Experimental and numerical study of soil-reinforcement effects on the low-strain stiffness and bearing capacity of shallow foundations     

Wilson Chung  Giovanni Cascante 《Geotechnical and Geological Engineering》2007,25(3):265-281

This paper presents results of meticulous laboratory testing and numerical simulations on the effect of reinforcement on the low-strain stiffness and bearing capacity of shallow foundations on dry sand. The effect of the location and the number of reinforcement layers is studied in the laboratory, whereas numerical simulations are used to study the reinforcement-foundation interaction. Laboratory tests show an increase of 100, 200, and 275% not only in bearing capacity but also in low-strain stiffness (linear load–displacement behaviour) of a square foundation when one, two, and three layers of reinforcement are used, respectively. The specimen preparation technique is found to be crucial for the repeatability and reliability of the laboratory results (less than 5% variability). Numerical simulations demonstrate that if reinforcements are placed up to a depth of one footing width (B) below the foundation, better re-distribution of the load to deeper layers is achieved, thus reducing the stresses and strains underneath the foundation. Numerical simulations and experimental results clearly identify a critical zone between 0.3 and 0.5B, where maximum benefits not only on the bearing capacity but also on the low-strain stiffness of the foundation are obtained. Therefore, soil reinforcement can also be used to reduce low-strain vibrations of foundations.  相似文献   

Focal mechanisms of recent earthquakes in the Southern Korean Peninsula     

Jong-Chan Park  Woohan Kim  Tae Woong Chung  Chang-Eob Baag  Jin-Han Ree 《Geophysical Journal International》2007,169(3):1103-1114

We evaluate the stress field in and around the southern Korean Peninsula with focal mechanism solutions, using the data collected from 71 earthquakes ( M_L = 1.9–5.2) between 1999 and 2004. For this, the hypocentres were relocated and well-constrained fault plane solutions were obtained from the data set of 1270 clear P -wave polarities and 46 SH / P amplitude ratios. The focal mechanism solutions indicate that the prevailing faulting types in South Korea are strike-slip-dominant-oblique-slip faultings with minor reverse-slip component. The maximum principal stresses (σ₁) estimated from fault-slip inversion analysis of the focal mechanism solutions show a similar orientation with E–W trend (269°–275°) and low-angle plunge (10°–25°) for all tectonic provinces in South Korea, consistent with the E–W trending maximum horizontal stress (σ_Hmax) of the Amurian microplate reported from in situ stress measurements and earthquake focal mechanisms. The directions of the intermediate (σ₂) and minimum (σ₃) principal stresses of the Gyeongsang Basin are, however, about 90 deg off from those of the other tectonic provinces on a common σ₂–σ₃ plane, suggesting a permutation of σ₂ and σ₃. Our results incorporated with those from the kinematic studies of the Quaternary faults imply that NNW- to NE-striking faults (dextral strike-slip or oblique-slip with a reverse-slip component) are highly likely to generate earthquakes in South Korea.  相似文献   

High-Mg potassic rocks from Taiwan: implications for the genesis of orogenic potassic lavas   总被引：15，自引：0，他引：15  

Sun-Lin Chung  Kuo-Lung Wang  Anthony J. Crawford  V. S. Kamenetsky  Cheng-Hong Chen  Ching-Ying Lan  Chang-Hwa Chen 《Lithos》2001,59(4):153-170

Taiwan is an active mountain belt formed by oblique collision between the Luzon arc and the Asian continent. Regardless of the ongoing collision in central and southern Taiwan, a post-collisional extension regime has developed since the Plio–Pleistocene in the northern part of this orogen, and led to generation of the Northern Taiwan Volcanic Zone. Emplaced at 0.2 Ma in the southwest of the Volcanic Zone, lavas from the Tsaolingshan volcano are highly magnesian (MgO≈15 wt.%) and potassic (K₂O≈5 wt.%; K₂O/Na₂O≈1.6–3.0). Whereas these basic rocks (SiO₂≈48 wt.%) have relatively low Al₂O₃≈12 wt.%, total Fe₂O₃≈7.5 wt.% and CaO≈7.2 wt.%, they are extremely enriched in large ion lithophile elements (LILE, e.g. Cs, Rb, Ba, Th and U). The Rb and Cs abundances, >1000 and 120 ppm, respectively, are among the highest known from terrestrial rocks. In addition, these rocks are enriched in light rare earth elements (LREE), depleted in high field strength elements (HFSE), and display a positive Pb spike in the primitive mantle-normalized variation diagram. Their REE distribution patterns mark with slight Eu negative anomalies (Eu/Eu*≈0.90–0.84), and Sr and Nd isotope ratios are uniform (⁸⁷Sr/⁸⁶Sr≈0.70540–0.70551; ¹⁴³Nd/¹⁴⁴Nd≈0.51268–0.51259). Olivine, the major phenocryst phase, shows high Fo contents (90.4±1.8; 1σ deviation), which are in agreement with the whole rock Mg-values (83–80). Spinel inclusions in olivine are characterized by high Cr/Cr+Al ratios (0.94–0.82) and have compositions similar to those from boninites that originate from highly refractory peridotites. Such petrochemical characteristics are comparable to the Group I ultrapotassic rocks defined by Foley et al. [Earth-Sci. Rev. 24 (1987) 81], such as orogenic lamproites from central Italy, Span and Tibet. We therefore suggest that the Tsaolingshan lavas resulted from a phlogopite-bearing harzburgitic source in the lithospheric mantle that underwent a recent metasomatism by the nearby Ryukyu subduction zone processes. The lavas exhibit unique incompatible trace element ratios, with Rb/Cs≈8, Ba/Rb≈1, Ce/Pb≈2, Th/U≈1 and Nb/U≈0.8, which are significantly lower than the continental crust values and those of most mantle-derived magmas. Nonmagmatic enrichment in the mantle source is therefore required. Based on published experimental data, two subduction-related metasomatic components, i.e., slab-released hydrous fluid and subducted sediment, are proposed, and the former is considered to be more pervasive for causing the extraordinary trace element ratios observed. Our observations lend support to the notion that dehydration from subducting slabs at convergent margins, as a continuing process through geologic time, can account for the fractionation of these elemental pairs between the Earth's crust and mantle.  相似文献   

The reservoir-associated earthquakes of April 1983 in western Thailand: Source modeling and implications for induced seismicity     

Wai-Ying Chung  Chao Liu 《Pure and Applied Geophysics》1992,138(1):17-41

On 22 April 1983, a very large area of Thailand and part of Burma were strongly shaken by a rare earthquake (m _b=5.8,M _s=5.9). The epicenter was located at the Srinagarind reservoir about 190 km northwest of Bangkok, a relatively stable continental region that experienced little previous seismicity. The main shock was preceded by some foreshocks and followed by numerous aftershocks. The largest foreshock ofm _b=5.2 occurred 1 week before the main shock, and the largest aftershock ofm _b=5.3 took place about 3 hours after the main shock. Focal mechanisms of the three largest events in this earthquake sequence have been studied by other seismologists using firts-motion data. However, the solutions for the main shock and the largest aftershock showed significant inconsistency with known surface geology and regional tectonics. We reexamined the mechanisms of these three events by using teleseismicP-andS-waveforms and through careful readings ofP-wave first motions. The directions of theP axes in our study range from NNW-SSE to NNE-SSW, and nodal planes strike in the NW-SE to about E-W in agreement with regional tectonics and surface geology. The main shock mechanism strikes 255°, dips 48°, and slips 63.5°. The fault motions during the main shock and the foreshock are mainly thrust, while the largest aftershock has a large strike-slip component. The seismic moment and the stress drop of the mainshock are determined to be 3.86×10²⁴ dyne-cm and 180 bars, respectively. The occurrence of these thrust events appears to correlate with the unloading of the Srinagarind reservoir. The focal depths of the largest foreshock, the main shock, and the largest aftershock are determined to be 5.4 km, 8 km, and 22.7 km, respectively, from waveform modeling and relative location showing a downward migration of hypocenters of the three largest events during the earthquake sequence. Other characteristics of this reservoir-induced earthquake sequence are also discussed.  相似文献   

Influence of depositional processes on the geotechnical parameters of Chicago glacial clays   总被引：1，自引：0，他引：1  

C.K. Chung  R.J. Finno   《Engineering Geology》1992,32(4):225-242

The effects of depositional environment on properties, stress history, and undrained and drained shear-strength parameters are evaluated for Chicago glacial clay. Recent geology and basic depositional environments are described. Both laboratory and in-situ shear-strength evaluations have been conducted at several sites in the study area. Results of the investigations indicate that, while depositional environment has a large impact on the engineering properties of these clays, identification of the depositional environment is in itself insufficient to strength parameters. Post-depositional events are shown to alter the stress history imparted during deposition and thus impact shear-strength parameters.  相似文献   

Radium-226 in the eastern equatorial Pacific     

Yu-chia Chung  Harmon Craig 《Earth and Planetary Science Letters》1973,17(2):306-318

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Elasticity and Equations of State of Olivines in the Mg₂SiO₄-Fe₂SiO₄ System     

D. H. Chung 《Geophysical Journal International》1971,25(5):511-538

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Experimental confirmation of the lack of carbon isotope exchange between methane and carbon oxides at high temperatures     

William M. Sackett  H.Moses Chung 《Geochimica et cosmochimica acta》1979,43(2):273-276

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Parametric studies of physical conditions in the Earth's upper mantle     

Dae H. Chung 《Tectonophysics》1980,64(3-4)

Seismic body-wave and surface-wave data indicate the existence of a substantial lowvelocity, low-Q zone in the upper mantle beneath western North America. Conditions in this zone are distinctively different from those that are typical of the upper mantle in shield regions. The present study, using Walsh's model for partially melted rock, suggests a common mechanism for low-velocity and low-Q zones. This parametric study also indicates that the pronounced low-velocity, low-Q zone and anomalous travel-time delays of both P and S waves in the Basin and Range Province are consistent with the combined effects of high temperature, chemical composition, phase changes, and partial melting. The observed low P_n velocity in this region is consistent with high temperature, chemical composition, and the presence of a partially molten layer within the upper mantle, but the observed teleseismic delay times result principally from the thickness of the lowvelocity zone. The teleseismic delay-time variations are therefore related to the seismic Q distribution in the asthenosphere. Conditions a few kilometers beneath the Moho boundary influence the P_n velocity; however, the observed correlation among the teleseismic signal amplitudes, travel-time delays, and the upper mantle Q indicates that the P_n velocity is a better indicator of upper mantle Q than suggested by the P_n path alone. This knowledge of the upper mantle seems to account for the anomalous effects of the Basin and Range Province and other regions of similar tectonic nature on observations of teleseismic events. This will provide a practical technique for comparing seismic observations made in unstable tectonic regions with observations made in shield areas.  相似文献   

A²²⁶Ra section across the East Pacific Rise     

Y. Chung 《Earth and Planetary Science Letters》1980,49(2):319-328

Four vertical Ra profiles have been measured across the East Pacific Rise (EPR) from Callao to Tahiti. These profiles show that Ra in the deep water (below 2 km depth) increases toward the EPR. However, this increase does not necessarily indicate a Ra source on the EPR. The increase from Tahiti toward the EPR reflects the general trend of the Pacific Ra distribution. The decrease from the EPR eastward to the Peru Basin is probably due to the continental effect with higher sedimentation rates.The hydrography, especially potential temperature and oxygen, indicates significant differences below about 3 km depth between the east and west flanks of the EPR indicating the effect of the cold bottom water to the west of the EPR. The benthic front is identified at 3.9 km depth at the westernmost station near Tahiti. Silicate and salinity data are by no means unique and reflect a complicated local circulation and mixing pattern with a minor intrusion of the Antarctic Bottom Water from the south into the Peru Basin.The θ-Ra and Ra-Si relationships both indicate an enrichment of Ra in the deep water below 2 km depth probably due to input from the underlying sediments. Above 2 km depth, Ra covaries almost linearly with θ as well as Si, mimicking a stable conservative property. This suggests that the radiodecay rate is nearly balanced by the input rate within the water column between 1 and 2 km depth in which θ is linearly correlated withS.Simple vertical model calculations show that the in-situ production of Ra by particulate dissolution in the deep water is negligible within a reasonable range of upwelling rates from 2 to 12 m/yr. Thus the Ra profiles show a net decay effect and so the θ-Ra relations are not linear in the deep water. In fact, the composite θ-Ra plots show a break at 25 dpm/100 kg (at 2 km depth) rather than a smooth curve, while theθ-S plots are essentially linear. A maximum Ra production rate of about 8 × 10^?3 (dpm/100 kg) yr^?1 is obtained from all the profiles with minimum upwelling rates between 0.7 and 3.5 m/yr.  相似文献