Comprehensive and scientifically reasonable planning and design of underground space is the premise for its development and utilization, reviewing the research context of underground space planning and design, predicting its development trend, providing reference for sustainable utilization and high-quality development of underground space. Through the visual analysis method of bibliometrics, the literature of underground space planning and design journals from CNKI and Web of Science database was analyzed, the number of papers, subject categories, main research forces and keywords were processed, then the following conclusions were drawn: the development trend of discipline types is diversified and interdisciplinary. The main research countries/regions are China, and the research institutions are Shanghai Municipal Engineering Research Institute (Group) Co., LTD and Tongji University, etc. Keyword emergence analysis indicates that future research trends will focus on: The improvement of underground space comfort and quality; Green and safe underground space design under the Sustainable Development Goals; Comprehensive planning and layout of three-dimensional and intensive underground space; Digital technology assisted underground space planning and design.

In the context of the China's vigorous promotion of construction industrialization, prefabricated assembly construction technology has received extensive attention and development. Compared with a large number of research and application of above-ground buildings, the application and development of prefabricated assembly construction technology in underground space still has great potential. At first, the Citespace software is used to visually analyze the literature related to underground assembly from 2000 to 2022. Then, taking three typical underground space buildings of underground comprehensive pipe gallery, subway station and tunnel as examples, and the research and application status of prefabricated construction technology in underground engineering in China are summerized. Five key research contents of prefabricated construction of underground engineering are proposed, including the assembly technology of prefabricated lining, the mechanical performance of prefabricated structures, the connection joints of prefabricated components, the seismic performance of prefabricated structures, and the waterproof performance of prefabricated structures. Finally, five research trends of prefabricated structures in underground spaces are summarized to provide references for the popularization and application of prefabricated technology in underground engineering.

The purpose of this study is to reveal the mechanism underlying the strength damage of granite in humid and hot environments. Uniaxial compression tests and Brazilian splitting tests were carried out on moderately weathered granite specimens experienced different forms and numbers of wetting-heating cycles. The effects of cooling-heating cycles at constant humidity, drying-wetting cycles at constant temperature, and hot drying-cool wetting cycles on the uniaxial compressive strength, elastic modulus, splitting strength and damage factor of moderately weathered granite were analyzed. The results show that: The uniaxial compressive strength and elastic modulus of moderately weathered granite exhibit exponential attenuation with increasing number of wetting-heating cycles. After 30 cooling-heating cycles, drying-wetting cycles and hot drying-cool wetting cycles, the reductions in uniaxial compressive strength are 13.63%, 19.76% and 21.54%, respectively, and those in elastic modulus are 42.78%, 50.34% and 53.78%, respectively. The splitting strength decreases linearly with an increase in wetting-heating cycles. After 30 cooling-heating cycles, drying-wetting cycles and hot drying-cool wetting cycles, the decline amplitude of the splitting strength are 38.59%, 65.65% and 71.53%, respectively. Based on damage analyses, it is found that the hot drying-cool wetting cycles that consider the coupling of temperature and humidity changes have the most significant damaging effect on the strength of moderately weathered granite, and the drying-wetting cycles have the second significant damaging effect. Compared to the uniaxial compressive strength, the splitting strength is more vulnerable to the damaging effect of long-term wetting-heating cycles.

A large number of studies believe that the superposition effect of the accessibility of the rail system and urban streets can gather urban space elements, and the coupling effect of the above-ground and underground pedestrian network systems in the rail transit station area affects the quality of public space obviously. The urban design of Qianhai in Shenzhen was taken as the research object. Based on the accessibility of the subway station area and the existing research results, the vitality indicators of the ground pedestrian streets and underground pedestrian paths in the rail transit station area were extracted and quantified by using space syntax, network analysis and attenuation superposition. Through the entropy weight method, the index integration of the above-ground and underground pedestrian networks is carried out respectively. Based on the GIS platform, the simulated values of the vitality of the above-ground and underground pedestrian networks are coupling calculated. Three coupling states in the pedestrian network in the scheme design stage are identified, and a preliminary improvement strategy is proposed for the areas with poor coupling.

The maximum depth of the excavation in No. 5 well of a scientific device project is 45.45 m, which is currently the deepest non-circular excavation project in Shanghai. The implementation of the project encountered many challenges and new technical problems, and relevant technological breakthroughs are achieved. Such as, the double-layer curtain design scheme combining deep wall and shallow curtain was adopted to control the safety risk caused by the leakage of the ultra-deep excavation in soft soil. The world's deepest TRD water-proof curtain with a depth of 69m was first successfully applied in the excavation project. And the ex-situ field trial wall test of TRD cement-soil mixing walls with a depth of 86m and a thickness of 1.10 m was carried out and completed for the first time. Based on the successfully implemented of No. 5 well project, the design and practice of the 45m-level extreme-deep excavation in Shanghai soft soil area was introduced. Including the overall design scheme, ultra-deep diaphragm wall design, ultra-deep TRD waterproof curtain design and ex-situ wall test, precipitation design and groundwater control effect of multiple aquifers, and project implementation effect. The successful design and implementation of this project can provide reference for the similar projects.

In order to improve the level of safety culture construction in underground shopping malls, prevent safety accidents and ensure operation safety, the article comprehensively analyzes the factors of safety culture construction in underground shopping malls from four levels of safety culture, it is the first time to construct the evaluation index system of safety culture construction level in underground market, which consists of 4 first-level indexes such as safety concept culture and 28 second-level indexes such as safety strategic consciousness. For the first time, the combination weight calculation model of OAHP, entropy method and matter-element extension theory are combined to construct the evaluation model of safety culture construction level of underground shopping malls. The evaluation model is applied to an empirical study of a large underground shopping mall in Xi 'an, and concludes that the construction of safety culture is at a high level, with a grade of II, which belongs to the stage of self-management, the evaluation results are in accordance with the actual situation, and through the correlation analysis to find out the deficiencies in the construction of safety culture, put forward targeted measures to improve. The study shows that the evaluation system is suitable for the evaluation of the level of safety culture construction in underground shopping malls. It provides a method for evaluating the level of safety culture construction in underground shopping malls.

In order to reveal the damage evolution of rock under high temperature environment, granite was heated to 600 ℃, 800 ℃, 1 000 ℃ and its fracture morphology was analyzed. Using digital image processing technology, damage mechanics and "damage micro element" theory, combined with the characteristics of granite micro cracks at various temperatures, a rock damage evaluation method was established and a quantitative study of rock damage was carried out. The results show that: The fracture characteristics of granite are related to the initiation and propagation of cracks, and the number and distribution density of cracks increase with temperature; In each temperature range, the micro crack length of granite obeys logarithmic normal distribution, and the internal damage forms are mainly short cracks, supplemented by long cracks; At different temperatures, the micro cracks of granite developed from unidirectional extension to multi-directional penetration, and the maximum damage degree was positively correlated with temperature. This study reveals the damage evolution law of granite internal cracks, and the damage evaluation method has important reference value for the stability evaluation of high-temperature formation rock and the maintenance of underground engineering.

In recent years, highway tunnel fire accidents have occurred from time to time. Because of its closeness and narrow length, once a fire occurs, it is more likely to cause mass casualties. In order to explore the evacuation safety of highway tunnel and the strategy to improve its evacuation efficiency, Nanjing Fugui mountain double line highway tunnel is selected as the research object. The simulation model is established by using pyrosim, and FDS is used to carry out the numerical simulation of fire under typical working conditions (fire source power is 3MW, 15MW, 20MW and 30MW respectively). The temperature, CO concentration and visibility in the tunnel are analyzed to determine the available safe evacuation time. The required safe evacuation time is obtained through the evacuation simulation by Pathfinder, and then the judgment and evacuation strategy optimization verification are carried out according to the safe evacuation criteria. The results show that: The greater the power of the fire source, the shorter the time to reach the dangerous state, and the fire conditions of 15MW and above can not meet the safety evacuation requirements, indicating that the safety evacuation requirements are not met in case of large fire. The safe evacuation can be ensured by increasing the longitudinal wind speed, adding smoke exhaust devices and optimizing the evacuation route. The research results can provide reference for emergency evacuation of highway tunnel fire.

The occurrence of mine dynamic disaster is often accompanied by coal rock failure. Study on the evolution characteristics of coal rock fracturing can provide a theoretical basis for the monitoring and early warning of mine dynamic disaster. Four typical coal rock samples, including coal, mudstone, sandstone and shale, which are common in coal measure strata of a mine, are selected for uniaxial compression tests to study the acoustic emission characteristics of their failure process. The results show that: The ringing counts can precisely reflect the failure law of coal and shale samples in each stage, and the increasing inflection point of cumulative ringing count curve appears at the beginning of plastic stage. In the failure process of mudstone and sandstone, the ringing count is less, and the inflection point of the cumulative ringing count curve appears in the late plastic stage. The failure modes of the four coal rock samples are mainly tensile failure and the average proportions of tensile failure of coal, mudstone, sandstone and shale samples are 64.97%, 73.12%, 84.45% and 92.21%, respectively. The number of peak frequencies of each frequency band shows a sudden increase before the failure. The main fracture frequency of coal and sandstone is Ⅲ (150~200 kHz), mudstone is Ⅰ (50~100 kHz) and Ⅴ (280~330 kHz), and shale is mainly concentrated in Ⅱ (100~150 kHz) and Ⅴ (280~330 kHz). The acoustic emission b-value of the four types of coal rock generally show the characteristics of "uptrend - fluctuation - decline stage". The b-value can effectively reflect the fracture process of the four kinds of coal rock, and the decreasing trend before the failure can be used as an important precursor information of the failure and instability of coal rock.

To solve the problem of large deformation of soft rock tunnel in Hengduan Mountains, Changning Tunnel of Changning-Baoshan Expressway in Yunnan Province is taken as the engineering background, and adopts the methods of theoretical analysis and field test to carry out the research on active control key technology of NPR cable in soft rock tunnel from the aspects of action mechanism, support scheme and construction technology. The results show that under passive support, the main causes of deformation and failure of surrounding rock in Changning tunnel are the development of joint fissures, high clay mineral content, low strength of surrounding rock, small dissolution pores in microstructure and loose structure. The active support technology of “NPR anchor cable + PR anchor cable + “ W” steel belt + high strength flexible net” is put forward, and the support parameters of NPR cable and PR cable are determined by field loose circle test. Aiming at the special environment of extremely broken surrounding rock and water-bearing soft rock, the optimization technology of NPR cable active support of “spray before support + re-spray” and “lower edge sealing of anchorage end + wire adding of steel strand end” is put forward. The field test results show that the NPR cable active control technology can effectively control the large deformation of soft rock tunnel, and the maximum deformation is controlled from 2 125 mm to 300 mm, which ensures the safety of tunnel support structure.

The service characteristic of rail transit stations is an important basis for evaluating the efficiency of rail transit services and guiding urban renewal and construction around the stations. This study uses mobile phone data as the measured data to analyze the actual service scope of the station. Taking Hangzhou Metro Lines 1, 2, and 4 as examples, the service characteristics of the metro station are comprehensively analyzed from the three aspects of service scope, passenger flow, and the service object. The description of this paper makes up for the limitations of previous studies in terms of research methods and data acquisition. On this basis, the influencing factors of metro station service characteristics are explored from the macro, meso, and micro levels. The study shows that the spatial structure and site location at the macro level have the most significant impact on the service characteristics of metro stations, other characteristics such as passenger flow and passenger distribution are significantly affected by surrounding land use, and if site location and surrounding land use are similar, other modes of transportation and road network structure will play a more obvious role.

The development and utilization of underground space in China is developing rapidly, showing the trend of deepening, scale, and compounding, which brings severe challenges to emergency evacuation safety. Evacuation signs are vital to the evacuation route-finding process of people in emergencies. This paper describes an experimental research method of the influence of evacuation signs on emergency evacuation route-finding behavior of people in underground space based on VR technology, and explores the impact of the position and color of evacuation signs on evacuation route-finding efficiency in underground space through empirical experiments. Two experimental control groups were designed, and five virtual scenes were used to test the performance of evacuation route selection and evacuation route length when the signs were located on the ground, in the corner, and at the top, and when the signs adopted three color schemes: green, red and blue. The results show that: 70% of the participants can be guided to the exit through the shortest path by the evacuation sign located in the corner, and the evacuation efficiency reaches 0.84, which is better than the sign located on the ground or at the top. The adoption of green signs is significantly superior to red and blue in the shortest path guiding the rate and efficiency. The study results supplement the basic knowledge of emergency evacuation behavior of underground space occupants and can improve the existing evacuation model of underground space and relevant emergency safety policies.

Rock discontinuities have a great influence on stress wave propagation. Nowadays, the influence of different filling states and filling material properties of rock discontinuities on stress wave propagation and dynamic fracture characteristic are unclear. The numerical models of rock mass with different discontinuities are established to study crack propagation under coupled static and dynamic loads, and the blasting failure process of coal mass with multi-group discontinuities is simulated. The results of stress analysis at each monitoring point and explosion damage analysis show that the reflection effect increased with the decrease of the mechanical properties of the filling material, and the transmission effect decreased with the decrease of the mechanical properties of the filling material. On the side of discontinuity with wave incidence, the “reflected stress waves induced cracks”, “layer-like cracks”, and “direction changed cracks” were formed due to the reflected stress waves, which aggravated the rock damage in this area. The transmitted stress waves can lead to the destruction of the discontinuities and the formation of macro-radial explosion cracks on the side of discontinuity without wave incidence. The number of main cracks formed in zone II (the side with discontinuities) in models 2~5 (containing rock discontinuities) is about 60%~75% higher than that in zone I (the side without discontinuities), and the total length of explosion cracks in Model 3 is the largest. The numerical simulation results of coal rock explosion show that the discontinuities control the crack expansion and the explosion effect with increasing rock discontinuities. The research results can provide certain technical support for engineering blasting construction design, rock burst prevention and rock burst disaster.

The tensile strength of soil is significantly lower thanits compressive and shear strengths, leading to its frequent neglect in theoretical and experimental research. This paper provides a comprehensive review of both direct and indirect methods for measuring soil tensile strength, comparing and analyzing the advantages and disadvantages of existing testing techniques. Our findings indicate the following: (1) The uniaxial tensile strength of soil can be categorized into vertical and horizontal methods based on the direction of applied force. The vertical method's accuracy is compromised by the weight of the soil sample above the failure plane. (2) Common methods for securing soil samples include bonding, anchoring, friction, and clamping, with clamping proving to be more convenient and practical than the other techniques. We recommend optimizing the horizontal uniaxial tensile test due to several issues, such as soil sample loss during preparation and demolding, uneven stress distribution across the tensile section, inapplicability to large-aggregate gravelly soils, cumbersome sample fixation, and challenges in minimizing friction between the soil sample and the testing platform.

In order to study the seismic performance of the scrap tire-sand composite foundation, six groups of quasi-static tests of the tire-sand composite foundation are carried out. The effects of the stacking mode of the tire-sand unit, the initial vertical load and the carbon fiber mesh on the hysteretic performance of the composite foundation are analyzed. Based on the pseudo static test, the restoring force model of the scrap tire-sand composite foundation is established by using the test fitting method. The results show that the hysteretic curve of the scrap tire-sand composite foundation is full, the overall shape is shuttle, thus it has good energy dissipation capacity. The staggered stacking of tire-sand unit, increasing the initial vertical load and adding carbon fiber mesh are conducive to the tire-sand composite foundation to participate in energy consumption. The calculated results of hysteretic curve of the restoring force model are in good agreement with the test results, which can reflect the stress process and main stress characteristics of the specimen.

In order to explore the rock breaking law of conical cutterhead for large-diameter vertical shaft boring machine with pilot hole, the rock breaking simulation model of cutter in conical cutterhead was established using discrete element method. The rock breaking characteristics of the cutter in the near and far face is studied, and the influences of cone angle, distance from the free face and space between cutters on the rock breaking state, cork crack propagation and the energy consumption ratio are deeply analyzed. The correctness of the simulation model is verified by cutter breaking conical rock. The results show that: The cone angle of cutterhead, distance from the free face and space between cutters have significant influence on the rock breaking. The optimal cutter spacing of near face and far face decreases with the increase of cone angle. Furthermore, the rock breaking efficiency of cutter in near face is higher than that of cutter in far face. The research results can provide reference for conical cutterhead design and cutter layout for vertical shaft boring machine.

The coupling effect of group pit in the excavation process of super large foundation pit group has a great influence on soil deformation and building structure, and its influence degree is more intense when it is constructed in soft strata such as deep silt layer. Therefore, it is of great significance to select the appropriate excavation sequence in the deep foundation pit group project with deep silt soil to reduce the soil disturbance in the protected area. Based on a complex deep foundation pit group project in Shenzhen, the influence of five different construction schemes on the retaining structure and sensitive buildings on both sides of the foundation pit group was explored through finite element three-dimensional numerical simulation. The results show that due to the high rheology and high compressibility of silt and muddy soil, the horizontal displacement of soil has a sudden change compared with the adjacent upper and lower soil layers. It reaches the maximum in the middle and lower part of the side wall in the southwest direction of area C, which is 4.46 mm ~ 7.01 mm, and the horizontal displacement of the diaphragm wall in the southeast direction is 2.67 mm ~ 5.00 mm. When there are multiple foundation pits around the sensitive building, the synchronous excavation of the deep foundation pit and the small foundation pit adjacent to the protected area can further reduce the vertical displacement of the site where the settlement sensitive building is located, which is 31.7 % lower than the original excavation sequence. The lateral displacement of the retaining structure is the smallest when the excavation is completed under the condition of excavating the deep and long foundation pit first and then constructing the small pit. However, the synchronous excavation of the deep and long foundation pit and the adjacent foundation pit can reduce the time effect of the group pit, and further coordinate and control the final deformation of the foundation pit after long-term construction.

Aiming at the problem of how to estimate the horizontal bearing capacity of the pile foundation after the pre-reinforcement treatment, this paper establishes a simplified p-y method model with reference to the port engineering pile foundation code, and the limit horizontal soil resistance P_u=m(x+x₀)ⁿ power function of the clay was given.The balance differential equation of the pile body was established, through the parameter substitution method, the relevant analytical solution was given by the series solution theory of ordinary differential equation, giving The Matlab source code for the calculation of the relevant parameters is obtained. Finally, through the engineering case and the analytical solution newly calculated in this paper, it is concluded that after the soft soil foundation is pre-reinforced by vacuum preloading, the characteristic value of the horizontal bearing capacity of the pile foundation is changed from the original 51.6 N to 121 N, and its rationality is verified by comparing the test results of the pile foundation after pre-reinforcement treatment.

Inclined pile combined support is a new type of foundation pit support, which is suitable for large area foundation pit without internal support. In this paper, based on a sloping piles supporting of foundation pit project of Tianjin, the design of 6 kinds of precast pile supporting structure, including four kinds of combination of inclined pile supporting, to carry on the excavation of large field test, measurement analysis under different environment surrounding the combination structure supporting the deflection of the foundation pit, and the finite element software Plaxis 3D analysis of the stability of foundation pit. The results show that among the different types of inclined pile combination support, the inner inclined straight combination pile displacement is the least and the supporting effect is the best. When there are adverse factors around the foundation pit, such as over-digging, it is obviously different from the conventional pile row. The rigid frame effect, the diagonal brace effect and the gravity effect of the inclined pile combination support determine that it can still play a good role of its own stability. And the influence of soft soil creep on inclined pile foundation pit support should not be ignored,when the excavation reaches the bottom of the pit, cushion and floor should be constructed in time.Numerical simulation analysis shows that the influence of over-excavation on the safety factor and critical failure mode of foundation pit for inclined pile combination bracing is less than that for conventional pile row bracing, and small over-excavation has little influence on the stability of foundation pit.

The formation mechanism of rock disintegration phenomenon of surrounding rock in deep rock mass tunnels has always been highly controversial. The article explores this issue theoretically from the perspective of stress wave propagation. A physical model of stress wave propagation in the surrounding rock of a semi-circular tunnel was established. The wave equation of the surrounding rock area was solved, and the amplitude distribution of stress waves in the surrounding rock area of the tunnel showed a characteristic of wave attenuation. The innovative proposal was made for the width and theoretical depth of the fracture zone in the surrounding rock area of the tunnel. Taking Dingji Mine as the object, the theoretical calculation of the central radius of the surrounding rock partition was carried out and compared with the measured results. Most of the partition radii were in good agreement. The research results of this article have a certain promoting effect on the theory of zoning and fracturing of surrounding rock in tunnels.

Combining correlation analysis and establishing empirical relationship is a common method for geotechnical parameters prediction in geotechnical engineering. This method can quickly and efficiently predict geotechnical parameters through some easily obtained geotechnical testing data. Taking the geotechnical parameters of the cohesive soil in the lower part of Gehu Formation in Changzhou area as the research object, 102 groups of geotechnical testing data were selected, and the geotechnical parameters prediction model based on the multiple regression model and information entropy was established. Firstly, the cohesion and internal friction angle of quick direct shear test were determined as the prediction objects, and the influencing factors were density, water content, void ratio and liquidity index. Then, through the regression analysis of SPSS software, the optimal single factor fitting model was determined, and calculated the weight of the influencing factors by using the method of information entropy to obtain the improved multiple regression forecast model. Finally, the standard error analysis method was used to analyze the prediction results. The results show that: The density has a positive correlation with the cohesion and the internal friction angle, respectively, and the other factors have a negative correlation with the cohesion and the internal friction angle, respectively. The mean error of the predicted value of cohesion is -1.34 kPa, and the normalized root mean squared error is 12.00%. The mean error of the predicted value of internal friction angle is -0.05°, and the normalized root mean squared error is 18.30%. The study shows that the prediction model has high reliability and can effectively predict the cohesion and internal friction angle of cohesive soil in the lower part of Gehu Formation in this area. This method provides a way of thinking for the prediction of geotechnical parameters.

In order to study the damage and deterioration mechanism of freezing and thawing of rocks in cold regions, the deterioration law of internal pore structure, the change of surface microstructure and the multifractal characteristics of sandstone after different freeze-thaw (FT) cycles (FT0, FT20, FT40, FT60, FT80, FT100) are discussed based on nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). Study results show that: The number of small pores in the freeze-thaw sandstone gradually increases and accounts for 99% of the newly added pores. When the freeze-thaw exceeds 80 times, the initiation rate of small pores exceeds the expansion rate, and the distribution of small pores changes from gradually uniform to non-uniform. The macropores in the freeze-thaw sandstone have fractal characteristics, and the overall NMR fractal dimension decreases with the increase of freeze-thaw cycles. After the action of freeze-thaw, the crystal surface inside the sandstone becomes rough, the intragranular cracks increase, the grains gradually fall off. The average lacunarity of the local structure of sandstone continues to increase after freeze-thaw 20 times, and the growth rate reaches the maximum at freeze-thaw 80-100 cycles, which is 0.1%. The SEM images of freeze-thaw sandstone show good multifractal characteristics. The weaker the rock, the more pronounced the multifractal features.

In order to study the mechanical properties of the interbedded samples mass of sand and mudstone, the mechanical parameters of sandstone and mudstone were first obtained through laboratory tests, the microscopic parameters of sandstone and mudstone were calibrated by PFC^2d software, and then the sandstone-mudstone interceded rock samples were tested in triaxial compression numerial test under different confining pressure and dip angles conditions. The influences of confining pressure and dip angle on the mechanical properties and failure characteristics of sand-shale interbedded rock samples are analyzed. The results show that: (1) Under the same confining pressure, with the increase of the dip angle of rock formation, the compressive strength, elastic modulus and cohesion all tend to decrease first and then increase, and the minimum value is when the rock formation dip angle is 60°. As the confining pressure increases, the axial strain also increases accordingly. (2) The mutation point of the number of cracks during the loading process of the specimen corresponds to the elastic, plastic and failure characteristic points of the stress-strain curve, and the proportion of the number of tensile cracks to the total number of cracks is greater than that of shear cracks. (3) Under the influence of rock formation dip angle and confining pressure, the failure modes of sand-mudstone interbedded rock samples can be divided into three types: tension shear failure, shear slip failure along the bedding plane, slip failure and tension shear failure Simultaneous composite failure. The research conclusions can provide reference for the deformation and stability analysis of related engineering of sand-shale interbedded rock mass.

The paper analyzed the geological condition and stratums distribution of underground constructions in Beijing area. And this paper also concluded the risky stratums that may lead to the engineering safety accidents in construction process. The risky stratums are as follows: the fill stratum and derivative formation (hole and water capsule in fill stratum); sandy stratum and interlayer phreatic; large-stone stratum and hypertonicity phreatic-confined aquifers; soil-rock compound stratum contained basement uplift and bedrock fissure water; fine-grained strata combination and multi-aquifer. Construction project safety risks are analyzed and control measures are provided including geotechnical investigation, engineering design and construction. This analysis provided condition for future safety risk management of underground construction in Beijing.

This paper discusses the influence of foundation pit excavation and inrushing for confined water to pile bearing capacity through a typical engineering case. In this case, the distribution of aquifer and the depth of water level are investigated by field test which are used to calculate and find the causes of inrushing for confined water, combined with the process of inrushing and engineering construction conditions, the causes of inrushing for confined water are found. Then in-situ static cone penetration test is carried out, which is used to find the disturbance depth and extend of soil layers caused by foundation pit excavation and inrushing for confined water, while the relations are suggested between disturbance degree of each soil layer and pile capacity parameters, with this relationship, it is easy to see the disturbance law of these influences. The results show that confined water going through the plug in pipe pile is the main reason of inrushing, the depth of influence of foundation pit excavation on the soil strength below the pit bottom is about 6.5 meters to 9 meters, and the disturbance degree decreases linearly with depth increase. By comparison, the inrushing's influence on the soil strength is much greater than foundation pit excavation, the influence range are from a distance of 2 meters above the pile tip to a distance of 4 meters under the pile tip, and the maximum disturbance degree reaches 0.91. Additionally, the lowest bearing capacity of pile foundation is at the location of inrushing point, the farther away from the inrushing point, the larger bearing capacity can be achieved.

Tunnel face stability is one of important issues affecting the safety of underground engineering construction. The limit analysis based on the upper and lower bound theorem is one of the commonly used methodologies for analyzing the stability of the tunnel face. Among such methods, the adaptive mixed constant-smoothed strain limit analysis (MCSE-LA) method has been proved to have certain advantages over traditional finite element limit analysis in terms of computational accuracy, efficiency, and convergence. Based on it, the feasibility of the adaptive MCSE-LA in the stability analysis of the tunnel face is verified first, and it is found that the stability index (stability number) of the tunnel face obtained by this method is the same as that of the traditional finite element limit analysis. At the same time, the failure modes of tunnel face can also be obtained by adaptive mesh refinement based on the maximum shear strain rate. In addition, this method is also used to analyze the influence of the length of unsupported section of the tunnel excavation on the stability of the face, and the change law of the stability number with the increase of the length is analyzed and summarized, which has certain significance for guiding the construction of underground engineering.

To calculate the ultimate bearing capacity of pile foundation in karst areas, a simplified analysis model is proposed, which fully considers the influence of the distance between the pile and the karst cave on the bearing capacity of pile foundation. Based on the upper bound limit analysis, the corresponding assumed failure mode is proposed. The triangular rigid block is used to discrete the failure mode, and the external force power and internal energy dissipation rate are calculated. Taking the ultimate bearing capacity of pile foundation as the objective function, the problem is transformed into a mathematical optimization model, which is solved by the MATLAB software. To verify the correctness of the present method, the calculation results of the present analysis are compared with those from the upper bound finite element limit analysis. Finally, the influence of material parameters and geometric parameters on the ultimate bearing capacity of pile foundation is analyzed. The parameter analysis shows that with the increasing distance between the pile and the karst cave, the influence of the karst cave on the bearing capacity of the pile tip becomes smaller and smaller. When the distance between the pile and the karst cave exceeds a certain value, the ultimate bearing capacity of the pile tip will not be affected by the karst cave.

Water inrush from coal seam floor is the result of the interaction between the underlying confined aquifer and the aquiclude rock mass, and its risk degree is affected by the characteristics of aquifer, aquiclude and structural plane. The comprehensive evaluation system is constructed by selecting 7 index factors, i.e. aquifer water pressure, unit water inflow, aquiclude thickness, aquiclude rock mass quality, number of bedding planes, proportion of mudstone and quantitative value of structural complexity. The actual risk level of water inrush in the mined area is characterized by combining fuzzy variable set theory and actual water inflow; The data set is constructed based on the mined area evaluation results. The convolutional neural network (CNN) model is trained and compared with BP neural network model to verify the reliability and accuracy of CNN model; Finally, the CNN model is used to predict the risk of water inrush from the coal seam floor in the unexploited area. The results show that CNN model has higher accuracy than BP model. The area of safety zone, low threat zone, medium threat zone and high threat zone in the unexploited area accounts for 21.48%, 45.78%, 24.11% and 8.63% respectively.

In southwest mountainous area of China, there are a large number of composite strata with thin covering layer, good engineering properties of overlying bedrock but difficult excavation, and the mountainous terrain is steep and complicated, which is not conducive to transmission tower infrastructure construction. To solve this problem, a short-pile foundation with inclined anchor is taken as transmission tower foundation, whose can make full use of the bearing capacity of the bedrock while reducing the excavation depth and construction difficulty. In order to explore the mechanical characteristics and main control factors of short pile foundation with inclined anchor, a numerical model was established by FLAC^3D, and the effects of anchor bar diameter and bolt angle on the tensile bearing characteristics of short pile foundation with inclined anchor were discussed. The results show that when the load is large, the bearing ratio of the anchor rod structure increases obviously with the increase of the diameter of the anchor bar, but if the diameter of the anchor bar is too large, the bearing ratio of the anchor rod has less room for lifting. As the bolt Angle decreases, the uplift bearing capacity of short pile foundation with inclined anchor increases under pure uplift load, but its resistance to horizontal load weakens. Considering comprehensively, In the siltstone stratum, anchor bar diameter 40mm and bolt Angle 25° are the optimal design parameters of short pile foundation with inclined anchor.

The elastic modulus of shale is of great significance for various projects. However, shale is a typical transversely isotropic rock, and predicting its elastic modulus is challenging. The commonly used method for predicting the elastic modulus of shale is the Niandou model, but the equation form and parameters determination of this model is complicated. Taking account of the anisotropy of elastic modulus of shale, in this paper a simple linear empirical model was proposed. The results show that the proposed empirical model which can predict the elastic modulus with the change of the bedding angle, is simpler than the classical Niandou model and requires less elastic parameters. For the proposed empirical model, the average relative error between the predicted value and the measured value is slightly smaller. Especially when the angle between the bedding plane and the loading direction is at 15°, 30° and 75°, the accuracy is higher than that of the Niandou model.

With the continuous development of transportation infrastructure building, a large number of tunnels have entered the peak period of maintenance and repair, and structural safety threats are bursting on a regular basis. However, the present level of information and intelligence of tunnel structural health monitoring is inadequate, making it difficult to detect safety performance, which has a negative impact on the tunnel's regular operation and maintenance. According to the tunnel structure health monitoring and decision-making demands, this study presents a framework for tunnel structure safety performance perception system based on numerical-physical coupling method and data fusion. First, the tunnel structure force state perception technology and sensor error propagation law are explored, and the numerical-physical coupling test is used to examine the mutual mechanical relationship of each element of the support structure. Then, the mathematical model and data fusion platform between each monitoring quantity of multivariate data are established. Finally, the overall tunnel structure and each component's safety performance was assessed. The structural safety performance perception system can serve as a foundation for decision making in tunnel disasters prevention and operation management, meanwhile, it is critical to enhance the degree of modernization, informatization and intelligent tunnel engineering management.

Focusing on the reform goal of modernization of urban underground space governance system and governance capacity, this paper studies the legal definition of underground space, and reveals the trend of the evolution of underground space policy,so as to provide ideas for policy supply at the national level.The research shows that in the past twenty years, the underground space policy can be divided into three stages: exploration, initial formation and standardization, centering on the construction of underground space engineering management system, property right management system and three-dimensional property right management system. However, The definition of underground space in existing policies mainly focuses on natural attributes, which confuses the distinction between surface and ground, underground space and underground engineering. Under the framework of the system of establishing the right to use construction land by layers in Article 345 of the Civil Code, underground space has legally got rid of the state of being attached to the surface since Roman law. As an independent object of the right to use underground construction land, underground space must be controlled by human beings, with specificity, independence and clear three-dimensional property rights boundary. The policy evolution shows the trend from natural attribute to legal attribute, from resources to asset capital, from engineering thinking to property right thinking, from plane thinking to three-dimensional thinking, from planned allocation to market allocation.

With the establishment of the territorial space planning system in the new era, a new round of special planning of civil air defense engineering needs to keep pace with The Times and constantly improve its transmission thinking, so as to solve the problems such as insufficient connection between the current special planning of civil air defense engineering and urban planning and insufficient content transmission. This paper first expounds the horizontal, vertical and internal transmission needs of the special territorial space planning, and based on the above needs, puts forward A new round of the framework and key points of the special planning of civil air defense engineering, and combines the planning practice of A city. From the five aspects of "strengthening the current problem identification and transmission planning objectives, strengthening the construction and guidance of municipal comprehensive protection system, highlighting the step-by-step transmission of urban civil air defense engineering system, building the transmission mechanism of air defense zone control elements, strengthening the planning transmission to promote various spatial integration", the paper elaborated how to implement the transmission requirements in the specific urban civil air defense engineering special planning. It is expected to provide reference for the compilation of special planning of civil air defense engineering in the new era.

Limestone immersion corrosion test was carried out in acid (pH = 3), neutral (pH = 7) and alkaline (pH = 11) solution environments. The uniaxial compressive strength, the micro morphology of dissolved limestone surface, the pH values and Ca²⁺ concentration of immersion solution were tested to discuss the deterioration mechanism of limestone. The results showed that the dissolution deterioration degree of limestone was the largest in acidic environment, followed by neutral environment and the smallest in alkaline environment. At the beginning of the test, the pH values of the three chemical solutions changed sharply, then gradually turned to neutral, and finally became weak alkaline. In the acid solution, the dissolution rate of Ca²⁺ was faster in the initial stage. In neutral and alkaline environment, the dissolution reaction was slow. With the increase of immersion time, the micro morphology of dissolved limestone showed the expansion of micro pores and the aggravation of surface roughness. According to the statistical results of micro damage area of limestone after dissolution, the uniaxial compressive strength of limestone decreased with the increase of damage area ratio in the three immersion solutions. The damage area ratio was the largest in acid environment, followed by neutral environment and the smallest in alkaline environment.

In order to solve the problem that the geological condition in front of the cutterhead is not clear in the shield construction process, this study proposes a stratigraphic classification model using machine leaning technology based on the relationship between shield parameters and geological characteristics. Shield parameters are dynamic response of geological characteristics during shield tunnelling. The transformed shield parameters, specific thrust and specific torque are used to reveal the changes of geological characteristics. CART model and random forest model are developed to predict stratigraphic categories during shield advancing. The operation parameters of shield in Pazhou railway project are collected and fed to machine learning-based model for training and prediction. The results show that the accuracy of CART prediction model and random forest model are 81% and 85%, respectively. There is a small error on the boundary of local adjacent categories, which meets the actual engineering requirements and can provide reference for the construction of similar projects.

In order to meet the need of the urban road above the underground traffic hub of Beijing sub-center put into operation first, a construction scheme combining cover excavation and open excavation is proposed. The main characteristics of the scheme are as follows: 1) The foundation pit of the underground transportation hub is divided into three parallel layout pits, namely “cover excavation pit, open excavation pit and slope excavation pit”;2) The supporting structure is shared between cover excavation pit and open excavation pit;3) First, the roof structure construction of the cover excavation area is completed to resume the urban road operation as soon as possible, and the negative layer construction of the cover excavation area is carried out by the reverse method, and then the open excavation pit and the slope excavation pit on both sides of the cover excavation area are simultaneously excavated;4) The negative second floor and negative third floor of the cover excavation area is constructed by open excavation method. The paper elaborated the construction procedure of the combined method of cover cut and open cut and analyzed the advantages of the combined method. Considering that the steel tube column in the cover excavation area is always disturbed by the excavation of the foundation pit, the deformation law of the steel tube column during the excavation of the foundation pit is analyzed by the numerical simulation method combined with the site monitoring results. The results show that the horizontal deformation and uplift deformation of steel tube column meet the control requirements. The combined construction scheme of cover cut and open cut proposed in this paper can not only ensure that the urban roads in the underground transportation hub area can be put into operation as soon as possible, but also each foundation pit excavation and structure pouring are basically independent of each other, effectively reducing the mutual influence of the foundation pit construction in cover cut area and open cut area, and improve the construction efficiency.

For the purpose of studying the calculation of composite anchor force of anchor rod and the influence of anchoring angle on the surface shear force of anchored structures under the condition that the shear direction and the anchor rod tend to be coplanar, FLAC3D finite element software is used for numerical simulation. Firstly, the numerical calculation models were established based on the solid elements and contact surface elements, and the parameters required for the numerical simulation are inverted by the physical experiment results.Secondly, fish language in FLAC3D was utilized to record the variation of shear force of structural plane with the increase of shear displacement during shearing. Finally, according to the geometric relationship in the mechanical model, the distribution function of the reaction force of the compressive side along the anchor rod was obtained. On the basis of the classical beam theory, the mechanical model was established, and the shear force calculation formula of the anchor rod at the structural surface was derived using the principle of minimum potential energy and the displacement variational method. The results demonstrate that the shear force on the anchorage structure surface first increases and then decreases with the increase of the anchoring angle. When the anchoring angle β≤90°, the “guide rail effect” of the anchor rod is more significant; When the anchoring angle β>90°, after shear deformation, the rocks are separated due to the deformation of the anchor rods .

The water-rich sand has the characteristics of poor flow plasticity and high permeability, which is easy to cause unsmooth soil dumping and water spewing during the Earth Pressure Balance (EPB) shield construction. For the EPB shield project of Xi'an Metro Line 10 crossing the water-rich sandy stratum, this paper used bentonite slurry and foam agent to condition the flow plasticity and decrease permeability of sand, put forward the flow plasticity evaluation method for conditioned sand, and determined the optimum conditioning scheme with workable flow plasticity and permeability, so as to provide reference for the project. The following conclusions are drawn from the study. (1) The flow plasticity is workable when the conditioned sand after slumping has no cracking or collapse, the slump shape is pear shaped, the slump is 180 ~ 210 mm, and the contact angle θ between the slumped sand and the ground is 0° ~ 90°. At this time, the permeability coefficient of the conditioned sand with workable flow plasticity is about 10^-5 cm/s within 90 minutes, meeting the engineering requirements. (2) The optimum conditioning scheme is to maintain the mass ratio of sand, bentonite and water between 200∶1∶40 ~ 200∶1.5∶44, with a volume specific concentration of foam agent solution of 2% and a foam injection ratio of 6%.

Particles will be crushed with the changes of the particle size distribution and the mechanical properties when they are subjected to impact load. With the increase of the degree of particle crushing, the final particle distribution will tend to self-similar distribution, which is called fractal distribution. The tests were carried out for clinker and marble particles in order to study the effect of impact load on particle size distribution, the PSD curves and the variation law of fractal dimension of the two kinds of particles are obtained when they are subjected to impact load. The results show that particles will not be crushed without limitation, the PSD curves consistent with the fractal model, the fractal dimensions increase with the degree of particles crushed which exist a limit value. The expression of energy dissipation and the strain energy of particle crushing are derived by contacting the final fractal dimension and mechanical properties. According to the theory of fracture mechanics, the energy balance equation of particle crushing can be well described by the law of energy conversion in the process by ignoring the friction between particles.

The environmental impact and control of deep foundation pit formed by underground space development in deep soft soil area has always been the industry focus. In order to study the influencing factors and laws of soft soil subgrade deformation under the excavation and unloading of deep foundation pit supported by row piles, taking the deep foundation pit project adjacent to a soft soil subgrade in Hengqin New Area as an example, the soft soil parameters after vacuum combined surcharge preloading are determined by HS model, and a numerical model considering the undisturbed soft soil on the roadside is established, and then the results are verified with the field measured results. The following conclusions are obtained: (1) Affected by the lateral pressure of undisturbed soft soil on the roadside, in the stage of shallow excavation, the horizontal displacement of soft soil subgrade far from the foundation pit is greater than that near the foundation pit; (2)With the increase of excavation depth, the maximum horizontal displacement slowly develops to 40.5 mm near the excavation surface. Finally, the overall shape of horizontal displacement is inclined at the far side of the foundation pit, and "bulging" near the excavation surface. (3) The subgrade settlement is affected by pavement load and foundation pit excavation at the same time, among which the settlement caused by the pavement load accounts for 64.4% of the cumulative value. (4) The numerical calculation of the first stage and the second stage of foundation pit excavation are in good agreement with the measured results. Due to the influence of soft soil rheology, the horizontal displacement will continue to develop, and the measured value of the third stage of excavation is significantly greater than the numerical calculation. The research results can provide a scientific basis for the deformation prediction and control of the environmental impact of foundation pit in deep soft soil area.