Main Characteristics and Technical Countermeasures for Blast Cutting of Frozen Earth in the Area.docx

1、Main Characteristics and Technical Countermeasures for Blast Cutting of Frozen Earth in the AreaMain Characteristics and Technical Countermeasures for Blast Cutting of Frozen Earth in the Plateau Area Abstract：Based on the blast experiment results achieved in 1974-1977 on the frozen earth in Fenghuo

2、 Mountain and Qingshui river in Kekexili area of Qingghai-Tibet plateau, this paper describes the importance of entironment protection during the blasting of frozen earth in the plateau. According to the geological and climate characteristic, it puts forward the technical countermeasures for the bla

3、st drill, protection of blast equipment from water, freeze and thunder, introduces the blast design and the cutting of railway cut and the foundation pit of the bridge and culvert on frozen earth. It also points out that when the principle of holding the frozen is followed, the blasting should be do

4、ne in cold season, while for the principle of thawing, warm season is more applicable, but the blast should meet the technical requirement of fast construction for the blast cutting engineering. Key words: Xining-Lhasa railway Frozen earth of plateau area Blast equipment Blast technology1. Forewords

5、Chinese government has launched the construction of Xining-Lhasa railway. Starting from Golumd , Qinghai province in the east and ending in Lhasa, Tibet in the west, the line has a total length of 1118km. 550km of the line have to be built on the frozen earth of the plateau. The blast technology for

6、 frozen earth of the plateau is the key technical issue faced by the construction team of Xining-Lhasa line. As early as in 1974-1977, the Ministry of Railways had set up experiment engineering project in Fenghuo Mountain (with altitude of 4500m) and Qingshui river (4700m) in Kekexili area of Qinggh

7、ai-Tibet plateau for scientific experiment aimed at railway construction on the frozen earth of the plateau. The experiments cover the blast-hole drill for building the railway cut and the fast blast cutting for the foundation pit of the bridge and culvert. Based on the achievements of the above exp

8、eriments and in combination with the development of the blast equipment and the technology in the last two decades, the paper describes the main characteristics and technical countermeasures of the blast cutting in the frozen earth area of the plateau. 2. General descriptions of the experiment of th

9、e blast cutting in frozen earth area of the plateau In 1975 and May-September, 1976, the following experiments had been carried out on the frozen earth in Fenghuo Mountain and Qingshui river in Kekexili area.(1) Drill experiment for the frozen earth. The experiment is to examine the drilling speed a

10、nd performance of the following drills for the frozen earth: type 71-05 small drill, the XJ-100 hand drill for geological purpose, the DPP-100 motorcar drill, the DG-1 drill for post installing car and the twist drill made by the Academy.(2) The experiment on such characteristics as water-proof, fre

11、eze-resistance, burst and safety of the Poly-2 slurry explosive and the related blasting devices (ammonium nitrate, detonator and explosive train, etc.). The results have been applied in the field.(3) The experiment on the primary data of the frozen earth blasting. It includes the standard blasting

12、cone and the blasting explosive-hole chambering. It also cover the test and measurement of the layout of the explosive cartridges, the relationship between the drill hole space, rank space and hole depth, as well as the destroy and compression radius of the blasting.(4) The experiment on blast-hole

13、drilling and deep explosive-hole chambering for the 40m long railway-cut in the Fenghuo Mountain test field. The depth of the railway-cut is 57m and width of the earth surface cutting is 1520m. The track shoulder (with slope of 1:1.5) is protected with retaining wall and all kinds of heat insulation

14、 materials respectively. The foundation base of the cut is treated by fine grain soil taking from the work site. The effective capacity of the explosion is 1820m3 with loading amount of 1108kg. (5) The experiment for two foundation pits of the bridge and culvert in the Qingshui river test field. (Th

15、e pits have respectively the built-up concrete pre-casting and the cold concrete pouring foundation base, the cutting capacity is 100 m3 and 140m3 in respective). The foundation pit was formed on the same day the blasting was completed. The cutting was fulfilled by type W46 grab. In addition, primar

16、y experiment for blast drilling on the frozen earth was carried out in the same field by using three different types of ten poly-energy bomb (50% and 50% TNT). . For the experiment field, the natural mountain slope is 510o, the original earth surface greensward coverage is 8090% and the thickness of

17、 the greensward 0.150.20m. About 1.55m depth of earth is years frozen savageness upper limit, 1.552.0m earth is soil contained ice layer, with bulk ice containing of 8090%. The framework is of amaranth sandy clay and debris. 2.02.8m of earth is ice saturated layer, with bulk ice containing of 6070%.

18、 5.37.0m earth is less or more ice frozen layer, with bulk ice containing of 510%. The framework is of amaranth sandy shale weathered zone. The temperature of the test zone is -1.5-5 for years. 3. Main characteristics of the blast cutting in frozen area of the plateau The geological problem of the y

19、ears frozen earth in the Qinghai-Tibet plateau is that for the high ice containing frozen earth with higher annual average temperature (such as the rich ice frozen earth, the saturated ice frozen earth and soil containing ice), the water in the soil is unstable (either frozen or melted) if the earth

20、 layer consists of fine grain soil. The earth layer is very sensitive to such elements as climate change, engineering construction, cutting, traffic and human interference. When the thick underground ice layer is exposed to the earth surface or disturbed, the underground ice will melt and result in

21、pitfall, heat melting and slide sink as well as solifluction. In this case, the engineering will be affected by such geological phenomenal as freezing expansion and melting sink. The blast cutting in the experimental field indicated that the remove of the greenswards from earth surface before the co

22、nstruction in some sections has resulted in melting collapse in some areas and caused serious solifluction. Which has brought about great difficulties for the construction. Due to oxygen shortage in the plateau, the drill machine is hard to start and its efficiency is low. The blast-hole drilling ma

23、y suffer from silt returning or re-freezing at any time. The explosive device has blast resistant problem in case the waterproof and anti-freezing measures are not taken properly or the loading time in the hole is too long. After blasting, the exposed burst heap and the foundation pit may melt rapid

24、ly. The melting in the foundation could be 16-18cm in two days. For the burst heap, the thawing is even more serious. In case the cutting and the spreading of heat insulation layer are delayed, it may cause melting collapse and slide and result in engineering disease.The Qinghai-Tibet plateau is lac

25、k of oxygen and the weather is very changeable. The area is always hit by strong wind, snow storm and thunder and lightning. Due to the complex geological conditions and terrible construction environment, the blast cutting technology for the frozen area of plateau has to face the following: (1) It h

26、as to minimize and control the disturbance of the blast cutting to the years frozen earth, such as to carry out the blast cutting strictly in accordance with the cutting clearance. Protect the entironment from being destroyed by the blast cutting process. Remove the waste and cut earth soon after th

27、e blast is fulfilled and spread the heat insulation layer and fill back the soil as soon as possible. (2) There are cold and warm seasons for frozen earth area of plateau. The melting, ground temperature and physical mechanics of frozen earth vary in different season. This will affect the blast desi

28、gn parameters or even the selection of the blast cutting solutions. (3) The particularity of the frozen geological conditions and the environment of oxygen shortage also have fresh requirement on type selection of blast drilling machines and its operation efficiency. (4) The blast equipment used for

29、 frozen earth of plateau should be water- proof and anti-freezing. The strong wind, snowstorm, thunder and lightning, as well as the strong ultraviolet radiator will bring about problems never experienced for the storage, transport of the blast equipment and blast cutting as well. Therefore, technic

30、al countermeasures should be taken to ensure proper management, safe operation of the equipment. 4. Blast hole drilling of the frozen earth4.1 Drilling machine used for the frozen earth Due to the special geological conditions of the frozen earth, pneumatic strike type sinkhole drilling trolley or d

31、rill should not be adopted in the warm season. During the test, such twist drills as the 71-50 small drill, XJ-100 geological drill, DDP-100 motorcar drill and DG-1 post installing car drill have been used. However, the rareness of the air (atmosphere pressure is about 560-600millibar) in the platea

32、u area has caused low efficiency of drilling operation. For instance, the real operation revolution of the drill is only 17-20rev./min. in compare with the designed data of 80rev./min. The average advance of each drill per shift is 4.010.1m. Even when the self-made twist drilling bit is used, the pu

33、re average rate is only 0.11m/min. Under the action of the drill melting, the frozen cutting material has become sticky mud pies that are pressed between the twist vanes and difficult to be thrown away. This also resulted in low efficiency. Therefore, in order to cope with the requirement the large-scale construction, it is ne