THANH PHAN KET CAU CUA DAT
Bang 2-14. Quan he giiira tdc do lang chim va do ldn hat
Tdc do lang chim cua hat, cm/s
Thdi gian lang chim diroc 1cm
Dudng kinh hat theo Xtoc, d (mm)
Dirang kinh hat theo thuc nghiem cua Xabanin, d (mm)
0,2 5s 0,05 0,05
0,022 45s 0,0168 -
0,02 50s 0,0156 0,01
0,0028 6ph 0,0053 -
0,00046 36ph 0,0023 0,005
0,00035 48ph 0,0020 -
< 0,00035 > 48ph < 0,002 -
0,00011 2h24ph 0,0012 0,001
< 0,00011 > 2h24ph <0,0012 <0,001
Ddi vdi dat loai set co the dung 2 phuong phap sau de phan tfch:
a) Phuong phap true tiep (Xabanin, pipet, binh ti trgng) cho phep tach rieng turng nhom hat, tmh true tiep ham lugng % khoi lugng cua chiing. Nd con dugc dung tach cac nhom hat de; nghien cuu thanh phan khoang vat cua dat loai set.
b) Phuong plidp gian tiep (ti trgng ke, thau quang, tmh truong nd...) dua vao su thay d6i mat do ciia hat trong huydn phu do lang chim (ti trgng, do thau quang) hoac dua vao do truang ndcua hat set de tmh ham lugng % khoi lugng ciia nhom hat set.
Phuong phap ti trgng ke dirge dung pho bien nhat trong nghien cuu va san xuat.
1. Cach lam the van va phuong phap thi nghiem:
Khi phan tich thanh phan hat dat vdi muc dich xay dimg, ket qua phan tich cho phep danh gia dugc dac diem kien true, cac tinh chat ky thuat cua dat, kha nang su dung dat lam ndn, mdi trudng xay dung va lam vat lieu xay dung, dung dich khoan...
Do vay, khi lam the van dat - nudc phai pha huy het cac hgp the khong on dinh va kem on dinh, co do ben va tmh chju nudc kem. Cac hgp the on dinh thi giu nguyen coi
chiing nhir hat dat, nen tlnidng dung phuong phap ban phan tan: Khi lam the van co the bop vd dat bang tay, nghidn dat trong coi su chay bit cao su, dun soi va cho them chat pha keo. Cac chat pha keo thudng dung la cac muoi co chua cation hoa tri 1 va mot goc axit yeu: NH4C 0 3, Na-,P^Ov, Na0SiO3, Na2C 0 3, N H C 03 va Na2C20 4 hoac amoniac.
Cho mSu dat co hat d < 0,1mm vao binh co bo phan lam lanh (ong thuy tinh xoan) ngirac roi do nude cat vao voi luong gap mudi, cho them vao do khoang lcnr’ amoniac (2g/l). Dun soi the van tren bep cat trong 1 gid de pha keo trong dat, de nguoi roi do vao chen sir khuay deu. Do the van nay vao ong do qua sang co 16 d < 0,1mm. Do them nude cat vao ong do sao cho the tfch the van la 1 lit. Tiep theo khuay the van bang que tron cho tdi khi khong con can lang d day thi bo que khuay ra, ghi ngay thdi diem nay, nhiet do the van va tha can than ti trong ke vao ong do sao cho, ban cua no khong chain vao thanh ong. Theo doi de lay sd doc tren thang cua ti trong ke tai cac thdi diem: 30s, 1', 2', S'1, 307, 60;, 1 h30;, 3h, 6h, va 24h. Vdi 3 sd do dau tien (30s, 11 va 2') khong nhac ti trong ke ra khoi ong do, d cac lan tiep theo phai rut ti trong ke ra khoi ong do, lira sach va lau kho rong tha vao ong do trudc luc do tir 5 ~ 10s va tai do sail ldn hon lan trudc mot chut. Ghi cac ket qua dudi dang cac sd do rut gon R 0 va thdi gian tuong ung (t). Hieu chinh chieu cao mat khum (c) va nhiet do (t°) cho mdi sd rut gon R 0 dd tmh dudng kinh hat dat (d) va ham luong % cua cac cd hat. Dudng kfnh cd hat tmh theo toan do diroc lap cho tirng ti trong ke. Luong chua % cua cac hat tmh theo cons thuc:
x -
{ \
a-Ys
v b ( Y s - ằ /
R (2-3)
trong do:
x - ham luong % cong don cua cac hat, co kfch thudc < d (da tim theo toan do);
a - ham luong % cua cac hat d > 0,5mm, co trong mSu do phan tfch bang sang.
Neu mfui khong co hat > 0,5mm thi lay a = 100%;
ys - khoi luong rieng ciia hat;
R - sd doc da duoc hieu chinh theo mat khum va theo nhiet do thd van.
2. Cach dung toan do:
Dua vao toan do de xac dinh dudng kinh ciia tirng nhom hat bang cach: ke dudng thang di qua gia tri ys (thang 1) va gia tri nhiet do thd vain t° (thang 2) ta tim duoc (tren thang 3) gia tri A. 10' . Biet gia tri R va thdi gian do t (s), ta ke dudng thang qua gia tri R (thang 4) va qua gia tri t (thang 5), dudng thang nay cat thang 6 d dau ta duoc gia tri v (cm/s). Sau do noi didm A.103 tim duoc d tren (thang 3) vdi diem co gia tri v tren thang 6, giao diem cua dudng thang nay vdi thang 7 la gia tri dudng kfnh cua nhom hat (hinh
2-12) can tim. De xac dinh dung trong cua the vain co the dung pipet dac biet lay ra mot lugng nho tai do sau quy dinh theo thai gian t.
Ket qua phan tich thanh phan hat bang ti trong ke cung dirge trinh bay nhu khi dung sang tieu chuan.
A.103 5 -
6 -
7 - 8 -
9 -
10 - 11 -
12 =
13 j
14 jj-
15 —
16 r ’
17 — 18 — 19
20 25 —
30 E-
35 E-
40
T °,C i . 30 4 2 5
- - 2 0
- M 5
+ 10
©
Ys 4-2.0
2.1 2.2
4 2 .3 2.4 2.5 4 2 .6
2.7
2.8
4 2 .9 3.0 3.1 + 3.2
©
®
d, mm
41
5 - : 6 7 "
9 - =0,001
2r
3 j- 4 J-
5--6-I-
7 : : 9 = =0,81 2 - 3-j- 45 + 6 - r
7 - r
9: : 2 f
3
44-
5--
V, cm/s
o .ooor
2-- 4^5
6 , - 7
8:19
1000ph
0,001
2--
: : 3
4 6 4-+ 57 0,01 j l9
0,1
600==10 600:
3004-
200
2 +
6-7
: : 9
2--
‘ I ô 6 * 7 : : 9
4 3-4
L 100s
P60 E40^-30 r20
Hr R
I- 3 r 4
100-:2
50 1
4 0 : 30 - 20 --1000s 1 0 - - 600
6 -E-400 r 300 200
2 — r 100*
1 - L 60 40 20 30
10 BiSu do thi du
©
30 — 25 — 20_
18 16 14 ■=
12 10
9 -j 8 ■j 7 i 6 -j 5
©
2 4 3 4 5
©
3 A.10
Ys d v
4
HrR
Hinh 2-12. Toan do Casagrande dung xac dinh dudng kinh cua cac nhom hat
2.5.2. S u dung va trinh bay ket qua phan tich thanh phan hat I. Su dung ket qua
Thanh phan hat khong chi dung de phan loai dat ma con de danh gia thanh ph&n cap phoi, tmh tham niroc, cai tao tmh chat cua dat, giai quyet nhi6u van d£ thirc tien trong xay dung cong trinh va lam vat lieu xay dung.
1) Diing de phan chia cac nhom hat (bang 2-13), phan loai dat (bang 2-15). Thong thuong dat loai set dugc phan loai de dang theo chi so deo Id, de tang do chinh xac can dua vao thanh phan hat phan tan min. Nhu ta thay tren bang 2-15, dat set hat co d < 0,002mm chiem > 30% khoi lugng dat, ham lugng nay lam cho dat set the hien hang loat tmh chat dac trung ma o dat khac khong co hoac the hien rat yeu.
7) D6 xac dinh va danh gia so bo tinh tham ciia dat bang cong thuc kinh nghiem, dua vao gia tri duong kinh huu hieu d10 va he so khong dong nhat Cu, lie so' cap phoi C .