General Requirements for Concrete Thrust Blocks ⬇️
1) Always consider the thrust forces in the design of buried pressurized pipelines, since it may cause separation of the joints and leakage of the pipeline. The most fundamental approach to resist a thrust force is to install a non-reinforced poured-in-place concrete block at the fitting.
2) The basic type of non-reinforced concrete block used for bends, tees, plugs and caps is referred to here as a concrete thrust block, but may also be referred to as an anchorage or buttress.
3) When concrete thrust blocks are used for fittings in close proximity to each other, ensure that no part of the blocks overlap and that the passive pressure soil zones do not overlap which could cause construction problems or block failure. See Passive Soil Pressure for Concrete Thrust Blocks, in this section.
4) Locate the thrust block such that its passive pressure zone of influence does not affect other
utilities or structures.
5) Provide a minimum soil cover of one (1) foot over all thrust blocks. For thrust blocks in existing or proposed roads or road rights of way, provide a minimum one and one half (1-1/2) feet of soil cover, unless otherwise directed or approved.
1) Always consider the thrust forces in the design of buried pressurized pipelines, since it may cause separation of the joints and leakage of the pipeline. The most fundamental approach to resist a thrust force is to install a non-reinforced poured-in-place concrete block at the fitting.
2) The basic type of non-reinforced concrete block used for bends, tees, plugs and caps is referred to here as a concrete thrust block, but may also be referred to as an anchorage or buttress.
3) When concrete thrust blocks are used for fittings in close proximity to each other, ensure that no part of the blocks overlap and that the passive pressure soil zones do not overlap which could cause construction problems or block failure. See Passive Soil Pressure for Concrete Thrust Blocks, in this section.
4) Locate the thrust block such that its passive pressure zone of influence does not affect other
utilities or structures.
5) Provide a minimum soil cover of one (1) foot over all thrust blocks. For thrust blocks in existing or proposed roads or road rights of way, provide a minimum one and one half (1-1/2) feet of soil cover, unless otherwise directed or approved.
numerical simulation of strength failure of buried polyethylene pipe under foundation settlement ⬇️
The failure mode for polyethylene pipes could be different, ranging from ductile failure to brittle failure. More precisely, as shown in Fig. 1, in addition to yielding, rupturing, impact and stress cracking are also among the most common causes of failure in polyethylene pipes and do not necessarily happen after the yielding.
There are two principle methods to analyze buried structures under the ground displacement. In the first method, which is the direct method, the load (i.e. external load and settlement) is applied on the soil environment, the whole model is analyzed in each step, and the response of the model is calculated (Fig. 2a).
in the other method (indirect method), which is widely used in the analysis of buried tunnels and pipelines, the reaction load between the pipe and soil (Fsoil-pipe) is calculated under the external load and settlement, then interaction of the pipe with soil (under this load only) is analyzed (Fig. 2b).
Apart from modeling of soil and the pipe, pipe-soil interaction is also important, and it can be very effective in the results of analysis. For example, if the pipe displaces due to ground settlement, two different cases can occur depending on the type of soil around the pipe. First case occurs where the soil is adhesive. Therefore, once the pipe is displaced, a gap occurs between the pipe and soil, and no more pressure is exerted on top of the pipe body by soil (Fig. 3a).
However, if the soil is coarse, once the pipe is displaced, soil would also move, and no gap occurs between the pipe and soil. Therefore, there will still be a pressure on top of the pipe body because of the overburden soil (Fig. 3b). So, in modeling the first case, interactions should be defined so as to consider the detachment of pipe-soil nodes.
Pipe-soil interaction is not clearly explained in the original article, and it is just mentioned that interaction is defined as a finite sliding. The authors should discuss the pipe-soil interaction in more detail and explain which friction coefficient was used for tangential friction and how the relative slippage and the separation between the pipe and soil were considered.
As shown in Fig. 4, after the foundation settlement, the displacement would be transferred to the pipeline, causing the pipeline to be divided into four sections: unaffected part, transition part, bent part and straight part. In fact, if a deflection occurs, these sections would appear as well. In the numerical model, the length of these sections can be calculated by solving the governing equations.