昌马水库右岸山体稳定性研究

昌马水库导流排砂洞塌方导致右岸山体发生松动 ,本文在大量地质资料的基础上 ,对右岸岩体裂隙网络进行模拟 ,同时 ,采用极限分析能量法和有限元数值模拟方法等对右岸山体的稳定性进行分析研究 ,并提出相应的加固方案。     

Overburden deformation associated with halokinesis in the Southern North Sea: implications for the origin of the Silverpit Crater

Gravitational collapse in response to the creation of salt swells and diapirs is a common phenomenon within regions such as the Southern North Sea. Although collapse faulting and slumping of linear salt swell flanks has previously been documented, the existence of concentric collapse structures surrounding diapirs and isolated salt lows is a recently recognised feature. 3-D seismic data from the Southern North Sea demonstrates that concentric collapse faulting around both diapirs and subcircular salt lows is common. The recognition of concentric collapse structures formed in response to salt withdrawal, and adjacent inflation, provides an alternative mechanism for the origin of the proposed Silverpit impact crater.     

Decompression reactions and P–T conditions in high-pressure granulites from Casares-Los Reales units of the Betic-Rif belt (S Spain and N Morocco)

High-pressure granulites are exposed in the Casares-Los Reales group (internal zones of Betic-Rif belt, S Spain–N Morocco) as part of the crustal envelope of Beni Bousera-Ronda Peridotites. They are mostly metapelitic but include intercalations of mafic composition. The metamorphic history is marked by the preservation of early high-pressure assemblages together with secondary low-pressure assemblages suggesting a state of textural and compositional disequilibrium. The P–T path constrained by geothermobarometry and reaction textures from mafic and pelitic lithotypes passes from 800 °C/15 kbar to 600 °C/5 kbar, to indicating a strong decompression related to cooling, followed by a near-isobaric cooling 430 °C and 4 kbar. Such P–T evolution of granulites is thought to reflect some sort of rapid tectonic collapse of crust previously thickened through collision.     

Sequence of faulting and deformation during the 2000 eruptions of the Usu Volcano, Hokkaido, Japan—interpretation and image analyses of aerial photographs

Significant faulting and deformation of the ground surface has been rarely known during volcanic eruptions. Usu Volcano, Hokkaido, Japan, is a unique example of deformation due to felsic magma intrusion. Usu Volcano has a history of such types of eruptions as phreatic, pumice eruption (Plinian type), pyroclastic flowing and lava doming since 1663. On March 31, 2000, phreatomagmatic to phreatic eruptions took place after 23 years of dormancy in the western piedmont, followed by explosions on the western flank of Usu Volcano. They were associated with significant deformation including faulting and uplift. The eruptions and deformation were continuing up to the end of May 2000.We identified the faulting using total nine sets of aerial photographs taken from before the eruption (March 31, 2000) to more than 1 year (April 27, 2001) after the end of the activity, and traced deformation processes through image processing using aerial photographs. We found that some of the new faults and the associated phreatic eruptions were related to old faults formed during the 1977–1981 eruptive episode.The image processing has revealed that the surface deformation is coincident with the area of faulting forming small grabens and the phreatic explosion vents. However, the faulting and main explosive eruptions did not take place in the highest uplift area, but along the margin. This suggests that the faulting and explosive activities were affected by small feeder channels diverging from the main magma body which caused the highest uplift.     

Seismic signature of a phreatic explosion: hydrofracturing damage at Karthala volcano, Grande Comore Island, Indian Ocean

Karthala volcano is a basaltic shield volcano with an active hydrothermal system that forms the southern two-thirds of the Grande Comore Island, off the east coat of Africa, northwest of Madagascar. Since the start of volcano monitoring by the local volcano observatory in 1988, the July 11th, 1991 phreatic eruption was the first volcanic event seismically recorded on this volcano, and a rare example of a monitored basaltic shield. From 1991 to 1995 the VT locations, 0.5<M_l<4.3, show a crack shaped pattern (3 km long, 1 km wide) within the summit caldera extending at depth from –2 km to +2 km relative to sea level. This N-S elongated pattern coincides with the direction of the regional maximum horizontal stress as deduced from regional focal mechanism solutions. This brittle signature of the damage associated with the 1991 phreatic eruption is a typical pattern of the seismicity induced by controlled fluid injections such as those applied at geothermal fields, in oil and gas recovery, or for stress measurements. It suggests the 1991 phreatic eruption was driven by hydraulic fracturing induced by forced fluid flow. We propose that the extremely high LP and VT seismicity rates, relative to other effusive volcanoes, during the climax of the 1991 phreatic explosion, are due to the activation of the whole hydrothermal system, as roughly sized by the distribution of VT hypocenters. The seismicity rate in 1995 was still higher than the pre-eruption seismicity rate, and disagrees with the time pattern of thermo-elastic stress readjustment induced by single magma intrusions at basaltic volcanoes. We propose that it corresponds to the still ongoing relaxation of pressure heterogeneity within the hydrothermal system as suggested by the few LP events that still occurred in 1995.Editorial responsibility: H Shinohara     

Caldera formation by magma withdrawal from a reservoir beneath a volcanic edifice

Caldera formation has been explained by magma withdrawal from a crustal reservoir, but little is known about the conditions that lead to the critical reservoir pressure for collapse. During an eruption, the reservoir pressure is constrained to lie within a finite range: it cannot exceed the threshold value for eruption, and cannot decrease below another threshold value such that feeder dykes get shut by the confining pressure, which stops the eruption. For caldera collapse to occur, the critical reservoir pressure for roof failure must therefore be within this operating range. We use an analytical elastic model to evaluate the changes of reservoir pressure that are required for failure of roof rocks above the reservoir with and without a volcanic edifice at Earth's surface. With no edifice at Earth's surface, faulting in the roof region can only occur in the initial phase of reservoir inflation and affects a very small part of the focal area. Such conditions do not allow caldera collapse. With a volcanic edifice, large tensile stresses develop in the roof region, whose magnitude increase as the reservoir deflates during an eruption. The edifice size must exceed a threshold value for failure of the roof region before the end of eruption. The largest tensile stresses are reached at Earth's surface, indicating that faulting starts there. Failure affects an area whose horizontal dimensions depend on edifice and chamber dimensions. For small and deep reservoirs, failure conditions cannot be achieved even if the edifice is very large. Quantitative predictions are consistent with observations on a number of volcanoes.     

基于地下水模型的岩溶塌陷风险性评价方法在临沂市城区的应用

岩溶塌陷是山东省临沂市区最重要的地质灾害类型,一旦发生,会带来较大的经济和财产损失,因此对岩溶塌陷的风险评价十分必要。风险评价包括现状评价和预测评价,主要分3个步骤来完成：危险性评价,易损性评价和期望损失评价。利用地下水流模型确定调采方案下的相关评价因子,预测了岩溶塌陷的风险性。通过比较发现,经过地下水调采后,原岩溶塌陷高风险区范围大为缩小。地下水流数值模型和风险评价方法结合,可以确定合理的岩溶水规划开采方案,对于指导和防治岩溶塌陷具有重要意义。     

基于离散元模拟的二元颗粒柱坍塌特性研究

常见的地质灾害如滑坡、泥石流、岩崩等通常都涉及不同形状的颗粒物质运动,这些形状不同的颗粒又多具有不同的尺寸和含量。基于典型的颗粒柱坍塌试验,首先根据试验方法确定了离散元模拟所需的各项参数,然后采用随机多面体方法生成了可控制长细比的大颗粒,利用离散元法就不同大颗粒含量下形态变化对二元颗粒柱坍塌特性的影响开展研究,研究结果表明:(1)利用离散元法可以较好地重现室内试验中小球和多面体组成的二元颗粒系统的颗粒柱坍塌过程;(2)在不同长细比的不规则大颗粒和小球组成的二元颗粒柱系统中,当大颗粒含量高于临界含量值20%时,二元颗粒柱坍塌持续的时间随非球形大颗粒长细比的增加而增加;(3)在不同长细比的不规则大颗粒和小球组成的二元颗粒柱中,当大颗粒含量高于临界含量值20%时,在相同百分比的大颗粒含量下,大颗粒长细比的增加会提高大颗粒平均配位数以及降低颗粒的运动能力,大颗粒间形成更强的互锁作用,降低了颗粒柱的整体流动性,使其最终堆积高度更高、最大跑出距离更短以及更小的归一化动能峰值。(4)在不同长细比的不规则大颗粒和小球组成的二元颗粒柱中,小颗粒可以较为明显降低大颗粒间摩擦及互锁作用,增加流动性,降低大骨料形态对坍塌过程的影响。     

灌注桩导管爆管与瘪管的原因分析

水下混凝土灌注是钻孔灌注桩施工中最关键工序之一,超深孔水下混凝土灌注的导管偶尔会出现爆管与瘪管现象。通过对导管受力分析,从理论上分析了造成爆管和瘪管现象的直接原因,从实践中罗列出可能导致爆管与瘪管的各种因素,并提出预防措施,有利于超深孔水下混凝土灌注质量的控制。     

Treatment Effects of Tunnel Entrance Collapse Section Based on Field Monitoring Results北大核心CSCD

为评价隧道洞口塌方段的安全性,基于累计变形预测和变形速率趋势分析模型,结合工程实例,研究隧道洞口塌方段的处理效果。实例分析表明：在累计变形预测方面,GA-VMD模型在隧道变形数据的信息分解过程中具有明显的优越性,可利用其将隧道变形数据分解为趋势项和误差项,且通过组合预测能有效保证预测精度,得出累计变形的后期仍具一定增加趋势,但增加速率相对较小;在变形速率趋势分析方面,变形速率具下降趋势,且随时间持续,下降趋势更为显著。综合对比两者结果,隧道变形无明显增加趋势,并趋于稳定方向发展,说明塌方处理措施是合理有效的,为其防治效果评价提供了理论依据。