An Elastic Solution for Twin Circular Tunnels’ Stress in Hydrostatic Stress Field

Geotechnical and Geological Engineering - In order to present an elastic solution for twin circular tunnels’ stress distribution in hydrostatic stress field, based on the complex variable...     

Cretaceous-Early Eocene Tectonic Stress Field in China

The Cretaceous-early Eocene tectonic stress field in China was reconstructed using the data of 369 largeand medium-scale flexural folds and 157 joint sets. It was found that the maximum compressive principal stress axis in eastern China dips 32° NE (nearly horizontal), and strikes SW 212°, whereas that in western China dips 15° NE (also nearly horizontal) and trends SW 195°. The estimation of the dip angles of fold limbs and the palaeotectonic stress values indicates that there was a tendency of gradual weakening of tectonism from southwestern to northeastern China in the Cretaceous-early Eocene. At the depth of 2-3 km, the differential stress value changes from 183 MPa in Tibet to 100 MPa in North and East China.The authors consider that the tectonic stress of this period was related to the north-northeastward movement and push of the Indian-Australian plate.     

Stress–Strain Behaviour of Flowable Fill

Flowable fill is a self-levelling and self-compacting, cementitious material which is primarily used as a backfill. It is a mixture of fine aggregates, small amount of cement, water and a by-product material. In this present experimental study, three industrial by-products namely fly ash, rice husk ash and quarry dust were used as constituent materials in flowable fill. Mix proportions were developed for different combination of these industrial by-products, in addition to small amount of cement content. The main objective of the present investigation is to study the stress–strain behaviour of these mixes, namely unconfined compressive strength (UCS), strain corresponding to peak stress, strain corresponding to fracture and modulus of elasticity. In addition, several mixes were tested for few other properties such as flowability, density, water-absorption and volume changes. The range of strengths, strains and moduli of elasticity obtained for these flowable fill mixtures represents different types of clay soils ranging from soft clays to very stiff clays. Thus, industrial by-products such as fly ash, rice husk ash and quarry dust can be beneficially added in flowable fill that offers comparable strengths to soils used for conventional fills and many other low-strength applications.     

Stress–Strain Analysis of Buckling Failure in Phyllite Slopes

Buckling failure occurs in the open pit mines in the Quadrilátero Ferrífero of the State of Minas Gerais, Brazil. In this study, this failure mechanism is evaluated through stress–strain analysis, using the finite element software named Phase². Many representative hypothetical models of the slopes were created in order to reproduce the conditions in open pit mines, like their geometry and foliated joints with kinematic conditions for buckling failure. Elastic and plastic simulations have been done. Strength and deformability parameters, such as discontinuity stiffness and cohesion, as well as the in situ stress field, are analyzed in order to understand their influence in the buckling failure mechanism in the global open pit mine slopes excavated in phyllites. As studies about this problem are extremely rare, the present research brings important contributions to establish the basic conditions for this kind of failure.     

Stress State of the Earth’s Crust in the Western Tien Shan in Central Asia (Uzbekistan): A Mathematical Stress Model

Geotectonics - Seismic and tectonic processes were analyzed, taking into account the dimensions of tectonic structures and geological factors that determine the features of the relationship between...     

Stress–strain behavior of cement-improved clays: testing and modeling

The results of a series of laboratory tests on unimproved and cement-improved specimens of two clays are presented, and the ability of a bounding surface elastoplastic constitutive model to predict the observed behavior is investigated. The results of the oedometer, triaxial compression, extension, and cyclic shear tests demonstrated that the unimproved soil behavior is similar to that of soft clays. Cement-improved specimens exhibited peak/residual behavior and dilation, as well as higher strength and stiffness over unimproved samples in triaxial compression. Two methods of accounting for the artificial overconsolidation effect created by cement improvement are detailed. The apparent preconsolidation pressure method is considerably easier to use, but the fitted OCR method gave better results over varied levels of confining stresses. While the bounding surface model predicted the monotonic behavior of unimproved soil very well, the predictions made for cyclic behavior and for improved soils were only of limited success.     

A New Method to Identify Quaternary Moraine：Acoustic Emission Stress Measurement

How to effectively identify glacial sediments, especially Quaternary moraine, has been in dispute for decades. The traditional methods, e.g., sedimentary and geomorphologic ones, are facing challenge in eastern China where controversial moraine deposits are dominatingly distributed. Here, for the first time, we introduce the acoustic emission （AE） stress measurement, a kind of historical stress measurement, to identify Quaternary moraine. The results demonstrate that it can be employed to reconstruct stress information of glaciation remaining in gravels, and may shed light on the identification of Quaternary moraine in eastern China. First, we measured the AE stress of gravels of glacial origin that are underlying the Xidatan Glacier, eastern Kunlun Mountains in western China. Second, we calculated the stress according to the actual thickness of the glacier. The almost identical stress values suggest that the glacial gravels can memorize and preserve the overlying glacier-derived aplomb stress. And then we introduce this new approach to the controversial moraine in Mount Lushan, eastern China. The results indicate that the stress is attributed to the Quaternary glacier, and the muddy gravels in the controversial moraine in Mount Lushan are moraine deposits but not others.     

Tensile Fractures and in situ Stress Measurement Data Constraints on Cretaceous–Present Tectonic Stress Field Evolution of the Tanlu Fault Zone in Shandong Province, North China Craton

Tectonic stress fields are the key drivers of tectonic events and the evolution of regional structures. The tectonic stress field evolution of the Tanlu fault zone in Shandong Province, located in the east of the North China Craton (NCC), may have preserved records of the NCC’s tectonic history. Borehole television survey and hydraulic fracturing were conducted to analyze the paleo and present tectonic stress fields. Three groups of tensile fractures were identified via borehole television, their azimuths being NNW–SSE, NW–SE and NE–SW, representing multiple stages of tectonic events. Hydraulic fracturing data indicates that the study region is experiencing NEE–SWW-oriented compression and nearly-N–S-oriented extension, in accordance with strike-slip and compression. Since the Cretaceous, the orientation of the extensional stress has evolved counterclockwise and sequentially from nearly-NW–SE-oriented to NE–SW-oriented and even nearly N–S-oriented, the stress state having transitioned from strike-slip-extension to strike-slip-compression, in association with the rotating and oblique subduction of the Pacific Plate beneath the NCC, with the participation of the Indian Plate.     

Numerical Method for Modeling the Constitutive Relationship of Sand under Different Stress Paths

Overonehundredconstitutivemodelsforsand havebeenproposed,howeveronlyafewmodelsare widelyappliedinengineering.Therearetwochief reasonsforthis.(1)Sandiscomposedofgeological materialsandsituatedinaneutralenvironmentthat hassufferedvariousactions.Therefore,itisdifficult todescribethecomplexbehaviorofsoilsbyusinga simplemathematicalmodelwithonlyafewparame ters.(2)Therealsoexistsabasicparadoxintradi tionalmodelingmethods.Oneaspectofthemodelsis neededtodescribetheconstitutiverelationofsoilac curatel…     

Effect of Initial Principal Stress Direction on the Dynamic Characteristics of Carbonate Sand

INTRODUCTION Theexploitationofoffshorenaturalresourcesin thetropichaspresentedgeotechnicalengineerswith theproblemofdealingwithinsitucarbonatesedi mentsinharshconditionsforwhichfewengineering dataareavailable.Thecarbonatesedimentsaresub jectedtolargestaticstressesduetotheweightof foundationstructuresaswellascyclicstressesdueto waveaction,andinsomecases,earthquakeloading.Ithasbeenprovedthatthenatureofcyclicstresschangesoccurringintheseabeddepositduetowave loadinginvolvesacontinuousrotationo…     

Effects of Rock Bolting on Stress Distribution around Tunnel Using the Elastoplastic Model

INTRODUCTIONThe stability of underground structures duringand after excavation is the most i mportant factor fordesigners because any kind of collapse may destroylarge parts of a finished tunnel,thereby causing ma-jor repairs and ti me loss.To avoid this problem,rock bolts are widely used as ani mportant support el-ement.These are economical,have a short installa-tion ti me,and provide reinforcement to maintain theintegrity of the stressed rock.The effect of the bearing capacity of rock b…     

Principle of Formation of the Earth’s Crust under Natural Stress Conditions

This article formulates the experimentally substantiated physical principle that the natural stress condition of the Earth’s crust is formed due to the superposition of stress fields, which is caused by the gravitational forces of the Earth and by tectonic and astrophysical forces that are produced by physical processes in space. The natural stress field is represented by the stress tensor regulatory components: \(\sigma _{z}^{{\text{N}}}\) = \( - \gamma H + {{\sigma }_{{zT}}} + {{\sigma }_{{z{\text{AF}}}}}\), \(\sigma _{x}^{{\text{N}}}\) = \( - \lambda \gamma H + {{\sigma }_{{xT}}} + {{\sigma }_{{x{\text{AF}}}}}\), \(\sigma _{y}^{{\text{N}}}\) = \( - \lambda \gamma H + {{\sigma }_{{yT}}} + {{\sigma }_{{y{\text{AF}}}}}\).     

Cretaceous Stress Fields Evolution and Its Geodynamic Implications in Jiaolai Basin, Northern China

正The Tan-Lu fault zone(TLFZ)along the East China continental margin experienced sinistral movement at the beginning of Early Cretaceous(ca.145)due to fast oblique subduction of the Izanagi Plate in the Pacific Ocean.It can     

Simulation of Stress Distribution around Tunnels and Interaction between Tunnels Using an Elasto-plastic Model

This article presents a computer simulation of stress distribution around tunnels and interaction between tunnels using an elasto-plastic model. A finite element method using ANSYS software has been used for the analyses of one and two tunnels at different overburden depths with different separating distances between the tunnels. The results of numerical analyses indicate that stress distribution and stress concentration around the tunnels vary with the overburden depths. It is found that the coefficients of stress concentration for elasto-plastic medium are smaller than those for elastic one by 1.9%. Furthermore, the interaction between the two tunnels rapidly decreases with the increase of separation distance between them. In addition, for quantitatively describing the interaction between the two tunnels, a critical separation distance is introduced. The critical separation distances between the two tunnels at different overburden depths are 8 m, 12 m, and 14 m respectively. This fact is very important and essential for the design of mining tunnels and to ensure safety in tunnel engineering.     

Time–Space Effect of Stress Field and Damage Evolution Law of Compressed Coal-Rock

Along with the increase of mining depth, the dynamic disasters related to the instability and destruction of coal-rock are becoming more and more serious. In this paper, the uniaxial compression model of coal-rock was established by means of the micro particle flow PFC2D software firstly, and then the variation of stress field and damage field of coal-rock were analysed. Finally, the time–space constitutive model of coal-rock was discussed and modified. The research results show that: the compression stress field of coal-rock has obvious time–space effect, and along with the change of compressive stress, the stress field was transferred to the inner coal-rock body; the coal-rock damage evolution process has a similar temporal and spatial relations with the stress field evolution, the number of damage cracks were increasing with the constant change of compressive stress, and transferred to the inner coal-rock body with “string wave” feature; the time–space damage constitutive model of coal-rock established on the basis of local crack and the stress concentration factor of coal-rock was reasonable and effective, the damage degree of the whole coal-rock could be predicted by the variation of local coal-rock stress and cracks. In overall, the successful verification of the time–space relationship of coal-rock damage and stress transfer indicated that the possibility of using the constitutive model developed in this study to investigate coal-rock stability in coal mine.     

Stress and Deformation Analysis of Concrete-Facing Sand–Gravel Dam Based on Inversion Parameters

With the long-term operation of the project, the material parameters of concrete-facing sand–gravel dam will change, which brings great difficulty to the scientific and effective stress and deformation analysis. Combining with the measured displacement data, the finite element analysis model of the concrete-facing sand–gravel dam of Heiquan reservoir was established, and the modulus of elasticity and internal friction angle of the dam body were inverted by the measured displacement of the dam, then the simulation analysis of the filling construction process and the reservoir storage process of dam was carried out, and the stress and deformation values of the dam during the construction period and the impoundment period were calculated. The results showed that the parameters obtained from the inversion are smaller than the original parameters, but there is little difference between them. The displacement calculated by finite element inversion was close to the measured displacement value, the overall displacement and stress distribution of the dam body and panel were in line with the general law, and the calculated displacement and stress values were at the normal level. This study provides a reference for parameter inversion and stress and deformation analysis of concrete slab dam through monitoring data analysis.

     

Characteristics of the Mesozoic and Cenozoic Tectonic Stress Fields of the Urumqi-Usu Region, Xinjiang

Based on the study of folds and related conjugate shear joints, the tectonic stress fields of the Urumqi-Usu region to the north of the North Tianshan Mountains have been reconstructed. Furthermore the author discussed the tectonic movements and their dynamic features. The early tectonic movement in the investigated region occurred from the end of the Late Jurassic to the initial stage of the Early Cretaceous, with the maximum (tensile) and minimum (compressional) principal stress trajectories in the tectonic stress field being in E-W and S-N directions respectively; the late tectogenesis took place from the end of the Early Pleistocene to the initial Middle Pleistocene, with the maximum and minimum principal stress trajectories in the late stress field striking in WNW and NE-NNE directions respectively. Through computer-aided simulated calculation by the finite element method and analysis of geological structure, it has been ascertained that the early tectogenesis is a nearly N-S compressive movement and the late one a NE to nearly N-S compressive movement with reverse shear. The dynamic force which caused the tectogeneses came from the movement of the southern major fault, i.e. the North Tianshan Mountains.