Field Evaluation of the Stiffness of Unbound Aggregate Base Layers in Inverted Flexible Pavements

2003 ◽  
Vol 1837 (1) ◽  
pp. 50-60 ◽  
Author(s):  
Ronald G. Terrell ◽  
Brady R. Cox ◽  
Kenneth H. Stokoe ◽  
John J. Allen ◽  
Dwayne Lewis
Keyword(s):  
Pore Water ◽  
Pressure Coefficient ◽  
Field Evaluation ◽  
The Other ◽  
Base Layer ◽  
Normal Stresses ◽  
Pore Water Pressures ◽  
Aggregate Base ◽  
Traditional Section ◽  
Unbound Aggregate

Unbound aggregate base layers in a quarry haul road in Georgia were characterized using embedded sensors and in situ seismic testing. Two sections of the road were constructed as inverted pavements, one using a South African Roads Board method and the other using a conventional Georgia Department of Transportation method. A third was constructed using a traditional method. Miniaturized versions of traditional cross-hole and downhole seismic tests were conducted to determine the stiffnesses of each base layer. Horizontally propagating compression and shear waves were measured under four different loading conditions to determine Young’s moduli and Poisson’s ratios of the base. An increase in stiffness with an increase in load was measured. Additionally, it was found that the Georgia and South Africa sections had similar stiffnesses. Surprisingly, the traditional section was found to be somewhat stiffer than the other sections. This higher stiffness is thought to be caused by a prolonged period of compaction before construction of the unbound aggregate base layer, which essentially transforms the traditional section into an inverted pavement. Using the vertical total normal stresses computed from ILLI-PAVE, a value of 0.3 for the earth pressure coefficient was found to be reasonable for this material in determining the radial total normal stresses. The radial effective normal stresses were calculated from the radial total normal stresses and experimentally determined pore water pressures. Additionally, the negative pore water pressures in the partially saturated granular base had a significant impact on the stiffness of the unbound aggregate base layer, especially under small load levels.

Moisture Accumulation and Pore Water Pressures at Base of Pavements

1996 ◽  
Vol 1546 (1) ◽  
pp. 151-161 ◽  
Author(s):  
K. D. Eigenbrod ◽  
G. J. A. Kennepohl
Keyword(s):  
Pore Water ◽  
Base Material ◽  
The United States ◽  
Base Layer ◽  
Frozen Ground ◽  
Extensive Field ◽  
Pore Water Pressures ◽  
Excess Moisture ◽  
Pavement Base ◽  
Granular Base

A unique mechanism based on extensive field and laboratory studies is presented to account for certain premature failures of flexible pavements in cold areas like those in Scandinavia and in northern parts of Canada and the United States. Water condensing at the interface between pavement and granular base accumulates at subzero temperatures resulting in excess moisture in this zone. During the thaw period of the uppermost base layer, the excess water in the aggregate is trapped between impervious layers of frozen ground to the sides and below as well as an impervious layer of asphalt pavement above. Because of this containment, high pore water pressures can occur, leading to loss in shear strength of the base material and thus to failure of the pavement structure itself. It was found that under special conditions, excess moisture can accumulate in granular base with a silt content greater than 20 percent and very high pore water pressures can develop during initial thaw at the pavement-soil interface. With silt contents of less than 2 percent, excess pore water pressures can be avoided during thaw. It was also shown that when a clean open gravel is placed below the pavement on top of a silty base material, moisture accumulation near the pavement-base interface can be prevented, and thus also the development of high pore water pressures.

scholarly journals Influences of Pore-Water Pressure on Slope Stability considering Strength Nonlinearity

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Di Wu ◽  
Yuke Wang ◽  
Fei Zhang ◽  
Yue Qiu
Keyword(s):  
Slope Stability ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Pressure Coefficient ◽  
Stability Evaluation ◽  
Slip Surfaces ◽  
Stability Of Slopes ◽  
Pore Water Pressures ◽  
Linear And Nonlinear

The pore-water pressure is a vital factor in determining the slope stability. To deal with the stability of slopes undergoing pore-water pressures, this paper used the pore-water pressure coefficient to develop the three-dimensional limit analysis method for slope stability evaluation with a nonlinear strength envelope. For numerical slope examples, the critical heights and corresponding critical slip surfaces associated with linear and nonlinear envelopes were derived by using a numerical optimization procedure. The influences of pore-water pressures on the slope stability were addressed by comparing the upper-bound solutions derived by linear and nonlinear strength envelopes (the linear and nonlinear results for short). The obtained two critical inclinations between the linear and nonlinear results both decrease and gradually approach with increasing pore-water pressure coefficient. For most slopes subjected to pore-water pressures, using the linear Mohr–Coulomb envelope will obviously overestimate the slope critical height. The overestimation resulted from the linear criterion will become more distinct for slopes with smaller widths. Besides, the presented results showed that the equivalent internal friction angle tends to have a weaker increasing trend for steeper slopes as pore-water pressure coefficient increases. Hence, when pore-water pressure coefficient increases, the critical slip surfaces of gentle slopes with nonlinear strength criteria become shallower, but the critical slip surfaces of steep slopes seem to have no consistent change law. These results and analyses can illustrate the significance of the application of nonlinear strength envelopes in slope stability evaluation considering pore-water pressures and provide certain reference advice in slope engineering design and landslide prevention.

Pore-water pressure response during undrained isotropic load changes in layered soils

1999 ◽  
Vol 36 (3) ◽  
pp. 544-555
Author(s):  
K D Eigenbrod ◽  
W H Wurmnest
Keyword(s):  
Pore Pressure ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Pressure Coefficient ◽  
Shear Stresses ◽  
Pressure Equalization ◽  
Pore Water Pressures ◽  
Internal Pore ◽  
Varved Clay

Low pore-water pressure responses observed during undrained isotropic loading of thinly interbedded varved clay specimens were related to internal pore-water pressure equalization and internal shearing between soft clay seams and stiff silt layers of the varved clay. Both processes were analyzed in two separate models: a finite element analysis of the layered soil specimen with different elastic properties for each layer showed that shear stresses can develop along the layer interfaces during undrained isotropic loading. However, because the shear stresses are small and restricted to a narrow zone close to the surface of the cylindrical specimen, it appeared that the effect of shearing on the overall pore-water responses is negligible. The analysis of the pore-water pressures during undrained, isotropic loading demonstrated that hydraulic gradients between the two layers will develop. As a result, pore water will drain from the clay into the silt, leading to consolidation of the clay and swelling of the silt seams. The stabilized pore-water pressures should be the same as the pore-water pressures measured for the overall specimen, if the effect of internal shearing is negligible. Comparison of the computed with the measured overall pore-water pressure responses during testing for Skempton's pore-pressure coefficient B indicated reasonable agreement.Key words: Skempton's pore-pressure coefficient B, pore-water pressure response, varved clays, internal shearing, internal pore-water pressure equalization.

A new approach to the stability analysis of thawing slopes

1980 ◽  
Vol 17 (4) ◽  
pp. 607-612 ◽  
Author(s):  
Luis E. Vallejo
Keyword(s):  
Stability Analysis ◽  
Water Content ◽  
Pore Water ◽  
Active Layer ◽  
Necessary Conditions ◽  
Mass Movements ◽  
New Approach ◽  
Pore Water Pressures ◽  
The Stability ◽  
Excess Pore

A new approach to the stability analysis of thawing slopes at shallow depths, taking into consideration their structure (this being a mixture of hard crumbs of soil and a fluid matrix), is presented. The new approach explains shallow mass movements such as skin flows and tongues of bimodal flows, which usually take place on very low slope inclinations independently of excess pore water pressures or increased water content in the active layer, which are necessary conditions in the methods available to date to explain these movements.

An analysis of the stability of thawing slopes, Ellesmere Island, Nunavut, Canada

2000 ◽  
Vol 37 (2) ◽  
pp. 449-462 ◽  
Author(s):  
Charles Harris ◽  
Antoni G Lewkowicz
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Active Layer ◽  
Factor Of Safety ◽  
High Arctic ◽  
Ellesmere Island ◽  
Sensitivity Analyses ◽  
Pore Water Pressures ◽  
Hot Weather ◽  
The Stability

Active-layer detachment slides are locally common on Fosheim Peninsula, Ellesmere Island, where permafrost is continuous, the active layer is 0.5-0.75 m thick, and summer temperatures are unusually high in comparison with much of the Canadian High Arctic. In this paper we report pore-water pressures at the base of the active layer, recorded in situ on two slopes in late July and early August 1995. These data form the basis for slope stability analyses based on effective stress conditions. During fieldwork, the factor of safety within an old detachment slide on a slope at Hot Weather Creek was slightly greater than unity. At "Big Slide Creek," on a slope showing no evidence of earlier detachment failures, the factor of safety was less than unity on a steep basal slope section but greater than unity elsewhere. In the upper slope, pore-water pressures were only just subcritical. Sensitivity analyses demonstrate that the stability of the shallow active layer is strongly influenced by changes in soil shear strength. Possible mechanisms for reduction in shear strength through time include weathering of soils and gradual increases in basal active layer ice content. However, we suggest here that soil shearing during annual gelifluction movements is most likely to progressively reduce shear strengths at the base of the active layer from peak values to close to residual, facilitating the triggering of active-layer detachment failures.Key words: detachment slides, Ellesmere Island, pore-water pressures, gelifluction.

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