【文章內(nèi)容簡介】 on work shall be done well for winter construction of earthworks and it shall be done continuously. For winter construction, measures for anti slip and anti fire shall be taken for transportation roads and construction site. Anti Freezing and Insulation of Earth The method of turning over to be loose and harrowing to be flat should be used to the earthworks of large area. The surface of the place to construct shall be turned over to be loose and harrowed to be flat. The thickness should be 25 ~ 30cm while the width should be two times of freezing depth plus bottom width of the trench (pit). The freezing depth after turning over to loose and harrowing to be flat should be estimated according to Appendix A of this specification. In earthworks construction area where in early winter the snow fall is large, snow cover method should be used. Before excavation, fence should be provided to the place to be excavated or other type of material should be used to make walls, the height should be 50 ~ — 10 — 100cm while the space should be 10 ~ 15cm and they shall be perpendicular to the leading wind direction. For trenches (pits) of small area, trenches (pits) for depositing snow should be excavated at anticipated places. The depth should be 30 ~ 50cm while the width should be two times of anticipated depth plus bottom width of the trench (pit). For trenches (pits) of small area to excavate, insulation material covering method should be used. The insulation material should be furnace slag, saw chips, wood shavings, straws, straw curtains or expansion pearlite, further covered with plastic cloth. The width of insulation material shall be 2 times of the width of the trench (pit) to excavate plus the bottom width of the trench (pit). The thickness shall be calculated according to Appendix A of this specification. Tent insulation method may be used for insulation and anti freezing of small trenches (pits) to excavate. Frames should be constructed over the trenches (pits) excavated, on which base shall be laid and covered with insulation material. Large plastic shed may also be constructed, in which heating supply measures shall be provided. Melting of Frozen Soil The method to melt frozen soil shall be determined according to the quantity of the works, the freezing depth as well as the conditions of the construction site. It may use the baking with smoke or fire, steam melting or electric heating. The construction sequence shall also be determined. The method of baking with smoke or fire may be used to works of small quantity. The fuel may be wood shavings, saw chips, husk, tree peels or other bustible materials. Ignite the fuel which is laid over the frozen soil to excavate and cover the fuel with a iron plate. The flame should not be very high and reliable measures for anti fire shall be taken. In case heat source is sufficient and the quantity of works is small, the steam melting method may be used. Put the steel pipe which has steam spraying holes into the predrilled frozen soil and connect steam to melt. The frozen soil borehole diameter shall be 1cm larger than the diameter of steam spraying pipe. The space should not be less than 1m. The depth shall be 30cm over the bottom of the base. In case the diameter of the steam spraying pipe, D, is ~ , plum blossom shape spraying holes shall be made on the steel pipe and the lower end shall be sealed. After melting, excavation shall be done timely to avoid freezing of the base. In the areas where power supply is sufficient, if the quantity of works is not large, the electric melting method may be used to melt frozen earth. Electrodes should be Ф16 ~Ф25 steel bars of sharp point at bottom end. The depth of electrodes punched into the frozen earth should not be freezing depth. Electrodes should also be extruded out from the ground 10 ~ 15cm. The space of electrodes shall be as per Table . The holding time of electric heating shall be determined according to depth of freezing and the voltage. When energizing to heat, saw chips may be laid to the ground surface. Its thickness should be 10 ~ 25cm and it shall be dampened with salt solution of 1%~2% concentration. When — 11 — electric heating method is used to melt frozen earth, safety protection measures shall be taken. Space of Electrodes (cm) Table Voltage (V) Freezing depth (cm) 50 100 150 200 380 60 60 50 50 220 50 50 40 40 Excavation of Frozen Earth The excavation of frozen earth layer may be done by manually, mechanical way or explosion according to the thickness of the frozen earth layer. For manual excavation of frozen earth, hammering iron wedge to split frozen soil in layers may be used to excavate. The length of the wedge shall be determined according to the thickness of the frozen earth layer, it should be 30 ~ 60cm. The mechanic excavation of frozen earth may use bulldozer to loose the earth, excavator to excavate or heavy hammer to break frozen earth. The equipment shall be as per Table . In case heavy hammer is used to break frozen earth, heavy hammer may be cast iron of wedge shape or ball shape and its weight should be 2 ~ 3T. The lifting equipment may use crane, simple bipod or tripod frame associated with winch. Equipment for Excavation of Frozen Earth Table Thickness of frozen earth (cm) Machinery for choice 50 Scraper, bulldozer, excavator 50 ~ 100 Big power bulldozer, soil looser, excavator 100 ~ 150 Heavy hammer For works of large area and large thickness of frozen earth layer, explosion may be used. In case the thickness of frozen earth layer is ≤ 2m, hole explosion method may be used. The diameter of explosion hole should be 50 ~ 70mm while the depth should be ~ times of the thickness of frozen earth layer and the included angle with the ground