Centrifuge study of seismic response of soil-nailed walls supporting a footing on the ground surface

Géotechnique ◽  
2021 ◽  
pp. 1-41
Author(s):  
Mohammad Hassan Baziar ◽  
Alireza Ghadamgahi ◽  
Andrew John Brennan
Keyword(s):  
Ground Surface ◽  
Soil Surface ◽  
Seismic Stability ◽  
Soil Nails ◽  
Model Soil ◽  
Centrifuge Tests ◽  
Axial Tensile ◽  
Tensile Forces ◽  
Surcharge Load ◽  
Seismic Loadings

Seismic design of soil-nailed walls requires demonstrations of tolerable ranges of wall movements, especially when a surcharge load exists near the wall. In this study, the effect of surcharge location on seismically induced wall movements was investigated using four centrifuge tests. The axial tensile forces, developed along the soil nails during the seismic loadings, were also measured during the tests. At 50g centrifugal acceleration, model tests represented a 12-m-high prototype wall reinforced with five rows of soil nails. To apply a surcharge stress of 30 kPa at the specified location relative to the wall for each model test, a rigid footing was placed on the soil surface. The model soil-nailed walls were subjected to three successive earthquake motions. Surprisingly, it was found that the model wall with the footing located behind the soil-nailed region experienced the largest seismic movements, even more than when the footing was directly behind the wall. Further, the tests showed that the lower soil nails played a key role in the wall stability during earthquake shaking, acting as a pivot for the pre-collapse cases tested, whereas the upper soil nails needed to be sufficiently extended to properly contribute to the seismic stability of the wall.

scholarly journals Experimental observation on laterally loaded pile in unsaturated silty soil

2019 ◽  
Vol 56 (11) ◽  
pp. 1545-1556 ◽  
Author(s):  
L.M. Lalicata ◽  
A. Desideri ◽  
F. Casini ◽  
L. Thorel
Keyword(s):  
Water Table ◽  
Ground Surface ◽  
Bending Moment ◽  
Data Interpretation ◽  
Partial Saturation ◽  
Laterally Loaded Piles ◽  
Silty Soil ◽  
Centrifuge Tests ◽  
Surface Data ◽  
Laterally Loaded

An experimental study was carried out to investigate the effects of soil partial saturation on the behaviour of laterally loaded piles. The proposed study was conducted by means of centrifuge tests at 100g, where a single vertical pile was subjected to a combination of static horizontal load and bending moment. The study was conducted on a silty soil characterized with laboratory testing under saturated and unsaturated conditions. During flight, two different positions of water table were explored. The influence of density was investigated by compacting the sample with two different void ratios. Finally, the effects of a variation of saturation degree on the pile response under loading were studied by raising the water table to the ground surface. Data interpretation allows drawing different considerations on the effects of partial saturation on the behaviour of laterally loaded piles. As expected, compared to saturated soils, partial saturation always leads to a stiffer and resistant response of the system. However, the depth of the maximum bending moment is related to the position of the water table and the bounding effects induced by partial saturation appear to be more important for loose soils.

Stability of a single tunnel in cohesive–frictional soil subjected to surcharge loading

2011 ◽  
Vol 48 (12) ◽  
pp. 1841-1854 ◽  
Author(s):  
Kentaro Yamamoto ◽  
Andrei V. Lyamin ◽  
Daniel W. Wilson ◽  
Scott W. Sloan ◽  
Andrew J. Abbo
Keyword(s):  
Upper Bound ◽  
Limit Analysis ◽  
Ground Surface ◽  
Soil Mass ◽  
Building Technology ◽  
Surcharge Loading ◽  
Large Size ◽  
Surcharge Load ◽  
The Stability ◽  
Frictional Soils

This paper focuses mainly on the stability of a square tunnel in cohesive–frictional soils subjected to surcharge loading. Large-size noncircular tunnels are quickly becoming a widespread building technology by virtue of the development of advanced tunneling machines. The stability of square tunnels in cohesive–frictional soils subjected to surcharge loading has been investigated theoretically and numerically, assuming plane strain conditions. Despite the importance of this problem, previous research on the subject is very limited. At present, no generally accepted design or analysis method is available to evaluate the stability of tunnels or openings in cohesive–frictional soils. In this study, a continuous loading is applied to the ground surface, and both smooth and rough interface conditions between the loading and soil are modelled. For a series of tunnel geometries and material properties, rigorous lower and upper bound solutions for the ultimate surcharge loading of the considered soil mass are obtained by applying recently developed numerical limit analysis techniques. The results obtained are presented in the form of dimensionless stability charts for practical convenience, with the actual surcharge loads being closely bracketed from above and below. As a handy practical means, upper bound rigid-block mechanisms for square tunnels have also been developed, and the obtained values of collapse loads were compared with the results from numerical limit analysis to verify the accuracy of both approaches. Finally, an expression that approximates the ultimate surcharge load of cohesive–frictional soils with the inclusion of shallow square tunnels has been devised for use by practicing engineers.

Effects of Grazing on Abundance and Distribution of Shortgrass Steppe Consumers

2008 ◽  
Author(s):  
Daniel G. Milchunas ◽  
William K. Lauenroth
Keyword(s):  
Plant Communities ◽  
Carbon Allocation ◽  
Ground Surface ◽  
Soil Surface ◽  
Bouteloua Gracilis ◽  
Shortgrass Steppe ◽  
Background Information ◽  
Long Term Effects ◽  
Grazing Effects

Although livestock are the most obvious consumers on the shortgrass steppe, they are certainly not the only consumers. However, livestock may influence the other consumers in a number of different ways. They may directly compete for food resources with other aboveground herbivores. There is behavioral interference between livestock and some species of wildlife (Roberts and Becker, 1982), but not others (Austin and Urness, 1986). The removal of biomass by livestock alters canopy structure (physiognomy) and influences microclimate. Bird, small-mammal, and insect species can be variously sensitive to these structural alterations (Brown, 1973; Cody, 1985; MacArthur, 1965; Morris, 1973; Rosenzweig et al., 1975; Wiens, 1969). There are both short- and long-term effects of grazing on plant community species composition, primary production, and plant tissue quality. Belowground consumers can also be affected by the effects of grazing on soil water infiltration, nutrient cycling, carbon allocation patterns of plants, litter accumulation, and soil temperature. The overall effects of livestock on a particular component of the native fauna can be negative or can be positive through facilitative relationships (Gordon, 1988). In this chapter we assess the effects of cattle grazing on other above- and belowground consumers, on the diversity and relative sensitivity of these groups of organisms, and on their trophic structure. We first present some brief background information on plant communities of the shortgrass steppe and on the long-term grazing treatments in which many of the studies reported herein were conducted. Details on the plant communities are presented by Lauenroth in chapter 5 (this volume), grazing effects on plant communities by Milchunas et al. in chapter 16 (this volume); and grazing effects on nutrient distributions and cycling by Burke et al. in chapter 13 (this volume). The physiognomy of the shortgrass steppe is indicated in its name. The dominant grasses (Bouteloua gracilis and Buchloë dactyloides), forb (Sphaeralcea coccinea), and carex (Carex eleocharis) have the majority of their leaf biomass within 10 cm of the ground surface. A number of less abundant midheight grasses and dwarf shrubs are sparsely interspersed among the short vegetation, but usually much of their biomass is within 25 cm of the g round. Basal cover of vegetation typically totals 25% to 35%, and is greater in long-term grazed than in ungrazed grassland. Bare ground (more frequent on grazed sites) and litter-covered ground (more frequent on ungrazed sites) comprise the remainder of the soil surface (Milchunas et al., 1989).

Physical Characteristics of Boulders Formed in the Tropically Weathered Granite

2015 ◽  
Vol 72 (3) ◽  
Author(s):  
Mohd Firdaus Md Dan ◽  
Edy Tonnizam Muhamad ◽  
Ibrahim Komoo ◽  
Mohd Nur Asmawisham Alel
Keyword(s):  
Ground Surface ◽  
Spherical Shape ◽  
Soil Surface ◽  
Physical Characteristics ◽  
Common Phenomenon ◽  
Weathering Profile ◽  
Hilly Area ◽  
Thick Stratum ◽  
Weathering Zone ◽  
Colour Chart

Deep weathering profile is a common phenomenon for humid tropic especially in Malaysia. The reactions of deep weathering under soil surface are decomposition of the massive rock and formation of thick stratum of soil and boulders. However, the occurrence of embedded boulders or loose blocks in the highly to completely weathered in the hilly area is not fully understood and investigated. This paper investigates the occurrence and physical characteristics of boulders in the granitic area. The parameters investigated are boulder’s discoloration, size, shape, rindlet properties and their distribution. Colour and shape were determined based on rock colour chart by Krumbein and Croft’s chart respectively. Size, rindlet and its distribution were determined based on field observation. Field results revealed that boulders in the hilly area can be found as shallow as 2 m from ground surface. In addition, it is found that boulder that embedded in deeper zone became larger in size and surrounded by thicker rindlet of up to 50 cm thick. Boulders embedded in soil stratum at weathering zone 4 and 5 are mostly independent and scattered around the weathering profile. The boulders can also be presented in various shapes; the smaller boulder is located at the upper zone more to flat to very spherical shape and rounded to well rounded edges, while the larger boulder that is located at lower zone more to sub-spherical shape and well rounded edges.

scholarly journals Refinement of Alternate Wetting and Drying Irrigation Method for Rice Cultivation

2014 ◽  
Vol 17 (1-2) ◽  
pp. 33-37 ◽  
Author(s):  
Priya Lal Chandra Paul ◽  
MA Rashid ◽  
Mousumi Paul
Keyword(s):  
Grain Yield ◽  
Water Level ◽  
Block Design ◽  
Water Productivity ◽  
Ground Surface ◽  
Soil Surface ◽  
Ground Level ◽  
Wetting And Drying ◽  
Alternate Wetting And Drying ◽  
Below Ground

Experiments were conducted at BRRI farm Gazipur during Boro season 2010-12 to determine maximum depth of water level below ground surface in alternate wetting and drying (AWD) method. The experiment was laid out in a randomized complete block design with four irrigation treatments. The treatments of AWD method were: T1 = continuous standing water, T2 = irrigation when water level reached 15 cm below ground level, T3 = irrigation when water level reached 20 cm below ground level and T4 = irrigation when water level reached 50 cm below ground level. The experiment involved BRRI dhan28 as a test crop. The treatment T2 gave the highest grain yield (5.9 and 6.2 ton/ha) in 2010-11 and 2011-12, respectively. Maximum benefits per hectare were found Tk. 5476 and 4931 for using 807 and 880 mm water during 2010-11 and 2011-12 respectively and thus water productivity was 7.1 kg/ha-mm in T2 for both the seasons. Continuous standing (T1) water (1013 and 1100 mm) gave comparable grain yield 5.7 and 6.0 ton/ha in 2010-11 and 2011-12, respectively. Minimum water productivity was found in treatment T1 (5.6 and 5.4 kg/ha-mm) for both the seasons. Application of irrigation when water was 15 cm below soil surface was found most profitable in AWD system and the grain yield was decreased when water level was below 15 cm depth. Therefore, the recommended AWD technology could increase rice yield and save irrigation water by 25-30 percent.DOI: http://dx.doi.org/10.3329/brj.v17i1-2.20899Bangladesh Rice j. 2013, 17(1&2): 33-37

Research on Negative Skin Friction on Pile by a Simple Model Experiment

2014 ◽  
Vol 580-583 ◽  
pp. 693-696
Author(s):  
Ting Huang ◽  
Jin Hai Zheng ◽  
Wei Ming Gong
Keyword(s):  
Skin Friction ◽  
Model Test ◽  
Soil Surface ◽  
Test Methods ◽  
Negative Skin Friction ◽  
Experimental Scheme ◽  
Test Conditions ◽  
Surcharge Load ◽  
Conventional Test ◽  
Pile Model

Accompanied by the substantive construction of domestic ports, the negative skin friction on pile becomes a common problem. In order to provide references for the related experiment research in the future, the designs of model experiments reported in the literatures were emphatically analyzed and compared. Compared to conventional pile model test, the model test on negative skin friction on pile needs to apply load on soil surface and it is difficult to simulate large surcharge by conventional test methods. An experimental scheme which could produce large surcharge load by conventional test conditions is given in this paper. Pile stress, displacement of pile top and layered settlement of soil was tested under different surcharge level. The depth of neutral point and the group effect of NSF are discussed.

The Implementation of the Gradual Movement of Sliding Blocks to a New Method for Evaluating the Seismic Stability of Slopes Reinforced by Geotextile

2018 ◽  
Vol 12 (04) ◽  
pp. 1841010
Author(s):  
Tadashi Kawai ◽  
Makoto Ishimaru
Keyword(s):  
Seismic Performance ◽  
Nuclear Power ◽  
Power Plants ◽  
Slope Failure ◽  
Failure Process ◽  
Tohoku Earthquake ◽  
Seismic Stability ◽  
Centrifuge Tests ◽  
Stability Of Slopes ◽  
Design Basis

Evaluating the seismic stability of a rock slope typically involves searching for the minimum value of calculated safety factors (SF) for each supposed sliding block. Because only the transient equilibrium is evaluated, the likelihood of any slope failure can be deemed negligible if all the calculated SFs are greater than unity. However, even if some of the calculated SF are less than unity, it cannot be assumed that the slope will collapse. Recently, in the wake of extremely large earthquakes in Japan, the design earthquake standards for nuclear power plants (NPP) have been extended. After the experience of the 2011 off the Pacific coast of Tohoku Earthquake, the designer is expected to consider beyond design basis earthquakes to determine whether more can reasonably be done to reduce the potential for damage, especially where major consequences may ensue [IAEA (2011). IAEA international fact finding expert mission of the Fukushima dai-ichi NPP accident following the Great East Japan Earthquake and Tsunami, Mission report, IAEA]. With this in mind, the method employed to evaluate the seismic performance of the slope surrounding an NPP needs to be capable of doing more than determining the likelihood of failure: it must also consider the process toward failure in the event of an earthquake beyond the design basis. In this paper, a new evaluation flow which considers the failure process is proposed to evaluate the seismic performance of slopes surrounding an NPP. This is followed by confirming the validity of the concepts in the proposed flow chart by re-evaluating centrifuge tests in past literature and the numerical simulations designed for those tests.

Three-dimensional seismic stability of slopes reinforced by soil nails

2020 ◽  
Vol 127 ◽  
pp. 103768 ◽  
Author(s):  
Tao Yang ◽  
Jin-Feng Zou ◽  
Qiu-Jing Pan
Keyword(s):  
Three Dimensional ◽  
Seismic Stability ◽  
Soil Nails ◽  
Stability Of Slopes

Amplification of seismic accelerations at slope crests

2009 ◽  
Vol 46 (5) ◽  
pp. 585-594 ◽  
Author(s):  
A. J. Brennan ◽  
S. P.G. Madabhushi
Keyword(s):  
Natural Frequency ◽  
Soil Layer ◽  
Ground Surface ◽  
Surface Structures ◽  
Centrifuge Modelling ◽  
Sloping Ground ◽  
Topographic Amplification ◽  
Tensile Forces ◽  
Seismic Accelerations

Earthquake accelerations can cause many problems in sloping ground. One such problem is that accelerations are greatly amplified at the crest of slopes. This topographic amplification can lead to acceleration gradients along the ground surface, which could create tensile forces in long surface structures that extend between areas of different amplifications. This paper uses centrifuge modelling to demonstrate and quantify this as a problem for a particular slope configuration. A special brittle structure has been constructed to undergo damage in the presence of large differential accelerations. The structure is seen to connect the crest to the level ground behind the crest during an earthquake, reducing the amplitude of the crest motion at the expense of structural tension. Topographic amplification is shown to be a clear function of frequency, and is especially serious for loading frequencies above the natural frequency of the soil layer.

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