22. May cam bac tham

De xu ly nen dat yeu, tang nhanh cuong do cua dat, giam do lun tong the trong thi cong duong oto, duong sat ben cang, san bay... su dung he thong mao dan thang dung che tao san ma ta thuong goi la bac tham. Nho bac tham nuoc trong long dat duoc thoat nhanh va deu nen cac cong trinh tren nen dat yeu se lun nhanh hon, toc do co ket nhanh va cong trinh on dinh hon.

Cau tao cua bac tham duoc mo ta o hinh 6-13 gom loi nhua 1 co ranh duoc che tao tu vat lieu nhua nhu polyeste, polyamid, polyetylen co do ben cao va lop vai boc dia ky thuat 2 khong det rat ben vung tu cac soi tong hop co tinh nang loc rat cao, cho phep nuoc tham qua mot cach de dang; dong thoi lai co kha nang can cac hat dat de tranh truong hop tac duong dan nuoc. Bac tham thuong co chieu rong 100mm, chieu day 34mm, do dai 1,83kN/m, dong goi thanh cuon co tong chieu dai 200300m.

Bac tham duoc cam xuong nen dat yeu nho thiet bi chuyen dung goi la may cam bac tham (hoac may an bac tham). Sau khi bac duoc cam vao nen dat, nuoc o cac lo rong trong nen dat yeu se chay theo huong nam ngang den bac tham xung quanh gan nhat roi theo duong dan cua bac tham thoat mot cach tu do len vung cat gan mat dat de thoat ra ngoai (hinh 6-14). De tang hieu qua thoat ra nhanh nen thoi gian co ket cua nen dat duoc giam rat nhieu va co the ket thuc ngay trong khoang thoi gian thi cong ma khong phai cho doi lau nhu khi khong dung bac tham.

Nguyen ly lam viec cua chung co the chia ra lam hai loai: Rung ep va ep tinh bang co hoc hoac thuy luc.

May cam bac tham lam viec theo nguyen ly ep tinh gom cac bo phan chinh sau (hinh 6-15):

Hinh 6-15. May cam bac tham

a. Bo tri chung; b. So do dan dong; 1. May co so; 2,5. Cac doan cot; 3,4. Bo phan dan dong; 6. Xy lanh giu can; 7. Bo phan dan huong; 8. Dui dan bac tham; 9. Tang cuon cap; 10. Nhanh cap rut dui; 11.Nhanh cap an dui.

May co so 1 dung de di chuyen toan bo thiet bi trong qua trinh thi cong, cung cap he thong dan dong cho dui bac tham, giu cho thiet bi on dinh trong qua trinh thi cong (cam, rut dui, va di chuyen may). May co so co the la may dao, may ui, can cau co he thong truyen dong co khi hay thuy luc, trong do may dao thuy luc la phu hop hon ca.

Cot la bo phan chinh cua thiet bi cam bac tham. Do la mot cot thep co dang hop hoac gian khong gian. Tren gian co gan co cau dan dong, gia dan huong cho dui dan bac tham va he thong palang cap de an va rut dui. Gian cot thuong co chieu cao lon hon chieu sau toi da va bac tham phai cam. Tuy theo

chieu cao ma gian co the che tao thanh mot hay nhieu doan co tiet dien giong nhau hoac khac nhau va lien ket voi nhau bang bulong. Gian cot duoc treo giu tren may co so (h.6.15a).

Khi lam viec bac tham duoc luon qua dui va duoc cai giu boi mot chiec neo mong bang ton co dien tich lon hon dien tich mat cat ngang cua dui de khi dui cam xuong dat se keo theo bac tham cung cam xuong. Khi rut dui len, nho chiec neo nay bac duoc giu lai trong nen dat.

Dui duoc tua tren cac con lan dan huong. He thong goi do con lan gan voi cot. Dui duoc cam xuong dat va rut len nho he thong palang cap (h.6.15b) duoc dan dong tu he thong thuy luc cua may co so.

Hien nay cac loai may cam bac tham duoc nhap vao nuoc ta hoac che tao trong nuoc cho phep cam bac sau toi 3040m voi nang suat cam bac 40008000m/ca may. Nho ap dung bac tham ma co the giam duoc 3060% gia thanh so voi cong nghe xu ly nen dat yeu khac ma van dam bao yeu cau ky thuat cao cua nen cong trinh. Chinh vi vay the gioi hien nay co hon 40 quoc gia su dung cong nghe thi cong co nen dat yeu bang bac tham voi so luong bac tham su dung hang nam tren 100 trieu met. Rieng o nuoc ta, hang nam cung da su dung toi gan mot trieu met bac tham.