the inlet boundary,the outlet boundary and the area in the field.Under the combined action of many factors,the change of seepage field of tunnels at the bottom river was very complex,and the related research needed to be deepened and perfected.Aiming at new type of tunnels like shallow-buried highway tunnel with small clearance at the bottom of river conscructed by mining method,this paper studied the characteristics of the boundary of water inflow and outflow and the distribution characteristics in the field of tunnel seepage field,and relevant engineering suggestions were put forward.The main research contents and achievements were as follows:(1)The variation of river water level above Liuyang River Tunnel was the key factor to determine the inflow boundary of seepage field.Based on the empirical formula of river level(verified by field observation),the variation characteristics of river water level above the tunnel during 2008～2018 were analyzed statistically.The results showed that the highest annual River position on the Liuyang River Tunnel occurred in the 4～8 months of the year,the annual lowest river level usually occurred in the 1～5 or 10～12 months of the same year.The response of the above rainfall increased slowly,and the specific values of the highest river level,the lowest river level and the annual average river level were also obtained.(2)The working behavior of perforated drainage pipe placed behind waterproof board at the foot of tunnel side wall was the key factor to determine the outflow boundary of seepage field.Based on the indoor test,the bearing capacity of the non erosion drain pipe was analyzed according to six kinds of side wall opening methods,the ring stiffness change characteristics of the drain pipe after being eroded by sulfate at different times were studied,and the reason of the drain pipe being blocked was analyzed.The results showed that:when the peak load of the drain pipe was more than 3.6k N/m,the ring flexibility of the drain pipe could not content the requirements;after being soaked and eroded by sodium sulfate solution for 4 months,the ring stiffness of the drain pipe was reduced to less than the minimum value of 6.3k Pa required by the design requirements;the reasons for the drain pipe being blocked might include the defects in its mechanical performance,the defects in the construction operation,the erosion of the environment,etc.(3)Based on the condition that the outlet boundary of tunnel was completely unblocked after full section grouting during construction period,and considering the influence of space-time variation of working face,a three-dimensional numerical model was established to study the distribution characteristics of seepage field during construction period.Firstly,the characteristics of tunnel seepage under the action of seven river water levels were compared and analyzed.The results showed that for about every 1 m rised of river water level,the difference between the increasement of the maximum seepage volume of the first and the second tunnel on the 18th day was about 0.007m~3/d,and the difference between the increasement of the maximum seepage velocity was about 0.03m/d.Secondly,the actual river water level changes with time during the construction period were approximated by an 8-fold function and embedded in the model to analyze the real-time variation of seepage field.The results showed that the maximum seepage volume and seepage velocity of the upper step of the double-hole were located near the arch foot of the upper step face far from the interlaid rock;when the upper and lower steps of the first tunnel were excavated and the initial lining was applied,the construction of the lower steps of the second tunnel would increased the water seepage flow rate of the first tunnel;when the second lining of the double tunnel was applied,the maximum hydraulic gradient of the surrounding rock outside the grouting reinforcement circle was directly above the interlaid rock.The results were compared with the field measurements,which verified the reference of the numerical simulation results.(4)Based on the situation that the outlet boundary of the tunnel may be blocked during the service period,a three-dimensional numerical model was established to simulate the four drainage pipes in the double holes.The distribution characteristics of seepage field in the tunnel during the service period were studied under 14 working conditions,i.e.progressive blockage along the transverse direction and progressive blockage along the longitudinal direction.The results showed that under the condition of transverse blocking of two drainage pipes,when the two drainage pipes were in the same tunnel,the water pressure behind the initial lining of the tunnel was the largest;under the condition of blocking of drainage pipes,the bottom of inverted arch may be the weak part of force and waterproofing,so it was suggested that the second lining of inverted arch of similar underwater tunnel should be thicker than the second lining of arch wall by 10 cm;when the drainage pipes were unobstructed during service period,the water outlet when the boundary was completely clear,it could reduce about 67%of the water loss.It was suggested that similar urban underwater tunnels tried to adopt the idea of"NITM"to carry out the construction. |
PDF Full Text Request