Effects of inertial and kinematic forces on pile stresses are studied based on large shaking table tests on pile-structure models with a foundation embedded in dry and liquefiable sand deposits. The test results show that, if the natural period of the superstructure, Tb, is less than that of the ground, Tg, the ground displacement tends to be in phase with the inertial force from the superstructure, increasing the shear force transmitted to the pile. In contrast, if Tb is greater than Tg, the ground displacement tends to be out of phase with the inertial force, restraining the pile stress from increasing. With the effects of earth pressures on the embedded foundation and pile incorporated in, pseudo-static analysis is conducted to estimate maximum moment distribution in pile. It is assumed that the maximum moment is equal to the sum of the two stresses caused by the inertial and kinematic effects if Tb<Tg or the square root of the sum of the squares of the two if Tb>Tg. The estimated pile stresses are in good agreement with the observed ones regardless of the occurrence of soil liquefaction. 相似文献
Karstification-based land subsidence was found in the Upper Tigris Basin with dimensions not seen anywhere else in Turkey. The area of land subsidence, where there are secondary and tertiary subsidence developments, reaches 140 km2. Subsidence depth ranges between 40 and 70 m. The subsidence was formed as a result of subsurface gypsum dissolution in Lower Miocene formation. Although there are limestones together with gypsum and Eocene limestone below them in the area, a subsidence with such a large area is indicative of karstification in the gypsum. The stratigraphical cross-sections taken from the wells and the water analyses also verify this fact. The Lower Miocene gypsum, which shows confined aquifer features, was completely dissolved by the aggressive waters injected from the top and discharged through by Zellek Fault. This resulted in the development of subsidence and formation of caprock dolines on loosely textured Upper Miocene–Pliocene cover formations. The Tigris River runs through the subsidence area between Batman and Bismil. There are four terrace levels as T1 (40 m), T2 (30 m), T3 (10 m) and T4 (4–5 m) in the Tigris River valley. It was also found that there were some movements of the levels of the terraces in the valley by subsidence. The subsidence developed gradually throughout the Quaternary; however no terrace was formed purely because of subsidence. 相似文献
This paper presents the findings from a study on gravity-induced slope deformations along the northern slope of Mt. Nuria (Rieti-Italy). The slope extends from the village of Pendenza to the San Vittorino plain and hosts the Peschiera River springs, i.e. the most important springs of the Central Apennines (average discharge: about 18 m3/s).
Detailed geological-geomorphological and geomechanical surveys, supported by a site stress-strain monitoring system and laboratory tests, led us to define the main evolutionary features of the studied phenomena. Based on the collected data, a “geological-evolutionary model” was developed with a view to identifying a spatio-temporal correlation between relief forms, jointing of the rock mass and its stress conditions. The geological-evolutionary model was expected to improve numerical simulations and to test our assumptions.
The numerical model also allowed us to simulate changes in the stress-strain conditions of the rock mass and correlate them with jointing, seepage, as well as with site-detected and site-monitored forms and deformations. In particular, significant relations between seepage, tensile stresses within the rock mass, karst solution and collapse of cavities were identified. 相似文献
The intensive agricultural and economic activities induce the increase of the risk of groundwater quality degradation through high groundwater pumping rates. The salinization and contamination are the main sources of this pollution, especially in coastal aquifers. The explanation of the origin of salinity for the shallow aquifer of Northern Sahel of Sfax was analysed by a chemical study of the groundwater main compounds. The partitioning of groundwaters into homogenous groups is undertaken by graphical techniques, including a Stiff pattern diagram, an expanded Durov diagram and several binary diagrams. The study indicates the presence of various salinization processes. In the recharge area, salinization is the result of dissolution/precipitation of the aquifer formation material (group I). The irrigation water return and the intensive pumping have been identified as major sources of salinization in the south by direct cation exchange and mixing reactions (groups II and III). The anomaly of high groundwater salinity observed near the Hazeg zone was explained by the presence of a seawater intrusion in this area. This hypothesis is related to the high chloride concentration, to the presence of inverse cation exchange reactions (group IV), and to the piezometric level inferior to sea level. To cite this article: R. Trabelsi et al., C. R. Geoscience 337 (2005).相似文献
A multi-layered aquifer, typical of riverbank alluvial deposits in Korea, was studied to determine the hydrologic properties.
The geologic logging showed that the subsurface of the study site was comprised of four distinctive hydrogeologic units: silt,
sand, highly weathered and fresh bedrock layers. The electrical resistivity survey supplied information on lateral extension
of hydrogeologic strata only partially identified by a limited number of the geologic loggings. The laboratory column tracer
test for the recovered core of the sand layer resulted in a hydraulic conductivity of 5.00×10−2 cm/s. The slug tests performed in the weathered rock layer yielded hydraulic conductivities of 4.32–7.72×10−4 cm/s. Hydraulic conductivities for the sand layer calculated from the breakthrough curves of bromide ranged between 2.08×10−3 and 2.44×10−2 cm/s with a geometric mean of 6.89×10−3 cm/s, which is 7 times smaller than that from the laboratory column experiment. The trend of increasing hydraulic conductivity
with an increase in tracer travel length is likely a result of the increased likelihood of encountering a high conductivity
zone as more of the aquifer is tested. The combined hydrogeologic site characterization using hydraulic tests, tracer tests,
and column test with geologic loggings and geophysical survey greatly enhanced the understanding of the hydrologic properties
of the multi-layered alluvial aquifer. 相似文献