Plane Strain Deformation of a Poroelastic Half-space in Welded Contact with Transversely Isotropic Elastic Half-Space

Plane Strain Deformation of a Poroelastic Half-space in Welded Contact with Transversely Isotropic Elastic Half-Space NEELAM KUMARI * And ASEEM MIGLANI ** * Assistant Professor, Department of Mathematics, Chaudhary Devi Lal University Sirsa-125055, Haryana (India) Email: neelamkumaricdlu@gmail.com ** Professor, Department of Mathematics, Chaudhary Devi Lal University Sirsa-125055, Haryana (India) Abstract The Biot linearized theory for fluid saturated porous materials is used to study the plane strain deformation of an isotropic, homogeneous, poroelastpic half space in welded contact with a homogeneous, transversely isotropic, elastic half space caused by an inclined line-load in elastic half space. The integral expressions for the displacements and stresses in the two half spaces in welded contact are obtained from the corresponding expressions for an unbounded transversely isotropic elastic and poroelastic medium by applying boundary conditions at the interface. The integrals for the inclined line-load are solved analytically for the limiting case i.e. undrained conditions in high frequency limit. The undrained displacements, stresses and pore pressure are shown graphically. Expression for the pore pressure is also calculated for undrained conditions in the high frequency limit. Key words: Inclined line-load, Transversely Isotropic, Plane strain, Poroelastic, Welded half-spaces Introduction Poroelasticity is the mechanics of poroelastic solids with fluid filled pores. Its mathematical theory deals with the mechanical behaviour of an elastic porous medium which is either completely filled or partially filled with pore fluid and study the time dependent coupling between the deformation of the rock and fluid flow within the rock. The study of deformation by buried sources of a fluid saturated porous medium is very important because of its applications in earthquake engineering, soil mechanics, seismology, hydrology, geomechanics, geophysics etc. Biot ([1],[2]) developed linearized constitutive and field equations for poroelastic medium which has been used by many researchers (see e.g. Wang [3] and the references listed there in). When the source surface is very long in one direction in comparison with the others, the use of two dimensional approximation is justified and consequently calculations are simplified to a great extent and one gets a closed form analytical solution. A very long strip-source and a very long line-source are examples of two dimensional sources. Love [4] obtained expressions for the displacements due to a line-source in an isotropic elastic medium. Maruyama[5] obtained the displacements and stress fields corresponding to long strike-slip faults in a homogeneous isotropic half-space. The two dimensional problem has also been discussed by Rudnicki[6], Rudnicki and Roeloffs[7],Singh and Rani [8] Rani and Singh[9], Singh et al. [10]. Different approaches and methods like boundary value method, displacement discontinuity method, Galerkin vector approach, displacement function approach and eigen value approach, Biot stress function approach etc. have been made to study the plane strain (two dimensional) problem of poroelasticity. The use of eigen value approach has the advantage of finding the solutions of the governing equations in the matrix form notations that avoids the complicated nature of the problem. Kumar et al.[11][12], Garg et al.[13], Kumar and Ailwalia [14],Selim and Ahmed [15], Selim[16], Chugh et al[17] etc. have used this approach for solving plane strain problem of elasticity and poroelasticity. In the present paper we study the plane strain deformation of a two phase medium consisting of an isotropic, homogeneous, poroelastic half space in welded contact with transversely isotropic, homogeneous, perfectly elastic half space caused by an inclined line-load in elastic half space. Using Biot stress function(biot[18],roeloffs[19]) and Fourier transform,we find stresses,displacement and pore pressure for poroelastic unbounded medium in integral form and using eigen value approach following Fourier transform,we find stresses and displacement for unbounded elastic medium in integral form. Then we obtain the integral expressions for the displacements and stresses in the two half spaces in welded contact from the corresponding expressions for an unbounded elastic and poroelastic medium by applying suitable boundary conditions at the interface. These integrals cannot be solved analytically for arbitrary values of the frequency.we evaluate these integrals for the limiting case i.e. undrained conditions in high frequency limit. The undrained displacements, stresses and pore pressure for poroelastic half space are shown graphically. ISSN : 0975-5462 Vol. 4 No.11 November 2012 4555

Geomechanics problems, such as loading by a reservoir lake or seabed structure that is very extensive in one direction on the earth s surface, can be solved as two dimensional plane strain problem. Bell and Nur[20]) used two dimensional half space models with surface loading to study the change in strength produced by reservoir-induced pore pressure and stresses for thrust, normal and strike-slip faulting. Formulation of the Problem Consider a homogeneous, transversely isotropic, elastic half space over an isotropic homogeneous, poroelastic half space which is in welded contact at the interface. A rectangular Cartesian coordinate system oxyz is taken in such a way that a plane x=0 coincides with the intersecting surface of the two half spaces. We take x-axis vertically downwards in the poroelastic half space so that isotropic homogeneous, poroelastic half space becomes the medium-i (x0) and the elastic half space becomes the medium-ii(x0). Further an inclined lineload of magnitude F 0, per unit length, is acting on the z-axis and its inclination with x-axis is (Fig. 1) The geometry of the problem as shown in figure 1 and it conforms to the two dimensional approximation. Fig.1 An inclined line load F 0 acting on z-axis with its inclination δ with x-axis Considering the cartesian coordinates (x, y, z) as (x 1, x 2, x 3 ), we have 0 and the displacement components U,U, U are independent of the Cartesian coordinate for the present two dimensional problem. Under this assumption the plane strain problem (U 0 and the antiplane strain problem U U 0 get decoupled, and can therefore be solved independently. Here, we consider only the plane strain problem. Solution For Poroelastic Half-space Medium-I (x0): An isotropic, homogeneous, poroelastic medium can be described by five poroelastic parameters; Drained Poisson s ratio (), undrained Poisson s ratio ( ), Shear modulus (G), hydraulic diffusivity (c) and Skempton s coefficient (B). Darcy conductivity (χ) and Biot-willis coefficient can be written in terms of these five parameters: χ 91 2GB 11, 3 B1 21, 1.1 1.2 Following the two dimensional plane strain problem for an isotropic poroelastic medium can be solved in terms of Biot s stress function F(Wang [3])as σ 11= F, σ 22 = F X, σ 12=- F X, (1.3) ( F 2 0, 1.4 ISSN : 0975-5462 Vol. 4 No.11 November 2012 4556

[ + B p 0, (1.5) where ij denotes the total stress in the fluid saturated porous elastic material, p the excess fluid pore pressure (compression negative) and = 1.6 is the poroelastic stress coefficient. From equations (1.4) and (1.5) we get the following decoupled equations c p 0, 1.7 c F 0, The general solution of equation (1.7) may be expressed as pp p, where p and p satisfies the following equations c p, p 0. Similarly, the general solution of equation (1.8) may be expressed as FF F, 1.8 1.9 1.10 1.11 1.12 where c F F, F 0. (1.13) 1.14 Separation of time and space variables can be made for each of the four functions, p, p, F 1 and F 2. Assuming the time dependence as exp (iωt), equations (1.10), (1.11), (1.13) and (1.14) become p ω p 0, p 0, F ω F 0, F 0, where p, p, F 1 and F 2 are now functions of x and y only. 1.15 1.16 1.17 1.18 Fourier transforms are now used to get suitable solutions of equations (1.15)-(1.18), which on using equations (1.9) and (1.12), can be written as P A e A e A e A e e dk, F 1 2 B e B e B B k xe B B k xe e dk, 1.19 1.20 For medium I(x0), using the relation conditions, we have p A e A e e dk, F 1 2 B e B B k xe e dk, 1.21 1.22 ISSN : 0975-5462 Vol. 4 No.11 November 2012 4557

where B, B, B, A and A are functions of k. From (1.4), (1.5), (1.21) and (1.22). We find A ω B η, A 1 v μbk B, m ω, Re m 0, 1.23 Using (1.22) in (1.3), the stresses in medium I(x0) are obtained as σ σ σ B m e B 2B B k xk e e dk, B e B B k xe k e dk, B me B B B k x k e ike dk. 1.24 1.25 1.26 Corresponding to these stresses, the displacements are obtained as (Singh and Rani[8]) 2GU 2GU B e B B 2 2 k xe ike dk, B me B B 1 2 k x k e e dk. 1.27 1.28 Also from equation (1.21), we have ma e k A e e dk, 1.29 Solution For Elastic Solid Half-space Medium-II(x0): The equilibrium equations in Cartesian coordinate system (,, ) in absence of body forces are 0, (1.30) 0, (1.31) 0, (1.32) where are components of stress tensor. The stress-strain relations for an transversely isotropic elastic medium are d d d 0 0 0 d d d 0 0 0 = d d d 0 0 0 0 0 0 d 0 0 2, 1.33 0 0 0 0 d 0 0 0 0 0 0 d 2 d 2 where are the components of the strain tensor and are related with displacement components (,, ) by the relations e,1 i,j 3, (1.34) The two suffix quantity d are the elastic moduli for the transversely isotropic elastic medium. We shall write (,, )=(x,y,z), (,, )=(u,v,w) for convenience. The equilibrium equations in terms of the displacement components can be obtained from equations (1.30)-(1.32) by using (1.33) and (1.34) and for the present two dimensional problem are d d d d d 0, (1.35) d d d d d We define Fourier transform(x, k) of (x, y) (Debnath,[21]) as 0, (1.36) ISSN : 0975-5462 Vol. 4 No.11 November 2012 4558

x, k Fx, y x, ye So that x, y 1 2 x, ke, where k is the transformed Fourier parameter. We know that (Sneddon,[22]), 1.37 1.38 F y x, y ik x, k, F y x, y ik x, k, 1.39 Applying Fourier Transform as defined above on equations (1.35) and (1.36), we get k uik, (1.40) k vik, (1.41) The above equations (1.40)-(1.41) can be written in the following vector matrix equation form as N A N (1.42) where u v 0 0 1 0 du N 0 0 0 1,A dx k, R 0 0 ikr dv 0 k R ikr 0 dx Where R, R, R and R are as follow 1.43 R d d, R 2d d d, R 2d 1, R R R R (1.44) Applying eigen value method to solve equation (1.42), we try a solution of the matrix equation (1.42) of the form N (x, k) =E (k) e, 1.45 where s is a parameter and E(k) is a matrix of the type 41.Substituting the value of N from equation (1.45) into equation (1.42),we get the following characteristic equation. s 2k s k 0, 1.46 The solution of the characteristic equation (1.46) gives the repeated eigenvalues as ss s s s k, An eigen vector X, corresponding to the eigenvalue ss k of multiplicity 2 is found to be i k k X, ik, (1.47) k k Second eigen vector X corresponding to the eigenvalue ss k can be obtained as by Ross (1984) ISSN : 0975-5462 Vol. 4 No.11 November 2012 4559

i k x4 X kx i k k x k k x, (1.48) An eigen vector X, corresponding to the eigenvalue s s k of multiplicity 2 is found to be X, i k k ik, (1.49) k k Similarly second eigen vector X corresponding to the eigenvalue ss k can be obtained as by Ross (1984) i k x4 X kx, (1.50) i k k x k k x Thus, a general solution of (1.42) for a transversely isotropic elastic medium is N D X D X e D X D X e, 1.51 Where D, D, D and D are coefficients to be determined from boundary conditions. From (1.43) and (1.47)-(1.51), we obtain. u id k D k x e D k D k x e, v kd D x 1 k e D D x 1 k e, du dx i D k D k k x 3d d d d e D k D k k x 3d d d d e (1.52) 1.53, 1.54 dv dx k k D D xe D D xe, 1.55 Inversion of equation (1.52) and (1.53) gives the displacements in the following integral forms D ux, y k D k x e D k D k x e e dk, 1.56 vx, y kd D x e D D x e e dk, 1.57 For the transformed stresses for plane strain deformation parallel to xy plane of a transversely isotropic elastic medium, we make use of equation (1.33)-(1.34) and (1.38)-(1.39), we get τ ikd vd, 1.58 τ d d iku, 1.59 where u, v used in equations (1.58)-(1.59) are Fourier Transform of u(x, y) and v(x, y). Putting the values of u and v from equations (1.52) and (1.53) and their derivatives into equations (1.58)- (1.59) we obtain,, as ISSN : 0975-5462 Vol. 4 No.11 November 2012 4560

3d 2d d d 2 2 2 kx 2 11 11 12 12 kx k d11 d12 D1e d11 d12 k x k D2e d11 d12 τ11 i, 2 2 2 kx 2 3d11 2d11d12 d 12 kx quations ) and (opic)k d11 d12 D3e d11 d12 k x k D4e d11 d 12 d d k k D e k k x D e k k D e k k x D e, (1.60) 1.61 Inversion of equations (1.60)-(1.61) gives the stresses in the following integral forms for a transversely isotropic elastic medium τ i 2 k d d D e d d k x k 3d 2d d d D d d e k d d D e d d k x k 3d 2d d d D d d e e dk, (1.62) τ d k k D d e k k x 2d k D d d e 2 k k D e k k x 2d e k dk, D d d e (1.63) The displacements and stress components for transversely isotropic elastic half space medium II (x0) are now obtained as from equations (1.56)-(1.57) and (1.62)-(1.63) ux, y D k D k x e e dk, 1.64 vx, y kd D x e e dk, 1.65 τ k d d D D d d k x k e e dk, (1.66) τ k k D k k x D e e dk, 1.67 Case (a) Normal Line-load Consider a normal line-load F, per unit length, acting in the positive x-direction on the interface x=0 along z- axis. Since the half spaces are assumed to be in welded contact along the plane x=0, the continuity of the stresses and the displacements give the following boundary conditions at x=0: σ τ, 2.1 σ τ F δy, 2.2 U x, y ux, y, 2.3 U x, y vx, y, 2.4 where in equation (2.2) is the Dirac delta function and it satisfies the following properties δydy 1, δy edk, (2.5) Also, if we assume that the interface is impermeable, the hydraulic boundary condition x=0 is 0. (2.6) ISSN : 0975-5462 Vol. 4 No.11 November 2012 4561

Fig.2 A Normal Line-load F, per unit length, acting in the positive x-direction on the interface x=0 along z-axis. Using equations (1.25)-(1.29), (1.64)-(1.67), and (2.1)-(2.6), we get the following system of equations mb k B k B m i k D 2m m id 0, 2.7 B B im D D F, (2.8) B B 2 2B 2GiD G D 0, B mb k k 1 2 B 2Gi k D 8Gim D 0, K 2.9 2.10 ma B k b B 0, (2.11) where a iω 2ηc,b 2 3 1 Bk, m d d d, m d d, m, 2.12 Solving the system of equations (2.7)-(2.11) using (2.12), we obtain B B, (2.13) B pb 2D D, B G D G D, 2.14 2.15 D D Fα, EFαα α isd, 2.16 2.17 where α α,p 12, r α 1,q2 2, E F, s, t, (2.18) ISSN : 0975-5462 Vol. 4 No.11 November 2012 4562

Case (a.1) (Undrained state, ) Putting the values of B 1, B 2 and B 3 from equations (2.13)-(2.15) into equations (1.24)-(1.29) which corresponds to the stresses,displacements and pore pressure for poroelastic half space medium 1(x 0 and then taking limit and then integrate, we get P x x y F P xx y x y, x x y F P xx y x y, P y P x y 2F P yx x y, 2GU N F P P 2 2tan y x F P xy x y, σ N F σ N F P 2P σ N F 2.19 2.20 2.21 2.22 2GU N F 2 P P 1 2 logx y F P x y, 2.23 p N 2F 1 BP x 3 x y, 2.24 Similarly Putting the values of D 1, and D 2 from equations (2.16)-(2.17) into equations (1.64)-(1.67) which corresponds to the stresses and displacements for transversely isotropic half space medium II(x 0 for normal line-load,we get u N x, y F 2 P 4m P logx y F P x x y, 2.25 v N x, y F P P tan y x F P xy x y, 2.26 τ N F m x P m P x y F m P xx y x y, 2.27 τ N F m y P 2m m P x y 2F m P yx x y, 2.28 Where P,P,P,P are as follow P G G, P G G, P G 2m, P m 2m m, P P P, P P P P P, P P, P P 1 P P 2 2 P 2 2,P 4GP 2G1 4m P, 3 4 x P 12 P 2GP 8Gm P, 2.29 Case (b) Tangential Line Load Consider a tangential line-load F, per unit length, is acting at the origin in the positive y-direction. Since the half spaces are assumed to be in welded contact along the plane x=0, the continuity of the stresses and the displacements give the following boundary conditions at x=0: σ τ F δy, 3.1 σ τ, 3.2 U x, y ux, y, 3.3 U x, y vx, y, 3.4 where in equation (3.1) is the Dirac delta function. Also, if we assume that the interface is impermeable, the hydraulic boundary condition x=0 is 0. (3.5) ISSN : 0975-5462 Vol. 4 No.11 November 2012 4563

Fig. 3: A Tangential line-load F, per unit length, is acting at the origin in the positive y-direction. Now using equations (1.25)-(1.29), (1.64)-(1.67)) and (3.1)-(3.5) we get the following system of equations mb k B k B m i k D 2m m id F, B B im D m D 0, B B 2 2B 2GiD G D 0, B mb k k 1 2 B 2Gi k D 8Gim D 0, 3.6 3.7 3.8 3.9 ma B k b B 0, (3.10) where,, are same as defined in (2.12) Solving the system of equations (3.6)-(3.10) using (2.12) we obtain B, (3.11) B pb 2D D, 3.12 B, 3.13 D F, EFα D D, where α,p,r,q,e,f,s,t are same as defined in equation (2.18) 3.14 3.15 Putting the values of B 1, B 2 and B 3 from equations (3.11)-(3.13) into equations (1.24)-(1.29) which corresponds to the stresses,displacements and pore pressure for poroelastic half space medium 1(x 0 and then taking limit and then integrate, we get σ T F q y x y 2F q yx x y, σ T F q 2q y x y 2F q yx x y, σ T F q x q x y F q xx y x y, 2GU T F q q 1 2 tan y x F q xy x y, 3.16 3.17 3.18 3.19 ISSN : 0975-5462 Vol. 4 No.11 November 2012 4564

2GU T F 2 q q 2 2logx y F q x y, p T 2F 1 Bq 3 y x y, x 3.20 3.21 Similarly Putting the values of D 1, and D 2 from equations(3.14)-(3.15) into equations (1.64)-(1.67) which corresponds to the stresses and displacements for transversely isotropic half space medium II(x 0 for tangential line-load are and then taking limit and then integrate, we get u T x, y F q 4q m tan y x F q xy x y, v T x, y F 2 q q logx y F q x y, τ T F m y q m q x y 2F m q yx x y, τ T F m x q 2m m q x y F m q where q,q,q,q are as follow q, q P,q P P, q G G, q 12 q 2Gq 8Gm q, P x xx y x y, 3.22 3.23 3.24 3.25 3.26 Case(c) Inclined Line-Load For an inclined line-load,per unit length, we get (Saada,[23]) F F cos δ, F F sin δ, 4.1 The stresses and displacements subjected to inclined line-load can be obtained by superposition of the vertical and tangential cases. The final deformation of the formulated problem is given by U IN x, y U N x, y U T x, y, (4.2) U IN x, y U N x, y U T x, y, (4.3) σ IN x, y σ N x, y σ T x, y, (4.4) σ IN x, y σ N x, y σ T x, y, (4.5) σ IN x, y σ N x, y σ T x, y, 4.6 p IN x, y p N x, y p T x, y, 4.7 Where deformation due to a normal line-load F and a tangential line-load F have been obtained in case (a) Normal Line-load and case (b) Tangential Line Load. The superscript (IN) indicates results due to inclined line-load F. N indicates results due to Normal line-load F and T indicates results due to Tangential line-load F. Stresses and displacements due to inclined line-load F, per unit length, in medium I (x0) are given by σ IN cos δ F P x x y F P xx y x y sin δ F q F σ IN cos δ F P y P x y 2F P sin δ F q x q x y F q, (4.8) yx x y xx y x y, 4.9 ISSN : 0975-5462 Vol. 4 No.11 November 2012 4565

σ IN cos δ F P 2P x x y F P xx y x y sinδ F q 2q y x y 2F q yx x y, U IN x, y 1 2G cos δ F 2 P P 1 2 logx y F P x y sinδ F q q 1 2 tan y x F q xy x y, U IN x, y 1 2G cos F P P 2 2tan y x F P xy x y sinδ F 2 q q 2 2logx y F q x y, x x 4.10 4.11 4.12 p IN x, y cos δ 2F 1 BP 3 x x y sinδ2f 1 Bq 3 y x y,4.13 Stresses and displacements due to inclined line-load F, per unit length, in medium II (x0) are given by τ IN cos F m x P m P x y F m P xx y x y sin F m y q m q x y 2F m q yx x y, τ IN cos F m y P 2m m P x y 2F m P yx x y sin F m x q 2m m q x y F m q xx y x y, x 4.14 4.15 u IN x, y cos F 2 P 4m P logx y F P x y sin F q 4q m tan y x F q xy x y, 4.16 v IN x, y cos F P P tan y x F P xy x y sin F 2 q q logx y F q x x y, 4.17 Numerical Results and Discussion For numerical computation, we use poroelastic constants correspond to Ruhr Sandstone Wang [3] and values of transversely isotropic constants given by Love [4] for Topaz material. We define the following dimensionless quantities X, Y, And Σ σ,,1,2,u G U, i=1,2. And to make dimensionless to displacements, we divide displacements by h. We have plotted graphs in figures (4-9) for the variation of the displacements and stresses against the horizontal distance X for a fixed value of X=1/2. Each figure has four curves corresponding to four different values of,namely; 0,45,60,90. The case 0 corresponds to a normal line-load and 90 for a tangential line load. Figures (4-5) show variation of normal displacement (U 1 ) and the variation of tangential displacement (U 2 ) respectively. These figures show that the displacements for 45,60 lie between the corresponding displacements for a normal line-load and tangential line-load. Figure (6-8) correspond to the variation of stresses. In figure (6-7) the curves for different values of changes steadily. Figure (8) points frequent inter crossing of various curves for different values of. Figure (9) shows the variation of the pore pressure against the horizontal distance X for a fixed value of X=1/2. ISSN : 0975-5462 Vol. 4 No.11 November 2012 4566

Fig.4 above and Fig 5 below ISSN : 0975-5462 Vol. 4 No.11 November 2012 4567

Fig.6 above and Fig 7 below ISSN : 0975-5462 Vol. 4 No.11 November 2012 4568

Fig.8 above and Fig 9 below ISSN : 0975-5462 Vol. 4 No.11 November 2012 4569

Appendix 0 2, 2, 2, 4, 1 2 tan, 1 log References [1] M.A.Biot, General theory of three dimensional consolidation, J.Appl.Phys., Vol.12, 155-164, (1941a). [2] M.A. Biot, General solutions of the equations of elasticity and consolidation for a porous material, J.Appl.Mech., Vol.78, 91-98, 1956. [3] H. F.Wang, Theory of Linear Poroelasticity,Princeton Univ. Press, Princeton, 2000. [4] A.E.H. Love, A Treatise on the Mathematical Theory of Elasticity, Dover Publications, New York, 1944. [5] T.Maruyama, On two dimensional elastic dislocations in an infinite and semi-infinite medium, Bull. Earthq.Res.Inst., Vol.44, 811-871, 1966. [6] J.W Rudnicki, Plane strain dislocations in linear elastic diffusive solids, J.Appl. Mech., Vol.54, 545-552, 1987. [7] J.W.Rudnicki, and E. Roeloffs, Plane strain shear dislocations moving steadily in linear elastic diffusive solids, J.Appl. Mech., Vol.57, 32-39, 1990. [8] S.J.Singh. and S.Rani, Plane strain deformation of a multilayered poroelastic half-space by surface loads, J. Earth Sys.Sci.,Vol. 115,685-694, 2006. [9] S.Rani and S.J.Singh, Quasi-static deformation due to two-dimensional seismic sources embedded in an elastic half-space in welded contact with a poroelastic half-space, J. Earth Syst. Sci., vol.116, 99-111, 2007. [10] S.J.Singh,S. Rani and N.R.Garg, Displacements and stresses in two welded half- spaces due to two dimensional sources,phys. Earth Planet. Inter.,70, 90-101, 1992. [11] R. Kumar, A.Miglani and N.R.Garg, Plane strain problem of poroelasticity using Eigen value approach, Proceeding Indian Acad. Sci. (Earth Planet. Sci.), Vol.109, 371-380,2000. [12] R.Kumar, A.Miglani and N.R.Garg, Response of an anisotropic liquid saturated porous medium due to two dimensional sourses, Proceeding Indian Acad. Sci. (Earth Planet. Sci.), Vol.111,143-151,2002. [13] N.R.Garg, A.Goel, A.Miglani and R.Kumar, Plane strain deformation of an orthotropic elastic medium using an eigenvalue approach, Earth Planets Space,Vol.55,3-9, 2003. [14] R.Kumar and P.Ailawalia, Viscous effect at an orthotropic micropolar boundary surface, Vol.30 (4), 513-525, 2005. [15] M.M. Selim, and M.K. Ahmed, Plane strain deformation of an initially stressed orthotropic elastic medium, Applied Mathematics and Computation, 175, 221-237,2006. [16] M.M. Selim, Static deformation of an irregular initially stressed medium, Applied Mathematics and Computation, Vol.188, 1274-1284,2007. [17] Samta Chugh,D.K.Madan and Kuldip Singh, Plane strain deformation of an initially unstressed elastic medium, Applied Mathematics and Computation, Vol.217(21), 8683-8692,2011. [18] M.A.Biot, General solutions of the equations of elasticity and consolidation for a porous material, J.Appl.Mech., Vol.78, 91-96, 1956d. [19] E.A. Roeloffs, Fault stability changes induced beneath a reservoir with cyclic variations in water level, J.Geophys. Res., Vol.93, 2107-2124, 1988. [20] M.L. Bell and A.Nur, Strength changes due to reservoir-induced pore pressure and stresses and application to Lake Oroville, J.Geophys. Res., Vol.83, 4469-4483, 1978. [21] L.Debnath, Integral Transforms and their Application,CRC Press. Inc., New York, 1995. [22] I.N Sneddon, Fourier transforms, McGraw-Hill, New York, 1951. [23] A.S.Saada, Elasticity-theory and application, Pergamon Press Inc., New York, 1974. [24] K.T.Chau, Fluid point source and point forces in linear elastic diffusive half-spaces, Mech.Mater., Vol.23, 241-253, 1996. [25] Ben-Menahem and S. J. Singh, Sesmic Waves and Sources (Springer-Verlag, New York) pp.1108, 1981. [26] T. H. Heaton, and R. E Heaton, Static deformation from point sources and point force couples located in welded elastic Poissonian half-spaces: implication for sesmic moment tensors, Bull. Seismological Soc. Am., Vol.79, 813-841, 1989. [27] G. Kumari, S. J. Singh and K.Singh, Static deformation of two welded half-spaces caused by a point dislocation source, Phys. Earth Planet.Int., Vol.73, 53-76, 1992. [28] E.Pan, Green s functions in layered poroelastic half spaces, Int J. Numer. Anal. Meth. Geomech., Vol. 23, 1631-1653, 1999. [29] R. K. N. D. Rajapakse and T.Seenjuntichai, Fundamental solutions for a poroelastic half space with compressible constituents, J.Appl. Mech., Vol.60, 844-856, 1993. [30] J. R. Rice and M. P. Clearly, Some basic stress diffusion solutions for fluid saturated elastic porous media with compressible constituents, Rev. Geophys. Space Phys., 14,227-241, 1976. [31] K. Aki and P.G. Richards, Quantitave Seismology.Theory and Methods W.H.Freeman,San Francisco,932,1980. ISSN : 0975-5462 Vol. 4 No.11 November 2012 4570