Compacted Zone Research Articles

Influence of Stress Shadow on Multi-fractures Initiation Mechanism under Volume Fracturing in Offshore Oil Drilling

Wang, S.; Dong, K.; Song, W.; Li, J., and Xing, C., 2018. Influence of stress shadow on multi-fractures initiation mechanism under volume fracturing in offshore oil drilling. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 172–178. Coconut Creek (Florida), ISSN 0749–0208.In order to reveal the multi-fractures initiation mechanism, according seepage theory, the full three-dimensional multi-fractures initiation local stress model was built by considering the existed of first fracture, the mechanism of stress shadow and initiation pressure change law of follow up fractures were given by simulation methods and combined the maximum tensile stress theory, the reliability was verified by application example. The analysis shows that: The stress shadow caused the existed of compaction zone near the fracture, the stress type was changed in the compaction zone, the minimum principal stress was increased, these lead that the fracture form changed or the fracture direction changed, and the initiation pressure increased; With the increased of elastic modulus and the fracture size, the compaction zone outward passage and affected area increased; After the number of existed fractures was more than 2, the increase of initiation pressure not obvious.

Investigating the Impact of Caving on Longwall Mine Ventilation Using Scaled Physical Modeling.

In longwall mining, ventilation is considered one of the more effective means for controlling gases and dust. In order to study longwall ventilation in a controlled environment, researchers built a unique physical model called the Longwall Instrumented Aerodynamic Model (LIAM) in a laboratory at the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Mining Research Division (PMRD) campus. LIAM is a 1:30 scale physical model geometrically designed to simulate a single longwall panel with a three-entry headgate and tailgate configuration, along with three back bleeder entries. It consists of a two-part heterogeneous gob that simulates a less compacted unconsolidated zone and more compacted consolidated zone. It has a footprint of 8.94 m (29 ft.) by 4.88 m (16 ft.), with a simulated face length of 220 m (720 ft.) in full scale. LIAM is built with critical details of the face, gob, and mining machinery. It is instrumented with pressure gauges, flow anemometers, temperature probes, a fan, and a data acquisition system. Scaling relationships are derived on the basis of Reynolds and Richardson numbers to preserve the physical and dynamic similitude. This paper discusses the findings from a study conducted in the LIAM to investigate the gob-face interaction, airflow patterns within the gob, and airflow dynamics on the face for varying roof caving characteristics. Results are discussed to show the impact of caving behind the shields on longwall ventilation.

Investigation of snow sintering at microstructural scale from micro-penetration tests

Snow sintering is investigated at microscopic and macroscopic scales with high-resolution cone penetration tests. In a cold room at −10 °C, vertical profiles of penetration force were measured periodically during 24 h using the SnowMicroPenetrometer in four snow samples, which differed only by their grain sizes. We estimated the evolution of snow micromechanical properties, namely the bond rupture force, the deflection at rupture and the number of ruptures per penetration increment, by applying a statistical analysis to penetration profiles. The upper part of the profiles is transient due to the progressive formation of a compaction zone in front of the cone tip. In order to explicitly account for this process in the statistical analysis, we used a non-homogeneous Poisson shot noise model which considers a depth dependency of the rupture occurrence rate. On simulated transient profiles, this analysis is shown to provide accurate estimates of the micromechanical properties. On our experimental data, the method effectively revealed that the vertical heterogeneity of penetration force was essentially due to variations of the rupture rate. Conversely, the time evolution of the macroscopic force was mainly due to microstructural bond strengthening. Both macroscopic force and bond rupture force followed a power law with an average exponent of 0.27 and 0.29, respectively. On our samples, a higher exponent for larger grains was observed on the microscopic bond force, while no trend with grain size was visible in the exponent characterizing the macroscopic force evolution.

The energy absorption and bearing capacity of light-weight bio-inspired structures produced by selective laser melting

Sandwich structures are widely used in aviation and aerospace fields because they can absorb vast energy due to their excellent continuous compression behaviors. And in this work, the light-weight bio-inspired sandwich structure of titanium alloy was designed based on cybister elytra and produced by selective laser melting (SLM). The results show that bio-inspired structures can realize the light-weight effectively by increasing the core height. The specific and ultimate flatwise compressive strengths first increase and then decrease when core height increases. The load-displacement curves of bio-inspired structures during flatwise compression consists of elastic deformation, buffer and compaction zone. Comparatively, the edgewise compression lacks buffer zone. And the bio-inspired structure has an excellent flatwise comprehensive performance when its core height is 6 mm, whose peak flatwise compressive strength and specific volume energy absorption are 84.30 MPa, 101.30 MJ/m3, respectively. The specific ultimate strength of bio-inspired structures is optimized at the core height of 4 mm on the edgewise compression tests. And the fracture of the side arc damaged area shows an obviously ductile fracture and the panel and core of the middle area are brittle fracture in the flatwise compressive tests. Finally, The ANSYS simulation results are consistent with experimental results during the whole compressions, which will provide an accurate guidance in next researches

New method developed for foundation strengthening in silty-clayed soils

The paper describes the new method developed for foundation strengthening by a drill and inject pile with controlled widening on its end. The method aims at increasing the useable area of the buildings under refurbishment. This is achieved by developing the underground space and/or adding floors. In-situ tests were carried out on a construction site in the city of Tyumen in order to implement the method on an industrial scale. The in-situ tests resulted in determining the radius of the compacted zone of soil massif, the geometric parameters of controlled widening, the vertical and horizontal deformations of the soil massif in the pile area and the changed physical and mechanical characteristics. The article describes the production of a new method for reinforcing foundations in the form of a drill-injected pile with controlled broadening at the end.

Representation of Plot‐Scale Soil Heterogeneity in Dual‐Domain Effective Flow and Transport Models with Mass Exchange

Core Ideas The heterogeneity of soil hydraulic properties can be described with effective parameters. Increasing model complexity can be used to represent plot‐scale soil heterogeneity. One‐dimensional dual‐domain flow models are used to reproduce 2D preferential transport. Local subscale variability effects are included as mass transfer in an effective model. Agricultural soils are characterized by a structure that is strongly dependent on farming practices like tillage and trafficking. These practices can create compacted zones in the soil, thus initiating preferential flow. Two‐ or three‐dimensional models can be used to account for the spatial variability of the soil hydraulic and transport properties. Since it is challenging to obtain such data, it is logical to find simpler approaches. Our objective was to design a one‐dimensional (1D) modeling approach that effectively accounts for plot‐scale soil structure variability. A 1D dual‐permeability model was tested in which compacted soil was represented by a matrix domain and uncompacted soil by a fracture domain and eventually by assuming an additional immobile water region (MIM) in the fracture domain representing compacted clods embedded within the uncompacted soil. Models (1D) were compared with two‐dimensional single‐porosity (2D_SP) modeling results for water flow and Br− transport based on a previously performed field tracer experiment. Results indicated good agreement between 1D dual‐domain approaches (1D_DPERM and 1D_DPERM_MIM) and the 2D_SP representative model simulation results with high model efficiency and with respect to the field observations. This implied that a 1D vertical model description was sufficient to represent plot‐scale variability if smaller scale soil structure heterogeneities could be accounted for as effective parameters in dual‐domain models. Variation in the mass transfer term had a large effect on the vertical Br− profile distribution. The parameters describing the sizes and shapes of the domains were most relevant for estimating mass transfer between soil structural features in heterogeneous agricultural fields. Still, the calibration of the upscaling approach of two‐domain interactions in larger scale models remains challenging.

A self-optimized software tool for quantifying the degree of left ventricle hyper-trabeculation

Left ventricular non-compaction is characterized by the presence of multiple trabecules in the left ventricle myocardium, associated with multiple inter-trabecular recesses communicated with the ventricular cavity. The medical community needs an objective quantification of non-compacted cardiomyopathy, characterized by a trabeculated mass in the left ventricle myocardium. A software tool for the automatic quantification of the exact hyper-trabeculation degree in the left ventricle myocardium for a population of hypertrophic cardiomyopathy (QLVTHC) patients is developed and tested. End-diastolic cardiac magnetic resonance images of the patients are the input of the software, while the volumes of the compacted zones and the trabeculated zones are necessary to produce the percentage quantification of the trabecular zone with respect to the compacted zone. Significant improvements are obtained with respect to the manual process, by saving valuable diagnosis time. The development of a self-optimized software tool (SOST) based on the outputs of 50 patients with hypertrophic cardiomyopathy automatically produces the volumes of the compacted zones and the trabeculated zones, as a percentage quantification. Now, the SOST is tested with a different population of patients, with different characteristics. Besides, a parallelization for the detection of the external layer of the compacted zone allows the real-time analysis per slice in a patient, obtaining important speedups with regard to the QLVTHC proposed and the manual process used traditionally by cardiologists.

Reinforcement of weak seasonally freezing soils at road consructing by double-cone hollow pile method

The article deals with the reinforcement method of weak seasonally freezing soils in subgrade base by using double-cone hollow piles, tridimensional geogrid, geotextile for roads in the northern regions of the Russian Federation. The method of calculating the road base in the form of pile strip foundation of double-cone hollow piles reinforced by tridimensional geogrid and geotextile on weak heaving soils taking into account traffic loads and weight of subgrade is considered. The developed method of calculation is based on the formation of soil compaction zones in the near-pile space as a result of pile driving into the ground, which leads to an increase in the structural strength of the weak soil, and also takes the arch effect that occurs in the soil between adjacent pile heads.

The fracturing characteristics of rock mass of coal mining and its effect on overlying unconsolidated aquifer in Shanxi, China

Due to coal mining taking place on a large scale in northern China, it is inevitable that wide-spread dewatering occurs in the aquifers overlying the resulting goaf. The purpose of this paper is to protect the groundwater of overlying unconsolidated aquifers. Based on physical model experiment, seepage experiments, and numerical simulation, this paper determines the patterns and distribution of the overburden rocks in the goaf, establishes the correlation between the fracture ratio and the hydraulic conductivity of the rock mass, and characterizes the groundwater flow pattern. The results show that (1) the residual fracture occurring ratio within the residual fracture zone is approximately 1.82 times that of the fracture compaction zone and 1.93 times that of the coal wall support zone; (2) the hydraulic conductivity of the rock mass in different parts of the goaf increases with increasing fracture ratio, the relationship of the two follows a power curve; (3) the predicted groundwater levels from numerical simulation is good fit with the measured and indicates that the hydraulic conductivities derived from seepage experiments are rational. We demonstrate how a laboratory-scale physical model can be used effectively to verify existing conceptual models in such a way that the impact of coal mining on groundwater resources can be predicted for similar regions.

SPATIAL VARIABILITY OF SOIL PENETRATION RESISTANCE IN COFFEE GROWING

The intensive use of machines in agriculture tends to cause soil compaction, which can hamper the expansion of root system and the absorption of water and nutrients, thus affecting the crop development. In view of the above, the present study aimed to identify critical zones of soil compaction, through the spatial distribution of soil penetration resistance (SPR), having positions within the coffee rows and soil depth ranges as variables. The study was performed in a coffee plantation of 7.32 ha, belonging to the Bom Jardim Farm, located in the municipality of Bom Sucesso, MG, Brazil. The SPR was measured using a penetrometer in the depth range from 0 to 0.40 m, with discretization in four layers of 0.10 m. The data were interpreted based on geostatistics, in order to identify if there is spatial dependence of the SPR and generate thematic maps demonstrating the variable’s spatial behavior. It is concluded that there is spatial dependence of soil penetration resistance, being possible to use geostatistical tools to generate thematic maps based on classes of soil penetration resistance. The values of SPR in the tractor trail, for layers from 0.10 to 0.20 and from 0.20 to 0.30 m, were classified in the high SPR class and could cause damage to the crop.

Amostral Optimization of Mechanical Resistance to the Penetration of a Yellow Oxisol Under Pasture

The degradation of pastures can be characterized by several factors, mainly due to the management adopted, so in view of the country’s territorial extension and the peculiarity of each region and soil type, it is essential to develop research to improve the monitoring of the system. The objective of this study was to evaluate the effect of different sample densities to establish a mesh that gives precision in maps of spatial variability of soil mechanical resistance to root penetration to pasture areas in the coastal tableland region of Northeast Brazil. In a pasture area, three sampling meshes were demarcated for georeferenced evaluation of soil mechanical resistance to root penetration: mesh 1 established in the dimensions of 50 × 50 m, mesh 2 of 100 × 100 m and mesh 3 of 150 × 150 m, totaling an area of 9 ha. The soil resistance to penetration was measured using an automated apparatus, coupled to a tractor. The variation found in the values of penetration resistance in subsurface can be related to the management adopted in the area, as well as the trampling of the animals. Data on soil penetration resistance in pasture showed that the most compacted zone was always below 30 cm depth by using different sample densities. The results allow us to conclude that the higher the density of the sampling mesh, the greater the accuracy of the data and that, independently of the sample mesh, it was possible to identify the layer of higher soil mechanical resistance to root penetration.

ФАКТОРЫ УПРАВЛЕНИЯ КАЧЕСТВОМ И ЭНЕРГОЗАТРАТАМИ ПРИ РЫХЛЕНИИ ПОЧВ

The process of soil deformation is a trajectory in a multidimensional space of principal stresses and principal deformations, as well as time, that is, the speed of application of deformer forces. Consequently, it is possible to achieve its destruction at various energy costs. With more rational technologies, volume deformations are minimal, and vice versa. The destruction of the soil massif should be along lines and planes characterized by the least strength. More preferred are working elements, the elements of which are executed in such a way that the sizes of the compaction zone inevitably arising as a result of their action on the soil layer are minimized. The dynamics of this process is influenced by the shape of the loading curve, the after-effect speed. The evaluation of efficiency with continuous oscillation by constant amplitude and frequency did not reveal the maximum of the energy efficiency. A promising direction is the additional oscillation of the working organ by single impulses. The construction of a soil-working working organ, self-adapting to changing operating conditions, is proposed. On the basis of the equation of motion, factors influencing the quality and energy costs of the loosening of the soil are established. Design changes are proposed to improve efficiency.

ТЕХНОЛОГИЯ ПЕРМАНЕНТНОГО КОНТРОЛЯ ПАРАМЕТРОВ ДОННОГО ОСНОВАНИЯ В ПЕРИОД ЭКСПЛУАТАЦИИ БУРОВЫХ ПЛАТФОРМ

Forecasting the process of interaction of the platform - offshore system includes calculations of the base stability. The process of immersing the supports of Jack-up drilling rigs into the bottom ground is accompanied by developing areas of plastic deformation, ground flowing, compaction zones and decomposition zones. This causes significant changes in soil parameters. In the context of this task, it is necessary to ensure the reliability of determining strength characteristics of the underlying grounds of bottom sediments at any given time. For this purpose, it is proposed to carry out geotechnical monitoring of the base of Jack-up using geophysical methods. The application of the geophysical method makes it possible to quickly perform predictive calculations based on actual information. According to the results of geomonitoring, it is possible to fulfil calculations reflecting the actual state of the soils underlying the platform. The interpretation of the results obtained is influenced by the multifactorial nature of the changes in the reflected signal. The environment under study in this case can be considered as a determinate system, which makes it possible to apply asymptotic methods for further research.

Numerical investigation of fluid injection into poorly consolidated geomaterial considering shear dilation and compaction

We present a fully coupled poroelastoplastic finite element model to simulate micro-fracture evolution, compaction failure and tensile fracture propagation during fluid injection into poorly consolidated geomaterial. The model includes shear dilation, strain hardening and fracture process zone with permeability evolution. We investigated the effects of geomechanics (stress anisotropy) and fluid injection (fluid rheology) on rock deformation and fracture behavior. Results indicate that fluid rheology dominate the rock failure. Pore pressure increase and water wedge effect can cause two kinds of shear dilation which are prior to tensile failure. The effect of compaction is significant to tensile fracture geometries, which differ from those under elastic and poroelastic conditions. The difference between shear band and compaction zone is the transition of fracture regime from the leak-off dominated to the storage dominated governed by fluid injection.

Analysis of the Interaction of Drill-Injection Piles with Soil Foundation

We study the design of drill-injection piles produced by the cup technology with injection of a solution in the mode of formation of "hydraulic fractures" and the formation of controlled broadening at the end of the pile. On the basis of the analysis of the results of laboratory and field tests and the existing methods for the prediction of interaction of the formed body of the pile with soil, we compute the principal design-basis parameters. We propose an algorithm for the evaluation of settlement of the drill-injection pile with controlled broadening taking into account both the variations of the characteristics of the compacted zone of soil near the pile and the influence of residual stresses.

Improving feeding powder distribution to the compaction zone in the roller compaction

In the roller compaction process, powder flow properties have a significant influence on the uniformity of the ribbon properties. The objective of this work was to improve the powder flow in the feeding zone by developing novel feeding guiders which are located in the feeding zone close to the rollers in the roller compactor (side sealing system). Three novel feeding guiders were designed by 3D printing and used in the roller compactor, aiming to control the amount of powder passing across the roller width. The new feeding guiders were used to guide more powder to the sides between the rollers and less powder to the centre comparing to the original feeding elements. Temperature profile and porosity across the ribbon width indicated the uniformity of the ribbon properties. Using the novel feeding guiders resulted in producing ribbons with uniform temperature profile and porosity distribution across the ribbon width. The design of the feeding guiders contributed to improving the tensile strength of the ribbons produced from the compaction stage as well as reducing the fines produced from the crushing stage.

CONSOLIDATION ZONES FEATURES FORMATION OF A GROUND AROUND SQUARE SHAPED PILES

Necessity to resolve the problem of concerning the analytical dimensions definition and constructing forms of compacted zones of ground around the lateral surface of square cross section pile in normal to pile axis direction are shown in this article. Various analytical methods of ground compacted zones radius determination around cylindrical elements driven into the ground considering its initial state were analyzed. Graph-analytical method of ground compaction zones construction around square cross-section piles was developed. Efficiency of the developed methodology and analytical expressions using possibility to determine the radius of compaction zone of a ground around the driven or jacked-in elements is confirmed by comparing obtained solutions with the experimental data. The developed methodology allows increasing the efficiency and reliability of piles and pile foundations use due to their rational design.

Diagenesis-porosity evolution and “sweet spot” distribution of low permeability reservoirs: A case study from Oligocene Zhuhai Formation in Wenchang A sag, Pear River Mouth Basin, northern South China Sea

Abstract The characteristics of low permeability reservoirs and distribution of sweet spots in the Oligocene Zhuhai Formation of Wenchang A sag, Pearl River Basin were investigated by core observation and thin section analysis. The study results show that there develop the fine, medium and coarse sandstone reservoirs of tidal flat – fan delta facies, which are of mostly low permeability and locally medium permeability. There are two kinds of pore evolution patterns: oil charging first and densification later, the reservoirs featuring this pattern are mainly in the third member of Zhuhai Formation between the south fault zone and the sixth fault zone, and the pattern of densification first and gas charging later is widespread across the study area. Strong compaction and local calcium cementation are the key factors causing low permeability of the reservoirs in the Zhuhai Formation. Thick and coarse grain sand sedimentary body is the precondition to form “sweet spot” reservoirs. Weak compaction and cementation, dissolution, early hydrocarbon filling and authigenic chlorite coating are the main factors controlling formation of “sweet spot” reservoir. It is predicted that there develop between the south fault and sixth fault zones the Class I “sweet spot” in medium compaction zone, Class II “sweet spot” in nearly strong compaction zone, Class III “sweet spot” reservoir in the nearly strong to strong compaction zone with oil charging at early stage, and Class IV “sweet spot” reservoir in the strong compaction and authigenic chlorite coating protection zone in the sixth fault zone.

A Probabilistic Approach to Investigate the Size and Boundary Condition Effects on the Fracture Response of Brittle Materials Loaded in Diametral Compression

The focus in this work is toward an investigation of the fracture response of brittle materials with different specimen size loaded in diametral compression using different boundary conditions. The compacted zone underneath the loading points is assumed to be limited and only responsible for the load transition to the rest of the material. Therefore, the theory of elasticity is used to define the stress state within a circular specimen. A tensile failure criterion is used, and the final load capacity is related to the formation of a subsurface crack initiated in a probabilistic manner in a region in the vicinity of the loaded diameter of the specimen. This process is described by Weibull theory, and it is assumed here that the growth of the subsurface crack occurs in an unstable manner. Therefore, the assumption in Weibull theory that the final failure occurs as soon as a macroscopic fracture initiates from a microcrack is fulfilled. The concept of disk effective volume used in Weibull size effect is presented in a convenient way that facilitates the application of the model to transfer the tensile strength obtained from different methods such as three point bending and Brazilian test. The experimental results for Brazilian test on a selected hard rock are taken from the literature and a fairly close agreement is obtained with the model predictions.

Investigation of permeability evolution in the lower slice during thick seam slicing mining and gas drainage: A case study from the Dahuangshan coalmine in China

During thick seam slicing, the permeability distribution of the lower slice has important significance for guiding the gas drainage. To investigate the characteristics of the permeability evolution in the lower slice during the upper slice mining, a stress-induced permeability evolution model was proposed, and then, based on the top slice mining of the Zhongdacao coal seam in the Dahuangshan coal mine, a series of numerical simulation was performed using the Universal Distinct Element Code (UDEC) software program. The results show that during top slicing, a compacted zone appears in the collapsed overlying strata, which causes more intense compaction in the lower slice. Permeability distribution of the lower slice develops regularly, and after a certain distance of top slicing, the regional distribution characteristic of permeability becomes significant. The lower slice can be divided horizontally into six zones: the original permeability zone with low permeability, the stress concentration zone with permeability decreasing, the initial pressure relief zone with permeability increasing, the full pressure relief zone with high permeability, the pressure recovery zone with permeability decreasing, and the compacted zone with low permeability. The length of each zone is not uniform in the depth direction. Furthermore, the lower slice can be divided vertically into a plastic zone with high permeability and an elastic zone with low permeability. The results are in good agreement with field investigations. Meanwhile, lower slice gas drainage was carried out in the Dahuangshan coal mine, which shows that gas drainage in the full pressure relief zone with high permeability is crucial to gas control during top slicing.