Lower Cretaceous turbidites in the Shiquanhe–Namco Ophiolite Mélange Zone,Asa area,Tibet:Constraints on the evolution of the Meso-Tethys Ocean

Turbidites from the Shiquanhe–Namco Ophiolite Mélange Zone(SNMZ) record critical information about the tectonic affinity of the SNMZ and the evolutionary history of the Meso-Tethys Ocean in Tibet.This paper reports sedimentologic,sandstone petrographic,zircon U-Pb geochronologic,and clastic rocks geochemical data of newly identified turbidites(Asa Formation) in the Asa Ophiolite Mélange.The youngest ages of detrital zircon from the turbiditic sandstone samples,together with ～115 Ma U-Pb concordant age from the tuff intercalation within the Asa Formation indicate an Early Cretaceous age.The sandstone mineral modal composition data show that the main component is quartz grains and the minor components are sedimentary and volcanic fragments,suggesting that the turbidites were mainly derived from a recycled orogen provenance with a minor addition of volcanic arc materials.The detrital U-Pb zircon ages of turbiditic sandstones yield main age populations of170–120 Ma,300–220 Ma,600–500 Ma,1000–700 Ma,1900–1500 Ma,and ～2500 Ma,similar to the ages of the Qiangtang Terrane(age peak of 600–500 Ma,1000–900 Ma,～1850 Ma and ～2500 Ma) and the accretionary complex in the Bangong–Nujiang Ophiolite Zone(BNMZ) rather than the age of the Central Lhasa Terrane(age peak of ～300 Ma,～550 Ma and ～1150 Ma).The mineral modal compositions,detrital U-Pb zircon ages,and geochemical data of clastic rocks suggest that the Asa Formation is composed of sediments primarily recycled from the Jurassic accretionary complex within the BNMZ with the secondary addition of intermediate-felsic island arc materials from the South Qiangtang Terrane.Based on our new results and previous studies,we infer that the SNMZ represents a part of the Meso-Tethys Suture Zone,rather than a southward tectonic klippe of the BNMZ or an isolated ophiolitic mélange zone within the Lhasa Terrane.The Meso-Tethys Suture Zone records the continuous evolutionary history of the northward subduction,accretion,arc-Lhasa collision,and Lhasa-Qiangtang collision of the Meso-Tethys Ocean from the Early Jurassic to the Early Cretaceous.     

Late Jurassic–Early Cretaceous Plutonism in the Northern Part of the Precambrian North China Craton: SHRIMP Zircon U–Pb Dating of Diorites and Granites from the Yunmengshan Geopark, Beijing

The Yunmengshan Geopark in northern Beijing is located within the Yanshan range. It contains the Yunmengshan batholith, which is dominated by two plutons: the Yunmengshan gneissic granite and the Shicheng gneissic diorite. Four samples of the Yunmengshan gneissic granite give SHRIMP zircon U–Pb ages from 145 to 141 Ma, whereas four samples of the Shicheng gneissic diorite have ages from 159 Ma to 151 Ma. Dikes that cut the Yunmengshan diorite record SHRIMP zircon U–Pb age of 162±2 and 156±4 Ma. The cumulative plots of zircons from the diorites show a peak age of 155 Ma, without inherited zircon cores, and the peak age of 142 Ma for granite is interpreted as the emplacement age of the Yunmengshan granitic pluton, whose igneous zircons contain inherited zircon cores. The data presented here show that there were two pulses of magmatism: early diorites, followed c13 Ma later by true granites, which incorporated material from an older continental crust.     

Detrital Zircon U‐Pb Ages and Geochemistry of the Silurian to Permian Sedimentary Rocks in Central Inner Mongolia,China: Implications for Closure of the Paleo‐Asian Ocean

The Solonker suture zone has long been considered to mark the location of the final disappearance of the PaleoAsian Ocean in the eastern Central Asian Orogenic Belt(CAOB). However, the time of final suturing is still controversial with two main different proposals of late Permian to early Triassic, and late Devonian. This study reports integrated wholerock geochemistry and LA-ICP-MS zircon U-Pb ages of sedimentary rocks from the Silurian Xuniwusu Formation, the Devonian Xilingol Complex and the Permian Zhesi Formation in the Hegenshan-Xilinhot-Linxi area in central Inner Mongolia, China. The depositional environment, provenance and tectonic setting of the Silurian-Devonian and the Permian sediments are compared to constrain the tectonic evolution of the Solonker suture zone and its neighboring zones. The protoliths of the silty slates from the Xuniwusu Formation in the Baolidao zone belong to wacke and were derived from felsic igneous rocks with steady-state weathering, poor sorting and compositional immaturity. The protoliths of metasedimentary rocks from the Xilingol Complex were wackes and litharenites and were sourced from predominantly felsic igneous rocks with variable weathering conditions and moderate sorting. The Xuniwusu Formation and Xilingol Complex samples both have two groups of detrital zircon that peak at ca. 0.9–1.0 Ga and ca. 420–440 Ma, with maximum deposition ages of late Silurian and middle Devonian age, respectively. Considering the ca. 484–383 Ma volcanic arc in the Baolidao zone, the Xuxiniwu Formation represents an oceanic trench sediment and is covered by the sedimentary rocks in the Xilingol Complex that represents a continental slope sediment in front of the arc. The middle Permian Zhesi Formation metasandstones were derived from predominantly felsic igneous rocks and are texturally immature with very low degrees of rounding and sorting, indicating short transport and rapid burial. The Zhesi Formation in the Hegenshan zone has a main zircon age peak of 302 Ma and a subordinate peak of 423 Ma and was deposited in a back-arc basin with an early marine transgression during extension and a late marine regression during contraction. The formation also crops out locally in the Baolidao zone with a main zircon age peak of 467 Ma and a minor peak of 359 Ma, and suggests it formed as a marine transgression sedimentary sequence in a restricted extensional basin and followed by a marine regressive event. Two obvious zircon age peaks of 444 Ma and 280 Ma in the Solonker zone and 435 Ma and 274 Ma in Ondor Sum are retrieved from the Zhesi Formation. This suggests as a result of the gradual closure of the Paleo-Asian Ocean a narrow ocean sedimentary environment with marine regressive sedimentary sequences occupied the Solonker and Ondor Sum zones during the middle Permian. A restricted ocean is suggested by the Permian strata in the Bainaimiao zone. Early Paleozoic subduction until ca. 381 Ma and renewed subduction during ca. 310–254 Ma accompanied by the opening and closure of a back-arc basin during ca. 298–269 Ma occurred in the northern accretionary zone. In contrast, the southern accretionary zone documented early Paleozoic subduction until ca. 400 Ma and a renewed subduction during ca. 298–246 Ma. The final closure of the Paleo-Asian ocean therefore lasted at least until the early Triassic and ended with the formation of the Solonker suture zone.     

The final collision of the CAOB: Constraint from the zircon U–Pb dating of the Linxi Formation, Inner Mongolia

The Linxi Formation occupies an extensive area in the eastern Inner Mongolia in the Central Asian Orogenic Belt(CAOB).The Linxi Formation is composed of slate,siltstone,sandstone and plant,lamellibranch microfossils in the associated strata.Major and trace element data(including REE) for sandstones from the formation indicate that these rocks have a greywacke protolith and have been deposited during a strong tectonic activity.LA-ICPMS U—Pb dating of detrital zircons yield ages of 1801 to 238 Ma for four samples from the Linxi Formation.425—585 Ma,together with the ~500 Ma age for the metamorphism event previously determined for Northeast China,indicates that their provenance is the metamorphic rocks of Pan-African age that have a tectonic affinity to NE China.A few older zircons with U-Pb ages at 1689-1801 Ma,1307-1414 Ma,593-978 Ma are also present,revealing the Neoproterozoic history of NE China.The youngest population shows a peak at ca.252 Ma,suggesting that the main deposition of the Linxi Formation was at late Permain.Moreover,the ca.250 Ma zircon grains of all four samples yield weighted mean ~(206)Pb/~(238)U ages of 250 ± 3 Ma,248 ± 3 Ma,249 ± 3 Ma,and 250 ± 2 Ma,respectively.These ages,together with the youngest zircon age in the sample ZJB-28(ca.238 Ma),suggest that the deposition of the Linxi Formation extended to the early Triassic.Combining with previous results,we suggest that the final collision of the Central Asian Orogenic Belt(CAOB) in the southern of Linxi Formation,which located in the Solonker-Xra Moron-Changchun suture,and the timing for final collision should be at early Triassic.     

The Geological Significance of the Deformation and Geochronology of the Xiaotian–Mozitan Shear Zone in the Dabie Orogenic Belt (East-Central China)

The Xiaotian–Mozitan Shear Zone(XMSZ) is the boundary of the Dabie High-grade Metamorphic Complex(DHMC) and the North Huaiyang Tectonic Belt. It was deformed in ductile conditions with a top-to-NW/WNW movement.Geothermometers applied to mineral parageneses in mylonites of the shear zone give a temperature range of 623–691°C for the predeformation and 515–568°C for the syndeformation, respectively, which indicates a retrograde process of evolution.A few groups of zircon U-Pb ages were obtained from undeformed granitic veins and different types of deformed rocks in the zone. Zircons from the felsic ultramylonites are all magmatic, producing a weighted mean 206 Pb/238 U age of 754 ± 8.1 Ma, which indicates the time of magmatic activities caused by rifting in the Neoproterozoic. Zircons from the granitic veins, cutting into the mylonites, are also of magmatic origin, producing a weighted mean 206 Pb/238 U age of 130 ± 2.5 Ma,which represents the time of regional magmatic activity in the Cretaceous. Zircons from the mylonitic gneisses are of anatectic-metamorphic origins and are characterized by a core-mantle interior texture, which yielded several populations of ages including the Neoproterozoic ages with a weighted mean 206 Pb/238 U age of 762 ± 18 Ma, similar to that of the felsic ultramylonites and the Early Cretaceous ages with a weighted mean 206 Pb/238 U age of 143 ± 1.8 Ma, indicating the anatectic metamorphism in the Dabie Orogenic Belt(DOB). Based on integrated analysis of the structure, thermal conditions of ductile deformation and the contact relations of the dated rocks, the activation time of the Xiaotian–Mozitan Shear Zone is constrained between ～143 Ma and 130 Ma, during which the DOB was undergoing a transition in tectonic regime from compression to extension. Therefore, the deformation and evolution of this shear zone plays an instrumental role in fully understanding this process. This research also inclines us to the interpretation of it as an extensional detachment, with regard to the tectonic properties of the shear zone. It may also be part of a continental scale extension in the background of the North China Block's cratonic destruction, dominated by the subduction and roll-back of the Paleo-Pacific plate, but more detailed work is needed in order to unravel its complicated development.     

Neoproterozoic Crustal Reworking and Growth in the Zhangbaling Uplift, Tan–Lu Fault Zone: Evidence from the Feidong Complex and Zhangbaling Group

Intensive mid-Neoproterozoic magmatism is the salient feature of the Yangtze Block, preserving abundant information about crustal reworking and growth. Zircon U–Pb–Lu–Hf isotope analysis was performed on material from the Feidong Complex (FDC) and Zhangbaling Group (ZBLG) of the Zhangbaling Uplift, in order to determine the age and magmatic source of the Neoproterozoic igneous rocks as well as the detrital provenance for the sedimentary rocks, to further provide important data for understanding the mid-Neoproterozoic crustal evolution of the Northeast Yangtze Block. The amphibolite and gneissic granites in the Feidong Complex (FDC) gave similar protolith ages of 782–776 Ma. The synmagmatic zircons exhibited variable negative εHf(t) values of ?26.9 to ?8.3. Early (ca. 2.4 Ga) to late Paleoproterozoic (ca. 2.0–1.9 Ga) inherited zircons were found in the gneissic monzogranite, with negative εHf(t) values of ?11.2 to ?7.2, indicating strong reworking of the ancient crustal materials of the Northeast Yangtze Block. Whereas the amphibolites represent minor crustal growth through emplacement of continental rifting-related mafic magmas. The quartz–keratophyres in the Xileng Formation of the ZBLG in contrast systematically yield young protolith crystallization ages of 754–727 Ma with high εHf(t) values of ?2.0 to +5.6, indicating their derivation from the reworking of juvenile crustal materials. The detrital zircons from the metasiltstone in the Beijiangjun Formation yield variable 206Pb/238U ages (871–644 Ma) with a peak age at 741 ± 11 Ma and εHf(t) values of ?4.3 to +5.3, which is consistent with those of the Xileng Formation, but distinct from the FDC, indicating that the provenance of the metasiltstone is primarily the underlying Xileng Formation. The mid-Neoproterozoic igneous and sedimentary rocks of the Zhangbaling Uplift were products from continental rifting zones along the northern margin of the Yangtze Block, situated in different positions from the Susong Complex and the Haizhou Group. The transition from ancient to juvenile crustal sources for felsic magmatic rocks is attributed to gradually increased crustal extension during continental rifting.     

Geochronology, Geochemistry, and Sr–Nd–Hf Isotopes of the Balazha Ore-Bearing Porphyries: Implications for Petrogenesis and Geodynamic Setting of Late Cretaceous Magmatic Rocks in the Northern Lhasa Block, Tibet

The study of Late Cretaceous magmatic rocks, developed as a result of magmatism and related porphyry mineralization in the northern Lhasa block, is of significance for understanding the associated tectonic setting and mineralization. This paper reports zircon chronology, zircon Hf isotope data, whole-rock Sr–Nd isotope data, and geochemistry data of Balazha porphyry ores in the northern Lhasa block. Geochemical features show that Balazha ore-bearing porphyries in the northern Lhasa block belong to high-Mg# adakitic rocks with a formation age of ~90 Ma; this is consistent with the Late Cretaceous magmatic activity that occurred at around 90 Ma in the region. The age of adakitic rocks is similar to the molybdenite Re–Os model age of the ore-bearing porphyries in the northern Lhasa block, indicating that the diagenesis and mineralization of both occurred during the same magmatism event in the Late Cretaceous. The Hf and Sr–Nd isotope data indicate that these magmatic rocks are the product of crust–mantle mixing. Differing proportions of materials involved in such an event form different types of medium-acid rocks, including ore-bearing porphyries. Based on regional studies, it has been proposed that Late Cretaceous magmatism and porphyry mineralization in the northern Lhasa block occurred during collision between the Lhasa and Qiangtang blocks.     

Detrital Zircon U–Pb Geochronology and Provenance of Bayan Obo Group, Northern Margin of North China Craton: New Implications for the Position of NCC in Rodinia

The paleoposition of North China Craton in Rodinia has long been in controversial. This paper mainly focuses on the U–Pb geochronological studies of detrital zircons obtained from Bayan Obo Group exposed in the Shangdu area, Inner Mongolia, aiming to provide more information for interprating this problem. Based on the acquired data, this paper comes to the following conclusions. Firstly, the depositional age of Bayan Obo Group might be from Meso– to Neoproterozoic according to the zircons U–Pb dating results. The lower succession of this group, namely Dulahala and Jianshan formations deposited between 1800 and 1650 Ma. The Halahuogete and Bilute formations deposited between 1500 and 1350 Ma. For Baiyinbaolage and Hujiertu formations, their depositional age was 1250–900 Ma. Secondly, for the provenance of Bayan Obo Group, this paper believes detrital zircons with age of 2.51–2.71 Ga and 2.00–2.48 Ga were from Guyang, Xi Ulanbulang and Zhuozi area; the Khondalite Belt provided detrital zircons with age of 1.95–1.80 Ga; zircons with age of 1.60–1.75 Ga might come from granitic rocks in Miyun Area. The magmatism after 1.60 Ga was rarely recorded in the NCC, therefore those zircons with ages younger than 1.60 Ga might come from outside of NCC. The magmatism with the same age existed in Baltic, Amazonia and Laurentia. Based on previous paleomagnetic researches, this paper proposes that NCC might receive detritus from Baltic during 1560–1350 Ma and had affinity with Laurentia and Amazonia at ～0.9 Ga in Rodinia. Baltic, Amazonia and Laurentia might be potential provenances for non–NCC detritus in Bayan Obo Group.     

Neoproterozoic ana texts of the yunkai metamorphic Complex; Evidence from U-Pb geochronology of zircon in migniatite北大核心CSCD

In order to determine the migmatization time of the Preeambrian metamorphic basement(the Yunkai metamorphic complex) of the Yunkai terrain, a study of LA-MC-1CP-MS U-Pb dating of zircon in matrixes and felsic veins of mig-matites from the Tiantangshan Group. Results show that the inherited magmatic cores of zircon grains from the matrix of migmatite have oscillatory zoning and yield a U-Pb age of 1086 ±24 Ma, representing the pmtolith age, whereas the metamprohic rims of zircon grains from the felsic vein of migmatite yield an age of 852. 6±8. 8 Ma, representing the timing of the anatex is (migmatization). These results imply that there is a Mesoproterozoic metamorphic basement with a Neoproterozoic anatexis event in the Yunkai area. The timing of this anatexis event is consistent with that of the Sibao Movement. Therefore, we conclude that the timing of the anataxis could be an important geological record for the amalgamation of the Yangtze and Cathaysian blocks.     

LA-ICP-MS U-Pb Zircon Dating for Felsic Granulite, Huangtuling Area, North Dabieshan: Constraints on Timing of Its Protolith and Granulite-Facies Metamorphism, and Thermal Events in Its Provenance

Information about the protolith of the Huangtuling granulite in North Dabieshan has been unavailable. The complex evolution history of the rock and its host basement must be further discussed. LA-ICP-MS U-Pb dating was conducted on three textural domains in zircon from a high-temperature, high-pressure felsic granulite in the Huangtuling area, North Dabieshan, Central China. The metamorphic growth-derived detrital zircon domain yields a 207Pb/206Pb age in the range of (2 493±54) -(2 500±180) Ma. The magmatic genesis-derived detrital zircon domain gives a 207Pb/206Pb age ranging from 2 628 Ma to 2 690 Ma, with an oldest 206Pb/238U age of (2 790±150) Ma. The metamorphic overgrowth or metamorphic recrystallization zircon domain yields a dicsordia with an upper intercept age of (2 044.7±29.3) Ma. Compositions of the mineral assemblage, major element geochemistry, and especially the complex interior texture of the zircon suggest that the prololith of the felsic granulite is of sedimentary origin. Results show that the protolith material of the granulite came from a provenance with a complex thermal history, i.e. ～2.8 Ga magmatism and ～2.5 Ga metamorphism, and was deposited in a basin not earlier than 2.5 Ga. The high-temperature and high-pressure granulite-facies metamorphic age was precisely constrained at (2.04±0.03) Ga, which indicates the granulite in Huangtuling area should be a relict of a Paleoproterozoic UHT (ultrahigh temperature) metamorphosed slab.     

Unity of the national and the international in the socio-cultural development of the peoples of the USSR

International unity is becoming ever stronger in this country owing to an increasing similarity in the development of the cultural environment. This comprises the provision of all the country's republics with a sufficient number of schools, theatres, and other institutions and cultural information media in accordance with the needs of the population. An important part is played by the rise in ‘the general educational level, as well as the level of professional qualifications and skills. Among all the Soviet nations and nationalities, this rise being more rapid among formerly backward peoples. Prominent among the factors of internationalization is the progressive development of the nationalities’ cultural resources, while professional culture is being increasingly brought within the reach of the masses.The implementation of the nationalities policy promotes the all-round development of all Soviet nations and nationalities, their drawing together, the upsurge of the individual capabilities of every Soviet citizen.     

Deviation of the major axis of the inertia ellipsoid of the Moon from the direction toward the Earth

It is known from observations that the center of mass of the Moon does not coincide with the geometric center of its figure, and the line connecting these two centers is not aligned with the direction toward the center of the Earth, instead deviating toward the Southeast. This stationary deviation of the axis of the inertia ellipsoid of the Moon to the South of the direction toward the Earth is analyzed. A system of five linear differential equations describing the physical libration of the Moon in latitude is considered, and these equations are derived using a new vector method taking into account perturbations from the Earth and partly from the Sun. The characteristic equation of this system is obtained, and all five oscillation frequencies are found. Special attention is paid to the fifth (zero) frequency, for which the solution of the latitude libration equations are stationary and represents a previously unknown additional motion of the rotational axis of theMoon in a cone with a small opening angle. In contrast to the astronomical precession of the Earth, the rotation of the angular-velocity vector is in the positive direction (counter-clockwise), with the period T ₃ = 27.32 days. On this basis, this phenomenon has been named “quasi-precession.” This quasi-precession leads to a stationary inclination of the major axis of the inertia ellipsoid of theMoon to the South (for an observer on Earth), making it possible to explain one component of the observed deviation of the center of mass of the Moon from the direction toward the Earth. The opening angle of the quasiprecession cone is approximately 0.834″.     

东濮凹陷北部沙河街组三段中亚段沉积环境分析

东濮凹陷北部沙三中亚段广泛发育盐岩和烃源岩,这两个看似不能共存的物质却在这里互层共生。该时期研究区沉积特征为多盐韵律与多层烃源岩互层共生、连续沉积,单个盐韵律厚度从几米到十几米,烃源岩有机质丰度高、类型好。平面上,两者在湖盆沉积沉降中心共生;垂向上,高有机质丰度、好干酪根类型与高盐度地层具有较好的对应关系。因而成为恢复古气候和古环境的重要研究对象。通过岩石学、古生物学以及Sr/Ba、B/Ga、(V+Ni+Mn)、Fe/Mn、Sr/Cu、Mg/Ca、V/(V+Ni)、稀土元素含量和氯同位素等方法对凹陷北部沙三中亚段的沉积环境进行研究。结果表明,凹陷北部沙三中亚段为深水沉积的还原环境,古盐度较高,达到半咸水-咸水沉积;微量元素和孢粉化石特征表明研究区沙三中亚段为温暖潮湿的环境。     

The Tendencies of the Development of the Mineral-Resources Sector at the Turn of the Century

Important tendencies in development of the world mineral-resources sector at the beginning of the 21st century were an increase in production and consumption of mineral materials differentiated by types of metals and nonmetallic mineral raw materials, by countries and regions, as well as the concentration of the production of mineral raw materials in a small number of countries, and a reduction in industrial reserves of minerals in the world economy, even at the current stage of their extraction. These tendencies should be taken into account in working out a strategy for development of the Russian mineral raw-material base.     

Causes of the famine among the rural population of the Sahelian zone of the Sudan

Taking the example of W Sudan, an analysis of the climatic incidents leading to the two recent famine disasters is made. On this natural background, the human side is investigated. Focus is directed towards the fragile economic structure of the famine-prone population groups. An early-warning system for famine in the Sahelian Zone is proposed taking grain production and storage, livestock development and the relationship between the prices of livestock and grain as major indicators.     

The Importance of the Precipitation and the Susceptibility of the Slopes for the Triggering of Landslides Along the Roads

In order to characterise the influence of the heavyrains on the observed landslides during the 1996–1997hydrological cycle, rainfall records for the last 100years are analysed from 104 stations in easternAndalusia. Regarding the amounts of rain recordedbetween October 1996 and March 1997 in the 104stations studied, 31 presented new all-time records;15 presented values that were 80–100% of thepre-1995 record; 49 stations, 80–50%; and 9stations, < 50%. A map has been devised of thesusceptibility of the materials through which thesouth-eastern Andalusian road network crosses,together with an inventory of the damage caused byinstability phenomena on banks and cuttings of theroad network during the winter of 1996–1997. Therelationships between the rainfall during the studyperiod, the damage caused to the road network and thesusceptibility of the materials affected are analysed.The results indicate that there is a clearcorrespondence between the rainfall recorded and thesusceptibility of the materials with the inventorieddamage. It is concluded that the widespread seriousdamage caused in early 1997 to the roads andsurrounding areas in the Alpujarra region and thecoast of the Province of Granada was mainly caused bythe extraordinarily heavy rains. However, considerablyless damage was observed where the susceptibility ofthe terrain is low, thus highlighting the extremeusefulness of terrain-susceptibility maps for riskprevention and territorial planning.     

塘口水电站坝基岩体透水性和渗漏问题分析

塘口水电站大坝基础座落在断层和裂隙较发育的龟裂纹灰岩上,岩体完整性差、透水性强,多年运行后,大坝灌浆廊道和排水廊道出现多处集中性漏水,为确保大坝安全和电站正常发电,根据渗漏性质和成因,采用对灌浆廊道补充帷幕灌浆,对排水廊道进行固结+帷幕+回填灌浆。通过灌浆处理后,效果良好,表明灌浆工程有效的将导致坝基渗漏的上下游的裂隙通道封闭,并顺利的经受了随后的汛期洪水考验,大坝安全得到保障。     

桩前溶洞对抗滑桩嵌固端稳定性影响物理模型试验研究

随着抗滑桩在工程中的大量运用,岩溶区抗滑桩嵌固端稳定性问题日益突出。当抗滑桩桩前存在溶洞时,溶洞在水平荷载下可能会发生变形,导致抗滑桩嵌固端失去稳定性。本文基于相似模型理论,建立了抗滑桩嵌岩段桩前存在两种不同形状溶洞（长轴方向水平和长轴方向竖直）试验模型。利用水平加载试验,针对椭圆形桩前溶洞对抗滑桩嵌固端的稳定性影响进行了研究,获得以下相关结论:溶洞长轴方向为竖直的试验模型嵌岩体变形分为弹性变形、裂纹稳定扩展及加速扩展三个阶段,加载到破坏荷载时溶洞顶板产生隆起破坏,最终形成的顶板处破坏断面与水平方向成45°左右;桩前溶洞长轴方向为水平的试验模型在达到溶洞长轴方向为竖直的模型破坏荷载增大一级荷载时,嵌固端保持整体稳定;相比于横长轴溶洞,纵长轴溶洞的存在更显著的降低了抗滑桩嵌固端的承载力,且溶洞顶板厚度越小,对抗滑桩嵌固端承载力影响越大,破坏形式为溶洞顶板受压破坏;基于极限平衡法,提出了桩前存在溶洞时嵌固端承载力验算方法,并对验算方法进行了验证。      

Calculation of the Inverse of the Covariance

In reservoir characterization, the covariance is often used to describe the spatial correlation and variation in rock properties or the uncertainty in rock properties. The inverse of the covariance, on the other hand, is seldom discussed in geostatistics. In this paper, I show that the inverse is required for simulation and estimation of Gaussian random fields, and that it can be identified with the differential operator in regularized inverse theory. Unfortunately, because the covariance matrix for parameters in reservoir models can be extremely large, calculation of the inverse can be a problem. In this paper, I discuss four methods of calculating the inverse of the covariance, two of which are analytical, and two of which are purely numerical. By taking advantage of the assumed stationarity of the covariance, none of the methods require inversion of the full covariance matrix.     

某高速公路下伏煤矿采空区稳定性分析

在论述某高速公路下伏砦脖煤矿采空区地质、采矿和工程地质特征的基础上, 进行了稳定性数值模拟分析, 定性与定量地分析与评价了该煤矿采空区的地表变形特征及稳定性。研究结果表明: 该煤矿采空区的变形尚未完成, 对拟建的高速公路将产生很大的危害, 必须采取相应的工程治理措施。