فشار حجمی شن و ماسه آهکی
Abstract
Nomenclature
1. Introduction
2. Soil characterization
3. Sample preparation and testing program
4. Results and discussions
5. Conclusion
References
Abstract
Post-cyclic settlement of saturated soil, due to dynamic loadings such as earthquake, causes severe damage to structures. Dissipation of excess pore water pressure generated during cyclic loadings results in the volumetric strain of soil materials. Many studies have been conducted on factors affecting post-cyclic volumetric strain (εre,v) of siliceous soils. The effect of important factors on post-cyclic settlement of calcareous sand is evaluated in this study. Calcareous soils are generally located in tropical and subtropical areas near oceans and gulfs. These deposits are usually saturated and consequently, post-cyclic settlement can be critical in these sediments. In this research, a series of hollow cylindrical torsional shear tests were performed on Hormuz calcareous sands obtained from the north coast of the Persian Gulf. The samples were loaded cyclically under different cyclic stress ratios (CSRs) in undrained condition and then, terminated at a desired pore water pressure ratio (ru). After that, the excess pore water pressure was allowed to dissipate, and volumetric strain occurred as a result. The effects of relative density (Dr), cyclic stress ratio (CSR), excess pore water pressure ratio (ru) and maximum cyclic-induced shear strain (γmax) on εre,v of the reconstituted sand were evaluated. The results showed that maximum shear strain is the most effective factor in estimating the post-cyclic settlement of the calcareous sand.
Introduction
Cyclic-induced deformation caused by dynamic loadings such as earthquakes can be divided into two categories: shear deformation and volume change. During dynamic loadings, pore water pressure increases in saturated soils. The liquefaction phenomenon occurs in cases of level- or mildly-sloping grounds, when the pore water pressure increases to the confining pressure in saturated soils during an earthquake. After that, excess pore water pressure dissipates and volume change takes place in the soil mass. These volume changes manifest as settlement in ground surface. Liquefaction may also cause sand boil, loss of bearing capacity, lateral spreading, etc. [1,2]. As reported by many researchers in different case studies and experimental investigations in siliceous deposits, excess pore water pressure dissipation causes cyclic-induced settlement. Retamal and Kausel [3] stated that the settlement was about 80 cm in some regions and was a result of soil densification after the Chile earthquake (1960). The cyclic-induced volumetric strain during the Niigata earthquake (1964) was reported to be about 3–۵% [۴]. Some regions experienced a 50 cm ground surface settlement after the earthquake, which resulted in significant damages. The non-homogenous nature of soils causes postcyclic differential settlements that result in severe structural damages. Non-uniform settlements and structural damages were reported in many earthquakes such as the Niigata earthquake in Japan (1964) [5], the Luzon earthquake in the Philippines (1990) [6], the Kocaeli earthquake in Turkey (1995) [7], the Christchurch earthquake in New Zealand (2011) [8] and the Tohoku earthquake in Japan (2011) [9], all of which occurred in regions with siliceous soils.