Mean effective stress

Note that the values given are increments over the initial state of stress once the FEBEX tunnel was open. They represent therefore the combined effect of temperature effects (the dominant phenomenon), the generation and dissipation of pore pressures and the swelling pressure effects. At the radial distance of 3 m the increments of mean effective stress dominate. Incremental shear stresses tend to be a fraction of the incremental mean... 

Figure 1 shows the loading paths in three-dimensional space (mean effective stress-shear stress-temperature). The procedure for carrying out the tests in triaxial conditions was as follows ... 

K is the volume change potential [= k In (Po/Pu)]/ where p = mean effective stress at critical state... 

Following the sign convention used in soil mechanics, we can write the mean effective stress as p = —< 33. Then the equilibrium equation (6.29) is given by... 

Empirical factor to correlate the undrained shear strength to the cone resistance Bearing capacity factors Mean effective stress Atmospheric pressure Allowable load Measured cone resistance... 

In sedimentary areas, porosity decreases nonlinearly with depth as a result of compaction. The controlling property for this compaction is the mean effective stress. The first empirical formulation is probably that of Athy (1930) ... 

A more important effect of prestressiag is its effect on the mean stress at the bore of the cylinder when an internal pressure is appHed. It may be seen from Figure 6 that when an initially stress-free cylinder is subjected to an internal pressure, the shear stress at the bore of the cylinder increases from O to A. On the other hand, when a prestressed cylinder of the same dimensions is subjected to the same internal pressure, the shear stress at the bore changes from C to E. Although the range of shear stress is the same ia the two cases (distance OA = CE), the mean shear stress ia the prestressed cylinder, represented by point G, is smaller than that for the initially stress-free cylinder represented by point H. This reduction in the mean shear stress increases the fatigue strength of components subjected to repeated internal pressure. 

Fig. 17. Effect of mean shear stress on the fatigue strength of EN25 for life of 10 cycles (92). To convert MPa to psi, multiply by 145.

In experiments with cultured cells it has been shown that osteocytes, but not periosteal fibroblasts, are extremely sensitive to fluid flow, resulting in increased prostaglandin as well as nitric oxide production [104, 105], Three different cell populations, namely osteocytes, osteoblasts, and periosteal fibroblasts, were subjected to two stress regimes, pulsatile fluid flow and intermittent hydrostatic compression [104], Intermittent hydrostatic compression was applied at 0.3 Hz with a 13-kPa peak pressure. The pulsatile fluid flow was a fluid flow with a mean shear stress of 0.5 Pa with cyclic variations of 0.02 Pa at 5 Hz. The maximal hydrostatic pressure rate was 130 kPa/sec and the maximal fluid shear stress rate was 12 Pa/sec. Under both stress regimes, osteocytes appeared more sensitive than osteoblasts, and osteoblasts more sensitive than periosteal fibroblasts. However, despite the large difference in peak stress and peak stress rate, pulsatile fluid flow was more effective than intermittent hydrostatic compression. Osteocytes, but not the other cell types, responded to 1 hour pulsatile fluid flow treatment with a sustained prostaglandin E2 upregula-... 

Infection by dwarf mistletoe and true mistletoe of conifer hosts is commonplace in the San Bernardino and Angeles National Forests. There is no experimental evidence to define the ozone sensitivity of the aerial shoots of the mistletoes relative to the foliage of their conifer hosts. Cursory observations of dwarf mistletoe on pines suggest no injury to dwarf mistletoe shoots. The dwarf mistletoes derive their elaborated carbohydrates entirely from their host (31), and ozone probably depletes the stored carbohydrates of needle tissue (26) which may have been translocated to the parasite. The combined effect of these agents probably means greater stress on the host. On the other hand, true mistletoes manufacture their own carbohydrates (31) and may benefit the host if they are less sensitive to oxidant than the host tree. 

Fig. 6. Effective stress has been color coded for its proximity to the hydraulic seal failure limit of 1000 psi. Green represents a low likelihood of seal failure. Yellow indicates uncertainty based on an analysis of the estimated error in effective stress. Certain basins stand out as either low risk (e.g.. Auger basin) or high risk (e.g., Amundsen basin). The updip margins of most basins show high risk in prospectivity. This allowed explorationists a quantitative means of not only highgrading prospects in this fairway but also opening new opportunities. The inset shows the extent of the area of study in the Gulf of Mexico.

There is three times more lymph fluid in the body than blood, yet it has no organ like the heart to pump it. That means it relies on deep breathing, movement, and massage to flow effectively. Stress plays a role in lymph flow,... 

Equation (1.387) for the mean velocity is formally identical to the original Navier-Stokes equation, provided that we absorb the Reynolds stress into a more general stress tensor. An effective stress tensor is thus defined by... 

Table 5. Mean effective and octahedral shear stresses recorded at a radial distance of 3m in borehole SG2 Incremental Incremental Incremental...

For the analysis of the FEB EX in situ test, a soil mechanics state-surface model was implemented. This state-surface approach provides a better representation of bentonite behavior under partially saturated conditions than a single effective stress approach. The logarithmic state surface model proposed by Lloret and Alonso (1985) was adopted in this analysis. In their model, void ratio (e) is a function of both net mean stress, (Ora" = Om - Pg. where = total mean stress and Pg is gas pressure) and suction (s = Pg -Pi, where Pg and pi is gas and liquid pressures, repectively). 

Figure 5. Identification of the yield points from different stress-strain criterion a) volumetric strain versus mean effective pressure and b) dissipated stress energy versus ratio q/p. ...

In assuming the transition from a normal effective stress a to normal effective stress a (with 0 2 ni since we are studying the stress variation due to pressure in the joint), we can write the effective stresses as a function of displacements starting with a zero effective stress, by means of the following relationships ... 

It can be seen from the above three Figures 6-8 that (1) Temperature has some effect to permeability for Nj and CH4 it decreases with increasing temperature at the same effective stress. While temperature has no obvious effect for COj it is very close to each other at 35°C, 40°C and 45°C. (2) Permeabihty is a httle higher at 35°C than 40°C and 45°C for Nj and CH4 at which the value is close to each other under the same effective stress while permeabihty is very close to each other for CO2 at all 35°C, 40°C and 45°C, which means temperature has no obvious effect to permeabihty for COj. (3) When effective stress reaches nearly 6 Mpa, permeability value gets close to one value for all temperatures. It is 0.15 for 0.04 for CH4 and 0.01 for CO,. 

Idealized void ratio versus log mean effective principal stress as a function of ICL, CVR, and rebound expansion line. 

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