A hydromechanical relation governing internal stability of cohesionless soil

2011 ◽  
Vol 48 (3) ◽  
pp. 413-424 ◽  
Author(s):  
Ricardo Moffat ◽  
R. Jonathan Fannin
Keyword(s):  
Seepage Flow ◽  
Hydraulic Gradient ◽  
Cohesionless Soil ◽  
Cohesionless Soils ◽  
Critical Hydraulic Gradient ◽  
Internal Instability ◽  
Short Period ◽  
Flow Through ◽  
Permeameter Tests ◽  
Novel Concept

Results are presented from permeameter tests involving unidirectional seepage flow through reconstituted specimens of four widely graded cohesionless soils. The onset of instability is defined by a significant decrease in local hydraulic gradient over a relatively short period of time. The novel concept of a hydromechanical path in stress ([Formula: see text]) – gradient (ijk) space is proposed, which describes the response to seepage flow during testing and terminates at the value of critical hydraulic gradient. The path terminus establishes a hydromechanical boundary governing the onset of seepage-induced internal instability in one-dimensional flow. The boundary represents a failure envelope, which is different for each of the four soils tested. A ranking of seepage-induced instability for each soil, from most unstable to least unstable, is found similar, but not identical to, the susceptibility to internal instability determined from empirical analysis of the gradation shape.

Spatial and temporal progression of internal erosion in cohesionless soil

2011 ◽  
Vol 48 (3) ◽  
pp. 399-412 ◽  
Author(s):  
Ricardo Moffat ◽  
R. Jonathan Fannin ◽  
Stephen J. Garner
Keyword(s):  
Seepage Flow ◽  
Hydraulic Gradient ◽  
Internal Erosion ◽  
Cohesionless Soil ◽  
Cohesionless Soils ◽  
Multi Stage ◽  
Internal Instability ◽  
Post Test ◽  
Erosion Test ◽  
Permeameter Tests

Permeameter tests were performed on four widely graded cohesionless soils, to study their susceptibility to internal erosion. Test specimens were reconstituted as a saturated slurry, consolidated, and then subjected to multi-stage seepage flow under increasing hydraulic gradient. The occurrence of internal instability is described qualitatively, from visual observations through the wall of the permeameter during a test and from post-test observations; it is also described quantitatively, from change of hydraulic gradient within the specimen and from axial displacement during a test. The results provide a novel insight into the spatial and temporal progression of seepage-induced internal instability. This insight yields an improved characterization of suffusion and suffosion in cohesionless soils, the progression of which appears governed by a critical combination of hydraulic gradient and effective stress.

scholarly journals Evaluation of the internal stability of well-graded silty sand through the long-term seepage test

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Hee-Jun Lee ◽  
In-Hyun Kim ◽  
Choong-Ki Chung
Keyword(s):  
Critical Value ◽  
Hydraulic Gradient ◽  
Silty Sand ◽  
Internal Erosion ◽  
Soil Behavior ◽  
Soil Particles ◽  
Critical Hydraulic Gradient ◽  
Internal Instability ◽  
Short Period

AbstractSuffusion is the phenomenon responsible for internal erosion, and is the process by which finer soil particles are moved through the constrictions between the larger soil particles by seepage forces. Generally, gap-graded soil is known to be susceptible to suffusion. Meanwhile, suffusion of well-graded silty sand and the resulting soil behavior are not well understood. Moreover, the previous researches on laboratory suffusion tests focused on the study of the critical hydraulic gradient, which triggers the internal instability of the soils within a short period of time. Therefore, in this study, long-term suffusion tests were conducted on well-graded silty sand under a hydraulic gradient lower than the critical value. As a result, abrupt increases in permeability and amount of soil discharged were observed due to the progressive migration of the soil particles, resulting in suffusion even at a relatively low hydraulic gradient.

scholarly journals Experimental Study on Stress-Dependent Nonlinear Flow Behavior and Normalized Transmissivity of Real Rock Fracture Networks

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Qian Yin ◽  
Hongwen Jing ◽  
Richeng Liu ◽  
Guowei Ma ◽  
Liyuan Yu ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Rock Fracture ◽  
Hydraulic Gradient ◽  
Nonlinear Flow ◽  
Fracture Networks ◽  
Critical Hydraulic Gradient ◽  
Boundary Load ◽  
Flow Through ◽  
Stress Dependent ◽  
Rock Fracture Networks

The mechanism and quantitative descriptions of nonlinear fluid flow through rock fractures are difficult issues of high concern in underground engineering fields. In order to study the effects of fracture geometry and loading conditions on nonlinear flow properties and normalized transmissivity through fracture networks, stress-dependent fluid flow tests were conducted on real rock fracture networks with different number of intersections (1, 4, 7, and 12) and subjected to various applied boundary loads (7, 14, 21, 28, and 35 kN). For all cases, the inlet hydraulic pressures ranged from 0 to 0.6 MPa. The test results show that Forchheimer’s law provides an excellent description of the nonlinear fluid flow in fracture networks. The linear coefficient a and nonlinear coefficient b in Forchheimer’s law J=aQ+bQ2 generally decrease with the number of intersections but increase with the boundary load. The relationships between a and b can be well fitted with a power function. A nonlinear effect factor E=bQ2/(aQ+bQ2) was used to quantitatively characterize the nonlinear behaviors of fluid flow through fracture networks. By defining a critical value of E = 10%, the critical hydraulic gradient was calculated. The critical hydraulic gradient decreases with the number of intersections due to richer flowing paths but increases with the boundary load due to fracture closure. The transmissivity of fracture networks decreases with the hydraulic gradient, and the variation process can be estimated using an exponential function. A mathematical expression T/T0=1-exp⁡(-αJ-0.45) for decreased normalized transmissivity T/T0 against the hydraulic gradient J was established. When the hydraulic gradient is small, T/T0 holds a constant value of 1.0. With increasing hydraulic gradient, the reduction rate of T/T0 first increases and then decreases. The equivalent permeability of fracture networks decreases with the applied boundary load, and permeability changes at low load levels are more sensitive.

scholarly journals Impacts of Consolidation Time on the Critical Hydraulic Gradient of Newly Deposited Silty Seabed in the Yellow River Delta

2021 ◽  
Vol 9 (3) ◽  
pp. 270
Author(s):  
Meiyun Tang ◽  
Yonggang Jia ◽  
Shaotong Zhang ◽  
Chenxi Wang ◽  
Hanlu Liu
Keyword(s):  
Yellow River ◽  
Yellow River Delta ◽  
Hydraulic Gradient ◽  
River Delta ◽  
Theoretical Formula ◽  
The Yellow River ◽  
The Yellow River Delta ◽  
Critical Hydraulic Gradient ◽  
Seepage Flows ◽  
The Yrd

The silty seabed in the Yellow River Delta (YRD) is exposed to deposition, liquefaction, and reconsolidation repeatedly, during which seepage flows are crucial to the seabed strength. In extreme cases, seepage flows could cause seepage failure (SF) in the seabed, endangering the offshore structures. A critical condition exists for the occurrence of SF, i.e., the critical hydraulic gradient (icr). Compared with cohesionless sands, the icr of cohesive sediments is more complex, and no universal evaluation theory is available yet. The present work first improved a self-designed annular flume to avoid SF along the sidewall, then simulated the SF process of the seabed with different consolidation times in order to explore the icr of newly deposited silty seabed in the YRD. It is found that the theoretical formula for icr of cohesionless soil grossly underestimated the icr of cohesive soil. The icr range of silty seabed in the YRD was 8–16, which was significantly affected by the cohesion and was inversely proportional to the seabed fluidization degree. SF could “pump” the sediments vertically from the interior of the seabed with a contribution to sediment resuspension of up to 93.2–96.8%. The higher the consolidation degree, the smaller the contribution will be.

Comportement de pieux d'essais instrumentés sous charge horizontale

1993 ◽  
Vol 30 (1) ◽  
pp. 1-11
Author(s):  
R. Frank ◽  
H. Zervogiannis ◽  
S. Christoulas ◽  
V. Papadopoulos ◽  
N. Kalteziotis
Keyword(s):  
Pile Foundation ◽  
Bending Moment ◽  
Standard Penetration Test ◽  
American Petroleum Institute ◽  
Full Scale ◽  
Test Method ◽  
Cohesionless Soil ◽  
Penetration Test ◽  
Cohesionless Soils ◽  
Final Design

This paper describes the behaviour of two test piles (one bored and postgrouted and one simply bored, both 31.7 m long and 0.75 m in diameter) subjected to horizontal loads. These full-scale pile tests were carried out for the actual design of the pile foundation of a pier of the Evripos cable-stayed bridge. This bridge will link the Euboea Island to mainland Greece. The two piles have already been subjected to bearing capacity tests under axial loadings. The inclinometer measurements, taken during the present tests, yielded, in particular, the deformed shape of the piles as well as the bending moments. Conclusions could be drawn for the final design of the pile foundation with respect to horizontal loadings. Furthermore, various calculation methods using p–y reaction curves for cohesionless soils have been checked: the Ménard pressuremeter method, the method of the American Petroleum Institute recommendations, and the Standard penetration test method of Christoulas. These pile tests show that simple measurements, taken on construction sites, can yield interesting results on the actual behaviour of horizontally loaded piles. Key words : pile, horizontal loading, full-scale test, horizontal loads, bending moment, subgrade reaction modulus, p–y curve, cohesionless soil, Standard penetration test, pressuremeter test.

Sign in / Sign up

Export Citation Format

Share Document