chuong3tracdiacongtrinhngam
Chuong 3: Dac diem va phuong phap thanh lap khong che trac dia trong xay dung duong ham.
3.1. Khong che trac dia tren mat dat.
3.1.1. Phuong phap va tuan tu thanh lap khong che trac dia tren mat dat.
1.Thu thap tai lieu
Sau khi nhan nhiem vu, viec dau tien la thu thap tai lieu. Viec nay thuc hien tot hay khong se anh huong trc tiep den chon diem, cau' thanh luoi, do dac va su dung luoi sau nay co dam bao chat luong va tien loi hay ko. Cac tai lieu can phai thu thap:
Ban do ty le lon (1:2000-1:5000) cua khu vuc duong ham
Binh do tuyen cua duong ham
Mat cat doc , mat cat ngang cua duong ham
Vi tri gieng dung, gieng nghieng, ham bang ..da thiet ke
Ban thiet ke ky thuat thi cong duong ham.
Tong binh do bo tri may moc, nha cua o khu vuc cua ham
Cac tai lieu ve luoi khong che da duoc thanh lap trong gia doan khao sat thiet ke.
Cac tai lieu dia chat, khi tuong thuy van, giao thong van tai cua khu vuc xay dung duog ham.
2. Khao sat hien truong va giao moc.
Sau khi nghien cuu cac tai lieu thu thap duoc, can phai khao sat ty my khu vuc duong ham de hieu ro thuc dia va tinh chinh xac cua cac tai lieu. Khi tien hanh khao sat thuong di doc theo tuyen truc ham tu cua ham nay den cua ham kia, quan sat va tim hieu dia hinh, nguon nuoc, diem dan cu va duong sa trong khu vuc. O hai cua ham can dac biet chu y huong cua tuyen duong, dia hinh va tinh trang phan bo cac thiet bi, phuong tien thi cong. Trong qua trinh khao sat, cac nhan vien khao sat thiet ke ban giao moc tai hien truong cho nguoi phu trach do luoi khong che thi thi cong, ban giao tung moc o vi tri, ly trinh va tinh chat cua diem moc. Neu mot phan cua duogn ham la duong cong thi phai dac bet chu y ban giao vi tri moc o diem dau, diem cuoi, diem chinh giua duong cong tron, diem dau, diem cuoi duong cong chuyen tiep.
3. Chom diem thanh lap luoi.
Trong truong hop khu vuc xay dugn duong ham chua co ban do dia hinh ty le lon thi chi co the ket hop khao sat voi chon diem tai hien truong de thanh lap phuong an luoi. Trong truong hop nay, can cu vao vi tri tuyen duong da xac dinh, vi tri cua ham, gieng dung, gieng nghieng, ham bang... de chon diem luoi khong che. Lan can moi mieng cua ham( cua ham, mieng gieng dung, gieng nghieng, cua ham bang) can phai co it nhat 3 diem khong che mat bang ( gom diem chieu va diem do noi) va 2 diem thuy chuan. Diem chieu o mieng ham cn phai thuan loi cho viec bo tri truc thi cong, thuan loi ch o do noi diem khong che tren mat dat voi diem chuyen trong ham. Chieu dai canh dinh huong de chuyen phuong vi vao ham khong nho hon 300m. Diem vao ham cung can co do cao thich hop, dc chon moc on dinh, tin cay, co loi cho bao ton va su dugn lau dai. Neu trong qua trinh thi cong ma moc bi chuyen dich hoac bi pha hoai thi phai khoi phuc hoac xac dinh lai voi do chinh xac nhu cu .
Diem thuy chuan o mieng ham can duoc dat o noi vung chac, co dieu kien nhin thong tot, tien do ngam, tien bao ton va co do cao thich hop. Hieu do cao giua hai diem thuy chuan o moi mieng ham duoc xac dinh cho qua mot lan dat may (mot tram may) la tot nhat.
Thanh lap loai luoi nao thich hop, dieu do phu thuoc vao quy dinh sai so huong ngang dao thong ham, may moc thiet bi trac dia hien co, dieu kien dia hinh khu vuc va kinh phai thanh lap luoi. Doi voi duong ham tuong doi dai, dau tu tuong doi lon, canh thanh lap nhieu phuong an thiet ke luoi va tien hanh thiet ke uu hoa luoi khong che.
3.1.2. Luoi tam giac tren mat dat.
Phan lon luoi tam giac tren mat dat trong xay dung duong ham truoc day la choi tam giac, do 1 hoac 2 canh day. Ngay nay may do dai dien quang da duoc su dung rong rai nen thuong thanh lap luoi do goc-canh. Nhung can luu y rang, trong truong hop nay, tieu chuan do chinh xac cua luoi khong phai la do chinh xac tuong doi cua canh yeu nhat nhu cac quy phamthuogn quy dinh ma phai la " gia tri anh huong" doi voi do chinh xac huong ngang dao thong ham doi huong duoc tinh theo cac phuong phap da trinh bay chuogn 2.
sau day se trinh bay cac nguyent ac thanh lap luoi tam giac.
Diem 1(O) va diem 10(C) la hai diem o cua ham. Chon he truc toa do cho luoi doc lap co truc Y vuong goc voi mat dao thong. Doi voi ham thang, duong thang noi hai diem cua ham OC trung voi truc Y. Doi voi ham cong, chung ta co dinh nghia: duong ham co OC song song voi truc Y la duong ham cong loai 1 ( mat dao thong tati P2); OC khogn song song voi truc Y la duong cong loai 2 (mat dao thong tai P3)
Cac nguyen tac thanh lap luoi tam giac:
- Chuoi tam giac nen co dang duoi thang doc heo duong thang OC; doi voi ham cong, cac diem dau va diem cuoi cua duong cong, diem ngoat tren cac doan thang phai duoc bao gom trong chuoi tam giac.
- So luong hinh tam giac va so luong diem khogn che tren duong tinh chuyen nen it nhat.
- Co the giam yeu cau ve cuong do do hinh cua cac tam giac
Doi voi duong ham thang va duong ham cong loai 1, "gia tri anh huong" sai so do luoi tam giac doi voi do chinh xac huong ngang dao thong ham khong co lien quan den vi tri diem khoi tinh, huong khoi dau va canh day.
Doi voi duong cong loai 2 "gia tri anhhuong" co quan he den vi tri va so luong canh do. Khi Xc - Xo cang lon thi anh huong sai so do canh den do chinh xac huong ngang dao thong ham cang lon. Vi vay khi thiet ke mat dao thong ham can luu y sao cho goc tao thanh giua duong thang OC va truc Y that nho gan nhu duong ham cong loai 1.
3.1.3. Duogn chuyen tren mat dat.
Trong thi cong duong ham, duong chuyen tren mat dat co the duoc dung lam khong che doc lap hoac duoc dung de tang day luoi tam giac. Trong muc nay se thao luan truong hop thu nhat.
Doi voi duong ham thang, de giam anh huong sai so do canh duong chuyen den do chinh xac huong ngang dao thong ham thi co gang thanh lap duong chuyen doc theo truc ham. So luong diem duong chuyen khong nen qua nhieu de giam anh huong sai so do goc den do chinh xac de tinh cac yeu to duong cong.
Trong truong hop co ham bang, gieng dung, gieng nghieng thi duong chuyen can di qua cac mieng ham de giam bot cac diem chuyen vao mieng ham. De tang them dieu kien kiem tra va nang cao do chinh xac, duong chuyen thuong duoc tao thanh vong khiep, giam so luong diem duong chuyen trong vong khep de han che pham vi kiem tra sai so khep. Vi du trong mot vong khep lon, chon vi tri thich op, lap duong chuyen phu de tao thanh nhieu vong khep nho hon. Ngoai ra, de tang cuong kiem tra cac goc co dieiu kien do khong tot, giam anh huong sai so cua may doi voi goc do, do chenh cao giua cac diem duong chuyen khong nen qua lon, tia ngam phai cach chuong ngai vat tren 1m. Doi voi tram may co chenh cao lon thi dung phuong phap can bang lai may cho moi lan do va do nhieu nhom, lay tri trung binh cua cac nhom lam ket qua cuoi cung cua tram may hoac dung ong thuy baac ngang do do nghieng cua truc ngang cua may khi do ngam moi huong de hieu chinh vao tri do huong.
Khi do cac goc cua duong chuyen khep kin, goc ben trai va goc ben phai cua duong chuyen duoc do rieng theo so thu tu vong do le va chan tron gtong so vong do tren mot tram may va lay huong khoi dau cua goc ben trai lam chuyen de phan bo vi tri ban do. Sai so khep goc toan vong tren mot tram may:
denta(tamgiac) = [goc trai]tb + [goc phai]tb - 360o khong duoc lon hon dentagh
Doi voi duong hcuyen hang II, dentagh la 2,0"
Doi voi duong chuyen hang III, dentagh la 3,5"
Doi voi duogn chuyen hang iV, dentagh la 5,0"
Sai so khep goc cua duong chuyen khep kin:
fbeta <= fbetagh = 2mbeta"can(n)
trong do: mbeta" la sai so trung phuong do goc theo thiet ke
n la so goc ben trong cua duong chuyen khep kin.
sai so trung phuong do goc cua duong chuyn co the uoc tinh theo cong thuc:
mbeta" = can{[fbeta2/n]/N}
trong do : fbeta la sai so khep goc cua duong chuyen khep kin
N la so luong vong khep kin.
Doi voi luoi duong chuyen trong do cac goc duoc do lap lai thi dua vao hieu so d cua moi goc do lap lai de tinh sai so trung phuong do goc theo cong thuc:
mbeta" = can {[dd]/2m}
trong do m la tong so goc do lap lai cua luoi duong chuyen.
Ung dung cong thuc nay voi dieu kien do chinh xac do goc lan dau va do lai la nhu nhau va cac diem duong chuyen trong thoi gian do khong bi chuyen dich dang ke.
Chieu dai canh duong chuyen duoc do voi do chinh xac thiet ke theo yeu cau dam bao do chinh xac huong ngang dao thong ham. Can dung may do dai dien quang hoac toan dac dien tu. neu dung may do dai dien quang thi phai do goc dung, khoang cach va goc dung can phai do di do ve., moi lan do hai vong, moi vong do khoang cach doc so 3 lan voi han sai phu hop voi quy dinh cua quy pham. Chieu dai nghieng can duoc hieu chinh hang so cua may, hieu chinh khi tuong va tinh chuyen thanh chieu dai ngang. Chenh lech ve chieudai cua 2 canh ke nhau cua duong chuyen khogn qua lon.
3.1.5. khong che do cao tren mat dat.
cap hang thuy chuan de thanh lap khong che do cao tren mat dat khong chi phu thuoc vao chieu dai duong ham ma quan trong hon la phu thuoc vao dieu kien dia hinh khu vuc duong ham vi chieu dai cua tuyen thuy chuan tuy thuoc vao dieu kien dia hinh do .
Quy dinh cap hang thuy chuan trong trac dia cong trinh duogn ham nhu sau:
Cap Chieu dai tuyen thuy chuan giua 2 mieng ham Loai may tc loai mia thuy chuan
II >36 S0.5 S1 Mia invar khac vach
III 13-36 S1 Mia invar khac vach
S3 Mia go chia khoang cm
IV 5-13 S3 Mia go chia khoang cm
Tuy nhien, tren thuc te, quyet dinh cap hang thuy chuan la tuy thuoc vao do chinh xac can thiet cua thuy chuan tren mat dat, duoc uoc tinh nhu da tb.
Khi do thuy chuan tren mat dat, dung do cao diem thuy chuan da co trong giai doan thuy chuan tuyen duong lam do cao khoi tinh. O moi mieng ham can co it nhat 2 moc thuy chuan. Tuyen thuy chuan nen tao thanh vong khep hoac lap hai tuyen doc lap xuat phat tu diem thuy chuan da biet do cao o mieng ham nay den diem o mieng ham khac.
3.2. Khong che trac dia trong ham.
3.2.1. Dac diem va phuong phap thanh lap duong chuyen trong ham.
Duong chuyen trong ham phai duoc thanh lap voi do chinh xac can thiet va cung chung trong he toa do thong nhat voi khong che tren mat dat de chi huong dao ham. Bo tri truc tim ham, bao dam thong ham doi huong voi do chinh xac quy dinh.
Diem va phuong vi khoi dau cua duong chuyen trong ham la diem va phuong vi cua luoi khong che mat dat o cua ham hoac duoc chuyen tu mat dat xuong ham qua gieng dung, gieng nghieng hoac ham bang. Duong chuyen trong ham co nhung dac diem sau:
1) hinh dang cua duong chuyen phu thuoc vao hinh dang cua duong ham
2) Duong chuyen trong ham la duong chuyen nhanh, duoc phat trine theo tien do dao ham. Vi vay khong the do toan bo duong chuyen cung mot luc ma phai do o hai diem cuoi ke nhau trong qua trinh phat trine, muon kiem tra phai do lai.
3) duong chuyen trong ham duoc thanh lap theo cach phan cap tu do chinh xac thap den do chinh xac cao.
Duong chuyen trong ham phai thoa man hai yeu cau:
- Vi tri diem duong chuyen phai o gan guong ham de tien chi huong dao ham va bo tri guong ham.
- Sai so huong ngang cua duong chuyen o mat dao thong khong duoc vuot qua gia tri quy dinh.
De dam bao yeu cau thu nhat, canh duong chuyen pahi ngan, so diem do goc ngoat nhieu. De dam bao yeu cau thu hai, canh duong chuyen phai dai, so goc ngoat it.
De thoa man 2 yeu cau nay, duong chuyen trong ham duoc thanh lap 3 cap(ko ke duong chuyen tiem can)
- Duong chuyen thi cong, co canh dai khoang 25-50m
- Duong chuyen co ban, co canh dai khoang 50-100m
- Duong chuyen chu yeu, co canh dai khoang 150-800m
4) Do chinh xac cua phuong vi khoi dau cua duong chuyen trong ham co khi con thap hon do chinh xac do goc cua duong chuyen. Sauk hi dao thong ham, hai tuyen duong chuyen nhanh tao thanh duong chuyen phu hop. Khi binh sai duong chuyen phu hop nay phai xet den sai so cua phuong vi khoi dau.
Tuy truong hop cu the co the bo cap duong chuyen chu yeu, tuc tren co so duong chuyen thi cong, truc tiep thanh lap duong chuyen canh dai. Noi chung, tren doan ham thang, chieu dai canh duong chuyen khong ngan hon 200m, tren doan ham cong, chieu dai canh duong chuyen khong ngan hon 70m.
Quy tac ky thuat va cac dieu can luu y khi thanh lap duong chuyen trong ham.
1) Duong chuyen trong ham co gang thanh lap doc theo truc tim ham hoac lech truc tim ham mot khoang thich hop. Co cac canh xap xi bang nhau. Cac diem duong chuyen duoc chon o noi an toan, on dinh it bi anh huong do thi cong, dieu kien nhin thong tot, tia ngam phai cach chuong ngai vat tren 0.2m
2) Chieu dai canh cua duong chuyen canh dai can duoc thiet ke theo yeu cau do chinh xac dao thong ham. Moi lan do de xac dinh mot diem moi cua duong chuyen can phai do kiem tra diem duong chuyen da lap truoc, o doan duong thang chi can do goc kiem tra goc, o doan cuong cong, can do kiem tra ca goc va canh.
3) Khi do goc can co gang giam thieu anh huong sai so dinh tam may va dinh tam tieu bang cach dinh tam lai may va tieu giua cac vong do.
4) Khi do canh bang thuoc thep thi cang thuoc tren khong bang lo xo, hai dau thuoc co do cao xap xi bang nhau va phai tinh den so hieu chiinh chieu dai cua thuoc va so hieu chinh do nhiet do.
5) Luoi duong chuyen duoc tao thanh boi cac vong khep deu phai duoc binh sai detinh toa do cua cac diem duong chuyen.
6) doi voi duong ham co dang hinh xoan oc, khong the thanh lap duong chuyen canh dai duoc thi moi lan phat trine duong chuyen ve phia truoc, phai do lai tu cua ham.
7) trong ham dai, co tiet dien lon, duong chuyen ko phai la duong chuyen nhanh ma tao thanh vong khep, cac diem duong chuyen khong dat dung tren truc tim ham ma o noi on dinh, tien do ngam, nhin thong
tot, it bi tro ngai.
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