5.4 Designs of Underground Pipelines Coordination in Special Geological Conditions
5.4.1 The architecture/structure and process facility to be built on collapsible loess region shall be divided into class A/B/C/D according to its importance，the possibility of foundation being soaked by liquid and the stringency for restriction of uneven settlement during operation period，and shall comply with the specifications in Table 5.4.1.
Table 5.4.1 Classification of architectures/structures and process facilities
Note:The overall critical facility and fire hazard classification shall comply with the specifications in the current applicable national standard GB 50160 Fire Prevention Code of Petrochemical Enterprise Design.
5.4.2 The protection distance between burial piping，drainage trench，open rainwater trench，basin and architecture/structure，process facility in collapsible loess region should be no less than the specifications in Table 5.4.2.When specifications may not be complied with，relevant waterproof measure（s）shall be taken for architecture/structure and process facility.
Table 5.4.2 Protection distance between burial piping，drainage trench，open rainwater trench，basin and architecture/structure，process facility
Notes:1 The protection distance for architecture is calculated from the axis of external wall.For towering structure，process facility，it is calculated from the external edge of foundation.For basin，it should be calculated from the edge of basin wall（for fountain basin it should be calculated from the edge of slope）.For piping，drainage trench，it should be calculated from their external wall.
2 At Longxi and Longdong-Northern Shanxi-Western Shanxi region，when the thickness of collapsible earth layer is larger than 12m，the protection distance between pressure piping and different types of architectures/structures，process facilities should be no less than the thickness of collapsible loess layer.
3 In case that the collapsible earth layer contains gravel soil，sandy-soil sandwiches，the protection distance may exceed the value in the table.
4 For the protection arrangement of architecture/structure，process facility，site drainage，roof drainage，ground waterproofing，water apron，drainage trench，piping laying，pipe materials and joints，basic waterproof measures to prevent process and potable water from leaking should be taken，and the protection distance shall be no less than the specifications for general area.
5 Foundation collapsibility class shall be classified according to applicable national standard GB 50025 Code for Building Construction in Collapsible Loess Regions.
5.4.3 In collapsible loess region，the leak inspection pipe trench and leak inspection well shall be set up for water piping including water supply piping，circulation water piping，fire fighting piping，drainage piping and thermal piping in the protection scope of architecture/structure and process facility.
5.4.4 In collapsible loess region，in case of the integrated pipe trench for underground pipelines containing water supply piping，circulation water piping，fire fighting piping，drainage piping and thermal piping，the accessible pipe trench should be used.The cover of pipe trench should not be exposed.In case the cover is exposed or on the man-hole，measures shall be taken to prevent the surface water from leaking into pipe trench.
5.4.5 In expansive soil and saline soil region，measures shall be taken to prevent the connection points of underground drainage piping from leaking，and the net distance between piping and external edge of the foundation of architecture/structure，process facility shall be no less than 3.0m.