Shear slip

An extension, by accounting for gas-liquid interfacial interactions via velocity-and shear-slip factors was then proposed by Al-Dahhan et al. [42] to lift the model disparities observed for conditions of high gas throughputs and elevated pressures. Later, Iliuta et al. [43] derived more general slip-corrective correlations. 

ESTIMATION OF CRITICAL PORE PRESSURE FOR SHEAR SLIP OF FRACTURES AT THE SOULTZ HOT DRY ROCK GEOTHERMAL RESERVOIR USING MICROSEISMIC MULTIPLETS... 

CALCULATION OF CRITICAL PORE-PRESSURE FOR SHEAR SLIP OF FRACTURE... 

We estimate distribution of critical pore-pressure of fractures for shear slip during hydraulic stimulation. 

According to Coulomb s law of friction, the relationship among shear stress, normal stress, coefficient of friction and pore-pressure at the moment of shear slip (critical condition) due to increasing of pore-pressure are described as follow. 

The estimated critical pore-pressure for shear slip suggests that the fluid pressure in fractures is higher value near the fractured zones 1 and 2 around 2,900 m, and declines as the fractures are away from the zones. 

Figure 5. Calculated critical pore-pressure for shear slip of fractures versus depth of estimated fractures. The zone of permeable fracture, which are detected by well loggings are indicated by shaded rectangles.

It is considered that some fractures opened with increasing pore-pressure maybe after shear slip because the maximum wellhead pressure is about lOMPa. However, Mode I fractures can not radiate seismic events having enough energy, and we can not detect these seismic events. Therefore, we consider only shearing fractures for estimation of critical pore-pressure using induced microseismic events. 

The rapid disappearance of these lamellae at EDR >4.6 suggests that when the chain tilt reaches at an angle, the lamellae suddenly broke into smaller blocks due to shear slip along the chain direction and are reorganized in microfibrils oriented along the draw direction. 

The measured shear stress-shear slip (v-v) curve of the adhesive layer as shown in Fig. 7 above was too cumbersome to be directly integrated into the simple calculation programme. It was first approximated by a 5th order polynomial as shown in equation (6). 

A recent bond strength model proposed by Chen and Teng [47] combines the fracture mechanics analysis with experimental data and provides a better prediction of the basic parameters and Pu. The model is a modified form of the model originally proposed by Yuan and Wu [45] and Yuan and co-workers [46] and based on a shear-slip behaviour of FRP plate to concrete as shown in Figure 5.15. The critical slip values of dj at peak shear stress and df at failure are taken as 0.02 mm and 0.2 mm, respectively, and the following forms are proposed for and P, ... 

Figure 5.15 Shear-slip models for FRP-to-concrete bonded joints [45]...

Compared to common monolithic beams, composite beams with deformable shear connection present additional difficulties. Even in very simple structural systems (e.g., simply supported beams), complex distributions of the interface slip and force can develop. Different finite elements of composite beams with deformable shear connection have been developed and presented in the literature (Spacone El-Tawil 2004, Dall Asta 8c Zona 2004). These elements include suitable models describing section deformations in order to compute the section force resultants of steel-concrete composite members. This requires the use of realistic material constitutive models for beam steel, reinforcement steel, concrete, and shear-slip behaviour of the studs connecting the two structural components (Zona et al. 2005, 2006, Barbato et al. 2007). 

Let us consider the shearing behavior of a heavily over-consolidated clay. We start to make it swell from a point A on the normally consolidated line (NCL) to a point B shown in Fig. 6.3d, e. When we perform an undrained triaxial test, the shear stress q attains the yield point P on the Hvoslev surface (namely the maximum point for the stress ratio rj = q/p ), and moves on the Hvoslev surface to reach the point C on the CSL. On the other hand, if a drained triaxial test is performed from the point B, the shear stress q attains the peak strength Q, then the stress reaches a residual state R through a softening process. Note that in practical experiments a shearing slip surface is commonly observed, and the whole specimen cannot reach the residual state. 

---