Instability mechanism and control technology of soft rock roadway affected by mining and high confined water

Based on deformation and failure characteristics of the second belt conveyor roadway at level II of Zhuxianzhuang coal mine, laboratory experiments, numerical calculation and field test were adopted to analyze the composition and microstructure of mudstone, the law of mudstone hydration and its strength weakening induced by water, the characteristics of surrounding rock deformation and failure under the action of confined water. Results showed that montmorillonite clay minerals accounted for as much as 76% of mudstone, with a large number of pores existing in the microstructure. Besides, as the molecular structure of montmorillonite changed, mudstone microstructure damage occurred with the macroscopic manifestation of its theological instability. Weakening degree of confined water on residual strength of mudstone was almost 50%. The instability mechanism of soft rock roadway caused by high confined water is that surrounding rock circulates the process of ＂fracture-seepage-mud ding-closed＂ twice, which weakens its strength and leads to roadway instability. A combined support technology, namely the, ＂high-toughness sealing layer ＋ hollow grouting cables ＋ full-length anchoring bolts with deep borehole＂ was proposed. Based on field observation, the soft rock roadway was controlled effectively, which also verified the effectiveness of new control technology for surrounding rock.

Characterization and modeling of long-term stress-strain behavior of water confined pre-saturated gypsum rock in Kurdistan Region,Iraq

In order to understand the effects of soaking time and confined water pressure on the strength of rock due to dissolution of gypsum,rock samples with 96% of gypsum content collected from Kurdistan Region in northern Iraq were investigated.Laboratory tests were then performed on the normal gypsum rock samples under pre-saturated condition to obtain their uniaxial compressive strength(UCS) values.The pre-saturated samples were submerged in distilled water for 35 d,70 d and 105 d,respectively,under confined water pressures of 0-0.5 MPa.The gypsum content decreased by 11% after 105 d of soaking under confined water pressure of 0.5 MPa.The UCS of the normal gypsum rock was 19.6 MPa and it decreased to 6.3 MPa and 2 MPa after 105 d of soaking under confined water pressures of 0 and 0.5 MPa,respectively.A nonlinear constitutive model was used to simulate the experimental stress-strain relationships of rock samples under various conditions.The constitutive model parameters were sensitive to the gypsum content.

Nano-/Micro-confined Water in Graphene Hydrogel as Superadsorbents for Water Purification

Confined water has been proven to be of great importance due to its pervasiveness and contribution to life and many fields of scientific research.However,the control and characterization of confined water are a challenge.Herein,a confined space is constructed by flexibly changing the pH of a graphene oxide dispersion under the self-assembly process of a graphene hydrogel(GH),and the confined space is adjusted with variation from 10.04 to 3.52 nm.Confined water content in GH increases when the pore diameter of the confined space decreases;the corresponding adsorption capacity increases from 243.04 to 442.91 mg g−1.Moreover,attenuated total reflectance Fourier transform infrared spectroscopy and Raman spectroscopy are utilized to analyze the hydrogen bonding structure qualitatively and quantitatively,and correlation analysis reveals that the improvement in the adsorption capacity is caused by incomplete hydrogen bonding in the confined water.Further,confined water is assembled into four typical porous commercial adsorbents,and a remarkable enhancement of the adsorption capacity is achieved.This research demonstrates the application potential for the extraordinary properties of confined water and has implications for the development of highly effective confined water-modified adsorbents.

Mitigation effects on the reflected overpressure of blast shock with water surrounding an explosive in a confined space

The mitigation of blast shock with water has broad application prospects. Understanding the mitigation effects on the reflected overpressure of the explosion shock with water surrounding an explosive in a confined space is of great significance for military explosives safety applications. To estimate the effects of the parameters on the reflected overpressure of blasted shock wave, a series of experiments were carried out in confined containers with spherical explosives immersed in a certain thickness of water,and numerical simulations were conducted to explore the corresponding mechanisms. The results reveal that the reflected overpressure is abnormally aggravated at a small scaled distance. This aggravation is due to the high impulse of the bulk accelerated water shell converted from the explosion. With increasing scaled distance, the energy will be gradually dissipated. The mitigation effects will appear with the dispersed water phase front impacting at a larger scaled distance, except in the case of a dense water phase state. A critical scaled distance range of 0.7-0.8 m/kg^(1/3) for effective mitigation was found. It is suggested that the scaled distance of space walls should be larger than the critical value for a certain water-to-explosive weight ratio range(5-20).

Vibrational features of confined water in nanoporous TiO_2 by Raman spectra

Raman spectra of confined water adsorbed in nanoporous TiOare obtained in experiment. TiOsamples with different pore diameters under different humidity conditions are investigated. The results indicate that the symmetric vibrational mode of water molecule is destroyed when relative humidity decreases. This indicates that the interaction between water molecules and surface of TiObecomes stronger when the distance between water molecules and surface turns smaller, and the interaction plays a major role in depressing the symmetric vibrational peak. The spectra of confined water in TiOand Vycor are compared. When filling fractions are the same, their spectra show distinctions no matter whether they are in partial filling condition or in full filling condition. The spectra of HDO confined in TiOwith different filling fractions are compared with each other. There is no clear distinction among their vibrational peaks, and the peaks mainly relate to asymmetric vibration. Therefore, the interaction between water molecules and the wall of pore decouples the symmetric vibrational mode only, and the influences on asymmetric vibrational mode show little differences among different filling fractions.

Implications of fine water mist environment on the post-detonation processes of a PE4 explosive charge in a semi-confined blast chamber

The effects of a fine water mist environment in a semi-confined blast chamber on the chemical and thermodynamic processes following detonation of a 20 g PE4 explosive charge have been investigated.The effects were quantified by the analysis of pressure profiles recorded where several parameters including arrival time of the shock at the sensors, peak overpressures, specific impulse of the positive phase, period of the negative phase and the specific impulse of the multiple reflections were quantified.The effect of the fine water mist on the arrival time, peak pressures and the specific impulse of the positive phase agrees with previous findings in literature. In this paper, the focus is on the implications of the fine water mist on the negative phase and the impulse of multiple pressure reflections. The period of the negative phase was found to have increased by 40% and with higher negative peak pressure in the mist condition compared to the atmospheric condition. The activities of the multiple pressure reflections were found to have decreased considerably, both in number and in amplitude leading to lower impulses(by about 60%) for the water mist conditions.

Layering of confined water between two graphene sheets and its liquid-liquid transition

Molecular dynamics （MD） simulations are performed to explore the layering structure and liquid-liquid transition of liquid water confined between two graphene sheets with a varied distance at different pressures. Both the size of nanoslit and pressure could cause the layering and liquid-liquid transition of the confined water. With increase of pressure and the nanoslit＇s size, the confined water could have a more obvious layering. In addition, the neighboring water molecules firstly form chain structure, then will transform into square structure, and finally become triangle with increase of pressure. These results throw light on layering and liquid-liquid transition of water confined between two graphene sheets.

Separation of Oil Phase from Dilute Oil/Water Emulsion in Confined Space Apparatus

A miniature process for separating the oil phase from dilute oil/water emulsion is developed.This process applies a confined space apparatus,which is a thin flow channel made of two parallel plastic plates.The space between the two plates is rather narrow to improve the collisions between oil droplets and the plate surface.Oil droplets have an affinity for the plate surface and thus are captured,and then coalesce onto the surface.The droplet size distribution of the residual emulsion resulted from the separation process is remarkably changed.The oil layer on the plate weakens the further separation of oil droplets from the emulsion.Three types of plate materials,polypropylene(PP),polytetrafluoroethylene(PTFE) and nylon 66,were used.It is found that PP is the best in terms of the oil separation efficiency and nylon 66 is the poorest.The interaction between droplets in the emulsion and plate surface is indicated by the spreading coefficient of oil droplet on the plate in aqueous environment,and the influences of formed oil layer and plate material on the separation efficiency are discussed.

Water Molecules in the Carbon C60 Confined Space

Experimental scenario of the world being successful in planting water molecule at binary level in fullerene C70 is of utmost importance to pursue the theoretical properties of predictive triple water molecules and poly water molecules in Vander Waals confined space like fullerenes. Here, we present a paper in these lines of exploration of embedding triple water molecules in a Carbon confined space through the studies of behavior of three water molecules in Fullerene C60 by ab-initio methods. This heterogeneous system manifests cyclic hydrogen bonds which may be working with flipping actions. The unusual structural property of water trimers is reported. There exists a dipole moment of 0.9 ± 0.1 Debye which indicates the probable semiconductor properties.

New Hexagonal-rhombic Trilayer Ice Structure Confined between Hydrophobic Plates

We perform molecular dynamics simulations for water confined between two smooth hydrophobic walls and observe two crystalline structures with one being first reported. Both of these structures obey the ice rule. The novel ice phase is a flat hexagonal-rhombic trilayer ice, obtained under 1 GPa load at wall separation of 1.0 nm. In this structure, the water molecules in the two layers next to one of the walls （outer layers） and in the middle layer form hexagonal rings and rhombic rings, respectively. For a molecule in the outer layers, three of its four hydrogen bonds are in the same layer, and the other one hydrogen bond connects to the middle layer. For a molecule in the middle layer, only two of its four hydrogen-bonds are located in the same layer, and the other two connect to two different outer layers. Despite their different motifs, the area densities of the three layers are almost equal. The other structure is a flat hexagonal bilayer ice produced at wall separation of 0.8 nm under lateral pressure of 100 MPa, analogous to a system demonstrated by Koga et al [Phys. Rev. Lett. 79, 5262 （1997）]. Both first-order and continuous phase transitions take place in these simulations.

Rock-breaking mechanism and experimental analysis of confined blasting of borehole surrounding rock

The rock-breaking mechanism and effect of confined blasting were analysed by blasting and impact dynamic mechanics, fluid dynamic mechanics, fracture mechanics as well as blasting experiment. The results showed that the fracturing of surrounding rock in confined blasting condition is the result of coaction of rock pre-cracking by shock wave and stress wave and the continuing expanding crackenhancement of confined medium, and the model of crack development of borehole surrounding rock in confined blasting condition was established. This study acquired the damage range of surrounding rock under the action of shock wave and stress wave, as well as the crack development characteristics of surrounding rock after the wedge-in confined medium into the crack space. Deep-hole confined blasting experiment on large rock showed that the high-efficient utilisation of in-hole explosive was achieved and the safety of rock blasting operation was ensured. Safe static rock-breaking under the action of high-efficient explosive blasting was achieved as well as the unification of super dynamic load of explosive blasting and static rock-breaking of water medium.

Determination of Rational Staggered Distance Between Double-Longwall Faces in Mining Operation on Confined Aquifer

The influence of staggered distance on the failure of floor bed is locally and temporarily defined in double longwall mining on the confined aquifer. When the longwall mining reaches a certain scale, the deepest failure of floor bed depends on macroscopic technological parameters of mining and geological conditions. The temporary as well as the terminal failure depth does not change with the mining staggered distance (5~30 m). Based on the mining and geological conditions on the 2 635 double longwall mining panel of Yangzhuang Coal Mine, the changes of abutment pressure was observed and numerically simulated. The result shows that the rational staggered distance should be not more than 10 m.

Roof pre-blasting to prevent support crushing and water inrush accidents

Support crushing and water inrush when mining under an unconsolidated confined aquifer in the Qidong Coal Mine was prevented by roof pre-blasting. The mechanism and applicable conditions for this method have been studied. The results show that when an overburden structure that may cause support crushing and a water inrush accident exists the weakening of the primary key stratum, which thereby reduces its weighting step, roof pre-blasting is both feasible and effective. If the position of the primary key stratum can be moved upward to exceed 10 times the mining height the possibility of support crushing and water inrush disaster caused by key stratum compound breakage will be lowered. The overburden structure of the number 7121 working face was considered during the design of a technical proposal involving roof pre-blasting. After comprehensively analyzing the applicability of roof pre-blasting the resulting design prevented support crushing and water inrush disasters from happening at the number 7121 working face and laid a solid foundation for mining safely.

Risk assessment of fault water inrush during deep mining

With the gradual depletion of shallow coal resources,the Yanzhou mine in China will enter the lower coal seam mining phase.However,as mining depth increases,lower coal seam mining in Yanzhou is threatened by water inrush in the Benxi Formation limestone and Ordovician limestone.The existing prediction models for the water burst at the bottom of the coal seam are less accurate than expected owing to various controlling factors and their intrinsic links.By analyzing the hydrogeological exploration data of the Baodian lower seam and combining the results of the water inrush coefficient method and the Yanzhou mine pressure seepage test,an evaluation model of the seepage barrier capacity of the fault was established.The evaluation results show the water of the underlying limestone aquifer in the Baodian mine area mainly threatens the lower coal mining through the fault fracture zone.The security of mining above confined aquifer in the Baodian mine area gradually decreases from southwest to northeast.By comparing the water inrush coefficient method and the evaluation model of fault impermeability,the results show the evaluation model based on seepage barrier conditions is closer to the actual situation when analyzing the water breakout situation at the working face.

Direct Vibrational Energy Transfer in Monomeric Water Probed with Ultrafast Two Dimensional Infrared Spectroscopy

Vibrational relaxation dynamics of monomeric water molecule dissolved in d-chloroform solution were revisited using the two dimensional Infrared （2D IR） spectroscopy. The vibrational lifetime of OH bending in monomeric water shows a bi-exponential decay. The fast compo- nent （T1=（1.2±0.1） ps） is caused by the rapid population equilibration between the vibrational modes of the monomeric water molecule. The slow component （T2=（26.4±0.2） ps） is mainly caused by the vibrational population decay of OH bending mode. The reorientation of the OH bending in monomeric water is determined with a time constant of t=（1.2±0.1） ps which is much faster than the rotational dynamics of water molecules in the bulk solution. Furthermore, we are able to reveal the direct vibrational energy transfer from OH stretching to OH bending in monomeric water dissolved in d-chloroform for the first time. The vibrational coupling and relative orientation of transition dipole moment between OH bending and stretching that effect their intra-molecular vibrational energy transfer rates are discussed in detail.

Experimental investigation on dilatancy behavior of water-saturated sandstone

It is important to study the dilatancy property of water-saturated rock for understanding the engineering behavior of loaded rock mass. This study carried out the uniaxial and triaxial compressive experiments on the water-saturated red sandstone, analyzed the influences of confining pressure and pore pressure on dilatancy property of water-saturated rock, and discussed the reasonable basis of the stress of dilatancy onset as a strength design parameter of rock engineering, finally established the prediction model of the stress of dilatancy onset under the impacts of confining pressure and pore pressure. The results show that the strength parameters(the stress of dilatancy onset and peak strength) and deformation parameters(axial strain and circumferential strain) of water-saturated sandstone increase with the confining pressure, and the relations can be fitted with a positive linear function. The cohesion and internal friction angle obtained from the stress of dilatancy onset decrease by 11.57% and 7.33%, respectively, when compared with those obtained from the peak strength. The strength parameters and deformation parameters of water-saturated sandstone decrease basically with the increase of pore pressure, in which the relations between strength parameters or axial strain and pore pressure can be fitted with a negative linear function. However, the relation between the peak circumferential strain and the pore pressure should be characterized by a negative exponential function, and the circumferential strain at dilatancy onset isn't affected by the pore pressure.

Control water molecules across carbon-based nanochannels

It is important to know the mechanisms of water molecules across carbon-based nanochannels, which is not only beneficial for understanding biological activities but also for designing various smart devices. Here we review the recent progress of research tbr water transfer across carbon-based nanochannels. In this review, we summarize the recent methods which can affect water molecules across these nanochannels. The methods include exterior factors （i.e., dipolar molecules and gradient electric fields） and interior factors （namely, cone-shaped structures, nonstraight nanochannels, and channel defects）. These factors can control water permeation across nanochannels efficiently.

Investigation on the relation between the gravity anomaly，crustal deformation and underground water

Trough the practice of earthquake prediction we have found that sometimes an earthquake doesn' t occur in the gravity anomaly region or the magnitude of earthquake that has occurred does not corrrespond to the value of gravity anomaly. The main reason of this is related to crust deformation or behavior of undergroud water.In this paper, based on the theory of elasticity and dynamics, the gravity effect associated with the elevation variation, density change and mass migration under the observation point as well as the relationshipe between gravity of feet and crustal activity are studied. The relationship between the variation of gravity and crust vertical deformation, underground water, precipitation are researched; besides the order of magnitude, time and pattern of the influence are studied in order to obtain the gravitational precursors directly related to earthquakes.Theory and practice have proved that crust deformation caused by pumping underground water or extracting petroleum and gravity changes are linearly related. This paper shows that the effect and influence produced by different aquifers to the gravity changes are also different. Phreatic water is the main factor which causes the gravity changes. The second factor is precipitation which influences the humidity of soil, as a result the gravity changes. The confined water, when there is no pumping, whatsoever the rise or fall of its level almost has no influence on the gravity changes.Observation data of Northern China and areas of South-western China verified the consistency of practice with theory.

Piezoelectric nanofoams with the interlaced ultrathin graphene confining Zn–N–C dipoles for efficient piezocatalytic H_(2) evolution under low-frequency vibration

Unique nanofoams consisting of interweaved ultrathin graphene confining Zn–N–C dipoles (ZnNG) are constructed via calcination of Zn-coordinated precursor.Due to the introduction of local polar Zn–N–C configurations,with hypersensitivity for mechanical stress,the piezoelectricity is created on the nonpiezoelectric graphene,and the hierarchical ZnNG exhibits obvious piezocatalytic activity of water splitting for H_(2) production even under mild agitation.The corresponding rate of H_(2) production is about 14.65 μmol g^(-1)h^(-1).It triggers a breakthrough in piezocatalytic H_(2) evolution under low-frequency vibration,and takes a significant step forward for piezocatalysis towards practical applications.Furthermore,the presented concept of confining atomic polar configuration for engineering piezoelectricity would open up new horizon for constructing new-type piezoelectrics based on both piezoelectric and nonpiezoelectric materials.

高承压水地层深基坑抗突涌技术

为了防止高承压水地层深基坑突涌破坏,以韩江-榕江-练江水系连通后续优化工程GX12号井深基坑为依托,采用有限元软件建立三维数值模型,对考虑地连墙深度以及布设减压井的5种技术方案进行模拟分析,研究各方案的抗突涌效果,并通过综合考虑基坑抗突涌效果及地连墙施工技术难度和工程造价等,确定基坑工程抗突涌的优化方案。结果表明:1)地连墙深度可由原设计的91.8m优化为78m;2)坑内增设减压井可有效减小坑底隆起和地连墙水平位移,但是增加了基坑周边地表沉降,而增加地连墙深度可显著减小基坑周边地表沉降和坑底隆起;3)增大地连墙深度的抗突涌效果优于增设减压井的效果。本文成果可为类似高承压水地层深基坑工程抗突涌技术提供一定的借鉴。