Thickness Of Compressive Layer Research Articles

Surface Subsidence Characteristics and Causes Analysis in Ningbo Plain by Sentinel-1A TS-InSAR

In recent years, the Ningbo Plain has experienced significant surface subsidence due to urbanization and industrialization, combined with the area’s unique geological and hydrological conditions. To study the surface subsidence and its causes in the Ningbo Plain, this study analyzed 166 scenes of Sentinel-1A SAR images between January 2018 and June 2023. The time series interferometric synthetic aperture radar (TS-InSAR) technique was used to acquire surface subsidence information in the area. The causes of subsidence were analyzed. The results show that: (1) the annual deformation rate of the Ningbo Plain ranges from −44 mm/yr to 12 mm/yr between 2018 and 2023. A total of 15 major subsidence zones were identified by using both the subsidence rate map and optical imagery. The most severe subsidence occurred in the northern industrial park of Cixi City, with a maximum subsidence rate of −37 mm/yr. The study reveals that the subsidence issue in the main urban area has been significantly improved compared to the 2017 subsidence data from the Ningbo Bureau of Natural Resources and Planning. However, three new subsidence areas have emerged in the main urban area, located, respectively, in Gaoqiao Town, Lishe Town, and Qiuyi Village, with maximum rates of −29 mm/year, −24 mm/year, and −23 mm/year, respectively. (2) The causes of subsidence were analyzed using various data, including land use data, geological data, groundwater-monitoring data, and transportation network data. It is found that a strong link exists between changes in groundwater levels, compressible layer thickness, and surface subsidence. The groundwater levels changes and the soft soil layer thickness are the main natural factors causing subsidence in the Ningbo Plain. Additionally, the interaction between static loads from large-scale industrial production and urban construction, along with the dynamic loads from transportation networks, contribute significantly to surface subsidence in the Ningbo Plain. The results from this study enhance the understanding of the driving factors of subsidence in the Ningbo Plain, which can provide necessary guidance for the economic development and decision-making in the region, helping to manage and potentially mitigate future subsidence issues.

Study on Land Subsidence Simulation Based on a Back-Propagation Neural Network Combined with the Sparrow Search Algorithm

Rapid simulation of land subsidence can provide an effective means of facilitating its management and control. This paper innovatively introduced a back-propagation (BP) neural network subsidence simulation model which was optimized by the sparrow search algorithm (SSA), hereinafter referred to as the SSA-BP model, to simulate land subsidence in Tongzhou District, Beijing. First, based on the time series interferometric synthetic aperture radar (InSAR) monitoring, different technologies such as spatial analysis, Google Earth Engine (GEE), and machine learning were utilized together with a variety of multi-source spatial data, including groundwater level, compressible layer thickness, Visible Infrared Imager Radiometer Suite (VIIRS) nighttime light images, and the OpenStreetMap (OSM) road distribution. Furthermore, we determined the optimal grid scale for land subsidence research and worked out a multifactor-driven SSA-BP land subsidence simulation model for which sensitivity analysis was performed with great care. Main conclusions: (1) From November 2010 to January 2020, the average annual surface displacement rate in Beijing’s subcentre, Tongzhou, ranged from −133.9 to +3.9 mm/year. (2) Our SSA-BP land subsidence simulation model allows for a relatively high overall accuracy. The average root mean square error (RMSE) is 5.00 mm/year, the average mean absolute error (MAE) is 3.80 mm/year, and the average coefficient of determination (R2) is 0.83. (3) Sensitivity analysis shows that the SSA-BP model driven by multiple factors has a far better simulation performance than the model driven by any single weighting factor, and displays the highest sensitivity to the groundwater level factor among all the weighting factors. In terms of subdividing the study area, our SSA-BP land subsidence model runs with multifunctional zones displayed a higher accuracy than that without. This paper made use of a machine learning model to simulate land subsidence in Beijing’s Tongzhou District and explored the sensitivity of different factors to land subsidence, which is helpful for its scientific prevention.

Land Subsidence Evolution and Simulation in the Western Coastal Area of Bohai Bay, China

Groundwater overexploitation and loading of buildings have been the main factors triggering land subsidence along the west coast of Bohai Bay, China, since the 2000s. Uneven subsidence has been causing damage to buildings and civil facilities, loss of elevation, increasing the risk of flood and seawater intrusion, and threatening the safety of people’s lives and property. This paper analyzed the spatial and temporal features of land subsidence along the coastal area from 2003 to 2010 and from 2015 to 2020, respectively. The relations between the initiating factors and land subsidence were explored. Then, the simulation model of land subsidence was constructed through a deep learning method. During the process, multiple data were collected, including land satellite (Landsat), environmental satellite advanced synthetic aperture radar (ENVISAT ASAR) and Sentinel-1 images, leveling data, lithological data, and groundwater level data. The area occupied by buildings and vertical displacement were extracted by using supervised classification, small baseline subset (SBAS), and persistent scatterer interferometry (PSI) technologies. The gated recurrent unit (GRU) neural network was adopted to simulate the evolution of land subsidence. Results showed that the maximum annual vertical displacement rate decreased from −94 mm/yr during 2003–2010 to −87 mm/yr during 2015–2020. The correlation efficiency between the groundwater level of the third confined aquifer group and land subsidence was larger than the area occupied by buildings and the compressible layer thickness with subsidence. The constructed GRU neural network model can simulate subsidence from September 2019 to December 2019, with the overall RMSE and MAE being 3.16 mm and 2.19 mm, respectively. This work can facilitate an understanding of the evolution and prevention of land subsidence along the west coast of Bohai Bay, which will provide information for policy decisions and flood-fighting plans of the worldwide coastal cities.

Mechanical properties and deformation dependent microstructural aspects of laser shock peened 7075-T6 aluminum alloy without coating

This work presents the mechanical properties and elaborately discusses microstructural aspects of LSPwC (laser shock peening without coating) peened 7075-T6 aluminum alloy using the results coming from various characterization techniques such as surface roughness, Vickers microhardness, residual stress analysis, tensile test, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD). The possibilities and consequences of thermo-mechanical interaction, deformation behavior, grain refinement, fractional change of grain boundaries, compressive residual stress and nucleation of precipitates during LSPwC are discussed along with the underlying mechanisms. Microhardness increased by about 25% post LSPwC with a work hardened layer of more than 1000 μm. Maximum compressive residual stress of −227 MPa (in sub-surface region of peened specimens) was induced with effective depth (i.e. thickness of compressive layer) of 900 μm. The defect (dislocation) concentration, volume fraction of precipitates, area fraction of fine grains (of below 50 μm) and number fraction of low angle grain boundaries (especially of 2°–5° misorientation) increased significantly after LSPwC. Besides, the effects of observed improvements (by LSPwC) in tensile behavior were also investigated. The near surface strengthening or modifications observed in this investigation are collectively attributed to LSPwC induced plastic deformation, compressive residual stress, additionally induced precipitates, grain refinement and increased fractions of LAGBs. • The compressive and work hardened layer of ~1000 μm is obtained with LSPwC. • Grains are refined from 197 μm to 32 μm post LSPwC. • It is possible to induce precipitates by LSPwC. • Increased fraction of LAGBs assisted in nucleation of precipitates.

Land subsidence along the Beijing–Tianjin Intercity Railway during the period of the South-to-North Water Diversion Project

ABSTRACTThe Beijing–Tianjin Intercity Railway (BTR) passes through the subsidence centre of the Chaoyang Wangsiying-Heizhuanghu subsidence funnel edge, which is the most serious subsidence areas in the Beijing Plain. In this paper, we performed Persistent Scatterers Interferometry (PSI) time-series analyses technique to investigate land subsidence along the BTR with ENVISAT-ASAR, TerraSAR-X, and Sentinel-1 data. We found the serious subsidence area occupies 14.6% of the total area and reaches a maximum rate of 70 mm yr−1 in Dougezhuang. Sequential subsidence aggregation obtained by global Moran’s I shows that the subsidence heterogeneity is the greatest in 2013. Using the Getis-Ord statistics, the uneven sections of spatial subsidence along the railway are DK7–11 and DK21–23. Combining the compressible layer thickness with groundwater data reveals that the greater the compressible layer thickness, the more serious the subsidence is and the correlation is highest between the extraction of groundwater from the second and third layers and the ground subsidence. With the start of the South-to-North Water Diversion Project, the extraction of groundwater began to slow, but the slowing trend of subsidence was not obvious because of the lag between groundwater and land subsidence.

Change in regional land subsidence in Beijing after south-to-north water diversion project observed using satellite radar interferometry

ABSTRACTOver-exploitation of groundwater has caused severe land subsidence in Beijing during the past two decades. Since the middle route of South-to-North Water Diversion Project (SNWDP), the biggest water diversion project in China, started to deliver water to Beijing in December 2014, the groundwater shortage has been greatly alleviated. This study aims to analyze the impact of SNWDP on the spatiotemporal evolution of land subsidence in Beijing. Change in surface displacement in Beijing after SNWDP was retrieved and the spatiotemporal patterns of the change were analyzed based on long time-series Envisat Advanced Synthetic Aperture Radar (ASAR) (2004–2010), Radarsat-2 (2011–2014), and Sentinel-1 (2015–2017) satellite datasets using Permanent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) techniques. Land subsidence unevenness index (LSUI) was proposed to represent the spatial unevenness of surface displacement. PS-Time approach was then adapted to examine the time series evolution of LSUI. The results showed that the InSAR measurements agree well with leveling measurements with R2 over 0.96. Although the maximum annual displacement rate reached −159.7 mm/year by 2017, over 57% of the area within 25 mm/year contour line showed decreasing or unchanged displacement rate after the south-north water delivered to Beijing. The settlement rate in Chaoyang-Dongbalizhuang (CD) subsidence center has decreased for 26 mm/year from 2011–2014 to 2015–2017. Only around 15% of the area experienced continued accelerating settlement rate through the three time periods, which was mainly located in the area with the compressible layer thickness over 190 m, while the magnitude of velocity increment considerably decreased after SNWDP. Land subsidence unevenness, represented by LSUI, developed more slowly after SNWDP than that during 2011–2014. However, LSUI at the edge of settlement funnel has kept developing and reached 1.7‰ in 2017. Decreasing groundwater level decline after SNWDP and the positive relationship (R2 > 0.74) between land subsidence and groundwater level clearly showed impacts of SNWDP on the alleviating land subsidence. Other reasons include geological background, increasing precipitation, and strict water management policies implemented during these years.

Effect of a moving automated shot peening and peening parameters on surface integrity of Low carbon steel

Abstract Shot peening is a widely utilized process in industry. It helps to increase fatigue and stress corrosion resistance by creating beneficial compressive residual surface stresses of materials. Whilst very good results are achieved with this process, there is always an increasing demand by industry and material researchers for improved material surface quality, system reliability, and consistency controls of the process. First main objective of this work was to study the effect of an automated moving shot peening process on the surface integrity of low carbon steel material. Second objective was to discuss and present peening saturation and intensity results and model in a new approach in terms of peening speeds along side the traditional procedure which shows peening saturation and intensity results in terms of peening times. Third objective of this study was to examine the effects of: process air pressure, nozzle stand-off distance, nozzle speed, and peening angle on coverage, saturation, and surface quality utilizing the moving shot peening. This study showed that 276 kPa air pressure, 203 mm stand-off distance, and 5.3 mm/sec nozzle speed are the optimum conditions for the shot peening process parameters examined on standard Almen strips samples which resulted in minimize surface irregularities, maximize compressed layer thickness and uniformity, and minimize process time.

Effects of preheating temperatures on the formation of sandwich compression and density distribution in the compressed wood

Sandwich compression of wood that can control the density and position of compressed layer(s) in the compressed wood provides a promising pathway for full valorization of low-density plantation wood. This study aims at investigating the effects of preheating temperatures (60–210 °C) on sandwich compression of wood, with respect to density distribution, position and thickness of the compressed layer(s). Poplar (Populus tomentosa) lumbers with moisture content below 10.0% were first soaked in water for 2 h and stored in a sealed plastic bag for 18 h, the surface-wetted lumbers were preheated on hot plates at 60–210 °C and further compressed from 25 to 20 cm under 6.0 MPa at the same temperature on the radial direction. The compressed lumbers were characterized in terms of density distribution, position and thickness of compressed layer(s). It was found that depending on preheating temperatures, sandwich compressed wood with three structural modes, namely, surface compressed wood, internal compressed wood and central compressed wood can be formed. Density of the compressed layer(s) in wood increased gradually as a result of the elevated preheating temperatures. Higher preheating temperatures gave rise to bigger distance between compressed layer(s) and the surface, and preheating temperature elevation from 90 to 120 °C contributed to a maximal distance increase of 2.71 mm. In addition, higher preheating temperatures resulted in bigger thickness of compressed layer(s) over 60–150 °C and temperature elevation from 120 to 150 °C lead to the layers integration from two into one. Further temperature elevation over 150 °C reduced the thickness of the compressed layer in wood. SEM scanning suggested that cell wall bucking rather than cell wall crack occurred in compressed layer(s) and transition layer(s).

Finite element analysis of the effect of tool edge radius on residual stresses when orthogonal cutting Ti6Al4V

A finite element analysis is presented based on the machining simulation software AdvantEdge FEM to investigate the effect of tool edge radius on residual stresses when orthogonal dry cutting Ti6Al4V alloy. Five types of cemented carbide tools with different tool-edge radius were used in the simulation. The results obtained from this study show that the residual stress at the machined surface is residual compressive stress and become more tensile than compressive beneath the machined surface for five radii. Tool-edge radius affects the magnitude and distribution of residual stress significantly, the magnitude of residual compressive stress, the thickness of compressive layer and the magnitude of residual tensile stress increase with the increase of tool-edge radius. A theoretical guidance for the control of residual stresses and optimization of tool-edge design can be provided in this study.

Multi-Scale Analysis of the Relationship between Land Subsidence and Buildings: A Case Study in an Eastern Beijing Urban Area Using the PS-InSAR Technique

Beijing is severely affected by land subsidence, and rapid urbanisation and building construction might accelerate the land subsidence process. Based on 39 Envisat Advanced Synthetic Aperture Radar (ASAR) images acquired between 2003–2010, 55 TerraSAR-X images acquired between 2010–2016, and urban building information, we analysed the relationship between land subsidence and buildings at the regional, block, and building scales. The results show that the surface displacement rate in the Beijing urban area ranged from −109 mm/year to +13 mm/year between 2003–2010, and from −151 mm/year to +19 mm/year between 2010–2016; two subsidence bowls were mainly distributed in the eastern part of the Chaoyang District. The displacement rate agreed well with the levelling measurements, with an average bias of less than six mm/year. At the regional scale, the spatial pattern of land subsidence was mainly controlled by groundwater extraction, compressible layer thickness, and geological faults. Subsidence centres were located in the area around ground water funnels with a compressible layer depth of 50–70 m. The block-scale analysis demonstrated a clear correlation between the block construction age and the spatial unevenness of subsidence. The blocks constructed between 1998–2005 and after 2005 showed considerably more subsidence unevenness and temporal instability than the blocks constructed before 1998 during both time periods. The examination of the new blocks showed that the spatial unevenness increased with building volume variability. For the 16 blocks with a high building volume, variability, and subsidence unevenness, the building-scale analysis showed a positive relationship between building volume and settlement in most blocks, although the R2 was lower than 0.5. The results indicate that intense building construction in urban areas could cause differential settlement at the block scale in Beijing, while the settlement of single buildings could be influenced by the integrated effects of building volume, foundation structures, and the hydrogeological background.

Measuring Spatiotemporal Features of Land Subsidence, Groundwater Drawdown, and Compressible Layer Thickness in Beijing Plain, China

Beijing is located on multiple alluvial-pluvial fans with thick Quaternary unconsolidated sediments. It has suffered serious groundwater drawdown and land subsidence due to groundwater exploitation. This study aimed to introduce geographical distribution measure methods into land subsidence research characterizing, geographically, land subsidence, groundwater drawdown, and compressible layer thickness. Therefore, we used gravity center analysis and standard deviational ellipse (SDE) methods in GIS to statistically analyze their concentration tendency, principle orientation, dispersion trend, and distribution differences in 1995 (1999), 2007, 2009, 2011, and 2013. Results show that they were all concentrated in Chaoyang District of Urban Beijing. The concentration trend of land subsidence was consistent with that of groundwater drawdown. The principle orientation of land subsidence was SW–NE, which was more similar with that of the static spatial distribution of the compressible layer. The dispersion tendency of land subsidence got closer to that of the compressible layer with its increasing intensity. The spatial distribution difference between land subsidence and groundwater drawdown was about 0.2, and that between land subsidence and compressible layer thickness it decreased from 0.22 to 0.07, reflecting that the spatial distribution pattern of land subsidence was increasingly close to that of the compressible layer. Results of this study are useful for assessing the distribution of land subsidence development and managing groundwater resources.

Land subsidence due to groundwater withdrawal in the northern Beijing plain, China

Beijing is an international metropolis, where over-exploration of water resource makes land subsidence becoming more and more serious. The related problems cannot be avoided in the coming years because of the giant increase of population. The aims of this study are to quantify land subsidence over the period 2003 to 2010, grasp the evolution of the process, and investigate the relation with the triggering factors in the northern area of the Beijing plain. Various data, including deep compaction from vertical multiple borehole extensometers, land subsidence from Persistent Scatterer Interferometry and leveling surveys, groundwater levels, hydrogeological setting from wellbores, and Landsat TM image were collected and effectively used to detect the spatial and temporal features of land subsidence and its possible relation with groundwater level changes, compressible layer thickness, and urban development. Results show that land subsidence is unevenly distributed and continuously increased from 2003 to 2010. The average loss of elevation over the monitoring period amounted to 92.5mm, with rates up to 52mm/y. The distribution of the subsidence bowl is only partially consistent with that of the groundwater depression cone because of the variable thickness of the most compressible fine deposits. In fact, extensometers reveal that silty-clay layers account for the larger contribution to land subsidence, with the 15m thick silty-clay layer between 102 and 117m depth accounting for about 25% of the total subsidence. Finally, no clear correlation has been observed between the subsidence rates and the increase of the load on the land surface connected to the impressive urban development. This study represents a first step toward the development of a physically-based model of the subsidence occurrence to be used for planning remediation strategies in the northern Beijing plain.

Deep Foundation Numerical Analysis Using Modified Compression Modulus

This paper is a study on the behavior and prediction of settlement values of bridge pile foundations due to con-struction loads. Field test results show new field technique using the single point of account settlement meter to estimate the thickness of compressed layer in the deep soft soils which is considered as a difficult task in the field. The settlement is predicted using hyperbolic model and statistical regression. The statistical models indicate that the structure would re-main safe for a long period of time, and the field measurements are compared with the hyperbolic model results and those predicted by the statistical regression. The finite element Plaxis 3D Foundation program is used in the analysis with a new empirical equation to modify the input parameters represented by the soil compression modulus. The foundation soils are modeled with the Mohr-Coulomb plasticity material model. The piles are represented with pile elements, between the pile and the surrounding soil, interface elements are automatically generated by the program. In the analysis, the effects due to soil stiffness, pile length and pile spacing are considered. The calculated results for the simulation of the pile installation sequence are compared with the measured results obtained from the field monitoring. The results of the numerical analy-sis using the proposed empirical equation provide insight to the settlement analysis of pile groups in soft clayey soils and the finite element Plaxis 3D program can be a useful tool for numerical analysis. In this paper, the numerical analysis cal-culations are modified using a new empirical equation to calculate the compression modulus from those obtained from the test which modify the results of the settlement and thus become close to the reality. Finally, the numerical finite element analysis produced logical and conservative results as compared to the statistically derived equations and those calculated by hyperbolic model analysis. This scenario can be applied to the similar problems in the theoretical applications of bridge foundations.

Experimental and Theoretical Static Analysis of High-Speed Railway Bridge Settlement for Deep Soft Soil

This paper is a study of Beijing-Shanghai high-speed railway and measuring the settlement values of the Bridge with the time and load. The structure is safe to carry the applied loads. The settlement is measured using the single point of settlement account meter and calculated using the norm codes. The results showed a new field measurement method to calculate the compressed layer thickness which is considered as a difficult task to monitor in the field. The final results calculated for the settlement of the pile foundation needed correction of factors to be conservative for the measurement of the project. The correction factors are proposed to modify the codes calculation within the permissible ranges.

Precisely estimating primary consolidation settlement of homogeneous NC clays with an alternate equation

<p>Estimating primary consolidation of NC clays with conventional 1-D consolidation equation underestimates the settlement value as the effective stress is merely taken at the mid-depth of a compressible layer. For thick compressible stratum, the error cannot be disregarded and is often minimized by dividing the entire stratum into a finite number of sub-layers. Computation with too many sub-layers is rather tedious and time-consuming as the settlement of each layer needs to be calculated separately and to be added up finally to get the settlement of the entire stratum.</p><p>An alternate equation is put forward in the present study wherein the effect of compressible layer thickness is eliminated altogether. The equation proposed herein is, in fact, an extension of classical primary consolidation equation for homogeneous NC clays and is based on the same assumptions. This paper lucidly explains the formulation of the proposed equation and validation of the same with a practical example. Comparison of results shows that the proposed equation subdues the conventional one by precisely computing the consolidation settlement not involving any iteration or time-consuming effort.</p>

Supersonic transverse rarefied gas flow past a strip

The supersonic flow of a monatomic gas consisting of hard spherical particles past a flat strip normal to the flow is investigated using the direct simulation Monte-Carlo (DSMC) method. The calculations are performed over the Knudsen and Mach number ranges 0.015–5 and 1.8–15, respectively. The structure of the compressed layer and the aerodynamic characteristics are systematically studied for the Mach number 5 and various Knudsen numbers. The dependences of the compressed-layer thickness in molecular free paths are found. The nonequilibrium processes in the neighborhood of the strip are described on the basis of the data on the temperature anisotropy with respect to three coordinates.

Polymer Bilayer Formation Due to Specific Interactions between β-Cyclodextrin and Adamantane: A Surface Force Study

The purposes of this study are to utilize the interactions between an adamantane end-capped poly(ethylene oxide) (PEO) and a cationic polymer of beta-cyclodextrin to build polymer bilayers on negatively charged surfaces, and to investigate the interactions between such layers. The association of this system in solution has been studied by rheology, light scattering, and fluorescence measurements. It was found that the adamantane-terminated PEO (PEO-Ad) mixed with the beta-cyclodextrin polymer gives complexes where the interpolymer links are formed by specific inclusion of the adamantane groups in the beta-cyclodextrin cavities. This results in a higher viscosity of the solution and growth of intermolecular clusters. The interactions between surfaces coated with a cationized beta-cyclodextrin polymer across a water solution containing PEO-Ad polymers were studied by employing the interferometric surface force apparatus (SFA). In the first step, the interaction between mica surfaces coated with the cationized beta-cyclodextrin polymer in pure water was investigated. It was found that the beta-cyclodextrin polymer adsorbs onto mica and almost neutralizes the surface charge. The adsorbed layers of the beta-cyclodextrin polymer are rather compact, with a layer thickness of about 60 A (30 A per surface). Upon separation, a very weak attractive force is observed. The beta-cyclodextrin solution was then diluted by pure water by a factor of 3000 and a PEO-Ad polymer was introduced into the solution. Two different architectures of the PEO-Ad polymer were investigated: a four-arm structure and a linear structure. After the adsorption of the PEO polymer onto the beta-cyclodextrin layer reached equilibrium, the forces were measured again. It was found that the weak repulsive long-range force had disappeared and an attractive force caused the surfaces to jump into contact, and that the compressed layer thickness had increased. The attractive force is interpreted as being due to a specific recognition between the hydrophobic adamantane groups on the PEO-Ad polymer and the hydrophobic cavity in the beta-cyclodextrin molecules. Furthermore, the attractive force observed on separation has increased significantly, which is a further indication of a specific interaction between the beta-cyclodextrin polymer and the adamantane groups.

Effect of Sodium Dodecyl Sulfate on Adsorbed Layers of Branched Polyethylene Imine

The effect of an anionic surfactant, sodium dodecyl sulfate, SDS, on the properties of adsorbed layers of a cationic highly branched polyelectrolyte, polyethylene,imine, PEI, has been investigated using surface force measurements, atomic force microscopy, and ESCA. The strategy used was to preadsorb PEI on negatively charged muscovite mica surfaces from a 20 ppm polyelectrolyte solution in 10 mM NaCl. The adsorption of PEI under these conditions gives rise to a strong recharging of the surface, i.e. after adsorption of PEI the surface carries a net positive charge. This conclusion was supported by ESCA measurements. Despite the high molecular weight of PEI (1.8 x 10(5) g/mol), the adsorbed layer is found to be very flat, and a repulsive double-layer force dominates at large separations. At smaller separation a strong attractive force is the main feature. Addition of SDS to a concentration of 0.01 cmc results in a nearly complete removal of the double-layer force, an increase in compressed layer thickness, and an increase in the magnitude of the adhesion force. Hence, significant SDS incorporation in the adsorbed layer occurs already at this low surfactant concentration. A recharging of the layer occurs at higher surfactant concentrations. At 0.5 cmc, the compressed thickness of the adsorbed layer is increased significantly and the adhesion between the surfaces has disappeared. We argue that each layer now is coated with an outer SDS layer oriented with the polar groups toward solution. In fact, there are striking similarities between the interfacial association between SDS and PEI and the adsorption of an ionic surfactant to an oppositely charged mineral surface. AFM imaging reveals that the adsorbed PEI layer is somewhat nonhomogeneous and contains polyelectrolyte patches. These surface features are smoothed out by addition of SDS to a concentration of 6 mM (1 cmc in 10 mM NaCl). ESCA measurements showed that exposure of the preadsorbed PEI layer to SDS concentrations around the cmc resulted in a limited desorption; about 15% of the initially adsorbed polyelectrolyte was removed after 16 h.

Estimating coefficients of volume compressibility from compression of strata and piezometric changes in a multiaquifer system in west Taiwan

This paper estimates the coefficients of volume compressibility from variation in compressible layer thickness and changes in piezometric heads by using detail ground surface surveys and a multilayer monitoring well at a selected site (Shigang) within the Choshui River alluvial fan in west Taiwan. The paper integrates various types of in situ monitoring tools, including leveling surveys, continuous global position system (GPS) stations, multilevel layer compression and groundwater pressure head-monitoring wells, to investigate the situation and progress of the subsidence problem in the region. The results from the cross-analyses of the measured data show that surface settlement caused by the compression of strata is between the depths of 60 and 210 m where the clayey stratum within 120–180 m was most pronounced and contributes up to 53% of the total compression. The results indicate that the clayey stratum is under normal consolidation. The results also reflect the fact that 20% of settlement contribution comes from the sandy stratum within 90–120 m; the elasto-plastic behavior of this sandy stratum is clear. The coefficients of volume compressibility of the clayey and sandy stratum analysed from the stratum's compression records; they were 6.38×10 −8 and 5.71×10 −9 m 2/N, respectively. Ultimately, this parameter estimation would permit to control and predict land subsidence based on change in pressure head which are related to groundwater extraction.

Factors Affecting Threshold Strength in Laminar Ceramics Containing Thin Compressive Layers

Compressive layers placed within a laminate can arrest cracks. With increasing applied stress, the arrested crack can propagate through the compressive layer. These phenomena produce a material with threshold strength, i.e., failure cannot occur below a critical applied stress. A previously reported stress intensity function describes different variables, e.g., magnitude of compressive stress, thickness of compressive layer, and distance between compressive layers, which govern threshold strength. Laminar composites composed of thicker Al2O3 layers separated by thinner Al2O3/mullite layers were fabricated to test the different variables that are predicted to govern threshold strength. The data agreed well with the predicted values only when the magnitude of compressive stress and/or the thickness of the compressive layer were low. For these conditions, the crack extended straight through the compressive layers, as assumed by the model used to predict threshold strength. On the other hand, when the compressive stress and/or layer thickness were large, threshold strength was larger than the predicted value. In addition, for these conditions, the crack bifurcated through the compressive layer. The angle between the bifurcated cracks increased with increasing compressive stress.