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According to ATV-A 161E [ATVA161], the equation for the permissible jacking force (per V) at the jacking or main jacking station taking the offset of its force application into account is according to Formel 14.3.1.1 : (Formula: Calculation of permissible jacking force according to ATV-A 161E [ATVA161]) According to the theoretical safety background of the ATV-A 161E [ATVA161], γ is a global safety coefficient that covers the possible overstepping … |
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(Image: Parabola-rectangle diagram for concrete [DINENV1992-1]) The method of calculating the acceptable jacking force to EN 1916 [DINprEN1916] is applicable to jacking pipes of concrete, steel fibre concrete and reinforced concrete. For this purpose, a non-linear stress-strain diagram is used (Bild 14.3.1.2) which permits determining the distributions of the stress and force accurately. Conditioned by these assumptions and the consideration of the … |
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(Image: Function of cross section with reference to the z-coordinates of the calculation example) In order to be able to calculate the stress distribution over the cross section, it is first necessary for the proposed cross section of the geometry to be described with a function depending on the diameter coordinates z corresponding to Bild 14.3.3.1, whereby, in the case of a circular cross section, the z-axis with origin at the outer border of the … |
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(Image: Typical stress and compression behaviour of a soft wood pressure transfer ring) As already mentioned, the stress-compression behaviour of pressure transfer rings used in practice is distinctly non-linear. Bild 14.3.3.2 shows a typical stress-compression behaviour diagram for a pressure transfer ring with a thickness of sD = 30 mm that would satisfy the following example calculation. The determination of the support points is carried out at … |
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In principle, the behaviour of the compression of the pressure transfer rings through the cross section and thus the function , must be divided into two sections:
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With the use of the valid stress-compression diagram (Bild 14.3.3.4) and the associated functions σel(ε), σpl(ε:) and σges(ε), every distortion ordinate εD(z) can be assigned a stress ordinate σD(z) and whereby three regions are differentiated. Region 1: Region 2: |
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If the contact compressive stress σD(z) that can be read off in Bild 14.3.3.5 is multiplied at each point on the z axis with the cross sectional width B(z) shown in Bild 14.3.3.5, the result is the contact compressive force per longitudinal unit of the z axis. The integration of this function shown in Bild 14.3.3.5 over the whole of the cut region of the z axis results in the permissible jacking force Vper in Formel 14.3.3.5.
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Contrary to the general calculation method according to S&P (CoJack), in the calculation method of the ATV-A 161E [ATVA161] and the basic theory by Scherle [Scher90], only a constant modulus of elasticity that is independent of the initial loading can be applied. Its numerical determination, even with the knowledge of the stress-compression curves, is very difficult and is mostly in the form of a very coarse estimate even though it is decisive in … |
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If a jacking distance consists of several successively arranged jacking sections with differing path elements (straight, left curve, right curve) then, as regards a pipe gap, a separate calculation can be made for each section to be traversed whereby the remaining effects of all previously traversed part sections can be taken into account. Thus, for instance, it is possible to carry out a trouble-free calculation of the pipe loads in S-curves while … |
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Not only the thickness but also the material of the pressure transfer ring has a critical influence on the permissible jacking force and thus on the economics of the jacking measures. On the basis of typical stress and compression diagrams, considering pressure transfer rings of approximately 30 mm thick in
permits, using the general calculation method of S&P (CoJack), the … |
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Nov 23, 2005 Trenchless Technology for Installation of Cables and Pipelines Assessments in the direction of the pipe axis - determination of the permissible jacking force Restrained pipe joints, for instance for steel or plastic pipes, are usually created by means of welding or gluing the pipe ends. These are rigid pipe joints (Abschnitt 13.2) which in the jacking under review usually require a planned straight line path with pressing-in or pushing-in. Nevertheless, according to ATV-A 161E [ATVA161], also in this case, due to unavoidable steering corrections, offsets in the jacking force must be taken into account. … |
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Nov 23, 2005 Trenchless Technology for Installation of Cables and Pipelines Assessments in the direction of the pipe axis - determination of the permissible jacking force For non-restrained as well as restrained pipe joints of steel pipes, the reference stress according to ATV-A 161E [ATVA161] must be assessed as in Formel 14.3.5 : (Formula: Assessment of the reference stress for non-restrained as well as restrained pipe joints of steel pipes according to ATV-A 161E [ATVA161]) |
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Nov 23, 2005 Trenchless Technology for Installation of Cables and Pipelines Additional information for calculating jacking pipes with a box section From the depiction of the influence of the horizontal and vertical loading on the behaviour of the bending moments for the rectangular cross section of Bild 14.4.1.1, Bild 14.4.1.1 and Bild 14.4.1.1, it can be derived that horizontal loads in this case do not necessarily act in a load-reducing manner as for circular cross sections (Abschnitt 14.1.2).
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Nov 23, 2005 Trenchless Technology for Installation of Cables and Pipelines Additional information for calculating jacking pipes with a box section The diagrams (Bild 14.1.5.1) (Bild 14.1.5.1) (Bild 14.1.5.1) (Bild 14.1.5.1) in Abschnitt 14.1.5.1 for determining the soil stresses due to traffic loads must not be transferred to box sections because with circular cross sections they were converted to unequally distributed loads on the circumference. In [Achm92a], it is recommended to apply the traffic loads in accordance with Bild 14.4.1.2. In this case the vertical stresses can be taken from Bild … |
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Nov 23, 2005 Trenchless Technology for Installation of Cables and Pipelines Additional information for calculating jacking pipes with a box section As it is only for rotationally symmetric cross sections that the determination for the position of the neutral fibres is independent of the angular deflection, not only the coordinates but also their orientation must be defined for box sections. In order to calculate the critical stress behaviour analogous to Bild 14.4.1.3, it is necessary to create its own diagram for the respective box section to be used. An example in this respect is shown in … |
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The calculation discussed in Abschnitt 14.1, Abschnitt 14.2, Abschnitt 14.3 and Abschnitt 14.4 apply to jacking pipes that were pressed or pushed into a cavity created by static load introduction with soil removal or displacement. In the case of the utilization of dynamic energy for ramming jacking pipes, then according to ATV-A 161E [ATVA161] special measures must be used. In [ATVA161] it is required that "Jacking pipes that are installed with ramming … |
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In contrast to the soil removal method, it cannot be assumed that there will be a reduction of the earth load due to load transfer with the displacement and compaction of the soil. Instead, an increased earth load is activated with the result of an increased load of the pipes in comparison to the primary stress condition. The increase earth pressure can be calculated:
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The mechanical soil processes of soil displacement are comparable to that of carrying out a pressiometer test [Bague87] [Vesic72]. The starting situation of the calculation assumes an inhomogeneous primary stress condition. Considering a radial symmetric strain within the semispace with the above primary stress condition, then additional stresses (secondary stress and deformation condition) are created in the soil, due to the strong deformation (… |
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If pipe jacking is carried out through pressing-in or pushing-in, then the jacking force is calculated according to Abschnitt 14.2. When jacking by means of pulling-in the pipe, the required pulling force (T) is calculated as follows under additional consideration of the friction forces (R) resulting from the outer earth pressure load: T = (Ws + π · da · p) · L · μ where: |
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