(2). fundamental disposal of channel bottom The underground pipe will generally bear its loading of covering soil and external additional loading (traffic vehicle and weight of the goods contained). So the bottom of the ditch must have fundamental disposal and pay high attention to it, the bad foundation will cause Z style of calligraphy of the tube shift and some stress will be centralized , make the security of the stress will be centralized , make the security of the cable threatened. a. terra for general earth ： Only need to lay 50-100mm sand in channel bottom b. terra of partial bad soil layer ： In order to prevent loose of channel ground soil and asymmetric sink. Fill lime mortar or concrete mortar 50-100mm and press them flat.
