Loess-like Loams Research Articles

Investigation of the bearing capacity of pyramidal piles

1. Pyramidal piles work most effectively not in the zone of their maximum cross section but beginning with a depth of 0.5–1 m from the ground surface, and therefore it is economically advisable to provide for a prismatic part in the upper end of the pyramidal pile. 2. An increase of bearing capacity of the pyramidal pile in comparison with prismatic is achieved as a consequence of the occurrence in the soil during their penetration of a passive earth pressure\(\sigma _{pa_2 } \) which provides additional skin friction. 3. The passive earth pressure and consequently the additional resistance of the pyramidal pile due to the arising thrust do not depend on depth, and within the length of the pile they vary inversely proportional to the size of the side of the pile cross section. 4. The additional skin friction of the pyramidal pile is greater, the greater the modulus of deformation of the soil and its angle of internal friction. 5. It is most advisable to use pyramidal piles at sites composed of soils homogeneous depthwise or in the case of a decrease of deformation and strength characteristics with depth. The maximum effect from the use of pyramidal piles can be obtained only in soils having relatively high moduli of deformation and angles of internal frictions, i.e., in sands, loamy sands, loams with a small plasticity index, loesslike loams, and loess. Pyramidal piles are not effective in clays having a high plasticity, whose strength properties depend mainly on cohesion.

Radiocarbon dates and late-Quaternary stratigraphy from Mamontova Gora, unglaciated central Yakutia, Siberia, U.S.S.R.

A fine exposure of perennially frozen ice-rich silt and associated flora and vertebrate fauna of late-Quaternary age exists at Mamontova Gora along the Aldan River in central Yakutia, Siberia, U.S.S.R. The silt deposit caps a 50-m-high terrace and consists of three units. An upper layer 1–2 m thick overlies a 10–15-m-thick brownish to black silt layer. The lower silt layer is greenish to gray and about 15 m thick. All the silt is well sorted with 60% of the particles falling between 0.005 and 0.5 mm in diameter and is generally chemically and mineralogically homogeneous. The middle unit contains may extinct vertebrate mammal remains and ice wedges. The lower unit contains little vegetation and no ice wedges. The silt is widespread and exists as a loamy blanket on terraces at various elevations on both sides of the lower Aldan River. The origin of the silt blanket of late-Quaternary age in central Yakutia has long been controversial. Various hypotheses have been suggested, including lacustrine and alluvial, as well as frost-action origins. It is sometimes referred to as loess-like loam. Péwé believes the silt at Mamontova Gora is loess, some of which has been retransported very short distances by water. The silt probably was blown from wide, braided, unvegetated flood plains of rivers draining nearby glaciers. The silt deposits are late Quaternary in age and probably associated with the Maximum glaciation (Samarov) and Sartan and Syryan glaciations of Wisconsinan age. On the basis of biostratigraphy, 10 radiocarbon dates, and their relation to the nearby glacial record, it is felt that the upper unit at Mamontova Gora is Holocene and the middle unit is Wisconsinan. The youngest date available from the middle unit at this particular location is 26,000 years. Dates greater than 56,000 years were obtained in the lower part of the middle unit. The lower unit is definitely beyond the range of radiocarbon dating and probably is older than the last interglacial. The sediment, fauna, ice wedges, stratigraphy, and age of perennially frozen slit deposits in central Alaska are remarkably similar to those of the deposits exposed in central Yakutia. Both areas consist of unglaciated rolling lowlands and river terraces surrounded by high mountains that were extensively glaciated in Pleistocene time. The glaciers extended from the high mountains to the edges of the ranges. In both regions, extensively braided, silt-charged rivers drained the mountains and flowed through the lowlands on their way to the sea. It follows that there should be a similar late-Quaternary history.

Geographical zonality of frozen ground formation

Abstract The zonal pattern of frozen ground formation (cryolithogenesis) in northern Eurasia derives from a complex set of factors, including latitude, continentality, crustal movements, lithology and the historical movement of natural zones during the Pleistocene and Holocene. The author defines a zonal pattern by limiting himself to the varying characteristics of three typical genetic layers in superimposed (cryoepigenetic) frozen ground consisting of unconsolidated sediment. The three layers (from top to bottom) are distinguished by (a) frost weathering (cryoeluvial processes); (b) by active frost metamorphism (cryodiagenetic processes); (c) by passive frost metamorphism. The products of frost weathering in the surface layer are loesslike mantle loams; active metamorphism is associated with polygonal wedge ice, pingo ice and finally textured segregated soil ice; passive metamorphism is associated with sill‐like sheet ice and coarsely textured pore ice. Mean annual temperature and winter temperature gra...

Comparative micromorphology of soddy-podzolic soils derived from loamy moraine and non-calcareous loesslike loam

Soddy-podzolic soils developed on different loamy parent materials possess several common fabric features which can be regarded as characteristic of this soil type. These features are: poor aggregation, considerable amounts of coarse plant residues in different (mainly weak and medium) stages of decomposition, predominance of brown-coloured peptized humus mainly bound up with sesquioxides, abundant clayey and silty illuviation cutans appearing in the A 2 or A 2 horizons where they show the strongest disruption and incorporation into the s-matrix, and different forms of biological segregations of iron and manganese hydroxides. Some differences in fabric of these soils are connected with mineralogical and physical properties of parent material.

Experience with chemical stabilization of saturated loesslike loams in the foundation beds of existing structures

As seen from the data presented in this article, the method of gas-silicatization with preliminary activation of the soil not only permits pumping the sodium silicate into the saturated loam without disturbing its structure, but also results in uniform distribution of the grout through the mass being stabilized and ensures a sufficiently high strength, which is important for soils in the foundation beds of buildings under complex hydrogeologic conditions.