Mechanical Properties of Frozen Glacial Tills due to Short Periods of Thawing

Due to the warming climate, glacier retreat has left massive glacial tills in steep gullies; ice in the soil is prone to change phase resulting in the decrease of the ice strength and bonding of soil particles; collapse of thawing tills can lead to debris flows with disastrous consequences for geotechnical infrastructures. To improve our understanding of the mechanics of thawing glacial tills, we conducted unconsolidated–undrained direct shear tests on glacial tills from Tianmo gully on the southeastern Tibetan Plateau. Control specimens were not subjected to freeze–thaw action. A total of 648 specimens with three different dry densities, three initial water contents, and 18 thawing times were tested. Peak shear strength, peak stress to displacement ratio (0.857), and cohesion were the highest in frozen specimens. After a thawing time of 0.25 h, there was a marked decline in shear strength; maximum friction was 2.58, which was far below the value of cohesive strength. For thawing times of 0.25–4 h, peak strength varied little with thawing time, but cohesion decreased and internal friction angle increased with increasing thawing time. Our results indicate that thawing of the solid ice in the till during the initial phase of till thawing is the key control of peak till strength; the effect of ice on cohesion is greater during the initial phase of thawing and in loose tills. Moreover, frequent sediment recharge of gullies may be explained by the decrease of cohesion with increasing thawing time caused by short-term destruction of ice bonding.

Shrinkage properties of natural and diesel oil-contaminated fine soils from central Poland

The objectives of this paper are to provide a regional description of the shrinkage parameters of Neogene clays and glacial tills from central Poland; and to present the effects of hydrocarbon contamination on the shrinkage behaviour of soils. Forty samples containing from 19 to 90% clay-size particles were tested. The comparison of the three methods applied has indicated that the shrinkage limit values obtained by the BS 1377-2 method provide a greater margin of safety when used in the classification of expansive soils and yield the best matching in the analysis of the variability of the shrinkage limit in relation to other soil index parameters. A good correlation was found between the shrinkability index and the consistency index, which leads to a new classification of soils. The shrinkage tests of clean and diesel oil-contaminated samples revealed that contamination has a significant and irregular effect on the values of shrinkage parameters. For low degree of contamination the shrinkage limit of both soils had the lowest values and the volumetric shrinkage was maximum, and then with increasing ON content the shrinkage limit values tend to increase, while the volumetric shrinkage decreased.

Statistical and numerical analyses of pressuremeter tests in glacial tills

This study is performed on pressuremeter tests (PMT) in glacial tills based on comprehensive geotechnical investigation programs for a light rail transit project in the City of Toronto. The main objectives are to establish a correlation between SPT-N values and PMT parameters, and the Menard “α” factors for glacial tills. Currently, there are no such relationships available. So first, the pairs of PMT data and SPT-N values are collected at the same depth and test area. With these paired data, two linear correlation equations are established. Then, the numerical simulation is performed for PMTs in glacial tills by using finite element software, Plaxis 2D. The Mohr-Coulomb material model is used to model the different types of soil. The Menard “α” factor is suggested based on the best match between numerical prediction and field PMT. Ranges of SPT-N, EPMT and PL are also suggested for glacial tills.

Statistical and numerical analyses of pressuremeter tests in glacial tills

This study is performed on pressuremeter tests (PMT) in glacial tills based on comprehensive geotechnical investigation programs for a light rail transit project in the City of Toronto. The main objectives are to establish a correlation between SPT-N values and PMT parameters, and the Menard “α” factors for glacial tills. Currently, there are no such relationships available. So first, the pairs of PMT data and SPT-N values are collected at the same depth and test area. With these paired data, two linear correlation equations are established. Then, the numerical simulation is performed for PMTs in glacial tills by using finite element software, Plaxis 2D. The Mohr-Coulomb material model is used to model the different types of soil. The Menard “α” factor is suggested based on the best match between numerical prediction and field PMT. Ranges of SPT-N, EPMT and PL are also suggested for glacial tills.

Effect of short-term thawing on the mechanical properties of frozen glacial tills

<p>       Glacial tills are ubiquitous in periglacial mountains and can be destabilized as the main source materials of glacial debris flows due to atmospheric warming. In general, these surface hillslope materials are internally mixed with debris, ice, fluids etc., where the constituent fluids may experience prolonged freeze-thaw cycles. Although many studies including laboratory tests, field investigations and numerical simulations have been conducted to examine the formation mechanism relating to glacial debris flows in a variety of circumstances, largely unknown mechanisms impel destabilization of loose, frozen, or non-frozen glacial tills on steep slopes. In the present study, a series of simple direct-shear tests were performed to further investigate the shear behavior and strength properties of glacial tills subjected to short-term thawing. The samples with differing water contents and dry densities were firstly frozen under the same period but sheared with varying thawing intervals. The results directly show that (1) the stress-strain curves of all tested samples depict strain-softening characteristic to some extents, but the difference between peak and critical resistance decreases with increase of thawing intervals; (2) the dry density can enhance the shear resistance but the initiation water content may result in the decrease of shear resistance for the relative denser samples; (3) the shear strength profiles manifest that the internal friction angle increases but the cohesion decreases with increase of thawing intervals. These laboratory results suggest that the frozen water content can have measurable effect on the strength properties of glacial tills in shear, and the phase transition process from ice to water may affect the water distribution as a consequence of thawing interval. It should be mentioned that the results preliminarily provide fundamental information regarding shear strength properties of glacial tills by considering short-term thawing effect, and further study will be needed to examine the shear behavior of glacial tills under other potential factors.</p>

Rivers Try Harder. Reversed “Differential Erosion” as Geological Control of Flood in the Large Fluvial Systems in Poland

We study cross-sections on the Detailed Geological Map of Poland (SMGP) to find a geologic and geomorphic pattern under river valleys in Poland. The pattern was found in 20 reaches of the largest Polish rivers (Odra, Warta, Vistula, Narew, and Bug) located in the European Lowland, in the landscape of old (Pleistocene, Saalian) glacial high plains extending between the Last Glacial Maximum (LGM) moraines on the North and the Upland on the South. The Upland was slightly folded and up-faulted during Alpine orogeny together with the thrust of Carpathian nappes and the uplift of Tatra Mts. and Sudetes. The found pattern is an alluvial river with broad Holocene floodplain and the channel developed atop the protrusion of bedrock (Jurassic, Cretaceous limestones, marlstones, sandstones) or non-alluvial, cohesive, overconsolidated sediments resistant to erosion (glacial tills, lacustrine or “ice-dammed lake” clays) of Cenozoic (Paleogene, Neogene, Quaternary—Elsterian). We regard the sub-alluvial protrusion as the limit of river incision and scour. It cannot be determined why the river flows atop these protrusions, in opposition to “differential erosion”, a geomorphology principle. We assume it is evidence of geological flood control. We propose an environmental and geomorphological framework for the hydrotechnical design of instream river training.

Evidence for a late glacial advance near the beginning of the Younger Dryas in western New York State: An event postdating the record for local Laurentide ice sheet recession

Widespread evidence of an unrecognized late glacial advance across preexisting moraines in western New York is confirmed by 40 14C ages and six new optically stimulated luminescence analyses between the Genesee Valley and the Cattaraugus Creek basin of eastern Lake Erie. The Late Wisconsin chronology is relatively unconstrained by local dating of moraines between Pennsylvania and Lake Ontario. Few published 14C ages record discrete events, unlike evidence in the upper Great Lakes and New England. The new 14C ages from wood in glacial tills along Buttermilk Creek south of Springville, New York, and reevaluation of numerous 14C ages from miscellaneous investigations in the Genesee Valley document a significant glacial advance into Cattaraugus and Livingston Counties between 13,000 and 13,300 cal yr B.P., near the Greenland Interstadial 1b (GI-1b) cooling leading into the transition from the Bölling-Alleröd to the Younger Dryas. The chronology from four widely distributed sites indicates that a Late Wisconsin advance spread till discontinuously over the surface, without significantly modifying the preexisting glacial topography. A short-lived advance by a partially grounded ice shelf best explains the evidence. The advance, ending 43 km south of Rochester and a similar distance south of Buffalo, overlaps the revised chronology for glacial Lake Iroquois, now considered to extend from ca. 14,800–13,000 cal yr B.P. The spread of the radiocarbon ages is similar to the well-known Two Creeks Forest Bed, which equates the event with the Two Rivers advance in Wisconsin.

Supplemental Material: Evidence for a late glacial advance near the beginning of the Younger Dryas in western New York State: An event postdating the record for local Laurentide ice sheet recession

An extended discussion relating to the identification of glacial tills at the critical sites in this investigation is provided as a Supplemental File to eliminate any concerns that the exposures might be landslide debris as opposed to primary glacial till. The supplement also speculates as to why the advance in western New York State may not have been obvious in the extensive research published for the St. Lawrence Valley.

Supplemental Material: Evidence for a late glacial advance near the beginning of the Younger Dryas in western New York State: An event postdating the record for local Laurentide ice sheet recession

An extended discussion relating to the identification of glacial tills at the critical sites in this investigation is provided as a Supplemental File to eliminate any concerns that the exposures might be landslide debris as opposed to primary glacial till. The supplement also speculates as to why the advance in western New York State may not have been obvious in the extensive research published for the St. Lawrence Valley.