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may khoan coc nhoi

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21. Phan tich uu, nhuoc diem, pham vi su dung cua cac loai may khoan coc nhoi

May khoan coc nhoi la mot thiet bi cho phep thuc hien duoc cong nghe xu ly nen mong , nhat la trong xay dung cau cong va nha cao tang.

Nguyen tac lam viec cua may khoan coc nhoi la tao nen nhung lo coc trong nen mong roi rot truc tiep vat lieu lam coc (co the ca cot thep) vao nhung lo do de tao thanh coc gia co nen mong. Day chinh la phuong phap che tao coc tai cho, ngay tai nen mong cong trinh.

Uu nhuoc diem: Khi thi cong khong lam anh huong den cac cong trinh khac lien ke; kich thuoc coc lon (phi tieu chuan); cho phep thi cong o nhung noi co khong gian han che va dieu kien dia hinh phuc tap. Ben canh cac mat uu diem cung co mot so nhuoc diem nhu doi hoi chuyen gia giau kinh nghiem, gia thanh may dat, khi xuyen di qua dia hinh hang hoc hoac dat da nut ne lon phai dung ong lot chong lai lam tang gia thanh; kho kiem tra chat luong thi cong; he so su dung may thap nen khong kinh te.

Cac phuong phap va thiet bi tao lo cho coc nhoi hien nay thuong duoc su dung cac dang sau:

- Loai su dung ong bang kim loai co duong kinh 50cm va dai toi 22m dong vao nen dat tao thanh coc, sau do rot vat lieu tao coc. ong kim loai co the de lai hoac rut khoi nen dat. Trinh tu thi cong duoc the hien tren hinh 6-7.

- Loai lam lo coc bang thiet bi khoan khac nhau: khoan xoan ruot ga, khoan xoay, khoan va dap, khoan rung, khoan xoay an, hut, khoan bang tia nuoc co ap luc cao... Cac loai may va thiet bi khoan coc nhoi co duong kinh toi hon 2m va chieu sau toi 200300m, khi dung nguyen ly va dap, cac loai may khoan xoay an thuy luc cho phep khoan ca vao tang lan da co do ben cao. Sau khi chuan bi xong lo khoan nguoi ta se tha cot thep va do be tong duc coc. Thi du mot trong nhung quy trinh thi cong khoan coc nhoi the hien tren hinh 6-8.

Thi cong coc nhoi bang ong kim loai:. Trinh tu thi cong; I. Chuan bi ong va de coc; II,III. Dong coc va de coc vao nen dat; 1- Bua; 2- ong dan huong bua; 3- ong kim loai va de coc; IV. Rut ong kim loai len. 1- De coc; 2- Be tong; 3- Cot thep.

Hinh 6-8. Trinh tu thi cong coc nhoi

a. Khoan lo ; b. Khoet rong chan lo; c. Dat gia do; d. Dat ong va pheu rot vat lieu; d. Rot vat lieu; q. Rut ong pheu rot vat lieu va gia do; h. Hoan thanh coc va dau coc.

Hinh 6-9. May khoan kieu xoan ruot ga

1. Cap nang; 2. Tru khoan; 3. Thanh ngang; 4,5. Cum dan dong; 6. Can khoan; 7.Xylanh; 8. Ruot ga; 9. Be dan; 10. Be ti; 11. Thanh gia do; 12. May co so.

b. May khoan coc nhoi kieu xoan ruot ga:

Cau tao gom may co so banh xich 12; do tru khoan 2. Tren dau tru co thanh ngang dau tru 3, cum dan dong gom dong co thuy luc qua roto - hop giam toc lam quay can khoan 6 va ruot ga 8 theo huong be dan 9. Co cau cong tac co the thay doi (ruot ga, gau ngoam dau khoan kieu roto...) tao ra cac loai may khoan khac nhau.

c. May khoan coc nhoi ong vach kieu dao dong

Nguyen ly hoat dong: ong vach voi chan cat phia duoi duoc kep chat va xoay dao dong (250) boi cac xylanh thuy luc voi momen xoan tu 16608350 kNm, luc ep tu 15307250kN (loai VRM cua Duc). Nho do, cac ong vach noi lien tiep voi nhau boi cac khop noi dac biet se khoan dan toi do khoan sau can thiet (toi 75m). Luc ep thang dung va momen dao dong co the dieu chinh hoac giu khong doi trong qua trinh khoan cua ong vach, dat da duoc lay ra khoi lo khoan nho gau ngoam roi dac biet. Khi gap da cung tren 45MPa (co the toi 250MPa), co the dung bua roi de pha vo nat da truoc khi gau ngoam dat da ra ngoai.

Loai may nay rat phu hop khi thi cong tren nen dia chat phuc tap, co the thi cong ngay ma khong can cho ket qua khao sat dia chat. Theo nguyen li khoan bang ong vach luc khoan cat da deu theo phuong tiep tuyen nen rang it bi hong hon so voi mui khoan ruot ga (luc cat thay doi tu tam mui khoan ra ngoai theo phuong huong kinh nen mui khoan ruot ga de bi gay khi gap da cung).

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