Study On The Coupling Effect Of Hydrological-Chemical-Mechanical In Deep Buried Tunnel With Gypsum Salt And Its Prevention And Control Countermeasures

The geological conditions in southwest China are complex and bad,and the gypsum bearing strata of the Padong formation of Triassic system are widely distributed.Among them,many deep buried tunnels built near the three Gorges Reservoir area are under the action of sulphate groundwater erosion.Tunnel lining has appeared light or heavy corrosion damage phenomenon,which often lead to leakage,spalling and other disease problems,in which the side wall and tunnel bottom erosion is especially serious,which has brought serious safety hidden danger to its normal operation.Tunnel engineering is always stored in a certain geological system.Environmental water,corrosion medium and in-situ stress are the three main influencing factors in the formation environment.These factors all exist in the form of field.The Hydrological(H),Chemical(C)and Mechanical(M)are always related to each other in the gypsum salt formation,which "promote" the failure of the bearing structure of surrounding rock and support together,if the coupling relation is neglected by studying each action field separately.So the conclusion of the research is difficult to match with the actual situation,lost the significance of engineering guidance.This paper takes the Fenjieliang tunnel on the G42 Hu-rong expressway and the Tanjiazhai tunnel on the G50 Hu-yu expressway as the engineering background.Above all,the mechanism of sulphate corrosion and damage is described systematically.Secondly,based on ABAQUS finite element software,Hydrological and Mechanical coupling numerical analysis is carried out,and a simplified simulation of Chemical is carried out by considering a certain strength reduction and thickness reduction.Finally,the corrosion prevention measures of the tunnel in the gypsum formation are studied systematically,and the effective prevention and control measures are put forward for the sulphate erosion disease in the Fenjieliang and Tanjiazhai tunnel respectively.The main research results of this paper are as follows:1.The damage degree and performance degradation rate of the structure caused by the three-field coupling effect of HCM are far more than that of single field and double field coupling.Although the erosive SO42-ion concentration of the Tanjiazhai tunnel is much higher than that of the Fenjieliang tunnel,the actual survey data show that the corrosion damage of the Fenjieliang tunnel is more serious.The explanation for this phenomenon is that the deterioration and damage of concrete is not determined by asingle factor of the concentration of erosive ions,but is the result of the coupling of several factors.2.The coupling disaster effect between Hydrological,Chemical and Mechanical or even more fields must be considered in the deep buried tunnel in the gypsum salt formation.For the effect of Chemical,based on the strength reduction theory,a suitable reduction coefficient can be selected to simplify the effect of the field.Because the corrosion effect of Chemical will vary with the environment,so the specific value of the reduction coefficient should be further analyzed and studied according to the actual situation.At the same time,a certain thickness reduction can be considered to improve the safety surplus of the structure.3.The ABAQUS numerical analysis shows that the load bearing performance of the structure is greatly affected by considering the coupling,the fluid-solid coupling and the three-field coupling of the strength reduction "equivalent" chemical field.On the basis of considering the thickness reduction of 5cm according to the degree of severe corrosion,the HCM three-field coupling analysis and calculation are carried out.It is concluded that the minimum safety factor of each characteristic section is 2.789 to meet the requirements of the specification.It is proved that it is reasonable and feasible to select the corrosion resistant reinforced concrete with C45 strength in the sulphate corrosion treatment design of the Fenjieliang tunnel.4.On the basis of accurately judging the corrosion types of sulfate and clarifying its erosion mechanism,the combined protection measures are combined in order to enhance the effectiveness of corrosion protection and prolong the service life of tunnels.Recommended Scheme for the treatment of sulphate corrosion disease:(1)for the tunnel structure in dry-wet alternate environment,the influence of material "wick effect" should be considered,and the anticorrosive measures should be taken in the design of anticorrosive mix ratio / high performance concrete+grouting water+surface treatment;(2)in the moist environment of the water rich tunnel,besides the anticorrosive mixture ratio design / high performance concrete + grouting water preventing corrosion measures,we should pay more attention to the design of the drainage system.In this paper,based on the engineering Fenjieliang tunnel,(1)scheme is selected as the disease treatment program.At present,the corrosion prevention effect of this scheme is obvious.