Advanced Search

Indexed by SCI、CA、РЖ、PA、CSA、ZR、etc .

2006 Vol. 17, No. 4

Display Method:
Sanmenxia Loess and Paleoenvironmental Change
Zhizhong ZHAO, Fuchu JIANG, Xihao WU, Shubing WANG, Yansong QIAO, Ke LIU, Sumin WANG
2006, 17(4): 283-290.

The Caocun (曹村) loess profile of Zhangbianyuan (张汴塬) is located at the southeast margin of the Loess Plateau, which is a typical representative of loess stratum in the Sanmenxia (三门峡) area. In the 145 m thick profile, a loess-paleosol sequence occurs from L1 to L33, underlain by a red clay bed. The B/M boundary was recorded at the bottom of L7, the Jaramillo event at S11 to S12, the Olduval event at L23 to L26, and the M/G boundary at the bottom of L33 near the red clay. The magnetic susceptibility of the loess deposits, as well as the carbonate and granularity components, indicates that there have been many periodic paleoclimate changes, including a total of 13 cold events that each lasted more than 40 000 a. A high-resolution chronostratigraphic profile has been established using an age model according to grain characteristics. A clear correlation exists between records of the paleomonsoon in the Caocun loess succession and SPECMAP from 3×105 a B.P. to the present. The Caocun profile can act as a control site in the southeastern Loess Plateau. Its paleoenvironmental records relate to eastern Asian paleomonsoon theory.

How High Are the P-T Conditions for Paleoproterozoic Metamorphism of the Huangtuling Felsic Granulite, North Dabieshan, Central China?
Nengsong CHEN, Songlin GONG, Min SUN, Yong YANG, Rong LIU
2006, 17(4): 291-301.

The 2.34 cm-wide garnet porphyroblast in the Paleoproterozoic felsic granulite from the Huangtuling area, North Dabieshan, has been reinvestigated for compositional variation in light of Ca-composition X-ray mapping to obtain peak P-T conditions of granulite-facies metamorphism. A new core-rim traverse was conducted through where there is little influence on Ca-profile and slight modification in Mn-, Mg- and Fe-profiles with the highest Mg/ (Mg+Fe) value of 0.467. Reasonable peak P-T conditions were estimated to be 1.50-1.70 GPa and 1 100-1 150 ℃ according to TWQ-based garnet-Al-orthopyroxene thermobarometry. These estimations suggest that the Huangtuling granulite once was subjected to ultrahigh-temperature (UHT) granulite-facies metamorphism following a high-pressure granulite-faices metamorphic stage, implying that a deep subduction and collision process relevant to the Yangtze block occurred in the Paleoproterozoic time, probably as a response to the global assembly event of the Columbia supercontinent.

Fission Track Geochronology of Xiaonanchuan Pluton and the Morphotectonic Evolution of Eastern Kunlun since Late Miocene
An WANG, Guocan WANG, Defan XIE, Demin LIU
2006, 17(4): 302-309.

Apatite fission track (AFT) thermochronology of seven samples from the Xiaonanchuan (小南川) pluton in the Kunlun (昆仑) pass area was carried out, for the purpose of determining the timing of cooling and the relation between the exhumation and the morphotectonic processes. The AFT ages yield low denudation rates of 0.020-0.035 mm/a during the late Miocene, which correspond to a stable geomorphic and weak tectonic uplifting environment. The low denudation rates can be considered as the approximate tectonic uplifting rates. The AFT geochronology shows paroxysmally rapid cooling since the Pliocene and an apparent material unroofing of more than 3 km in the Xiaonanchuan area. This was not the result of simple denudation. The rapid cooling was coupled with the intensive orogeny since the Pliocene, which was driven by tectonic uplifting. The accelerated relief building was accompanied by a series of faulting, which caused the basin and the valley formation and sinking. The space pattern of the AFT ages also shows differential uplifting, which decreases northwardly. This trend is supported by the regional AFT data, which indicate that the exhumation decreases northwardly in eastern Kunlun. This trend also exists in east-west orientation from the western Kunlun range to the eastern. The uplifting trend is also supported by geomorphic characteristics including the elevation and the relief differences as well as the distribution of the Late Cenozoic volcanism.

Environmental Assessments of Trace Metals in Sediments from Dongting Lake, Central China
Zhigang YAO, Zhengyu BAO, Pu GAO
2006, 17(4): 310-319.

To examine the degree of contamination in the Dongting Lake (洞庭湖) area, surface sediments samples were collected and investigated in this study. This lake lies in the south of the middle Yangtze River, and it is the second largest fresh-water lake in China. These samples were analyzed for the concentrations of the following 6 elements (Cd, Cr, Cu, Ni, Pb and Zn) collected from 46 locations. The index of geo-accumulation was used to assess the degree of contamination of the total trace elements and the assessments showed that the contamination of Cd reached strong to very strong pollution. The speciation of metal in sediments was analyzed using the modified BCR (Community Bureau of Reference) sequential extraction technology and the water column-contamination risk was evaluated by the calculated contamination factors. The results of the speciation of metal indicated that more easily mobilized forms (exchangeable, water soluble, and acid soluble) were predominant for Cd, especially in the samples from East Dongting Lake. In contrast, the largest amount of lead was associated with the iron and manganese oxide fractions, and Cu, Zn, Cr, and Ni analyzed were mainly distributed in residual phase at an average percentage higher than 60% of the total metals. The potential risk to the lake's water contamination was the highest in East Dongting Lake based on the calculated contamination factors. The assessment results using geo-accumulation index were compared with the information obtained by trace metal speciation and both results were consistent.

Stratal Carbonate Content Inversion Using Seismic Data and Its Applications to the Northern South China Sea
Yan XIONG, Guangfa ZHONG, Qianyu LI, Nengyou WU, Xuejie LI, Zaitian MA
2006, 17(4): 320-325, 354.

On the basis of the relationship between the carbonate content and the stratal velocity and density, an exercise has been attempted using an artificial neural network on high-resolution seismic data for inversion of carbonate content with limited well measurements as a control. The method was applied to the slope area of the northern South China Sea near ODP Sites 1146 and 1148, and the results are satisfactory. Before inversion calculation, a stepwise regression method was applied to obtain six properties related most closely to the carbonate content variations among the various properties on the seismic profiles across or near the wells. These include the average frequency, the integrated absolute amplitude, the dominant frequency, the reflection time, the derivative instantaneous amplitude, and the instantaneous frequency. The results, with carbonate content errors of mostly ±5% relative to those measured from sediment samples, show a relatively accurate picture of carbonate distribution along the slope profile. This method pioneers a new quantitative model to acquire carbonate content variations directly from high-resolution seismic data. It will provide a new approach toward obtaining substitutive high-resolution sediment data for earth system studies related to basin evolution, especially in discussing the coupling between regional sedimentation and climate change.

Changes in Atlantic Thermohaline Circulation under Different Atmospheric CO2 Scenarios in a Climate Model
Lin MOU, Dexing WU, Xueen CHEN
2006, 17(4): 326-331.

The changes in the thermohaline circulation (THC) because of the increased CO2 in the atmosphere play an important role in future climate regimes. In this article, a new climate model developed at the Max-Planck Institute for Meteorology is used to study the variation in THC strength, the changes of North Atlantic deep-water (NADW) formation, and the regional responses of the THC in the North Atlantic to increasing atmospheric CO2. From 2000 to 2100, under increased CO2 scenarios (B1, A1B, and A2), the strength of THC decreases by 4 Sv (106 m3/s), 5.1 Sv, and 5.2 Sv, respectively, equivalent to a reduction of 20%, 25%, and 25.1% of the present THC strength. The analyses show that the oceanic deep convective activity significantly strengthens in the Greenland-Iceland-Norway (GIN) Seas owing to saltier (denser) upper oceans, whereas weakens in the Labrador Sea and in the south of the Denmark Strait region (SDSR) because of surface warming and freshening due to global warming. The saltiness of the GIN Seas is mainly caused by the increase of the saline North Atlantic inflow through the Faro-Bank (FB) Channel. Under the scenario A1B, the deep-water formation rate in the North Atlantic decreases from 16.2 Sv to 12.9 Sv with increasing CO2.

Experimental Study on Aero Conductivity of Porous Media
Jiajun CHEN, Guanguang YANG, Yunwu LIU, Bing ZHENG, Jian YANG
2006, 17(4): 332-336.

To study the variation pattern of aero conductivity of different porous media under low pressure conditions, three kinds of media are selected. These include sandy clay loam, fine sand, and medium sand, and air as fluid to conduct soil column ventilation tests. Pressure at both ends of the columns is measured under different ventilation flow rates during testing. The test results show that the aero conductivity, solved by Darcy's law, is not a constant. It is a variable, which increases first when air flow velocity is less than 0.258 7 cm/s for sandy clay loam, 0.637 3 cm/s for fine sand and then decreases when air flow velocity is bigger than that with the increase of the ventilation flow rate when the medium is determined. By analyzing various factors that influence the flow resistance, the reasons for variation in aero conductivity are found as follows: first, the change of pore structure results in better ventilation; second, the relationship between pressure head loss and air flow velocity is nonlinear, and it is beyond the condition of the laminar flow domain to which Darcy's law can be applied, when the air flow rate increases to a certain value and the flow velocity is in the transition range to turbulent flow.

Effects of Rock Bolting on Stress Distribution around Tunnel Using the Elastoplastic Model
Muya MS, Bo HE, Jingtao WANG, Guocheng LI
2006, 17(4): 337-341, 354.

To ensure the stability of a tunnel during construction, rock bolts are usually installed, which affects the stress distribution around the tunnel. Therefore, it is necessary to study the effects of rock bolting on the stress distribution around the tunnel. In this article, the effects of rock bolting on the stress distribution around the tunnel, including the position and orientation of bolts, the overburden depths, and the bolt lengths, are simulated using the ANSYS software with an elastoplastic model. The effect of multiple bolts of 2 m and 1 m lengths on the stress distribution in the roof and on the lateral sides of a tunnel and at different overburden depths is considered. An important finding is that the tensile stress region that is very dangerous for rock in the bottom of the tunnel grows rapidly with increasing overburden depths when rock bolts are installed only in the roof or on the lateral sides of a tunnel. The determination of the length of the rock bolt used around a tunnel is dependent on the loads and the integrity of the rock mass around the tunnel. In addition, rock bolting around the tunnel can obviously reduce the coefficients and the size of the region of stress concentration, especially when installed in high-stress areas. This fact is very important and essential for the design of tunnels and ensures engineering safety in tunnel engineering.

Sulfate Attack on Concrete in an Inland Salt Lake Environment
Rongzhen DONG, Baoguo MA, Xingyang HE, Hongbo ZHU, Jun WEI
2006, 17(4): 342-348.

Several cracks were found on the surface of the concrete foundations that support the steel towers of the Luohe -Huaiyang high-voltage electricity transmission line that is 20 years old and situated in an inland salt lake environment in North China. To analyze the deterioration mechanism that led to this condition, field investigations were carried out and several tests were conducted on the soil and the affected concrete, including XRD (X-ray diffraction), electric probe analysis, and chemical analysis. The results show that the concentration of sulfates is very high (0.39% wt.-0.67%wt.) in both the surrounding soil and the material around the coarse aggregates inside the concrete. Hence, sulfate attack could be one of the main causes of concrete deterioration. The percentage of sulfates in the surface layer of the concrete was higher than that in the inner layers of the concrete. The sulfates penetrate into the concrete and react with the hydrates of cement to form ettringite (AFt), which leads to increase in the volume and cracking of the concrete.

Numerical Analysis of Asphalt Pavements under Moving Wheel Loads
Hui LUO, Hongping ZHU, Xingzhou HAO
2006, 17(4): 349-354.

The responses of the pavement in service are the basis for the design of the semi-rigid base course asphalt pavement. Due to the dynamic characteristics of wheel loads and the temperature loads, the dynamic response analysis is very significant. In this article, the dynamic analysis of asphalt pavement under moving wheel loads is carried out using finite element method coupled with non-reflective boundary method. The influences of the base modulus, thickness, the vehicle velocity, the tire pressure, and the contact condition at the interface are studied using parametric analysis. The results of numerical analysis show that it is not appropriate to simply increase the base modulus or thickness in the design. It would be beneficial if the base design is optimized synthetically. The increase of damping is also beneficial to the pavements because of the surface deflection and the stresses declination. Furthermore, the good contact condition at the interface results in good performance because it combines every layer of the pavement to work together. As overload aggravates the working condition of the pavement, it is not allowed.

Method of Numerical Modeling for Constitutive Relations of Clay
Baochun ZHOU, Jingtao WANG, Jun WEI
2006, 17(4): 355-360.

In order to study the method of numerical modeling for constitutive relations of clay, on the basis of the principle of interaction between plastic volumetric strain and plastic generalized shear strain, the two constitutive functionals that include the function of stress path were used as the basic framework of the constitutive model, which are able to demonstrate the dependence of stress path. The two partial differential cross terms appear in the expression of stress-strain increment relation, which are used to demonstrate the interaction between plastic volumetric strain and plastic generalized shear strain. The elasoplastic constitutive models of clay under two kinds of stress paths, CTC and TC, have been constracted using the triaxtal test results. The three basic characteristics of deformation of soils, pressure sensitivity, dilatancy, and dependence of stress path, are well explained using these two models. Using visualization, the three-dimensional surfaces of shear and volume strains in the whole stress field under stress paths of CTC and TC are given. In addition, the two families of shear and volmetric yield Ioei under CTC and TC paths are plotted respectively. By comparing the results of deformation under these two stress paths, it has been found that, there are obvious differences in the strain peaks, the shapes of strain surfaces, and the trends of variation of volumetric yield loci, however both families of shear yield loci are similar. These results demonstrate that the influences of stress path on the constitutive relations of clay are considerably large and not negligible. The nmericul modeling method that can sufficiently reflect the dependence of stress path is superior to the traditional one.

Genetic Programming Approach for Predicting Surface Subsidence Induced by Mining
Shuhua ZHAI, Qian GAO, Jianguo SONG
2006, 17(4): 361-366.

The surface subsidence induced by mining is a complex problem, which is related with many complex and uncertain factors. Genetic programming (GP) has a good ability to deal with complex and nonlinear problems, therefore genetic programming approach is proposed to predict mining induced surface subsidence in this article. First genetic programming technique is introduced, second, surface subsidence genetic programming model is set up by selecting its main affective factors and training relating to practical engineering data, and finally, predictions are made by the testing of data, whose results show that the relative error is approximately less than 10%, which can meet the engineering needs, and therefore, this proposed approach is valid and applicable in predicting mining induced surface subsidence. The model offers a novel method to predict surface subsidence in mining.