Limiting resistance of peat to transverse pipeline displacement

Abstract

Fedorovskii [1] presents a solution to the problem of the limiting resistance of soil to transverse pipeline displacement using the variational method within the framework of the theory of limiting equilibrium. For a soil loaded horizontally by a pipe when δ = 0, it is recommended that the limiting force q li (kN/m) causing the bed to fail be determined from the formula (1) where h 0 is the distance from the surface of the uniform soil bed to the center of the pipe in m, c is the specific cohesion of the soil in kN/m 2 , γ is the specific weight of the soil in kN/m 3 , D is the diameter of the pipe in m, and A and B are coefficients taken from Tables 1 and 2 of [1], depending on h 0 /D and the angle of internal friction ϕ of the soil (deg).Since Fedorovskii [1] addresses pipelines for the most part, let us make a brief note of the following. The absolute majority of cases involving loss of bearing capacity of a bed for underground pipelines with an arbitrarily configured axis in the horizontal plane (for which δ = 0) occur in marshlands where the thickness of peat h m h 0 + 0.5D [2]. Here, the pipelines are displaced along a curvilinear path on the surface of the marshlands, forming so-called floating sections, which are unacceptable with respect to operating norms and which require costly repair to restore the underground position of the pipe. In that case, bed failures are manifested as an uplifted section of the peat mass to the side of the pipe onto the surface of the marshland; this corresponds to the conditions of solution (1). In completely saturated weak mineral soils (silty sand, sandy loam, clayey loam), losses of longitudinal stability of an underground pipeline are extremely rare in the horizontal plane.We have examined application of solution (1) to a peat bed. It was first necessary to select strength parameters, since determination or adoption of c and ϕ for peat is extremely difficult for designers. In [3][4][5], data on c and ϕ are nonexistent for exposed peat; this can be explained by its pecu-