Research progress and application of deep in-situ condition preserved coring and testing

With the depletion of shallow resources,the exploration of deep earth resources has become a global strategy.The study of the different patterns in the physical mechanical properties of rocks at different occurrence depths is the basis for exploring deep into the earth,with the core and premise being the acquisition and testing of deep in-situ core specimens.Based on the original idea of deep in-situ condition preserved coring(ICP-Coring)and testing,combined with theoretical modeling,numerical analysis,test platform development,indoor testing and engineering application,the principles and technologies of deep ICP-Coring are developed.This principle and technology consists of five parts:in-situ pressurepreserved coring(IPP-Coring),in-situ substance-preserved coring(ISP-Coring),in-situ temperaturepreserved coring(ITP-Coring),in-situ light-preserved coring(ILP-Coring),and in-situ moisturepreserved coring(IMP-Coring).The theory and technology of temperature and pressure reconstruction at different occurrence depths and in different environments are proposed,and prototype trial production was completed by following the principle of displacement and tests based on the in-situ reconstructed environment.The notable advances are as follows:(1)Deep in-situ coring system:A pressure-preserved controller with an ultimate bearing capacity greater than 140 MPa,highperformance(temperature-resistant,pressure-resistant,and low thermally conductive)temperaturepreserved materials,an active temperature control system,and high-barrier quality-preserved membrane materials were developed;a deep ICP-Coring capacity calibration platform was independently developed,a deep in-situ coring technology system was developed,and the acquisition of deep in-situ cores was realized.(2)In-situ storage displacement system:Following the dual-circuit hydraulic design idea,a single-drive source push-pull composite grabbing mechanism was designed;the design of the overall structure for the deep in-situ displacement storage system and ultrahigh pressure cabin structure was completed,which could realize docking the coring device and core displacement in the in-situ reconstructed environment.(3)Test analysis system:A noncontact acoustic-electric-magnetic test system was developed under the in-situ reconstructed environment,and the errors between the test results and traditional contact test results were mostly less than 10%;a detachable deep in-situ core true triaxial test system was developed,which could perform loading tests for deep in-situ cores.The relevant technological achievements were successfully applied to the exploration and development of deep resources,such as deep mines,deep-sea natural gas hydrates,and deep oil and gas.The research results provide technical and equipment support for the construction of a theoretical system for deep in-situ rock mechanics,the development of deep earth resources and energy,and the scientific exploration of different layers and occurrence depths(deep and ultradeep)of the Earth.

Research on in-situ condition preserved coring and testing systems

As shallow resources are increasingly depleted,the mechanics'theory and testing technology of deep insitu rock has become urgent.Traditional coring technologies obtain rock samples without retaining the in-situ environmental conditions,leading to distortion of the measured parameters.Herein,a coring and testing systems retaining in-situ geological conditions is presented:the coring system that obtains in-situ rock samples,and the transfer and testing system that stores and analyzes the rocks under a reconstructed environment.The ICP-Coring system mainly consists of the pressure controller,active insulated core reactor and insulation layer and sealing film.The ultimate bearing strength of 100 MPa for pressurepreservation,temperature control accuracy of 0.97%for temperature-retained are realized.CH_(4)and CO permeability of the optimized sealing film are as low as 3.85 and 0.33 ppm/min.The average tensile elongation of the film is 152.4%and the light transmittance is reduced to 0%.Additionally,the pressure and steady-state temperature accuracy for reconstructing the in-situ environment of transfer and storage system up to 1%and±0.2 is achieved.The error recorded of the noncontact sensor ring made of lowdensity polymer is less than 6%than that of the contact test.The system can provide technical support for the deep in-situ rock mechanics research,improving deep resource acquisition capabilities and further clarifying deep-earth processes.

Laboratory pull-out tests on fully grouted rock bolts and cable bolts:Results and lessons learned

Laboratory pull-out tests were conducted on the following rock bolts and cable bolts:steel rebars,smooth steel bars,fiberglass reinforced polymer threaded bolts,flexible cable bolts,IR5/IN special cable bolts and Mini-cage cable bolts.The diameter of the tested bolts was between 16 mm and 26 mm.The bolts were grouted in a sandstone sample using resin or cement grouts.The tests were conducted under either constant radial stiffness or constant confining pressure boundary conditions applied on the outer surface of the rock sample.In most tests,the rate of displacement was about 0.02 mm/s.The tests were performed using a pull-out bench that allows testing a wide range of parameters.This paper provides an extensive database of laboratory pull-out test results and confirms the influence of the confining pressure and the embedment length on the pull-out response(rock bolts and cable bolts).It also highlights the sensitivity of the results to the operating conditions and to the behavior of the sample as a whole,which cannot be neglected when the test results are used to assess the bolt-grout or the grouterock interface.

Pull-out tests and slope stability analyses of nailing systems comprising single and multi rebars with grouted cement

The pull-out capacities for soil nailing systems comprising of one single 29 mm diameter(type A) and four 16 mm diameter(type B) rebars with grouted cement were examined.A field test and numerical analysis for the type A and type B systems were carried out to investigate the pull-out capacities and the slope stability reinforcement efficiency in soil and rock slopes.The results of the pull-out tests show the mobilized shear force and load transfer characteristics with respect to soil depth.The load-displacement relationship was examined for both type A and type B systems.Slope stability analyses were carried out to study the relationships between soil and nail reinforcement and bending stiffness as well as combined axial tension and shear forces.Factors of safety were calculated in relation to the number of nails and their outside diameters.Both soil and rock slopes were included in this evaluation.

Assessment of rapid impact compaction in ground improvement from in-situ testing

Ground improvement has been used on many construction sites to densify granular materials, in other word, to improve soil properties and reduce potential settlement. This work presents a case study of ground improvement using rapid impact compaction （RIC）. The research site comprises the construction of workshop and depots as part of railway development project at Batu Gajah-Ipoh, Malaysia. In-situ testing results show that the subsurface soil comprises mainly of sand and silty sand through the investigated depth extended to 10 m. Groundwater is approximately 0.5 m below the ground surface. Evaluation of improvement was based on the results of pre- and post-improvement cone penetration test （CPT）. Interpretation software has been used to infer soil properties. Load test was conducted to estimate soil settlement. It is found that the technique succeeds in improving soil properties namely the relative density increases from 45% to 70%, the friction angle of soil is increased by an average of 3°, and the soil settlement is reduced by 50%： The technique succeeds in improving soil properties to approximately 5.0 m in depth depending on soil uniformity with depth.

In-Situ Test on Fatigue Characteristics of Top-Mounted Dividable Pile-Board Subgrade for High-Speed Railway

To simulate the fatigue characteristics of the pile-board structure under long-term dynamic load, using the in-situ dynamic testing system DTS-1, the forced vibration loading was repeated one million times at different cross-sections of the pile-board structure for high-speed railway. The dynamic deformation, permanent deformation and dynamic stress of main reinforcements were measured. The test results show that the dynamic responses of the pile-board structure almost did not vary with the forced vibration times under the simulated trainload. After one million times of forced vibration, the permanent deformations of the midspan section of intermediate span and midspan section of side span were 0.7 mm and 0. 6 mm, respectively, and there was no accumulative plastic deformation at the bearing section of intermediate span.

Effects of temperature and wavelength choice on in-situ dissolution test of Cimetidine tablets

The effects of temperature and wavelength choice on in-situ dissolution test instrument of Cimetidine were studied. Absorbance （A）〈 1.0 is required when using a fiber-optic dissolution test system. The detection wavelength of 2 （218 nm） was replaced by 244 nm to carry out this test. The absorbance of Cimetidine solution at different temperature showed an obvious change. Calibration of Cimetidine solution should be tested at the same temperature （37° C） with the test solution. A suitable wavelength with smaller tangent slope could be chosen for in-situ dissolution test of Cimetidine tablets.

Characterization of microstructure and strain response in Ti-6Al-4V plasma welding deposited material by combined EBSD and in-situ tensile test

Additive layer manufacturing （ALM） of aerospace grade titanium components shows great promise in supplying a cost-effective alternative to the conventional production routes. Complex microstructures comprised of columnar remnants of directionally solidifiedβ-grains, with interior inhabited by colonies of finerα-plate structures, were found in samples produced by layered plasma welding of Ti-6Al-4V alloy. The application of in-situ tensile tests combined with rapid offline electron backscatter diffraction （EBSD） analysis provides a powerful tool for understanding and drawing qualitative correlations between microstructural features and deformation characteristics. Non-uniform deformation occurs due to a strong variation in strain response between colonies and across columnar grain boundaries. Prismatic and basal slip systems are active, with the prismatic systems contributing to the most severe deformation through coarse and widely spaced slip lines. Certain colonies behave as microstructural units, with easy slip transmission across the entire colony. Other regions exhibit significant deformation mismatch, with local build-up of strain gradients and stress concentration. The segmentation occurs due to the growth morphology and variant constraints imposed by the columnar solidification structures through orientation relationships, interface alignment and preferred growth directions. Tensile tests perpendicular to columnar structures reveal deformation localization at columnar grain boundaries. In this work connections are made between the theoretical macro- and microstructural growth mechanisms and the observed microstructure of the Ti-6Al-4V alloy, which in turn is linked to observations during in-situ tensile tests.

Research of in-situ hydraulic test method by using double packer equipment

Double packer equipment for hydraulic test can be used to measure pressure of test zone directly, and it is frequently used to perform many kinds of hydraulic tests and take groundwater sample from borehole. The test method of this equipment mainly includes the test design, implementation, interpretation and synthetic analysis. By adopting the double packer equipment for hydraulic test, the parameter distribution of rock permeability along borehole can be acquired, as well as the connectivity, water conductivity and water bearing capacity of the disclosed structure and the chemical characteristics of the deep groundwater. It is a necessary method for the research and evaluation of the complex hypotonicity terrace site selection under geological conditions. This method is not only suitable for the geological disposal of high level radioactive waste, but also can be used in the site selection of underground facilities such as storage of petroleum and carbon dioxide. Meanwhile, it has a good application prospect in other hydrogeological investigation fields.

Discussion on bearing capacity of soft rock ground based on in-situ load test

The suitability of five methods was discussed here,taking the typical results from in-situ load test of Renshou Mansion and Caifu Plaza in Yueyang City for example.It shows that bearing capacity can be obtained by the proportion load and limit load from p-s curve with the first and the second point of contraflexure easily.It is recommended that the accurate value of bearing capacity can be obtained by hyperbola fitting method and minimum curvature radius method theoretically.The rebound method is clear in principle,in which the elastoplasticity characteristic is thought about.Out of consideration for the unsteadiness and unobviousness of bearing capacity from relative settlement method,it can be only adopted as reference.So bearing capacity of soft rock ground should be determined by weathering condition of soft rock and curve type.

Study on determination method of in-situ stress using formation fracturing test and Kaiser effect method

A new method, which is based on formation fracturing test and Kaiser effect method, has been developed for confirming the oilfield in-situ stress in this paper. The new method has been used in a certain oilfield of China and the determined oilfield in-situ stresses is more accurate than that based on one single method.

Design and feasibility analysis of a new completion monitoring technical scheme for natural gas hydrate production tests

As a prerequisite and a guarantee for safe and efficient natural gas hydrates(NGHs)exploitation,it is imperative to effectively determine the mechanical properties of NGHs reservoirs and clarify the law of the change in the mechanical properties with the dissociation of NGHs during NGHs production tests by depressurization.Based on the development of Japan’s two offshore NGHs production tests in vertical wells,this study innovatively proposed a new subsea communication technology-accurate directional connection using a wet-mate connector.This helps to overcome the technical barrier to the communication between the upper and lower completion of offshore wells.Using this new communication technology,this study explored and designed a mechanical monitoring scheme for lower completion(sand screens).This scheme can be used to monitor the tensile stress and radial compressive stress of sand screens caused by NGHs reservoirs in real time,thus promoting the technical development for the rapid assessment and real-time feedback of the in-situ mechanical response of NGHs reservoirs during offshore NGHs production tests by depressurization.

In-situ X-ray computed tomography tensile tests and analysis of damage mechanism and mechanical properties in laser powder b e d fused Invar 36 alloy

Laser powder bed fusion(LPBF)is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry.Whereas it inevitably introduces specific microstructures and pore defects,which will further influence the mechanical properties.Hence,aiming at exploring the LPBF process-related microstructures and pore defects,and especially their influences on the damage mechanism and mechanical properties,Invar 36 alloy was manufactured by LPBF under designed different laser scanning speeds.The microstructure observations reveal that higher scanning speeds lead to equiaxed and short columnar grains with higher dislocation density,while lower scanning speeds result in elongated columnar grains with lower dislocation density.The pore defects analyzed by X-ray computed tomography(XCT)suggest that the high laser scanning speed gives rise to numerous lamellar and large lack-of-fusion(LOF)pores,and the excessively low laser scanning speed produces relatively small keyhole pores with high sphericity.Moreover,the insitu XCT tensile tests were originally performed to evaluate the damage evolution and failure mechanism.Specifically,high laser scanning speed causes brittle fracture due to the rapid growth and coalescence of initial lamellar LOF pores along the scan-ning direction.Low laser scanning speed induces ductile fracture originating from unstable depressions in the surfaces,while metallurgical and keyhole pores have little impact on damage evolution.Eventually,the process-structure-property correlation is established.The presence of high volume fraction of lamel-lar LOF pores,resulting from high scanning speed,leads to inferior yield strength and ductility.Besides,specimens without LOF pores exhibit larger grain sizes and lower dislocation density at decreased scanning speeds,slightly reducing yield strength while slightly enhancing ductility.This understanding lays the foundation for widespread applications of LPBF-processed Invar 36 alloy.

Anchoring mechanical characteristics of Ductile-Expansion bolt

The application of ductile rock bolts has been a crucial method for solving the problems of large deformations,energy absorption and stability control issues in deep rock masses.To study the anchoring mechanism of the key expansive structure,this paper proposes a novel type of bolt—the Ductile-Expansion bolt,and conducts research on anchoring mechanics,energy absorption characteristics,and failure modes of the bolt.In addition,this paper defines the concept of load-volume ratio of metal rock bolts and proves the Ductile-Expansion bolt is capable of better improving the unit volume bearing capacity of the bolt material.Furthermore,laboratory and field tests verify the Ductile-Expansion bolt had better anchoring effect than the traditional rebar bolt,with the expansion structure favorably enhancing the ductility and energy absorption performance of the bolt.Finally,this paper microscopically analyzes the crack propagation and distribution morphology of the bolts by establishing a 3D coupled numerical model based on FDM-DEM.Numerical results illustrate the interface at the variable diameter of the Ductile-Expansion bolt serves as the transition zone between high and low stress levels.The expansion structure can impose radial compression on the medium around the bolt,which can improve the bolt anchorage performance.

In-situ Horizontal Extrusion Test of Herbaceous Root-Soil with Different Root Types

The influence of different types of roots on the soil is complex and still remains unclear.Four in-situ extrusion tests were conducted on two types of root systems,namely fibrous and tap root system,for three plants,Eleusine indica,Potentilla anserine,and Artemisia argyi,according to the classification in Botany,and the thrust-displacement curves and failure patterns of different samples were analysed by comparison to fill the aforementioned gap.Results reveal that the roots can reduce the characteristics of soil brittleness and enhance its capability to resist large deformation,and different root types contribute different effects to the strain-hardening behavior of the root-soil mass.The contribution of the fibrous root system to strength is limited,whilst the tap root system substantially enhances strength and stiffness.Results of failure patterns show that fibrous and tap root systems affect soil solidification and surface cracking reduction.However,the effect of the tap root system depends on the composition of lateral and tap roots:long and rich lateral roots are effective for resisting the creation of cracks,but thick tap roots with few and thin lateral roots may lead to several surface cracks.

Effects of different pull-out loading rates on mechanical behaviors and acoustic emission responses of fully grouted bolts

Due to the influence of mining disturbance stress,it is of great significance to better understand the bearing characteristics of fully grouted bolts under different pull-out loading rates.For this purpose,a series of laboratory pull-out tests were conducted to comprehensively investigate the effects of different pull-out loading rates on the mechanical performance and failure characteristics of fully grouted bolts.The results show that the mechanical performance of the anchored specimen presents obvious loading rate dependence and shear enhancement characteristics.With the increase of the pull-out loading rates,the maximum pull-out load increases,the displacement and time corresponding to the maximum pull-out load decrease.The accumulated acoustic emission(AE)counts,AE energy and AE events all decrease with the increase of the pull-out loading rates.The AE peak frequency has obvious divisional distribution characteristics and the amplitude is mainly distributed between 50-80 dB.With the increase of the pull-out loading rates,the local strain of the anchoring interface increases and the failure of the anchoring interface transfers to the interior of the resin grout.The accumulated AE counts are used to evaluate the damage parameter of the anchoring interface during the whole pull-out process.The analytical results are in good agreement with the experimental results.The research results may provide guidance for the support design and performance monitoring of fully grouted bolts.

In-situ investigation of deformation behavior and fracture forms of Ti/Al/Mg/Al/Ti laminates

In-situ bending and stretching were conducted on hot-rolled and annealed Ti/Al/Mg/Al/Ti laminates,with a focus on crack initiation and propagation of intermetallics and component layers,which helps to clarify their deformation behavior and fracture forms.The results show that delamination is the early fracture form of laminate with or without intermetallics at Al/Mg interface,so Al/Mg interfacial bonding strength determines the mechanical properties of laminate.Various and irregular intermetallics cracks lead to Al/Mg interface delamination in annealed laminate and help to release stress.Necking and fracture of component layers are observed at the late deformation stage,and the sequence is Al,Mg and Ti layers,resulting from their strength.Angle between crack propagation direction and stretching direction of Mg layer both in rolled and annealed laminates is around 45°due to the effect of shear deformation,and crack convergence leads to final complete fracture of Mg layer.

Loading characteristics of mechanical rib bolts determined through testing and numerical modeling

Underground coal mines use mechanical bolts in addition to other types of bolts to control the rib deformation and to stabilize the yielded coal ribs.Limited research has been conducted to understand the performance of the mechanical bolts in coal ribs.Researchers from the National Institute for Occupational Safety and Health(NIOSH)conducted this work to understand the loading characteristics of mechanical bolts(stiffness and capacity)installed in coal ribs at five underground coal mines.Standard pull-out tests were performed in this study to define the loading characteristics of mechanical rib bolts.Different installation torques were applied to the tested bolts based on the strength of the coal seam.A typical tri-linear load-deformation response for mechanical bolts was obtained from these tests.It was found that the anchorage capacity depended mainly on the coal strength.Guidelines for modeling mechanical bolts have been developed using the tri-linear load-deformation response.The outcome of this research provides essential data for rib support design.

Microstructure and mechanical properties of Al-Mg_2Si composite fabricated in-situ by vibrating cooling slope

An innovative semisolid technique termed as vibrating cooling slope(VCS)has been applied to producing in-situ Al-25%Mg2Si(mass fraction)composite.The molten Al-16.5Mg-9.4%Si(mass fraction)alloy with 100°C superheat was poured on the surface of an inclined copper plate(set at 45°inclined angle)while it was vibrated at a frequency of 40 Hz and an amplitude of 400μm.After travelling the length of 40 cm on the slope,the resultant semisolid alloy was cast into a steel mold.For the purpose of comparison,reference composite samples were made by gravity casting(GC)and conventionally still cooling slope casting(CS)methods using the same alloy under identical conditions.The samples were hot extruded at 500°C.It was concluded that the size of Mg2Si particles was decreased by about 50%and 70%for the CS and VCS produced samples respectively when compared to that of the GC produced sample.Despite of their higher porosity contents,both the as-cast and hot-extruded VCS processed samples exhibited higher hardness,shear yield stress(SYS)and ultimate shear strength(USS)values as compared with their GC produced counterparts.These results were attributed to the refined and modified microstructure obtained via this newly developed technique.

In-situ analysis of slip transfer and heterogeneous deformation in tension of Mg-5.4Gd-1.8Y-1.5Zn alloy

Slip transfer is influential in determining damage nucleation of polycrystalline material.The interactions between dislocations and grain boundaries(GBs)was investigated using in-situ tension test in a multi-directionally forged Mg-5.4Gd-1.8Y-1.5Zn(wt%)alloy.It was found that strain accommodation of individual grains by means of slip occurred more easily than slip transfer when several slip systems were operable.The basal-basal slip transfer occurred when the GB misorientation was smaller than 34.2°,whereas basal-pyramidal type took place when the crystallographic misorientation was larger than 48.8°.The product of Luster-Morris m factor and the sum of the Schmid factors of the two correlated slip systems indicated that the threshold for basal-basal slip transfer may exist,however,basal-pyramidal slip transfer shows no such threshold and is more complicated.These results presented here demonstrated that besides the geometrical alignment,the deformation details(such as the number of operable slip systems)and stress state in each individual grain must be considered.