Quasi-overconsolidation and creep phenomena in shallow marine and estuarine organo-calcareous silts, Fiji

1995 ◽  
Vol 32 (1) ◽  
pp. 89-105 ◽  
Author(s):  
Graham G. Shorten
Keyword(s):  
Organic Content ◽  
Strain Rates ◽  
Radiocarbon Dates ◽  
Secondary Compression ◽  
Compression Creep ◽  
Preconsolidation Pressure ◽  
Stress Dependent ◽  
Oedometer Tests ◽  
Foundation Failure

Nearshore, estuarine deposits of Holocene organo-calcareous silt provide the most common setting for foundation failure in Fiji. Creep is implicated in long-term settlement. Although the geological history indicates the deposits should be normally consolidated throughout, there is increasing apparent overconsolidation towards the surface. This finding is contrary to what might be expected if delayed compression alone was operating. The phenomenon appears to be related instead to organic content and may be affected by strain rates during consolidation. Oedometer tests extending over 7 months indicate the rate of volume change due to creep follows the Singh–Mitchell relationship, but calculation of secondary compression from radiocarbon dates suggests that the very long-term rate is higher than might be expected. Creep appears to be stress dependent, at least below the preconsolidation pressure, in common with other marine sediments. Key words : silt, organic, preconsolidation pressure, overconsolidation ratio, secondary compression, creep, radiocarbon dating.

Creep Characteristics of Organic Soft Clay Soil Using Large–Scale Model

2021 ◽  
Author(s):  
Raid Al-Omari ◽  
◽  
Mohammed Fattah ◽  
Mudhafar Hameedi ◽  
◽  
...  
Keyword(s):  
Large Scale ◽  
Large Fraction ◽  
Soft Clay ◽  
Laboratory Data ◽  
Soil Surface ◽  
Organic Content ◽  
Scale Model ◽  
Secondary Compression ◽  
Large Scale Model

The long-term settlements in organic clay can create a kind of an engineering challenge that appear in most facilities design and construction in areas with deep deposits of soft clay. Peat ground is widely distributed throughout the southern part of Iraq. Peat contains a large amount of organic matter and has a very high natural water content. Three soil samples were collected from depths of 1.5 m, 2.5 m, and 3.5 m, below the soil surface in Halfaya oilfield, which lies east of Missan governorate southern Iraq. A series of tests were conducted in a large-scale model using a plate footing and considering three different percent of organic content. The percent of secondary settlement found is dependent on the stress level applied. A large fraction of the total settlement may be due to secondary compression. The assumption of a constant coefficient of secondary compression, Cα, may not be valid for a long-term settlement of peats. Laboratory data indicate that Cα generally increases with time. Thus, settlement predictions using constant Cα may underestimate field settlement.

Water-level fluctuations in Lake Ontario over the last 4000 years as recorded in the Cataraqui River lagoon, Kingston, Ontario

1990 ◽  
Vol 27 (10) ◽  
pp. 1330-1338 ◽  
Author(s):  
Robert W. Dalrymple ◽  
John S. Carey
Keyword(s):  
Great Lakes ◽  
Water Level ◽  
Lake Ontario ◽  
Organic Content ◽  
Water Level Fluctuations ◽  
Great Lakes Basin ◽  
Radiocarbon Dates ◽  
Western Great Lakes ◽  
Low Levels

The modern sediments in the Cataraqui River lagoon and marsh (Kingston, Ontario) consist of mixtures of organic material and clayey silts, the organic content of which increases as water depth decreases; gyttjas are accumulating in the deeper water parts of the lagoon, whereas peat is the dominant sediment in the very shallow water portion of the lagoon (< 0.7 m) and in the adjacent marsh. Cores show that one partial (modern) and two complete depositional cycles (gyttja passing upwards into peat) have formed within the last 4000 years. The contact between cycles (gyttja over peat) is abrupt. These cycles are interpreted as resulting from fluctuations in the level of Lake Ontario about the long-term rising trend. Radiocarbon dates show that relatively low levels prevailed from 4100 to 3300 BP and from 2300 to 1900 BP; rapid rises in water level, which are indicated by the abrupt contact between cycles, occurred at 3300–3100 BP and some time between 2000 and 1500 BP. These water-level changes are synchronous with those shown by other studies in Lake Ontario and with century-scale paleoclimatic events. The high stands correlate with wet periods, and perhaps also with warm periods in the eastern part of the Great Lakes basin, but an inverse relationship between precipitation and temperature in the western Great Lakes suggests that the Great Lakes basin does not respond uniformly to climatic changes.

Investigation of the long-term tunnel settlement mechanisms of the first metro line in Shanghai

2013 ◽  
Vol 50 (6) ◽  
pp. 674-684 ◽  
Author(s):  
C.W.W. Ng ◽  
G.B. Liu ◽  
Q. Li
Keyword(s):  
Soft Clay ◽  
Groundwater Pumping ◽  
Secondary Compression ◽  
Compression Creep ◽  
Subsurface Soil ◽  
Sandy Aquifer ◽  
Sandy Aquifers ◽  
Large Tunnel ◽  
Soil Compression

The long-term performance of a metro tunnel is obviously a major concern for the authority and designers responsible for its construction, as excessive tunnel settlement would affect the serviceability and safety of the entire metro system. In this study, measured long-term settlement of the 16.4 km long tunnel of Shanghai Metro Line 1 from 1994 to 2007 (a period of 12.5 years) is reported and discussed. The tunnel settlement was continuous with time, and reached a maximum of 288 mm. To assist in the investigation of the mechanisms of long-term tunnel settlement, records of groundwater pumping and subsurface soil compression between 1985 and 2007 are analyzed. Four possible causes — namely, effects of tunnel construction, cyclic loading due to running trains, secondary compression of soft clay, and groundwater pumping in sandy aquifers — are investigated. From the measurements of subsurface soil compression, it is revealed that the observed large tunnel settlement was mainly caused by the compression of sandy Aquifer IV due to groundwater pumping. The measured compression of sandy Aquifer IV accounted for about 65% of the maximum tunnel settlement of Line 1. Soil yielding due to an increase in effective stress was induced by a significant decline in groundwater level. The observed continuing settlement of the tunnel over the 12.5 years was the result of secondary compression (creep), which is a common feature of Aquifer IV at various locations in Shanghai.

scholarly journals Paleoclimatic Implications of Radiocarbon Dating Of Speleothems from the Cracow-Wieluń Upland, Southern Poland

Radiocarbon ◽  
1995 ◽  
Vol 37 (2) ◽  
pp. 103-110 ◽  
Author(s):  
Anna Pazdur ◽  
Mieczysław F. Pazdur ◽  
Jacek Pawlyta ◽  
Andrzej Górny ◽  
Michał Olszewski
Keyword(s):  
Systematic Study ◽  
Radiocarbon Dating ◽  
Karst Region ◽  
Radiocarbon Dates ◽  
Preliminary Results ◽  
Last Glaciation ◽  
Geological Museum ◽  
Paleoclimatic Records ◽  
Age Range

We report preliminary results of a long-term systematic study intended to gather paleoclimatic records from precisely dated speleothems. The research project is limited to speleothems deposited in caves of the Cracow-Wieluń Upland, the largest and best-explored karst region in Poland, covering ca. 2900 km2 with >1000 caves. Speleothem samples were selected from collections of the Geological Museum of the Academy of Mining and Metallurgy in Cracow. Radiocarbon dates of these samples from ca. 45–20 ka bp almost exactly coincide with age range of the Interplenivistulian. A break in speleothem formation between ca. 20 and 10 ka bp may be interpreted as a result of serious climatic deterioration associated with the maximum extent of the last glaciation. We observed differences among 14C, U/Th and AAR dating results. Changes of δ13C and δ18O in speleothems that grew between ca. 30 and 20 ka bp may be interpreted as changes of paleoclimatic conditions.

scholarly journals Isoniazid and Rifampicin Produce Hepatic Fibrosis through an Oxidative Stress-Dependent Mechanism

2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Ayan Biswas ◽  
Suman Santra ◽  
Debasree Bishnu ◽  
Gopal Krishna Dhali ◽  
Abhijit Chowdhury ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Liver Injury ◽  
Hepatic Fibrosis ◽  
Stellate Cell ◽  
Progressive Increase ◽  
Drug Induced ◽  
Drug Induced Liver Injury ◽  
Stress Dependent ◽  
Liver Collagen

Background & Aims. Chronic hepatitis (CH) has emerged as a distinct outcome of drug-induced liver injury (DILI). Combination therapy of Isoniazid (INH) and Rifampicin (RMP) which is widely used for prolonged periods can cause acute hepatotoxicity and has been also incriminated in chronic DILI. We sought evidence of the production of hepatic fibrosis on long-term INH-RMP treatment through experiments in BALB/c mice exposed to INH-RMP. Methods. A combined dose of INH (50 mg) and RMP (100 mg) per kg body weight per day was administered to mice by oral gavage, 6 days a week, for 4 to 24 weeks for the assessment of liver injury, oxidative stress, and development of hepatic fibrosis, including demonstration of changes in key fibrogenesis linked pathways and mediators. Results. Progressive increase in markers of hepatic stellate cell (HSC) activation associated with changes in matrix turnover was observed between 12 and 24 weeks of INH-RMP treatment along with the elevation of liver collagen content and significant periportal fibrosis. These were associated with concurrent apoptosis of the hepatocytes, increase in hepatic cytochrome P450 2E1 (CYP2E1), NADPH oxidase (NOX) activity, and development of hepatic oxidative stress. Conclusions. INH-RMP can activate HSC through generation of NOX-mediated oxidative stress, leading to the development of liver fibrosis.

scholarly journals Evaluating Bayesian radiocarbon-dated event-count [REC] models for the study of long-term human and environmental processes

2020 ◽  
Author(s):  
William Christopher Carleton
Keyword(s):  
Forest Fires ◽  
Simulated Data ◽  
Radiocarbon Date ◽  
Radiocarbon Dates ◽  
New Class ◽  
Environmental Processes ◽  
Growth Decline ◽  
Marine Ingression ◽  
Event Times

Chronological uncertainty complicates attempts to use radiocarbon dates as proxies for processes like human population growth/decline, forest fires, and marine ingression. Established approaches involve turning databases of radiocarbon-date densities into single summary proxies that cannot fully account for chronological uncertainty. Here, I use simulated data to explore an alternate Bayesian approach that instead models the data as what they are, namely radiocarbon-dated event-counts. The approach involves assessing possible event-count sequences by sampling radiocarbon date densities and then applying MCMC to estimate the parameters of an appropriate count-based regression model. The regressions based on individual sampled sequences were placed in a multilevel framework, which allowed for the estimation of hyperparameters that account for chronological uncertainty in individual event times. Two processes were used to produce simulated data. One represented a simple monotonic change in event-counts and the other was based on a real palaeoclimate proxy record. In both cases, the method produced estimates that had the correct sign and were consistently biased toward zero. These results indicate that the approach is widely applicable and could form the basis of a new class of quantitative models for use in exploring long-term human and environmental processes.

scholarly journals Ecology of the collapse of Rapa Nui society

2020 ◽  
Vol 287 (1929) ◽  
pp. 20200662 ◽  
Author(s):  
M. Lima ◽  
E. M. Gayo ◽  
C. Latorre ◽  
C. M. Santoro ◽  
S. A. Estay ◽  
...  
Keyword(s):  
Recurrent Events ◽  
Dynamic Models ◽  
Ecological Factors ◽  
Long Term Effects ◽  
Rapa Nui ◽  
Radiocarbon Dates ◽  
Underlying Causes ◽  
Capita Food ◽  
Past Population

Collapses of food producer societies are recurrent events in prehistory and have triggered a growing concern for identifying the underlying causes of convergences/divergences across cultures around the world. One of the most studied and used as a paradigmatic case is the population collapse of the Rapa Nui society. Here, we test different hypotheses about it by developing explicit population dynamic models that integrate feedbacks between climatic, demographic and ecological factors that underpinned the socio-cultural trajectory of these people. We evaluate our model outputs against a reconstruction of past population size based on archaeological radiocarbon dates from the island. The resulting estimated demographic declines of the Rapa Nui people are linked to the long-term effects of climate change on the island's carrying capacity and, in turn, on the ‘per-capita food supply’.

A 1000-year record of Adélie penguin diets in the southern Ross Sea

2002 ◽  
Vol 14 (4) ◽  
pp. 327-332 ◽  
Author(s):  
MICHAEL POLITO ◽  
STEVEN D. EMSLIE ◽  
WILLIAM WALKER
Keyword(s):  
Ross Sea ◽  
Prey Selection ◽  
Ice Age ◽  
Adélie Penguin ◽  
Pleuragramma Antarcticum ◽  
Adelie Penguin ◽  
Radiocarbon Dates ◽  
Antarctic Silverfish ◽  
The Antarctic

Non-krill prey remains were recovered from ornithogenic sediments at three active Adélie penguin colonies on Ross Island, to assess long-term dietary trends in this species. Radiocarbon dates place the age of these deposits from a maximum of 947 years ago to the present. We identified 12 taxa of fish and two of squid with the Antarctic silverfish (Pleuragramma antarcticum) as the most abundant prey species represented at all sites. In addition, silverfish have decreased in importance in Adélie penguin diet over the past 600 years, perhaps in response to climate change since the onset of the Little Ice Age, though it remains much more abundant in current penguin diet in the Ross Sea than in the Antarctic Peninsula. Other prey taxa reflect the diversity of prey selection by Adélie penguins in Antarctica.

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