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chuong2tracdiacongtrinhngam

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Chuong 2. Cong tac trac dia trong xay dung duong ham 

2.1. Do ve ban do phuc vu thiet ke duong ham 

1. Doi voi duong tau dien ngam 

Giai doan thiet ke so bo: Can dung ban do dia hinh ty le 1:2000 hoac 1:5000. Tren ban do co ve duong do quy hoach thanh pho, cac cong trinh ngam da co cua thanh pho, vi tri lo khoan va hao khao sat dia chat. Khi thiet ke ga, loi xuon gham, gieng dung va khu vuc dao lo thien, can co ban do ty le 1:500, pham vi do ve tuy theo yeu cau cua don vi thiet ke. Khoang cao deu giua cac duong dong muc: 0,25m-0,50m. 

Giai doan thiet ke ky thuat: Can do ve ban do ty le 1:500 doc theo tuyen duong ham thiet ke. Chieu rong cua dai do ve tuy thuoc vao do sau cua duong ham va dieu kien dia chat cua khu vuc. Trong dieu kien binh thuong, chieu rong cua dai do ve cung khong nho hon 3 lan do sau cua duong ham. O cua ham lon, noi co nhieu cong trinh kien truc can co ban do ty le 1:200 hoac 1:100. Tren ban do loai nay, cac goc nha lon deu phai do va xac dinh toa do. 

Giai doan thiet ke thi cong: khong yeu cau do ve ban do. Cong tac trac dia chu yeu luc nay la kiem tra, doi chieu hien truong. 

2. Doi voi duong ham xuyen nui. 

No la mot phan cua tuyen duong sat, duong bo hoac cua mot tuyen van chuyen nao do nen vi tri duong ham da duoc xac dinh khi khao sat chon tuyen duong. Luc do vi tri duong ham duoc xac dinh so bo tren ban do dia hinh ty le 1:10000 hoac 1:50000. 

Giai doan thiet ke so bo: Ty le ban do can do ve tuy thuoc chieu dai duong ham. 

Chieu dai duong ham L<=2km, Ty le ban do can do ve 1:2000 

Chieu dai duong ham 2km <=L<=5km, ty le ban do can do ve 1:5000 

Chieu dai duong ham L>= 5km, ty le ban do can do ve 1:10000 

Chieu rong cua dai do ve ban do ty le 1:2000-1:5000 tuy thuoc chieu dai cua ham va dieu kien dia chat ma xac dinh trong khoang 400m-1000m. Doi voi khu vuc co dia hinh phuc tap thi do ve ban do tren dai rong hon. Khu vuc cua ham , can do ve ban do ty le 1:2000. 

Giai doan thiet ke ky thuat: Can do ve ban do ty le 1:2000 doc theo tuyen duong ham, chieu rong dai do ve 200-400m. Khu vuc cua ham va gieng dung can do ve ban do ty le 1:1000-1:500. 

2.2. Phuong phap bo tri duong ham. 

Bo tri duong ham co nghia la chuyen truc duong ham tu ban thiet ke ra thuc dia. co 2pp bo tri duon gham. 

1. Phuong phap hinh hoc hay con goi la phuong phap truc tiep. 

Trong phuong phap nay, vi tri mat bang cua truc duong ham dc vach va danh dau truc tiep tren mat dat dung lam can cu cho thi cong duong ham. 

Doi voi duong ham thang, phuong phap nay duoc trinh bay nhu sau: 

Gia thiet A va B la hai diem da biet tren truc ham tai hai cua ham, nhung khong the nhin thong nhau. Can xac dinh hai diem B va C tren huong truc ham de lam can cu chi huong dao ham, hinh 2-1 

Dua vao toa do thiet ke cua A va D tinh duoc phuong vi cua AD. Tren thuc dia chon diem B' nam tren huong AD voi kha nang co the. Tai B' dat may kinh vi va dung phuong phap thuan dao ong kinh de keo dai doan AB' den C'. Dat may kinh vi tai C', dungphuong phap thuan dao ong kinh de keo dai B'C' den D'. Diem D' chech diem D mot doan DD'. Do truc tiep chieu dai doan DD' tren thuc dia. Do chieu dai AB', B'C', C'D' bangphuong phap thi cu hoac do tren ban do. Tinh" 

CC' = DD'. AC' / AD' 

de dieu chinh vi tri diem C' ve diem C. 

Sau do dat may tai C, voi phuong phap nhu tren, keo dai DC den B va tu B keo dai CB den A. Lan nay diem A duoc xac dinh tren duong keo dai, ky hieu A', co the van chua trung diem A da biet. Do truc tiep do lech AA', Tinh va dieu chinh vi tri cac diem B,C cho den khi hai diem B, C thuc su nam tren huong truc AD. 

Cuoi cung dong coc danh dau hai diem B, C tren thuc dia de lam can cu thi cong duong ham.  

Doi voi duong ham cong, dua vao cac yeu to duong cong da thiet ke, theo phuong phap bo tri duong cong de vach va danh dau truc duong ham tren thuc dia voi do chinh xac theo yeu cau. Sau do do lai chinh xac hon chieu dai va goc ngoat cua truc ham lam can cu thi cong duong ham. 

Phuong phap bo tri truc tiep tai hien truong co uu diem la khong can lap luoi khong che trac dia, viec do dac don gian va khong tinh toan phuc tap. Nhung phuong phap nay co nhuoc diem lon la rat kho bao dam do chinh xac thong ham doi huong trong dieu kien dia hinh vung nui hoac thanh pho, rat kho khan cho viec do dac va bo tri. Vi vay, phuong phap nay chi ung dung de bo tri duong ham ngan tron ggiao thong va cac cong trinh thuy loi-thuy dien, khi dieu kien dia hinh khong phuc tap lam va yeu cau do chinh xac khong cao. 

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