| Japanese built the world’s first modern high-speed railway since 1960s. It opened up a new era that high-speed railway engineering have mushroomed and been paralleled all around the world. In China, the operation of Beijing-Tianjin intercity high-speed railway, which has been serviced in 2008 at a speed of 350 km/h.This marked the rapid development and brilliant achievement of the high-speed railway. With the rapid construction of highway network, it can’t be avoided that a large number of tunnels will be built through mountain areas. The drilling and blasting method is the most commonly method that has been adopted in China, while the single method during the construction has significantly lagged. Because of the complex and various land forms and geological conditions, the excavate conversions are highly required to satisfy security and rapid construction procedure. However, theoretical analyses on excavate conversion by drilling and blasting method on high-speed railway tunnels are rared. Thus, it can easily prone to the excavate conversion between different construction method on the characteristics of engineers’subjectivity and empirical judgments. The inappropriate construction method or delayed excavate conversion will result in construction delaying or tunnel collapse issues. Therefore, this dissertation conducted specific analysis on controlling standards of excavation conversions by drilling and blasting methods can provide references for design and construction of similar projects.The dissertation was cased on the Shanghai-Kunming Passenger Dedicated Line of Changkun-Hunan Section DC, which emphasizes on controlling standards of tunnel excavation conversions by drilling and blasting method. By options of 44 practical construction head faces from 23 tunnels of research area, and based on many researchers both at home and abroad, the dissertation did specific research on its theoretical and practical analysis. Firstly, the suitability in different geological conditions by drilling and blasting construction techniques was expounded specifically, and detailed estimate of different construction methods which had been applied in research area were conducted. Then, based on the basis statistical analysis theory, deformation monitoring data from different surround rock classes and excavation methods, it analyzed the relationships between displacement-surround rock classes, deformation time-surround rock classes and deformation distance-surround rock classes. Then it established the judgment criteria on balance and stability of surround rock-support system. Meanwhile, relayed on the basic theory of rock stress redistribution, it deeply analyzed the three dimensional deformation characteristics on the aspects of stress values and stress orientations of surrounding rock, thus it proposed the three dimensional deformation models of surrounding rock under different excavation methods. Furthermore, a rather important concept, termed as displacement angle of surrounding rock deformation, was put forward accordingly. Afterwards, in accordance with the practical geological conditions, such as the different strength, distribution length, and oblique angle of surrounding rock between both sides of stratigraphic interfaces, it established three dimensional numerical geological models, and carried on simulation calculations and obtained basic law of displacement angle of surrounding rock deformation under the condition of passing through different stratigraphic interfaces of the tunnel.Then it proposed methods on prediction geological conditions ahead of tunnel faces, thus established its evaluation criteria accordingly. According to these research achievements, it put forward the control principles and methods as well as the establishment of controlling standards of tunnel excavation conversions. Additionally, they were applied on the construction of Yaojia Tunnel and Cuijiachong Tunnel to verity its practicality and feasibility.Specific findings and researches are highlighted as followed:(1) Comprehensive suitability assessments on high-speed railway tunnel construction by the application of drilling and blasting method was conducted. According to the practical geological conditions of research area, mainly consisting of bury depth, geological layered lithology, geological structure and hydrogeology, the tunnel constructions were adopting the following five different excavations methods:full face excavation method, heading and bench method, arc gate and core soil reserved method, the three benches and seven steps excavation and two sides drift method. First of all, it describes their excavation procedure, technical features and adoptions, afterwards, depending on their practical application in-suit respectively, the suitability assessments on each excavation methods were carried out from feasibility, security, controlling on construction period and economic efficiency. It showed that:appropriate and adopted excavation method can not only guarantee the security in construction, but also satisfy excavation period to a large extend. Therefore, the suitable option of excavation method plays an important role in its security, progressive, and effectiveness. Additionally, it highly required the optimal excavation method by the comprehensive consideration of various factors with combination of geological conditions.(2) Based on criterion of tunnel surrounding rock deformation, coupled with monitoring deformation data which were originated from 23 of tunnels located in research area, it proposed statistical analysis theory on surrounding rock deformations as well as the establishment on quantitative relationship between deformation-class and time-spatial effect-class of surrounding rock. It proved that the displacement, time and stability distance of surrounding rock are all proportional to surrounding rock class. With the increasing of surrounding rock class, the stability displacement raises, and the stability time and distance increase correspondingly.(3) The three marketable aspects such as stability displacement, stability time and stability distance were acted as indexes to judge the balance of rock-support system. And based on statistical analysis’s quantization indexes on monitoring deformation data respectively, relative suggestive values were proposed. Thus the up and down baseline can also be determined accordingly, and afterward, the judgment on stability of rock-support system was conducted. And it obtained the following three states:(a) If the quantization indexes were below the down baseline, it indicated the surrounding rock have been under normal statement, and it can conduct excavation, (b) If the quantization indexes were between the up and down baseline, it can be judged that the surrounding rock were almost in normal stability, therefore, it can organize the normal construction. Taking certain kinds of measurements if necessary in order to control surrounding rock deformations. (c) If the quantization indexes were above the up baseline, it demonstrated surrounding rock were in the condition of unstability. It should conduct immediately and early warning and enhancements on monitoring. Furthermore, it required a good understanding of large deformation cautions and after this, it can organize the construction process.(4) Based on the basic theory of rock stress redistribution, the paper proposed the feature region (e.g.:Stability region, Working face region, Not affected region) and expounded the deformation forms for each feature region. The FLAC3D had been applied on three dimensional simulation calculations in five different excavation methods respectively, involving full face excavation method, heading and bench method, arc gate and core soil reserved method, three benches seven steps method and two sides drift method. From the views of stress magnitude and direction, it deeply analyzed the spatial deformation characteristics of surrounding rock during different excavation methods, especially the arch and side-wall deformations additionally. Based on the three dimensional deformation features, and coupled with crack extension mechanism, it summarized the following 4 kinds of three dimensional deformation models mainly in transformation of maximum stress orientation, namely:(a) by full face method, it varied from vertical to horizontal statement. (b) heading and bench method exhibits that:it varied from longitudinal to vertical statement. (c) arc gate and core soil reserved method, three benches seven steps method, both varied from horizontal to vertical statement. (d) multiple-steps excavations while following every step with installation of temperate supports behaves three directions of it with rotation statement.(5) Based on the simultaneous monitoring on vertical deformation and longitudinal deformation of surrounding rock mass, displacement angle of surrounding rock deformation turned out as a vital notion to account for its deformation laws under the tunnel constructions. Regardless of the geological condition, in front of the tunnel face was hard rock mass or soft rock mass, the normal state, which was named after the phenomena, was the displacement angles of every relative across section which were almost the same, it is also the trend line foamed by the concatenate of each across section presents approximation to a horizontal line. Therefore, it easily demonstrated that:when the excavation face is closed to or through geological interface, due to the significant effects of different rock mass and geological structures on surrounding rock deformation, it showed that its displacement angles diverged from the normal state, and gave rise to relatively apparently ups and downs of trend line. As for the surrounding rock of stratum interface, with focusing on their different strength, lengths and dip angles, the paper established three dimensional numerical models under two different excavation statements, one is from hard rock mass to soft rock mass, the other is from soft rock mass to hard rock mass, and from the simulation calculations. It obtained the basic characteristics of vertical deformation, longitudinal deformation as well as the displacement angles, which can be well performed as prediction of the geological conditions ahead the head faces.(6) The multi-peak Gaussian function was used to analyze the change of displacement direction angle which means it used the value of fitted curve’s first derivative in the inflection point, peak point and FWHM as judgment basis of surrounding rock’s relative strength, the length of relative distribution and interface of formation’s dip in front of tunnel face. What’s more, through the quantization, it produced the upper and lower limits of classification, length and dip angle of stratum interface of surrounding rock, which indicated that:during the tunnel construction, when the quantitative values of indexes is limited, it can well predicted the ahead geological conditions in accordance with the above criterion.(7) Two principle presuppositions have been proposed, the first one was the balance of the rock-support system located on the excavation finished section and the second one was the accurate prediction of the geological condition in front of the tunnel face. Thus relatively, it put forward the general principle of controlling standards of tunnel excavation conversions. That is, after the strictly check if the quantitative values of indexes were contained on the suggested permission ranging, corresponding excavation conversion was conducted.(8) The methods were proposed to judge stability of the surrounding rock and to predict the geological conditions in front of the tunnel face. The first method was put forward to establish the statistical regression model by using the unitary nonlinear regression function. And then the tunnel surrounding rock stability is determined by using the index quantization value which is obtained from this model. The second method was based on Gauss fitting curve of the surrounding rock displacement angle by the algorithm of discrete Frechet distance, then the geological conditions in front of tunnel face was predicted by accessed the index quantitative values.(9) Case on the Yaojia Tunnel and Cuijiachong Tunnel, which located in the research area. The research theories and achievements were applied practically in tunnel excavation conversions:from hard rock to soft and form soft rock to hard rock. Also, a suit of observation results, via the field geological survey, timely monitoring data collection, acoustic wave tests and laboratory physical tests, were adopted to verify its practicality and efficiencies. The results have exhibited good performance. The controlling standards of tunnel excavation conversions by drilling and blasting method not only performed in eximious reliability and applicability but also ensured excavation security and construction progress improvement additionally. It has achieved good economic and social benefits.The following innovation points can be concluded from the conducted study:(1) Based on monitoring measurement data in-suit and the adoption of statistical analysis theory, quantitative analysis was applied to establish the relationships between arch settlement-surrounding rock class, the side wall convergence-surrounding rock class, time effect-surrounding rock class and spatial effect-surrounding rock class. Accordingly, it put forward a new judgment measurement on stability of rock-support system, which treated the stability displacement, stability time and stability distance as the indexes. Therefore, it provided a new way to evaluate surrounding rock stability.(2) Based on three-dimensional stress change rule of surrounding rock, the three-dimensional deformation mode of surrounding rock under different excavation methods were described. The concept of displacement direction angle for surrounding rock was defined. From the point of different relative strength, different relative length and different angle of strata interface, the change rule of surrounding rock displacement direction angle was displayed and summarized.(3) The multi-peak Gaussian function was used to analyze the change of displacement direction angle which means it used the value of fitted curve’s first derivative in the inflection point, peak point and FWHM as judgment basis of surrounding rock’s relative strength, the length of relative distribution and interface of formation’s dip in front of tunnel face. And it not only established the criterion to judge the geological condition but also gave some suggestions about the value range of decision index so that we can find a new way to assess the geological condition in front of tunnel face.(4) It found out the controlling standards and techniques of tunnel excavation conversions. It can be conducted in excavation conversions under the satisfactions of the rock-support system of excavated part which has tended to be stable and the accurate prediction of geological conditions ahead. The controlling standard of excavation method conversion was established, which provided the theoretical basis for the selection and conversion of tunnel excavation method. |
