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在中国甘肃省的黑方台阶地上从上世纪60年代开始出现人类定居和开垦活动,并自1968年发展为灌溉农业。随着灌溉的进行地面已出现沉陷和滑坡。地表沉陷是由灌溉水的充填引起黄土结构崩塌造成的。然而崩塌和湿润化对剪切特征的影响目前还不清楚。为了研究湿化后的黄土剪切特征的变化,进行了对马兰黄土未经扰动和重塑土样的直接剪切盒测试。结果显示未扰动土样的粘合力和内摩擦角在湿润化后都下降了,而所观察到的重塑土的弹度参数只有少许变化。未扰动土的不饱合粘合力,据认为其受胶结物质的影响,在饱合后消失了。经灌溉的土的不饱合强度参数与未灌溉土相比表现出差异,它们可能受土壤水分的强烈影响。 相似文献
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The recovery of drill cores involves changes in pressure and temperature conditions, which inevitably alter the mechanical properties of unlithified sediments. While expansion from unloading after core recovery is well studied, the effects from cooling on standard geotechnical tests are commonly neglected. Along the central portion of the Nankai margin sediments were recovered from high in-situ temperatures of up to 110 °C during IODP Leg 190. So far, the interpretation of the consolidation state of the Lower Shikoku Basin facies (LSB) entering the accretionary Nankai margin is ambiguous. Results from laboratory consolidation tests at room temperature show high pre-consolidation stresses. These were interpreted as hardening caused by cementation, while the field-based porosity vs. depth trend points towards normal consolidation. As an explanation for this discrepancy, the change of the mechanical properties by cooling from in-situ to laboratory conditions is proposed. In this paper, the results of a thermo-mechanical model are compared to published field data. This comparison suggests that the observed hardening is at least partially an artefact from cooling during core recovery, and that the strata may be considered normally consolidated to slightly overconsolidated. The latter can be explained by minor cementation or the influence of secondary consolidation. The results suggest that cooling from high in-situ temperatures may be important for the interpretation of the consolidation state of other sedimentary successions elsewhere. 相似文献
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The 2001 Bhuj earthquake (Mw 7.6) source zone is examined in the light of crack density (ε), saturation rate (ξ) and porosity parameter (ψ) using new data set derived from a large aftershock sequence recorded by the Gujarat seismic network (GSNet) during November, 2006–December, 2009. Processes of rupture initiations of the mainshock and its aftershock sequence are better understood by synthesizing the dynamic snapshots of the source zone using the new dataset. Pattern of crustal heterogeneities associated with high-ε, high-ξ and high-ψ anomalies at depths varying from 20 km to 25 km is similar to those of earlier study by Mishra and Zhao (2003). The anomalous zone is found extended distinctly by 50–60 km in the lateral direction, indicating the reinforcement of cracks and fractured volume of rock matrix due to long aftershock sequence since 2001 Bhuj earthquake in the source area. It is inferred that the presence of a fluid-filled fractured rock matrix with super saturation may have affected the structural and seismogenic strengths of the source zone and is still contributing significantly to the geneses of earthquakes in and around the source zone. Anomalous pattern of high-ε with wider distribution of high-ξ indicates the existence of micro-cracks in the lower crust, while high-ψ suggests the cementation of cracks through permeation of residual magma/metamorphic fluids into the hypocenter zone. The results suggest that the existence of residual fluids in the fractured rock matrix in the mid to lower crust might have played a key role in triggering the 2001 mainshock and is still responsible for its continued long aftershock sequences. 相似文献
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The construction of large offshore wind turbines in seismic active regions has great demand on the design of foundations. The occurrence of soil liquefaction under seismic motion will affect the stability of the foundations and consequently the operation of the turbines. In this study, a group of earthquake centrifuge tests was performed on wind turbine models with gravity and monopile foundations, respectively, to exam their seismic response. It was found that the seismic behavior of models was quite different in the dry or saturated conditions. Each type of foundation exhibited distinct response to the earthquake loading, especially in the offshore environment. In the supplementary tests, several remediation methods were evaluated in order to mitigate the relatively large lateral displacement of pile foundation (by fixed-end pile and multi-pile foundation) and excessive settlement of gravity foundation (by densification, stone column, and cementation techniques). 相似文献
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Permeability characteristics of lime treated marine clay 总被引：1，自引：0，他引：1
An attempt has been made to investigate the lime induced permeability changes in the permeability and engineering behavior of different lime column treated soil systems. Lime columns treated marine clay shows an increase in permeability up to a maximum value of 15–18 times that of untreated soil with time. The shear strength of the treated soil systems show an increment up to 8–10 that of untreated soil within a period of 30–45 days curing. In the case of lime injection systems, the permeability has been increased up to 10–15 times that of untreated soil, whereas the strength of the soil has been higher by 8–10 times that of untreated soil. Further, consolidation tests show a reduction in the compressibility up to 1/2–1/3 of original values. The test results revealed that both lime column and injection techniques could be used to improve the behaviour of underwater marine clay deposits. 相似文献
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油气充注对成岩作用的影响 总被引：5，自引：0，他引：5
油气充注对成岩作用的影响有三个方面 :抑制石英和伊利石的胶结作用、油气中所有机酸对深部孔隙的溶蚀改造作用、油气超压对压实的缓冲作用。英国北海Miller油气藏等的资料显示 ,油气充注较早时 ,油区的石英胶结速率比水区的明显要低 ,石英的胶结丰度比一般预测值低 ,而孔隙度比一般的预测值要高。我国渤海湾盆地东营凹陷油田资料显示 ,无论浅部或深部 ,凡是含油砂岩 ,其长石类及碳酸盐类矿物的溶解都十分强烈 ,次生孔隙很发育 ,而不含油的砂岩 ,其矿物溶解及次生孔隙发育一般较差 ;油层的方解石、白云石含量一般比水层低 ,深层尤为明显。干酪根生成油气时的流体体积增加 ,可大大增加孔隙流体压力 ,产生超压 ,并可传递到储集层 ,因而大大增加对压实作用的抵抗能力。上述三方面实质上都为深部油气成藏改善了储层基础 ,对深部油气勘探具有非常现实的意义。 相似文献
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Comparison of chalk on the Ontong Java Plateau and chalk in the Central North Sea indicates that, whereas pressure dissolution is controlled by effective burial stress, pore-filling cementation is controlled by temperature. Effective burial stress is caused by the weight of all overlying water and sediments as counteracted by the pressure in the pore fluid, so the regional overpressure in the Central North Sea is one reason why the two localities have different relationships between temperature and effective burial stress. In the chalk of the Ontong Java Plateau the onset of calcite-silicate pressure dissolution around 490 m below sea floor (bsf) corresponds to an interval of waning porosity-decline, and even the occurrence of proper stylolites from 830 m bsf is accompanied by only minor porosity reduction. Because opal is present, the pore-water is relatively rich in Si which through the formation of Ca–silica complexes causes an apparent super-saturation of Ca and retards cementation. The onset of massive pore-filling cementation at 1100 m bsf may be controlled by the temperature-dependent transition from opal-CT to quartz. In the stylolite-bearing chalk of two wells in the Gorm and Tyra fields, the nannofossil matrix shows recrystallization but only minor pore-filling cement, whereas microfossils are cemented. Cementation in Gorm and Tyra is thus partial and has apparently not been retarded by opal-controlled pore-water. A possible explanation is that, due to the relatively high temperature, silica has equilibrated to quartz before the onset of pressure dissolution and thus, in this case, dissolution and precipitation of calcite have no lag. This temperature versus effective burial stress induced difference in diagenetic history is of particular relevance when exploring for hydrocarbons in normally pressured chalk, while most experience has been accumulated in the over-pressured chalk of the central North Sea. 相似文献
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The Upper Cretaceous Phosphate Formation in the Western Desert of Egypt displays a characteristic facies association that includes marine phosphorites interbedded with black shales and glauconitic sandstones. The upper part of the formation is characterized by the presence of thin phosphatic beds, which are filled-extensively-with disordered and non stoichiometric (mean MgCO3 = 41.4 ± 0.34 mol%) authigenic dolomite cement. SEM and the back scattered images of these coarse crystalline dolomite cements reveal that they display planar euhedral crystal boundaries, polymodal crystal size distribution and variable inclusion pattern. The relatively low and wide ranged δ18O (− 0.87 to − 4.15‰ VPDB) values of the dolomite cements coupled with their depleted Sr (mean = 187 ± 26 ppm) and high iron and manganese values (mean = 6851 ± 554 ppm and 11599 ± 229 ppm respectively) invoke that they were formed from mixed hypo-saline fluids within a mixing marine-meteoric zone probably during a low stand period at the vicinity of the Maastrichtian/Early Tertiary unconformity. Meanwhile, their negative δ13C (− 1.31 to − 3.56‰ VPDB) values argue for a possible involvement of isotopically light carbon, derived from degradation of organic matter, during their precipitation. 相似文献