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Zhang T.,State Oceanic Administration | Gao J.,State Oceanic Administration | Chen M.,East China Construction Engineering Corporation of Zhejiang | Yang C.,State Oceanic Administration | And 4 more authors.
Acta Oceanologica Sinica | Year: 2015

Spreading rate is a primary factor of mantle melting and tectonic behavior of the global mid-ocean ridges. The spreading rate of the Gakkel ridge decreases gradually from west to east. However, the Gakkel ridge can be divided into four thick-and-thin zones with varying crustal thicknesses along ridge axis. This phenomenon indicates that mantle melting of the Gakkel ridge is not a simple function of spreading rate. Mantle temperature, water content, mantle composition, and other factors are important in crustal accretion processes. Based on gravity-derived crustal thickness and wet melting model, we estimate that the mantle potential temperatures of the four zones are 1 270, 1 220, 1 280, and 1 280°C (assuming that mantle water content equals to global average value), with corresponding mantle water contents of 210, 0, 340, and 280 mg/kg (assuming that mantle potential temperature is 1 260°C), respectivly. The western thinned crust zone is best modeled with low mantle temperature, whereas the other zones are mainly controlled by the enhanced conduction caused by the slower spreading rate. Along the Gakkel ridge, the crustal thickness is consistent with rock samples types. Predominated serpentinized peridotite and basalt are found in the area with crustal thickness 〈1.5 km and 〉2.5 km, respectively. The rock samples are including from basalt to peridotite in the area with crustal thickness between 1.5 and 2.5 km. Based on this consistency, the traditional magmatic accretion zone accounted for only 44% and amagmatic accretion accounted for 29% of the Gakkel ridge. The amagmatic accretion is a significant characteristic of the ultra-slow spreading ridge. © 2015, The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg. Source


Li Z.-C.,Zhejiang University | Chen R.-P.,Zhejiang University | Chen Y.-M.,Zhejiang University | Rao M.,East China Construction Engineering Corporation of Zhejiang
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2015

The factor of safety (FS) is a very important design index for deep excavation in soft clay. The existing methods for FS mainly include the conventional methods and finite element method (FEM) based on the reduced shear strength technique. In this study, the conventional methods and reduced shear strength FEM are used for FS evaluation of a failed deep excavation in soft clay. By comparing the values of FS of the excavation using different soil strength parameters and methods, the applicability of the analysis methods and soil strength parameters is evaluated. The research results indicate that the values of FS of the excavation calculated by the conventional methods and the reduced shear strength FEM using the total stress indexes, i.e., su, φ=0, are very close to 1.0 and those from Terzaghi's method, while the values of FS of the excavation are much greater than 1.0 using the soil strength parameters c and φ from triaxial tests. When the reduced shear strength FEM is applied for FS evaluation, the values of FS obtained from the convergence criterion method are much greater than those from the intersection method. The values of FS of the excavations using the intersection method and Terzaghi's method are both very close to 1.0, which is consistent with the limited equilibrium state of the excavations at failure. ©, 2015, Chinese Society of Civil Engineering. All right reserved. Source


Chen R.P.,Zhejiang University | Li Z.C.,Zhejiang University | Chen Y.M.,Zhejiang University | Ou C.Y.,National Taiwan University of Science and Technology | And 2 more authors.
Journal of Performance of Constructed Facilities | Year: 2015

Collapse of a 15.7-m-deep excavation in very sensitive organic soft clay in Hangzhou, China, is presented in this paper. The collapse of the excavation caused the break and/or inclination of the retaining walls, the wracking of the supporting system, significant sinking of a major road adjacent to the excavation site, and also the break in a water main beneath the road. After the collapse, the ground disturbance due to the collapse was investigated by cone penetration tests (CPTs) and field vane shear tests (VSTs). A simplified method, based on the CPT and VST test results, was used to evaluate the strength reduction ratio (SRR) of the in situ soils. According to the SRR values of the soils at different depths, the lower boundaries of the severely disturbed soils were determined and a possible slip failure surface passing through the bottom of the severely disturbed soils was justified. The factors of safety (FOSs) against basal heave of the excavation calculated from various methods were 1.05, 0.74 and 0.89, respectively. These computed values were much smaller than the corresponding recommended values. The stability number N of the excavation was calculated to be 7.4. The overall FOS was studied using the shear strength reduction technique based on a finite-element method (FEM) program. The FEM analysis results indicated that the FOS of the excavation was 0.97, and the computed slip failure surface fit well with that from the soil disturbance investigation. The failure mechanism of the excavation was then justified to be a basal heave. The main reasons leading to the collapse and lessons learned from the collapse are discussed. The investigation of the failure provides experiences and lessons for deep excavation design in very sensitive organic soft clay. © 2014 American Society of Civil Engineers. Source


He N.,CAS Chengdu Institute of Mountain Hazards and Environment | He N.,University of Chinese Academy of Sciences | He N.,Henan Polytechnic University | Chen N.-S.,CAS Chengdu Institute of Mountain Hazards and Environment | And 4 more authors.
Yantu Lixue/Rock and Soil Mechanics | Year: 2014

On the basis of 182 gravelly soil samples taken from debris flow source area, the particle size distribution are obtained through laboratory test, fractal dimensions of samples are calculated by fractal theory. Analysis of calculated results show that the gravelly soil samples are mainly one dimension fractal; and it account for 88.46% of the total samples, the value of one dimension fractal is between 2.250-2.798. Based on the calculated fractal dimension, soil samples are configured; and self-made constant head device with controllable waterhead are used to conduct penetration experiment. The experimental results indicate that the correlation between permeability coefficient and fractal dimension is significant. When dry density equals 1.8 g/cm3, the correlation of permeability coefficient and fractal dimension is best; and the relationship between permeability coefficient and fractal dimension shows obvious power function using multiple regression analysis under different density conditions. Moreover, under same fractal dimension (condition), the permeability coefficient decreases with the increase of density; the power function relation between fractal dimension and permeability coefficient is obvious when fractal dimension ranges from 2.450 to 2.600. This study results can provide theory basis for future critical rainfall research; meanwhile, these can improve the universality and accuracy of the existing forecasting models. Source

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