Micromechanical Properties of Nanostructured Clay-Oxide Multilayers Synthesized by Layer-by-Layer Self-Assembly

Clay-based nanostructured multilayers, such as clay-polymer multilayers and clay-oxide multilayers, have attracted growing attention owing to their remarkable mechanical properties and promising application in various fields. In this paper, synthesis of a new kind of nanostructured clay-oxide multilayers by layer-by-layer self-assembly was explored. Nano-mechanical characterization of 18 clay-based multilayer samples, prepared under as-deposited (i.e., air-dried) and annealing conditions at 400 °C/600 °C with different precursor cations and multilayer structure, were carried out using nanoindentation testing, atomic force microscopy (AFM), and X-ray diffraction (XRD). The influencing factors, including as-deposited and annealing conditions and clay concentrations on the mechanical properties were analyzed. Results show that all of the multilayers exhibit high bonding strength between interlayers. Higher modulus and hardness of clay-based multilayers were obtained with lower clay concentrations than that with higher clay concentrations. Different relationships between the modulus and hardness and the annealing temperature exist for a specific type of clay-oxide multilayer. This work offers the basic and essential knowledge on design of clay-based nanostructured multilayers by layer-by-layer self-assembly

Interpretation of increased deformation rate in aquifer IV due to groundwater pumping in Shanghai

International audienceShanghai is a typical example of a region in China suffering from severe land subsidence. Previous investigations have shown that land subsidence is strongly related to groundwater pumping in both the temporal and spatial domains. A series of field investigations shows that the deformation rate of aquifer IV (AqIV) has increased, contributing significantly to the total subsidence in Shanghai. To predict the deformation behavior of AqIV in Shanghai due to groundwater pumping, four different models have been applied in this study: (i) a model based on groundwater flow theory, (ii) an elastic model based on Cauchy mechanics, (iii) a creep model incorporated into Cauchy mechanics, and (iv) a recently proposed land subsidence model by Budhu based on Cosserat mechanics. Based on a number of assumptions, Budhu’s concept was extended to consider the time-dependent behavior of groundwater potential in aquifers and the consolidation behavior of overburdened aquitards. The calculated results of AqIV’s deformation were compared with the field-measured data. The results show that when using groundwater flow theory and Cauchy mechanics, it is difficult to predict the increased deformation rate of the sandy layers in aquifers even when the creep behavior is incorporated into the calculation. However, Budhu’s method based on Cosserat mechanics can predict this increased deformation rate well. The predicted result indicates that increased deformation of aquifer IV is due to volumetric contraction caused by shear stress rather than the creep of aquifer sand. The phenomenon of deformation delay in aquifers can also be interpreted with the proposed model

Numerical Investigation of the Undrained Compression and Pull-Out Capacity of Suction Foundations in Clay

This paper presents the results of three-dimensional finite difference analysis of suction foundations in uniform and non-uniform clays under undrained conditions. The Tresca criterion was used to simulate the stress-strain response. The bearing capacity of the foundations was investigated, with the degree of nonhomogeneity (kD/sum) of soil varying from 0 to 5, and the embedment depth being up to four times the foundation diameter. The end bearing capacity factor in compression and the reverse bearing capacity factor in tension were both calculated and were compared with each other under different foundation displacements. Numerical results showed that the ultimate bearing capacity factor can have the same value in cases of both compression and tension. The recommended ultimate bearing capacity factor is determined on the basis of the embedment ratio and displacement magnitude, and the displacement is not more than 30% of the foundation diameter. Finally, two equations are proposed to evaluate both the bearing capacity factor and the effective depth factor

Mechanism of tunneling-induced cave-in of a busy road in Fukuoka city, Japan

A road cave-in accident caused by tunneling is described, and the possible mechanism of failure is analyzed. The cave-in measured about 30 m × 27 m in plane, and about 15 m in depth. At about 19 m below the ground surface at the site, a tunnel construction was underway. Immediately above the tunnel, there was a weathered shale layer approximately t 2.66 m thick; above this layer, there were sand and gravel layers. The groundwater level was estimated to be about 5 m below the ground surface. By arch analysis, it is shown that the most likely cause of the accident was the low strength of the weathered shale layer and the high water pressure above the tunnel, which resulted in tensile failure of the weathered shale layer. The All Ground Fasten (AGF) pre-support measure was adopted, but it might make very limited contribution to the increase in the tensile strength of the shale layer in the cross-sectional direction of the tunnel. Keywords: Tunneling, Road cave-in, Arch analysis, Tensile failur

Assessment of Geohazards and Preventative Countermeasures Using AHP Incorporated with GIS in Lanzhou, China

This research investigates geohazards and preventative countermeasures for Lanzhou City, China. To investigate the factors related to the development of geohazards in Lanzhou, the regional geological conditions around Lanzhou were investigated. The geomorphology of the region is comprised of a loess landform underlying quaternary loess deposits. A large number of faults induced by strong neotectonic movements are present in the area. Therefore, earthquakes frequently occur around Lanzhou. Earthquakes cause numerous rock falls and landslides, with landslide masses found scattered on the upper middle level of the area’s mountains. When intense rainfall occurs, a lot of loose deposits are brought together along steep gullies, forming debris flows; hence, a disaster chain of earthquake–landslide–debris flow is formed. To evaluate the georisks around Lanzhou, the Analytic Hierarchy Process (AHP) was employed to assess geohazards. The spatial distribution of the evaluated georisk levels was mapped using a Geographic Information System (GIS). Based on the assessed results, about 55% of the urban area and 44% of Gaolan County have high or very high-risk levels. The ratio of relatively high disaster risk levels is up to 31% of the total area. To mitigate these geohazards, both strategic decision making and technical countermeasures should be implemented

Consolidation analysis of clayey deposits under vacuum pressure with horizontal drains

A method has been developed for the consolidation analysis of dredged mud or clayey soil deposits containing strip-type, prefabricated horizontal drains (PHDs), based on either the axisymmetric or plane strain unit cell theory. An approximate consolidation theory has also been proposed for a surface soil layer subjected to vacuum pressure applied through the PHDs at a shallow depth from the surface. The proposed method and the consolidation theory have then been applied to the analysis of a field project in Japan involving dredged mud consolidated by vacuum pressure with PHDs. By comparing the field-measured and analyzed results in terms of water content distributions with depth and the thickness variation of the deposit, the usefulness of the proposed method has been demonstrated

Long-term Settlement Behaviour of Metro Tunnels in the Soft Deposits of Shanghai

International audienc

Investigation of Collapsed Building Incidents on Soft Marine Deposit: Both from Social and Technical Perspectives

A collapsed incident occurred on 10 October 2016 in Wenzhou City, China, which resulted in 22 casualties and 6 injuries. Most of victims were migrant laborers (rural dwellers who move to urban for a temporary work), who rented apartments in these residential buildings, which were originally constructed by local rural residents. This case report investigates the collapsed incident as well as other similar previous incidents. From the perspectives of both social and technical aspects, this report analyzed the Chinese rural land use policy with relevant technical factors. These incidents reveal social problems of the existing dual structure land-use policy in China. Chinese dual structure land-use policy caused deficiencies in the supervision of the construction market in rural area so that the following technical factors were not well supervised by the various quality control departments: (1) poorly quality of residential buildings, (2) unauthorized rooftop additions, and (3) differential settlement caused by the uneven distribution of underlying Wenzhou clay under creep conditions. Mandatory regulation by the government for any construction in China, particularly for the construction of self-constructed house building sites in rural areas, was recommended to minimize the resettlement issue of migrant workers

Pore pressures induced by piezocone penetration

The excess pore water pressures (u) induced by piezocone penetration and their dissipation around the cone have been investigated by laboratory model tests and theoretical/numerical analyses. Based on the test results, a method for predicting the cone penetration induced distribution of u has been proposed. By numerical analysis using the predicted initial distribution of u it has been demonstrated that dissipation of the pore water pressure measured at the shoulder of the cone (u2-type cone) is a two-dimensional (horizontal radial and vertical) process. By comparing the simulated and laboratory-measured 2D dissipation curves, a back-fitted coefficient of consolidation in the horizontal direction (ch) can be obtained. It has also been shown that a published method for estimating ch from measured non-standard dissipation curves (in which u2 increases initially and then reduces) results in values of ch that agree well with values of ch deduced from the 2D analysis.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Assessment of Social-Economic Risk of Chinese Dual Land Use System Using Fuzzy AHP

The Chinese dual land use system (DLUS) has played a crucial role in the industrialization of China since 1950s. However, this dual system caused/causes obstacles in urban development under the new market economic conditions. This paper presents an approach to assess the social-economic risks during urban development in China by integrating the strategic environment assessment (SEA) principle into the fuzzy analytic hierarchy process (AHP) method. In the proposed approach, SEA principles are set as the influencing factors in AHP. Fuzzy AHP is used to assess the relative importance degree of the six principles in SEA. To illustrate the application procedure of the proposed approach, a building collapse incident in Wenzhou is used as a case for the risk analysis. The assessment results show that the index of the manage system has the greatest importance to social-economic risk. The principle of sustainable development (A) and monitoring measures (E) have more importance than the other principles in SEA. It can be concluded that the DLUS in the market management of China may be responsible for building collapse incidents in rural areas. It is suggested that the principles of sustainable development and monitoring measures in SEA should be strictly implemented during urbanization, and it is recommended that the government establish a unified management system and ensure the effective implementation of sustainable urbanization