scholarly journals Centrifuge tests to evaluate the effect of depth of water table on seismic response of shallow foundations on silty sands

2020 ◽  
Vol 195 ◽  
pp. 01005
Author(s):  
Amin Borghei ◽  
Majid Ghayoomi ◽  
Matthew Turner
Keyword(s):  
Amplification Factor ◽  
Free Field ◽  
Groundwater Table ◽  
Saturated Soil ◽  
Silty Sand ◽  
Saturated Soils ◽  
Amplification Factors ◽  
Centrifuge Tests ◽  
Short Period ◽  
Dry Soil

A set of dynamic centrifuge experiments were performed to assess the effect of the depth of the groundwater table on the seismic site response of silty sand. Silty sand was prepared in a laminar container. The testing program consists of experiments on dry as well as saturated soils and a test, which the groundwater table was below the soil surface. The specimens were spun in a centrifuge, then they were excited with a suite of seismic motions. Results show that 1) while the for peak ground acceleration amplification factor of the saturated soil was smaller than those for the dry soil, the Arias intensity amplification factor of the saturated soil was larger than those for dry soil. 2) as the depth of the groundwater table increased, peak ground amplification factor and short-period amplification factors increased, the mid-period amplification factors decreased. 3) the depth of the groundwater table influences the frequency content of the free field motion. 4) the unsaturated soil behaved stiffer than dry and saturated soils.

Empirical Site Amplification Modelling for Horizontal and Vertical Ground Motions in Taiwan

2020 ◽  
Author(s):  
Chun-Hsiang Kuo ◽  
Shu-Hsien Chao ◽  
Che-Min Lin ◽  
Jyun-Yan Huang ◽  
Kuo-Liang Wen
Keyword(s):  
Ground Motion ◽  
Amplification Factor ◽  
Ground Motions ◽  
Free Field ◽  
Site Amplification ◽  
Amplification Factors ◽  
Taipei Basin ◽  
Vertical Ground Motions ◽  
Vertical Ground ◽  
Site Amplification Factor

<p>Site amplification behavior are important in ground motion prediction. Seismic waves were amplified and caused significant building damages in the Taipei Basin by the 1986 Hualien offshore (subduction interface) and the 1999 Chi-Chi earthquakes (crustal), for which both of the epicentral distances were nearly 100 km. To understand local site amplifications in Taiwan, empirical site amplification factors for both horizontal and vertical ground motions are studied using recently constructed strong motion and site databases for the free-field TSMIP stations. Records of large magnitude earthquakes of M<sub>W</sub> larger than 5.5 from 1991 to 2016 were selected for this study. Site amplification factors at site conditions with Vs30 between 120 m/s to 1600 m/s and bedrock accelerations up to 0.8 g were evaluated using ratios of spectral accelerations at different periods. The reference site condition, i.e. the engineering bedrock, is assumed as Vs30 of 760 m/s (B/C boundary) in this study. Our empirical site amplification form are borrowed from the site response function of ASK14 and CY14 ground motion models in NGA-West2 project with slight modification. Therefore our site amplification model includes a linear amplification term and a nonlinear deamplification term. The coefficients of the empirical models were obtained by a nonlinear regression analysis using the selected Taiwan data. Site amplification factor is a function of Vs30 and spectral intensity in the model. Similar linear site amplification factor to the NGA models is derived in our model; however, more significant soil nonlinearity behavior than the NGA models is likely captured from the empirical data. The amplification factor in vertical component is smaller than that in horizontal.</p>

Response of Non-Homogeneous Saturated Soils and Free-Field to Incident Plane SH Wave

2014 ◽  
Vol 580-583 ◽  
pp. 273-277
Author(s):  
Feng Xi Zhou ◽  
Rui Xia Song
Keyword(s):  
Dynamic Response ◽  
Incident Angle ◽  
Dynamic Stiffness ◽  
Free Field ◽  
Saturated Soil ◽  
Saturated Soils ◽  
Sh Wave ◽  
Reflection And Transmission ◽  
Incident Plane ◽  
Plane Sh Wave

Based on the Biot’s Theory, the dynamic response of non-homogeneous saturated soil has been studied using Helmholtz vector decomposition principle and Exact Dynamic Stiffness Method (EDSM). Reflection and transmission of SH wave in non-homogeneous saturated soil have also been analyzed in considering the continuous variation of physical and mechanical properties of saturated foundation along the thickness. The general calculation formula about the reflection and transmission coefficients of bedrock and free field on both surfaces was achieved. Assuming that the material properties have an exponential law distribution and gradient variation along the thickness-coordinate, the dynamic response of non-homogeneous saturated soils under incident plane SH wave was discussed by numerical examples. The results show that the incident angle, the thickness and heterogeneity index of saturated soil have significant influences on the ratio of the ground displacement and bedrock displacement.

CHARACTERIZATION OF LIQUEFACTION RESISTANCE OF SAND: EFFECT OF INITIAL FABRIC

2014 ◽  
Vol 08 (01) ◽  
pp. 1450001 ◽  
Author(s):  
BO LI ◽  
XIANGWU ZENG ◽  
HAO YU
Keyword(s):  
Depositional Environment ◽  
Design Method ◽  
Free Field ◽  
Recent Experience ◽  
Permeability Test ◽  
Fabric Anisotropy ◽  
Liquefaction Resistance ◽  
Liquefaction Potential ◽  
Centrifuge Tests

The micro-fabric of deposition reflects the imprints of its geologic and stress history, its depositional environment, and its weathering history. Recent experience shows that the fabric anisotropy does influence the static and dynamic behavior of granular materials. In this study, a series of centrifuge tests are conducted to investigate the effects of fabric anisotropy on the dynamic response in the free field. The results show the acceleration, pore pressure, and residual settlement is significantly affected by the fabric anisotropy of the ground, which shows the liquefaction resistance of the ground. Meanwhile, the response of acceleration is analyzed in frequency domain, which shows that the model prepared by 90° absorbs more energy than that of 0°. To verify the effects induced by the initial fabric, permeability test are conducted and related to the liquefaction potential. The results indicate the fabric anisotropy should be incorporated into the design method.

Factors affecting the phenology of the first brood of the sugar-cane froghopper Aeneolamia varia saccharina (Dist.) (Homoptera, Cercopidae) in Trinidad

1975 ◽  
Vol 65 (3) ◽  
pp. 359-372 ◽  
Author(s):  
A. B. S. King
Keyword(s):  
Adult Emergence ◽  
Dry Season ◽  
Soil Conditions ◽  
Factors Affecting ◽  
Expected Time ◽  
Short Period ◽  
Incubation Periods ◽  
Close Relationship ◽  
Dry Soil ◽  
Predictive Relationship

AbstractThe size and occurrence of the first brood of adults of Aeneolamia varia saccharina (Dist.) are examined in relation to the pattern of egg eclosion and rainfall. The proportion of eggs hatching within a month of oviposition in the laboratory (short-period eggs) decreased from over 90% in August to less than 20% in January, but the incubation periods of the remaining, long-period eggs were longest in those laid during October and November. The overall hatching distributions tended to be bimodal with most eggs hatching during the early months of the year under moist conditions at 26°C. Dry soil conditions delay eclosion, and eggs obtained from fields during the dry season and then incubated under moist conditions tended to hatch at the normally expected time of the first rains in May. The numbers of eggs expected to produce the first brood, computed from laboratory hatching data and estimates of the numbers and fecundities of froghoppers during the second, third and fourth broods, were less than the actual numbers sampled just before the first rains. There was a close relationship between the first rainfall of over one inch within 48 h and adult emergence 27 and 34 days later, and 85% of field egg populations in May had hatched and/or died by the week after the first rains. However some variation in the date of their occurrence accounted for non-synchrony of first broods over the region. The numbers of diapause eggs in fields sampled during the dry season failed to give a good predictive relationship with first brood adult populations, probably because of density dependent mortality of eggs or hatchling nymphs.

RIGID CONTAINMENT WALLS FOR LIQUEFACTION REMEDIATION

2012 ◽  
Vol 06 (04) ◽  
pp. 1250017 ◽  
Author(s):  
HELEN MITRANI ◽  
S. P. G. MADABHUSHI
Keyword(s):  
Deep Layer ◽  
Ground Improvement ◽  
Free Field ◽  
Frame Structure ◽  
Lateral Movement ◽  
Existing Buildings ◽  
Centrifuge Tests ◽  
Structural Connection

Many typical ground improvement techniques that are used for liquefaction remediation, such as in situ densification, are not appropriate for application under existing buildings and more novel techniques are required. This paper describes centrifuge tests investigating the performance of rigid containment walls as a liquefaction remediation method. A simple frame structure, founded on a deep layer of loose, liquefiable sand was tested under earthquake shaking. Centrifuge tests were then carried out with containment walls around the base of the structure, extending through the full depth of the liquefiable layer and also partial depth. It is found that rigid containment walls can be very effective in reducing structural settlements primarily by preventing lateral movement of the foundation sand but the impermeability of the walls may also be important. Improvements in structural settlement are observed even when the walls do not extend through the full depth of the liquefiable layer, if the depth of the walls is greater than the depth of the free field liquefaction. In addition, it is found that the accelerations of the structure are not increased, provided there is no rigid, structural connection between the structure and the containment walls.

Fire as a Tool for Controlling Tamarix spp. Seedlings

2012 ◽  
Vol 5 (2) ◽  
pp. 139-147 ◽  
Author(s):  
Michelle K. Ohrtman ◽  
Sharon A. Clay ◽  
David E. Clay ◽  
Alexander J Smart
Keyword(s):  
Water Loss ◽  
Seedling Survival ◽  
Seed Viability ◽  
Moisture Loss ◽  
Grass Species ◽  
Saturated Soils ◽  
Invasive Grass ◽  
Dry Soil ◽  
Tamarix Spp ◽  
Water Saturated

AbstractFire is often used in northern grasslands to control invasive grass species but has unknown effects on Tamarix spp., more recent invaders. Temperature (using an oven as a fire surrogate) and duration combinations that would be most lethal to Tamarix seeds and seedlings were determined. Tamarix seeds were sown in soil-lined dishes, water added to saturation, and seedlings grown for 1 to 5 d. Seeds were also placed in water-saturated or dry soil just before temperature exposure (79 to 204 C [175 to 400 F]) by duration (1 to 5 min) treatments. After treatment, soil water loss was measured by weight difference, and surviving seedlings were counted for 6 d. Tamarix seedling establishment and survival decreased with increasing temperature and duration. The 5-d-old seedlings were the most affected. No 5-d-old seedlings survived 1- and 2-min exposures to 204 C, whereas 1-d-old seedlings had greater than 25% survival. If soils were saturated, two to four times more seedlings established following seed exposure to 177 and 204 C. Longer durations at lower temperatures were required to reduce Tamarix survival. Increasing duration from 2 to 5 min at 121 C decreased 5-d-old seedling survival from more than 80% to less than 10% and eliminated those seedlings at 149 C. Five minutes at 149 C decreased dry-soil seed viability to about 15%, whereas germination on saturated soils remained high (∼75%). No seeds survived the exposure to 177 and 204 C. Soil moisture loss values associated with 90% mortality of 5- and 1-d-old seedlings were 1.7 and 2.2%, respectively. On saturated soils, 90% of seeds died with 2.5% water loss. Under suitable conditions, fire can decrease Tamarix seedling survival. Fire may be useful for controlling Tamarix seedlings in northern grasslands and should be considered for management of new invasions.

Effect of consolidation on responses of a single pile subjected to lateral soil movement

2015 ◽  
Vol 52 (6) ◽  
pp. 769-782 ◽  
Author(s):  
L.Z. Wang ◽  
K.X. Chen ◽  
Y. Hong ◽  
C.W.W. Ng
Keyword(s):  
Soft Clay ◽  
Bending Moment ◽  
Coefficient Of Consolidation ◽  
Construction Period ◽  
Soil Movement ◽  
Centrifuge Tests ◽  
Short Period ◽  
Lateral Soil Movement ◽  
Pile Response ◽  
Pile Length

Given extensive research carried out to study pile response subjected to lateral soil movement in clay, the effect of consolidation on the pile–soil interaction is rarely considered and systematically investigated. For this reason, four centrifuge tests were conducted to simulate construction of embankment adjacent to existing single piles in soft clay, considering two typical drainage conditions (i.e., drained and undrained conditions) and two typical pile lengths (i.e., relatively long pile and short pile). The centrifuge tests were then back-analyzed by three-dimensional coupled-consolidation finite element analyses. Based on reasonable agreements between the two, numerical parametric studies were conducted to systematically investigate and quantify the influence of construction rate and pile length on pile response. It is revealed that by varying drainage conditions, the piles respond distinctively. When the embankment is completed within a relatively short period (cvt/d2 < 2, where cv, t, and d denote the coefficient of consolidation, construction period, and pile diameter, respectively), the pile located adjacent to it deforms laterally away from the embankment. Induced lateral pile deflection (δ) and bending moment reduce with construction period. On the contrary, embankment constructed within a relatively long period (cvt/d2 > 200) leads the pile to deform laterally towards the embankment, with δ and bending moment increases with construction period. By halving the length of pile embedded in the drained ground, the maximum induced bending moment (BMmax) was slightly reduced (by 23%). On the other hand, shortening the length of the pile in the undrained ground is much more effective in reducing BMmax, i.e., halving pile length resulting in 78% reduction in bending moment. A new calculation chart, which takes various drainage conditions and pile lengths into account, was developed for estimation of BMmax.

scholarly journals Kompatibilitas Sumber Inokulan Fungi Mikoriza Arbuskular pada Kedelai dengan Budidaya Jenuh Air

2016 ◽  
Vol 35 (3) ◽  
pp. 229 ◽  
Author(s):  
Ridwan Muis ◽  
Munif Ghulamahdi ◽  
Maya Melati ◽  
Purwono Purwono ◽  
Irdika Mansur
Keyword(s):  
Relative Efficiency ◽  
Block Design ◽  
Dry Weight ◽  
P Uptake ◽  
Saturated Soil ◽  
Soil Culture ◽  
Randomized Block Design ◽  
Two Factors ◽  
Dry Soil ◽  
Water Saturated

The main problem encountered by soybean crop in acid sulfate tidal lands is less availability of P, because of its chemical bond with Fe. Heavy dose of  fertilization often lead to high fertilizer residue, wich could be used for crops farming using AMF. Research was conducted to study the effect of soybean culturing technique and AMF inoculants source on growth of  soybean. The treatments consisted two factors, arranged in a randomized block design with three replications. The first factor was four inoculants sources of AMF, namely AMF and without inoculation AMF, inoculants from rhizospheres of kudzu (Pueraria javanica), sorghum (Sorghum bicolor), corn (Zea mays) and soybean (Glycine max). The second factor was culturing tehnique, namely water saturated and dry soil culture. Soybeans were grown in pots containing 5 kg soil derived from tidal land,  Simpang Village, District of Berbak, East Tanjung Jabung Regency,  Jambi Province. Results showed that the interaction saturated soil culture with inoculants from corn’s rhizosphere had positive effect on the variability of N, P and K uptake, N and P content in the plant, relative efficiency of inoculants and relative efficiency of P uptake, stem diameter, biomass dry weight, the number of filled pods and seed dry weight of soybeans. Dry soil culture with inoculants of corn’s rhizosphere had greater root colonization, but overall for the growth and grain yield of soybean, saturated soil culture with inoculants from corn rhizosphere has better effect on other growth variables.

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