共查询到20条相似文献，搜索用时 31 毫秒
1.
Bally, R.J., 1988. Some specific problems of wetted loessial soils in civil engineering. Eng. Geol., 25: 303–324. Loessial soils, wetted above the limit of collapsibility, remain in the category of difficult foundation grounds. Some case histories are presented herein: surpassing soil bearing capacity and non-stabilized settlements of buildings after initially dry loess wetting; slow but nondamped settlements or damped but great and, eventually, non-uniform settlements of structures erected on wet loess; supplementary settlements by water level lowering in loessial ground; great settlements of deep foundations passing through the collapsible loess to the underlaying wet but noncollapsible loess. Research on wetted loess performed in the laboratory (oedometer, triaxial) or in situ (full-scale experiments or real constructions) have emphasized the dependence of the soil structural resistance, deformability (compressibility and deformation under constant volume) and final resistance on both the moisture content or stress-state and on their history; the depth propagation of the active zone of surface loadings on wetted loess is different from that of the linear elastic theory; some suggestions to estimate the depth of the active zone are presented. The usual foundation systems on wetted loessial grounds, or in their vicinity, adopted in Romania include: loessial or gravel cushions; surface compaction (very efficient results of intensive dynamic compaction); foundation “stamping” or loessial ground “reinforcing”. It is recommendable to take into consideration: surveyed wetting under construction until maximum moisture content of the loessial ground; in situ columns of stabilized loess; the efficiency of geotextiles for filter-drainage and antierosional functions in loessial soils. 相似文献
2.
Rendell, H.M., 1988. Comparison between naturally consolidated and laboratory consolidated loess. Eng. Geol., 25: 229–233. Preliminary results of a comparison between naturally consolidated and laboratory consolidated loess are presented. Mercury intrusion porosimetry was used to compare nominal pore size distributions of loess before and after laboratory consolidation with those for samples that had undergone “natural” compaction. Although changes in density appear to be modelled well by the oedometer tests, the pore size distributions approach, they do not mirror exactly those for naturally consolidated loess. 相似文献
3.
Derbyshire, E. and Mellors, T.W., 1988. Geological and geotechnical characteristics of some loess and loessic soils from China and Britain: a comparison. Eng. Geol., 25: 135–175. Loess and loessic deposits cover some 630,000 km2 of the surface of mainland China, the Loess Plateau of Shanxi, Shaanxi, Gansu and Ningxia being the type region of this formation. Loess thickness generally exceeds 100 m over large areas of the Loess Plateau, the maximum recorded thickness being 335 m in eastern Gansu Province near the city of Lanzhou. In Britain loess and loessic deposits form part of a group of materials collectively known as “brickearth”. They occur predominantly as sporadic accumulations in the southeast of England and rarely attain a thickness of more than four metres. Despite their geographical separation, the deposits from China and Britain have a remarkable similarity in some of their physical and geotechnical characteristics. Samples from both locations have been examined and tested in the laboratory and the results are presented. The scope of the testing programme involved mineralogical analyses, soil microfabric studies using a scanning electron microscope, index testing including plasticity, grading and density measurements and the investigation of the compressibility characteristics of the soils with particular reference to their susceptibility to collapse. A soil structure model based on scanning electron microscope studies is presented and discussed in relation to the perceived mode of formation of the soils and their postdepositional history. 相似文献
4.
Buraczynski, J., 1988. Lithological, mineralogical and geochemical characteristics of loess in the Rhinegraben. Eng. Geol., 25: 201–208. Lithological properties of loesses have considerable practical significance. Together with the origin of the material and the genetic–facial variability they are characterised by granulometry, chemical and mineral composition and textural features. In particular, the clay fraction and carbonate content point to the fraction and carbonate content point to the geotecnical properties of loesses. 相似文献
5.
Loess on the high mountains of northwestern China is largely controlled by the topographic features, distributed mainly on the northern slopes of the Tianshan and Kunlun Mountains as well as in the Ili Valley (between the northern and central Tianshan ranges). Loess distributed in different regions has different ages, with the oldest (early Pleistocene) loess occurring in the Ili Valley. Geochemical, mineralogical and granulometric analyses demonstrate that the loess in the three different regions has different provenance. The loess on the northern Tianshan and Kunlun Mountains is mainly derived from the Junggar and Taklimakan Deserts, respectively, whereas the loess in the Ili Valley is derived mainly from the Sary–Ishikotrau Desert located in the Republic of Kazakhstan. However, these deserts serve mostly as holding areas for the silts rather than original source regions. The production of the silt-sized particles is mainly associated with glacial abrasion and tectonic-induced rock denudation. Thus, the loess in the studied regions can be described as “mountainous” loess rather than simply “glacial” loess or “desert” loess. It is unlikely that the mechanisms of loess formation are the same in different regions, given their dependence on specific geomorphological conditions and associated processes. 相似文献
6.
The tectonic setting of British Columbia (BC) differs from classic diamond-bearing intracratonic regions such as the Northwest Territories and South Africa. Nevertheless, several diamond occurrences have been reported in BC. It is also known that parts of the province are underlain by Proterozoic and possibly Archean basement. Because the continents of today are composites of fragments of ancient continents, it is possible that some of the regions underlain by old crystalline basement in eastern British Columbia were associated with a deep crustal keel. The keel may have predated the break-up of the early Neoproterozoic supercontinent called Rodinia and was preserved possibly until the Triassic. Some of these old continental fragments may have been displaced relative to their position of origin and dissociated from their keel, or the keel may have since been destroyed. Such fragments represent favourable exploration grounds in terms of the “Diamondiferous Mantle Root” model (DMR model) if they were intersected by kimberlites or lamproites prior to displacement or destruction of their underlying deep keel. Therefore, extrapolation of fragments of the diamond-bearing Precambrian basement from the Northwest Territories or Alberta to BC provides a sufficient reason for initiating reconnaissance indicator mineral surveys. The “Eclogite Subduction Zone” model (ES model) predicts formation of diamonds at lower pressure (i.e., depth) than required by the DMR model in convergent tectonic settings. Although not proven, this model is supported by thermal modeling of cold subduction zones and recent discoveries of diamonds in areas characterized by convergent tectonic settings. If the ES model is correct, then the parts of BC with a geological history similar to today's “cold” subduction zones, such as Honshu (Japan), or to continental collision zones, such as Kokchetav massif (Kazakhstan) and the Dabie–Sulu Terrane (east central China), may be diamondiferous. The terranes where geological evidences suggest an ultrahigh pressure (UHP) metamorphic event followed by rapid tectonic exhumation (which could have prevented complete resorption of diamonds on their journey to the surface) are worth investigating. If UHP rocks were intercepted at depth by syn- or post-subduction diamond elevators, such as kimberlites, lamproites, lamprophyres, nephelinites or other alkali volcanic rocks of deep-seated origin, the diamond potential of the area would be even higher. 相似文献
7.
Gao, G., 1988. Formation and development of the structure of collapsing loess in China. Eng. Geol., 25: 235–245. It is well known that in China the regional variations in microstructure of loess are in phase with the overall tendency for collapsibility, gradually decreasing from the northwest to the southeast. These differences are consistent with variations in climatic conditions. This indicates that the structure of collapsing loess is closely related to the climatic condition and geological environment. Based on the microstructure analyses, it can be assumed that the formation and development of the structure of collapsing loess in China has undergone five stages: the loessization stage, the formation stage, the development stage, the degeneration stage and the clayization stage. The five stages of loess regularly exist in different regions of the Loess Plateau. This also shows that under the modern climatic condition the collapsing loess in the northwest of the Loess Plateau in China is still developing. However, the feature of collapsing loess is gradually disappearing in the southeast of the Loess Plateau. 相似文献
8.
Loesses of the Lower Mississippi Valley (LMV) are world-famous. Sir Charles Lyell (1847), Hilgard (1860), Stafford (1869), Call (1891) and Mabry (1898), thought the LMV loess was a single water deposit although “double submergence” was noted by Call (1891) and Salisbury (1891). Shimek (1902) and Emerson (1918) recognized LMV loess as a wind deposit which came from the valley. Although wind-deposited loess gained wide acceptance, Russell (1944a) published his controversial theory of “loessification” which entailed weathering of backswamp deposits, downslope movement and recharge by carbonates to form loess. Wascher et al. (1947) identified three LMV loesses, mapped distributions and strongly supported eolian deposition. Leighton and Willman (1950), identified four loesses and supported eolian deposition as did Krinitzsky and Turnbull (1967) and Snowden and Priddy (1968), but Krinitzky and Turnbull questioned the deepest loess. Daniels and Young (1968) and Touchet and Daniels (1970) studied the distribution of loesses in south-central Louisiana. West et al. (1980) and Rutledge et al. (1985) studied the source areas and wind directions which deposited the loesses on and adjoining Crowley's Ridge. B.J. Miller and co-workers (Miller et al., 1985, 1986, Miller and Alford, 1985) proposed that the Loveland Silt was Early Wisconsin rather than Illinoian age and advanced the name Sicily Island loess. They proposed the underlying loess was Illinoian and advanced the name Crowley's Ridge. We termed the loesses, from the surface downward, Peoria Loess, Roxana Silt, Loveland/Sicily Island loess, Crowley's Ridge Loess and Marianna loess. Researchers agree that the surfical Peoria Loess is Late Wisconsin and the Roxana Silt is Late to Middle Wisconsin, but little agreement exists on the age of the older loesses. Pye and Johnson (1988) proposed Early Wisconsin for the Loveland/Sicily Island. McKay and Follmer (1985) suggested this loess correlated with a loess under Illinoian till. Clark et al. (1989) agreed on Crowley's Ridge, but suggested the Loveland/Sicily Island loess on Sicily Island was older. Mirecki and Miller (1994) and Millard and Maat (1994) suggested an Illinoian age for the Loveland/Sicily Island loess. Miller and co-workers suggested, as did Pye and Johnson (1988), an Illinoian age for the Crowley's Ridge loess. McKay and Follmer (1985) suggested it correlated with a loess under “Kansan” till. Stratigraphy indicates the Marianna is the older of the five loesses. Researchers identified loess on both the east and west side of the LMV as well as on higher terraces within the valley. Many researchers assumed unaltered loesses were commonly yellowish brown, and silts or silt loams (West et al., 1980; Miller et al., 1986). The nonclay fraction of unweathered LMV loesses was dominated by quartz followed * Corresponding author. by carbonates, mainly dolomites, followed by feldspars, and micas. Clays were dominated by montmorillonite followed by micaceous minerals, kaolinite and vermiculite (Miller et al., 1986). Soils in the Crowley's Ridge loess are most developed, followed by the soils in the Loveland/Sicily Island which are more developed than the modern soils in the Peoria Loess. Soils in the Roxana and Marianna loesses are least developed and the Farmdale Soil of the Roxana is the weaker of the two (Miller et al., 1986). There is certainly overlapping range in the degree of soil development in the various loesses. 相似文献
9.
Sweeney, S.J. and Smalley, I.J., 1988. Occurrence and geotechnical properties of loess in Canada. Eng. Geol., 25: 123–134. There are modest amounts of loess in Canada. As in most of North America it is probably produced by a combination of glacial grinding and cold weathering. Atterberg limits of Canadian loess are comparable with reference samples from the U.S.A. A deposit at Kamloops in British Columbia suffers a 15% linear collapse when loaded and wetted. Earlier estimates that the deposit was more than 100 m thick are probably in error; only the top part of the sedimentary deposit is loess. 相似文献
10.
The deep-seated landslide located at the intersection of the Gradenbach and Möll valleys near Döllach, Austria, has been the target of many previous investigations [Kronfellner-Kraus, G., 1980. Neue Untersuchungsergebnisse in Wildbächen — Der Talzuschub in Abhängigkeit von Niederschlägen. Int. Symp. Interpraevent Bad Ischl 1: 179–192; Weidner, S., Moser, M., Lang, E., 1998. Influence of hydrology on sagging of mountain slopes (“Talzuschübe”) — New results of time series analysis. 8th International IAEG Congress, Vancouver, Canada, Balkema, Rotterdam, 1259–1266; Weidner, S., 2000. Kinematik und Mechanismus tiefgreifender alpiner Hangdeformationen unter besonderer Berücksichtigung der hydrologischen Verhältnisse. Dissertation, Friedrich–Alexander-Universität Erlangen–Nürnberg, 246.]. In this paper, photogrammetric, GPS and geophysical data have been utilized to derive a constraint on the kinematics of the sagging process. The photogrammetric models have been based on aerial photographs from 1962 and 1996. Displacement vectors of about 50 individual characteristic points have been determined; these clearly show the area of the sagging slope. From 1999 to 2004, eleven GPS campaigns have been carried out, yielding very accurate displacement vectors at four monitoring points. Information about the internal structure of the slope was determined using seismic surveys. The displacements observed by photogrammetry and GPS have shown a rather uniform movement of the whole sagging slope, with a slight longitudinal compression of 0.6%. In order to extend the kinematic consideration to 3D, a special form of the equation of continuity (conservation of mass) has been applied to the 1962–1996 photogrammetric data, together with the cross-sections derived from the seismic data. The average velocities through cross-sections have been calculated by integrals of the mass-balance above and below these cross-sections. Changes of the total rock mass, due to accumulation and especially to erosion, as well as an overall compaction of 1.5% between 1962 and 1996, have been considered. The calculated average velocities through a cross-section and the surface velocities independently determined by photogrammetry agree within an uncertainty of 15%. The results indicate a block movement with shear concentration at the basal sliding surface. 相似文献
11.
Feda, J., 1988. Collapse of loess upon wetting. Eng. Geol., 25: 263–269. The results of a series of tests conducted on loess samples from one locality, tested under the condition of confined and hydrostatic compression are presented and analyzed. The samples are of different water content and saturation and display different degrees of collapse upon wetting. Based on the experimental results, a collapse surface is depicted and the phenomenon hypothetically generalized for other types of collapse. The structural collapse causes the mechanical behaviour of samples to be more uniform. The effect of the hydrostatic stress conditions is reflected in the tendency of samples to deform isotropically, although, originally, they are anisotropic. The phenomenon of collapse cannot be explained by the principle of effective stresses. 相似文献
12.
利用动三轴试验系统,对兰州、固原、潼关地区饱和原状黄土进行了液化试验。通过对饱和黄土液化的动应力、动应变和动孔压发展特点等问题的对比和分析,研究了我国不同地区饱和原状黄土的液化特性。研究表明:(1)黄土液化有其自身的特点,一旦发生液化,抗液化强度将迅速丧失;(2)黄土的区域性结构特性对黄土液化的影响非常明显,表现为不同地区、不同结构的黄土,其液化强度是不同的。而不同地区间黄土的干密度等物性指标对黄土液化的影响远小于区域性结构特性的影响;(3)基于黄土的结构破坏特性和液化特性,给出了饱和黄土的液化破坏应变标准。 相似文献
13.
我国适合露天开采的煤田,主要分布在西部及西北部的黄土高原地区。黄土基底构筑物在加载过程中,曾出现过某些惨痛的工程教训。基于黄土基底排土场形成后黄土底工程性质演化规律及失稳机制分析,提出其边坡稳定的研究方法,对黄土高原地区煤炭资源开发建设具有重要的理论与实际意义。 相似文献
14.
Holocene loess in the middle reaches of the Yellow River can be subdivided into three formations, which are composed commonly of upper loess and lower dark loessial soil (a kind of paleosol): the Xifeng Formation of Late Holocene, the Longxi Formation of Middle Holocene and the Luochuan Formation of Early Holocene. The layers of dark loessial soil at similar stratigraphic levels in different localities show such a change in age that samples from south are older than those from north, indicating a northward shift of the climate belt during pedogenesis. 相似文献
15.
For the Xiashu loess–palaeosol sequence in Nanjing, China, further to our work on the cyclic variability in its chemical composition and swelling-shrinkage properties [Xia, J., Huang, G.L., Liu, Z. T., Chen, X.M., 2007. Cyclic variability in chemical composition and swelling–shrinkage properties of the Xiashu loess stratum near Nanjing, China. Pedosphere 17 (5), 666–672.], this paper studies the cyclic variability in its microstructure and physico-mechanical properties and the corresponding influence on its engineering behaviour for geotechnical and geological practices. In addition, the cyclic variability in the soil's grain-size distribution and geochemical characteristics is compared with that of the loess–palaeosol sequences at two other sites in China, indicating a geographical pattern of cyclic variation of the sequences. 相似文献
16.
High-pressure (HP) metamorphic rocks, including garnet peridotite, eclogite, HP granulite, and HP amphibolite, are important constituents of several tectonostratigraphic units in the pre-Alpine nappe stack of the Getic–Supragetic (GS) basement in the South Carpathians. A Variscan age for HP metamorphism is firmly established by Sm–Nd mineral–whole-rock isochrons for garnet amphibolite, 358±10 Ma, two samples of eclogite, 341±8 and 344±7 Ma, and garnet peridotite, 316±4 Ma. A prograde history for many HP metamorphic rocks is documented by the presence of lower pressure mineral inclusions and compositional zoning in garnet. Application of commonly accepted thermobarometers to eclogite (grt+cpx±ky±phn±pg±zo) yields a range in “peak” pressures and temperatures of 10.8–22.3 kbar and 545–745 °C, depending on tectonostratigraphic unit and locality. Zoisite equilibria indicate that activity of H2O in some samples was substantially reduced, ca. 0.1–0.4. HP granulite (grt+cpx+hb+pl) and HP amphibolite (grt+hbl+pl) may have formed by retrogression of eclogites during high-temperature decompression. Two types of garnet peridotite have been recognized, one forming from spinel peridotite at ca. 1150–1300 °C, 25.8–29.0 kbar, and another from plagioclase peridotite at 560 °C, 16.1 kbar. The Variscan evolution of the pre-Mesozoic basement in the South Carpathians is similar to that in other segments of the European Variscides, including widespread HP metamorphism, in which P–T–t characteristics are specific to individual tectonostratigraphic units, the presence of diverse types of garnet peridotite, diachronous subduction and accretion, nappe assembly in pre-Westphalian time due to collision of Laurussia, Gondwana, and amalgamated terranes, and finally, rapid exhumation, cooling, and deposition of eroded debris in Westphalian to Permian sedimentary basins. 相似文献
17.
Grabowska-Olszewska, B., 1988. Engineering-geological problems of loess in Poland. Eng. Geol., 25: 177–199. In Poland, loess covers are limited to a latitudinal belt in the southern part of the country. The covers vary from 2 to 30 m in thickness and the loesses are developed in three major facies: eolian, deluvial and alluvial. Stratigraphically, they represent four major horizons correlated with the Vistulian (Würm) Glaciation and some older ones. The paper presents characteristics of granulometric, mineral and chemical compositions with reference to origin, facies and stratigraphic position of these soils, as well as their lithofacies classification. The classification gives the basis for analysis of local and regional variability in engineering-geological properties of the loess. 相似文献
18.
The interpretation of newly released commercial 2D reflection seismic data in the Kattegat area, Denmark, has provided us with a better understanding of the Palaeozoic tectonic processes along the Tornquist Fault Zone. A Base Palaeozoic time structure map, a Lower Palaeozoic TWT isopach map, a “true” Lower Palaeozoic TWT isopach map, an Upper Carboniferous/Lower Permian syn-rift TWT isopach map, a Top pre-Zechstein time structure map and a Zechstein combined TWT isopach and Palaeogeography map have been generated. The uniform Lower Palaeozoic sequence thickness in the Kattegat, both inside and outside the Tornquist Zone indicates only minor lateral movements if any, whereas the extensive Upper Silurian sequence, increasing in thickness to the north, indicates a relatively fast regional subsidence. The Base Palaeozoic time structure map and the Late Palaeozoic syn-rift isopach map show a clear Late Palaeozoic extension in the area. The syn-rift isopach map, in combination with the time-equivalent opening of the Skagerrak graben at right angles to the Tornquist Zone in the Kattegat, indicates that this extensional tectonic event had a dextral slip component. Measurements on internal extensional faults in the Tornquist Zone, give a minimum right-lateral displacement of 10.4 km. The footwall blocks were deeply eroded during the Early Permian rifting, and at Zechstein times the area became a peneplane. The Tornquist Zone was later exposed to several tectonic phases, where dextral slip played a role, indicated by the “push up” and “pull down” structures caused by restraining and releasing bends of the Børglum Fault. The dextral displacement along the Børglum Fault since the beginning of the Permian is in the order of 5–7 km based on the displacement of a Lower Palaeozoic local depocentre. Early Permian depocentres and faults, which gives a total amount of right-lateral displacement since the Early Palaeozoic in the order of 15–20 km. The continuously repeated tectonic episodes along the Tornquist Zone throughout most of the Phanerozoic, show that the zone was easily reactivated, implying deep-seated basement faults. The Tornquist Zone can be seen as a “buffer zone”, between continental blocks, whenever changes in the regional stress field are induced. 相似文献
19.
Sr–Nd isotopic analyses on some mantle xenolith samples from the Northern, Southern and Austral Andean volcanic zones exhibit radiogenic Sr enrichment without dramatic changing of the Nd isotopic composition. This anomalous effect (Sr–Nd decoupling) makes these samples plot displaced to the right side of the “mantle array” trend (here called the “MORB–OIB–BSE trend”) in the 87Sr/ 86Sr vs. 143Nd/ 144Nd isotopic diagram. Such behavior reflects processes that took place in the mantle and can be related to: i) the mixture of a depleted mantle and an enriched source (enriched mantle II—EMII); ii) the mixture of a depleted mantle and a mixture of mantle-derived and slab-derived melts; and iii) a chromatographic process that occurs during the percolation of a metasomatic agent through the mantle. 相似文献
20.
Lutenegger, A.J. and Hallberg, G.R., 1988. Stability of loess. Eng. Geol., 25: 247–261. The natural stability of loess soils can be related to fundamental geotechnical properties such as Atterberg limits, water content and void ratio. Field observations of unstable conditions in loess deposits in the upper midwest, U.S.A. show relationships between instability and the in situ moisture content and the liquidity index of the loess. Unstable loess can attain natural moisture contents equal to, or greater than, its liquid limit. Implications of these observations for applied engineering works are described. 相似文献
|
