Unconsolidated Layer Research Articles

The Characteristics of Rock Thermal Conductivity of Coal Measure Strata and its Influence on Geothermal Field in Huainan-Huaibei Coalfield

The rock thermal conductivity of coal measure strata in Huainan-Huaibei Coalfield ranges from 0.37 W/mK to 4.36W/mK and the average value is 2.54W/mK. The thermal conductivity closely relates to lithology,buried depth,stratigraphic age and density, the thermal conductivity of sandstone is generally greater than the one of mudstone and coal, and thermal conductivity and depth, density all show the positive correlation relationship; The differences of thermal conductivity of rocks have greater effects on the Geothermal field characteristics, unconsolidated layers and coal seams with poor heat conductivity tend to cause the abnormal ground temperature.

Dynamic pore-pressure variations induce substrate erosion by pyroclastic flows

Field evidence shows that pyroclastic flows can entrain blocks from underlying substrates formed by earlier geological events, yet, counterintuitively, they are less likely to erode unconsolidated layers of fine particles. Here we report laboratory experiments that reproduce these seemingly contradictory observations and also offer a means to infer pyroclastic flow velocity. Experiments demonstrate that the sliding head of a granular flow generates a dynamic upward pore-pressure gradient at the flow-substrate interface. Associated upward air flux is enough to fluidize a substrate of fines, so that particles are not entrained individually but the substrate instead is subject to small shear instabilities. In contrast, coarse particles forming a non-fluidized substrate are lifted at a critical upward force due to the pore-pressure gradient, according to their individual masses, which provides a basis for a model to calculate the flow velocity. Application to the 18 May 1980 pyroclastic flow deposits at Mount St. Helens (Washington State, USA) gives velocities of ∼9-13 m s-1 at ∼6-7 km from the vent on gentle slopes (<4°-6°), in agreement with field observations at this volcano and at others.

Study on the Coefficient of Surface Subsidence by Mining on the Condition of Thick Unconsolidated Layers and Thin Stratum

Aim at the phenomenon of sidestep subsidence on surface by mining on the condition of thick unconsolidated layers and thin stratum,article bases on the theory analysis and calculation, and uses determining key strata and key strata flexibility calculation, and expatiates the characters of η, and makes it divide into subsection function. Contrast with project example and simulation test, it shows:if subsection function η is applied, then using it to forecast the quantity of surface subsidence that will be more approach to fact, which can syllabify explain phenomenon of sidestep subsidence on surface, and has definite meaning to coach locale.

Seasonal thermoelastic strain and postseismic effects in Parkfield borehole dilatometers

Strainmeter records in three 176–323 m deep boreholes near Parkfield, CA, are dominated by seasonal fluctuations. We show that a significant part of the seasonal data may result from thermoelastic strain induced by atmospheric temperature variations. We test this hypothesis by computing thermoelastic strain in an elastic half-space covered by a thin unconsolidated layer from atmospheric temperature and comparing the results to the borehole strain records. The strain at depth is produced by the temperature field at the bottom of the unconsolidated layer. The model provides reasonable fits to the amplitudes and phases of the seasonal borehole signals. The two key model parameters, thickness of the unconsolidated layer (∼0.3–1.2 m at the used sites) and wavelength of the temperature field (3 km), are sufficiently plausible to support the physical validity of the model. Two instances with persistent deviations between the trends of the predicted thermoelastic strain and observed records may reflect shallow postseismic effects of M⩾4 nearby earthquakes.

Determining Velocity and Q-factor Structure using Crosshole Tomography

In this study, we have conducted a crosshole tomography survey to obtain seismic data from two boreholes on the ITB campus. The first borehole was 39 meters deep while the second was 19 meters deep. The aim of the study was to determine the subsurface velocity and Q-factor for the region between the two boreholes for geotechnical purposes. Sources of seismic waves were produced by an impulse generator and sparker and were recorded by 12 channels of borehole hydrophones. In the tomography inversion, the pseudo-bending ray tracing method was employed to calculate travel times. The initial velocity model was a 1-D model with 1x1 m 2 block dimensions. The non-linear inversion problem was solved by delay-time tomography with the LSQR method. Also, a checkerboard resolution test (CRT) was conducted to evaluate the resolution of the tomography inversion. Using the velocity structure results, a LSQR Q-tomography inversion was carried out using spectral curve fitting to obtain the attenuation structure ( t * values). The resulting tomogram shows that there are 3 layers, with an unconsolidated layer (down to 8 meters), a consolidated layer (from 8 meters deep to 20 meters), and bedrock (more than 20 meters). From the results, the ground water level is estimated at a depth of 14 meters.

Prediction of mining subsidence under thin bedrocks and thick unconsolidated layers based on field measurement and artificial neural networks

The deformation characteristics of subsidence and movement induced by mining under thin bedrocks and thick unconsolidated layers are researched using field measurement and the prediction method of artificial neural networks (ANN). Firstly, the occurrence characteristics of thin bedrock and thick unconsolidated layers were analyzed in a research coal field. Based on the measured data, the characteristics of ground movement show that the surface subsidence deformation of mining under thin bedrock is more intensive than that of mining under normal thickness bedrock. Such is evident through the settlement time concentrating, the maximum surface subsidence being greater than the thickness of coal seam, the distribution of ground movement and deformation being concentrated, the range extension being wide, the active period being intensive and concentrated, the surface damage being very serious, and the crack development being significant. A quantitative prediction method is made on mining subsidence under thin bedrocks and thick unconsolidated layers by means of ANN. The improved neural network was used for modeling and predicting the mining subsidence. The ANN output can reflect the change trend of ground movement and deformation. The forecasting results are in good agreement with the real observation results.

Numerical Simulation of Safe Strip Mining under Thick Unconsolidated Layers

It is found in the mine rock mass moving observation that the ground movement characteristics of mining under thick unconsolidated layers are significantly different from the thin surface mining, such as surface cracks developing into a ditch-like shape, and large spread range of subsidence[1-2]. According to incomplete statistics, the coal below constructed projects reached up to 137.64 billion tons in China [3], and strip mining as one of the important measures in “green mining technology” system has become an effective technical way [4]. This paper combined double-layer media model theory of mining under thick unconsolidated layers and the specific geological conditions, established numerical model of strip mining under thick unconsolidated layers. By employing finite element simulation software ANSYS10.0, the author of this paper studied the changes of stress and displacement in overburden rocks，learned the general laws of subsidence in surface and overburden rocks when mining under thick unconsolidated layers, and analyzed the influence that the existence of deep clay layer on development of caving fracture zone and water flowing fractured zone. The simulation results are basically consistent with experimental results, and provided theoretical guidance for the safety production practices.

Buckling and Post-Buckling Behavior for Roof Strata in Longwall Mining

In accordance with the occurrence behavior of roof strata and the fracture characteristics of key stratum in shallow seam longwall mining, this paper studied the post-buckling behaviors of key roof stratum in the process of mining by using initial post-buckling theory, which derived a critical load and a breaking span of the main roof during the first weighting, determined the final subsidence for broken key stratum, and presented an application with the example of Daliuta 1203 face. The results indicate that the rock blocks a in are state of non-equilibrium after main roof breaking, the equilibrium path of main roof is unstable from breaking to final subsidence; thick unconsolidated layers above roof have effect on post-buckling behaviors of key stratum; the stability for bifurcation point equilibrium configuration and post-buckling equilibrium path of roof strata could be revealed and an effective method for determining displacement field of imperfection structure could be provided by using initial post -buckling theory.

Numerical simulation of surface movement laws under different unconsolidated layers thickness

Based on specific geology and mining conditions of certain coal working face in China, a series of numerical models under different unconsolidated layers thickness were respectively established by employing FLAC 3D. The relationship between the unconsolidated layers thickness and surface movement laws was studied. Maximum surface subsidence, Maximum horizontal displacement and surface subsidence degree were obtained. Contours of surface subsidence/horizontal displacement and curves were drawn. Some laws of surface subsidence/horizontal displacement were analyzed. The role of the unconsolidated layers in surface subsidence was revealed. It is significant to predict surface subsidence of thick unconsolidated layers for coal mine and take effective measures to control surface subsidence.

Estimation of velocity function parameters in unconsolidated sands using semblance velocity analysis

To properly understand seismic wave propagation in unconsolidated sand layers, it is important to estimate the parameters of their continuous velocity–depth functions. This study proposes a procedure to estimate the V0 and k parameters of a specific velocity function, where V0 is the direct P-wave velocity at the ground surface and k is the velocity gradient. The V0 and k parameters are generally independent of each other. However, it is possible to relate them numerically because both depend strongly on the porosity (ϕ) and water saturation (Sw). The proposed procedure starts by tabulating V0 and k for 0.05 ≤ ϕ ≤ 0.5 sampled at Δϕ = 0.05 and Sw = 0.6, so that only V0 is needed for fitting. Then, time–distance (T-X) type curves of the direct arrival are calculated for the corresponding values of V0 and k parameters values. The type curves are fitted then to the observed shot gather through a modification of the classic semblance velocity analysis method. Once the best-fit V0 value is found, the corresponding k, ϕ, and Sw values are picked from a V0–k–ϕ lookup table. The procedure is applied on synthetic shot gathers with various amounts of additive Gaussian random noise. Results show that the method is robust and tolerant to low to moderate amounts of noise.

Spatial distribution and controlling factors of sedimentary bodies in Jiaozhou Bay and Adjacent Sea Areas, Qingdao

The distributions of thickness of unconsolidated Quaternary sedimentary layers in Jiaozhou Bay and Qingdao offshore area were studied by using 1079-km high-resolution shallow seismic profiles and drilling core data, and the factors controlling the Quaternary evolution were discussed. The results show that such thickness distributions resulted from the coactions of geologic structures and marine hydrodynamic conditions since the Holocene. The geologic structures controlled the slope deposit, proluvial and fluvial fillings since the late Pleistocene. Holocene marine hydrodynamics eroded away sediments at the bay mouth, and tides carried these eroded materials to the sides of the bay mouth and released them there, forming channel-ridge-alternating geomorphic features. During transgressive processes, the sea level rose rapidly, and insufficient sediment supply and tidal actions yielded the relict sediments in the east of Qingdao offshore area.

Hurricanes Affect the Sediment and Environment in Lake Okeechobee

Three hurricanes (Frances and Jeanne in 2004 and Wilma in 2005) passed over Lake Okeechobee causing a number of changes in its sediment and environment. The unconsolidated sediment atop the mud sediments in the central region of the lake became thicker due to the settling and deposition of resuspended sediments after the hurricanes passed. The increased unconsolidated sediment layer was more easily resuspended, and resulted in sustained higher solids and nutrient concentrations and lower light transparency in the water column for more than 4 years after the hurricanes passed. Hurricanes Frances and Jeanne disturbed consolidated sediments to a depth of 7–15 cm from the surface while Hurricane Wilma extended the disturbance to a depth of 25 cm. Concentrations of total suspended solids (TSS) in the water column increased four to sixfold after the hurricanes. The high concentration of TSS was continuous and maintained 2–4 times higher than a normal situation in the lake until present. Hurricanes contributed to a decrease of submerged aquatic vegetation (SAV) density from 4–34 g dw/m2 to 0.1–4 g dw/m2 primarily through scouring. SAV recovery was very slow due to the increasing turbidity and reduced light transparency.

Mining-induced variation in water levels in unconsolidated aquifers and mechanisms of water preservation in mines

Abstracts Phreatic water resources are widely found in thick unconsolidated surface layers in western China, where water levels respond sensitively and quickly to large-scale underground mining in conjunction with shallow coal seams. Longwall face #32201 of the Bulianta Coal Mine, in the Shendong coalfield was selected as an industrial trail base, where field observations on groundwater levels were conducted when the working face was below a water-rich area. The space-time variation in the behavior of unconsolidated water levels in response to underground mining and its relation with of advance were observed through the field trials. The basic conditions for water preservation in mines are presented and the mechanisms of water preservation in mining analyzed, given the geological condition of two key strata and a severely weathered layer buried in the overburden. The field trails show that water preservation in mining shallow coal seams can be successful under suitable conditions, providing new technology for environmental protection in the desert coalfields of northwestern China.

Groundwater budget for the upper and middle parts of the River Gash Basin, eastern Sudan

The River Gash Basin is filled by the Quaternary alluvial deposits, unconformably overlying the basement rocks. The alluvial deposits are composed mainly of unconsolidated layers of gravel, sand, silt, and clays. The aquifer is unconfined and is laterally bounded by the impermeable Neogene clays. The methods used in this study include the carry out of pumping tests and the analysis of well inventory data in addition to the river discharge rates and other meteorological data. The average annual discharge of the River Gash is estimated to be 1,056 × 106 m3 at El Gera gage station (upstream) and 587 × 106 m3 at Salam-Alikum gage station (downstream). The annual loss mounts up to 40% of the total discharge. The water loss is attributed to infiltration and evapotranspiration. The present study proofs that the hydraulic conductivity ranges from 36 to 105 m/day, whereas the transmissivity ranges from 328 to 1,677 m2/day. The monitoring of groundwater level measurements indicates that the water table rises during the rainy season by 9 m in the upstream and 6 m in the midstream areas. The storage capacity of the upper and middle parts of the River Gash Basin is calculated as 502 × 106 m3. The groundwater input reach 386.11 × 106 m3/year, while the groundwater output is calculated as 365.98 × 106 m3/year. The estimated difference between the input and output water quantities in the upper and middle parts of the River Gash Basin demonstrates a positive groundwater budget by about 20 × 106 m3/year

Low temperature deposition of nanocrystalline titanium dioxide from titanium tetraisopropoxide

Effect of ozone and water vapor on the chemical deposition of TiO2 from the gas phase in the system of titanium tetraisopropylate-oxygen was examined. Introduction of ozone in the reaction medium was shown to result in the precipitation of smooth TiO2 layers at 240°C, and the addition of water vapor leads to the formation with higher rate of unconsolidated layers. Adding ozone to the reaction medium with low moisture content (up to 0.65 Pa) allows obtaining at temperatures 250–350°C with high rate of growth the TiO2 layers with the anatase nanocrystals of high photocatalytic activity.

Near-surface absorption compensation technology and its application in the Daqing Oilfields

High-frequency seismic data components can be seriously attenuated during seismic wave propagation in unconsolidated (low-velocity) layers, resulting in reduced seismic resolution and signal-to-noise (S/N) ratio. In this paper, first, based on Wiener filter theory, inverse filter calculations for near-surface absorption attenuation compensation were accomplished by analysis of the direct wave spectral components from different distances near the surface. The direct waves were generated by detonators in uphole shots and were acquired by receivers on the surface. The spatially varying inverse filters were designed to compensate for the frequency attenuation of 3D pre-stack CRG (common receiver-gather) data. After applying the filter to CRG data, the high frequency components were compensated with the low frequencies maintained. The seismic resolution and S/N ratio are enhanced and match better with synthetic seismograms and better meet the needs of geological interpretation.

Water Behavior in Layered Porous Media with Discrete Flow Channels: Results of a Large‐Scale Experiment

A meter‐scale experimental system (2‐m high by 2‐m deep by 3‐m wide) was used to investigate the behavior of water in a model system consisting of two unconsolidated sediment layers separated by a layer containing discrete flow channels. Stainless steel tubes were inserted vertically through a clayey matrix to represent the discrete flow‐channel layer. The experimental system was well characterized, and results from water infiltration experiments were analyzed. A time series of water arrival at a network of 86 probes located in the unconsolidated sediment layers is presented, as well as water pressure histories at specific locations. Some probes were located at opposite ends of the flow channels to assess water migration through the discrete flow‐channel layer. Analyses of the experimental results focused on capillary break phenomenon at the interface between the overlying unconsolidated layer and the underlying discrete flow channels. Dissimilar water pressure histories were measured at probes near the upper boundary of the discrete flow‐channel layer, suggesting varied and complex water flow behavior. At some locations, a steady or periodic “leaking” of water through the discrete flow channels appeared to occur, contrary to capillary break theory. The authors advocate larger‐scale experiments to advance our understanding and ability to model fluid flow across a wide range of spatial and temporal scales.

POSSIBLE SYMBIOSIS OF BERKELEYA ADELIENSIS MEDLIN, SYNEDROPSIS FRAGILIS (MANGUIN) HASLE ET AL. AND NITZSCHIA LECOINTEI VAN HEURCK (BACILLARIOPHYTA) ASSOCIATED WITH LAND-FAST ICE IN ADÉLIE LAND, ANTARCTICA

Berkeleya adeliensis Medlin is a tube-dwelling diatom commonly associated with the bottom level of land-fast ice and the underlying unconsolidated layer or “platelet ice”, in Antarctica, particularly in Adélie Land. This taxon often accounting for a great proportion of the biomass (up to 108 cells 1−1) exhibits a colonial life habit. Cells are grouped in large mucilaginous tubes, sometimes centimetric, which show a polarity: new cells are closely grouped toward one pole of the tube, whereas at the other pole cells are scarce, loosely arranged and with a large proportion of degraded and empty cells. Small pennate diatoms belonging to Synedropsis fragilis (Manguin) Hasle, Syversten & Medlin live as epiphytes on the external wall of the mucilaginous tube, but without any selective distinction with regard to the polarity of the Berkeleya colony; they are arranged in small stellate colonies of three or more cells. Other tiny pennate cells of Nitzschia lecointei Van Heurck are frequently observed in the inner part of the mucilaginous tube where they seem to live free, and this latter species is suspected to live in symbiosis with B. adeliensis and perhaps may be commensal. The life habit of these three diatom taxa are described and illustrated in LM and SEM.

Face stabilization methods for excavating unconsolidated soil with high groundwater level in the Sambongihara Tunnel

The Sambongihara Tunnel of the Tohoku Shinkansen is 4280 m long NATM tunnel under a tableland. The cover is 23 m on average, and 45 m at maximum. Geological features around the tunnel are sand, volcanic ashy silt and clay. Problems to excavate this tunnel are high groundwater level and an unconsolidated layer of poorly grained fine sand, so various pre-support systems and additional methods were adopted. The excavation method was short bench cut by machine. To lower the groundwater level, which was at around 25 m above the tunnel crown where ground around the tunnel was unconsolidated, the deep well method was adopted. Wells were arranged every 20 m alternately on either side, at a distance of 10 m from the tunnel centerline. However, since there was an impermeable clay layer in the upper section, it was impossible by the deep wells to draw off the groundwater completely between the clay layer and an upper layer of sand. Therefore, well point drainage and horizontal drain boring were adopted additionally. At the beginning, the ground around the tunnel crown was clay and forepoling was adopted. Then a sand layer, of low uniformity coefficient around the crown, and forepoling was replaced by AGF injecting urethane series chemical, since it was difficult to hold the face and crown. However, groundwater inflowed from the tunnel face drawing soil grain so that the face was partly washed out, and relatively dry sand avalanched from the crown between the forepoles. The cause of these phenomena was thought to be that the ground was loosened by the inflow of groundwater, drawing fine grain even as groundwater head had been lowered by the deep wells, and that sand layer of poor fine grain content, whose water content had been lowered by the deep wells, collapsed while loosened zone around the face became larger. To meet this situation, such as groundwater remaining on impermeable layer and easily avalanching sand layer of poor fine grain content, two measures were taken. One was inserting a drain material made of compound fiber of polypropylene and polyethylene into each well point and horizontal drain boring, to prevent soil grain from being drawn by inflowing groundwater. The other was adopting AGF injecting sodium silicate series chemical to strengthen cohesion, since shear strength of sand soil is weak in case with groundwater. According to experience, target for ground improvement to excavate without major trouble is 1 N/mm2 measured by Yamanaka's method for soil hardness. These additional methods and execution management made it possible to hold the face and crown, and to excavate the tunnel without troubles. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Analytical solutions of linear finite- and small-strain one-dimensional consolidation

Analytical solutions are presented for linear finite-strain one-dimensional consolidation of initially unconsolidated soil layers with surcharge loading for both one- and two-way drainage. These solutions complement earlier solutions for initially unconsolidated soil layers without surcharge and initially normally consolidated soil layers with surcharge. Small-strain solutions for the consolidation of initially unconsolidated soil layers with surcharge loading are also presented, and the relationship between the earlier solutions for initially unconsolidated soil without surcharge and the corresponding small-strain solutions, which was not addressed in the earlier work, is clarified. The new solutions for initially unconsolidated soil with surcharge loading can be applied to the analysis of low stress consolidation tests and to the partial validation of numerical solutions of non-linear finite-strain consolidation. They also clarify a formerly perplexing aspect of finite-strain solution charts first noted in numerical solutions. Copyright (C) 2004 John Wiley Sons, Ltd.