Kapangidwe ka nthaka
Mwa kapangidwe ka nthaka timatanthauza makonzedwe a gawo lolimba m’thupi la dothi. Monga momwe zimadziŵika, nthaka imapangidwa ndi tinthu tolola ndi mipata yodzazidwa ndi madzi, mpweya kapena nthunzi ya madzi, nthawi zambiri pang’ono ndi mpweya pang’ono ndi madzi. Malinga ndi makonzedwe a tinthu tolola m’nthaka, kapangidwe kake kamatsimikizika. Kapangidwe ka nthaka yosasunthika ndi ya yolumikizana zimasiyana kwambiri pakati pawo.
Kapangidwe ka nthaka yosasunthika
Kapangidwe ka nthaka yosamangirizidwa kamakhala pansi pa mphamvu ya kukoka. Tinthu tating’ono tolimba ta nthaka iyi ndi tokulirapo ndipo timatsikira pansi, timakhazikika chifukwa cha kukoka, pamene mphamvu zokopa pakati pa mamolekyu za tinthu tating’ono tomwe sizingakhalepo kapena n’zochepa kwambiri ndipo zimagonjetsedwa ndi kukoka. Chifukwa chake mu nthaka yosamangirizidwa, tinthu tolimba timakhala pafupi pafupi, likupeza malo aulere pakati pa tinthu toikidwa pamodzi (chith. 1_a_). Ngati tinthu ta nthaka yosamangirizidwa tili pafupifupi ozungulira ndipo ofanana kukula, monga momwe zingakhalire mchenga wa kapangidwe kofanana, ndiye kapangidwe kangakhale kolimba kwambiri (chith. 1_b_) kapena kosalimba kwambiri (chith. 1_c_), kutengera mmene tinthu tolimba takonzedwera m’nthaka. Kapangidwe kolimba kwambiri kamafanana ndi kutha kwakukulu kopanikizika kwa nthaka yosamangirizidwa ndipo porosity yake ndi nmin=26%. Kapangidwe kosalimba kwambiri kamafanana ndi kutha kochepa kwambiri kopanikizika kwa nthaka yosamangirizidwa ndipo porosity yake ndi nmax=48%. Choncho mwachitsanzo mchenga womasuka wa m’maduna uli ndi n=47%.
Sl. 1 Kapangidwe ka nthaka yosamangirizidwa
Ngati nthaka yosamangidwa ili ndi kukula kosiyanasiyana kwa mbewu, kotero kuti tinthu tating’ono timalowetsa mipata pakati pa akuluakulu (chith. 2), porosity ya nthaka imakhala yocheperapo kwambiri (n=20% ndi yocheperapo).
Chith. 2. Kapangidwe ka nthaka yosamangirizidwa ya kukula kwa tinthu kosiyanasiyana
Kapangidwe ka nthaka yolumikizidwa
Pa nthaka yogwirizana kapangidwe kake n’kosiyana ndi ka nthaka yosamangika. Pa nthaka yogwirizana pamachitika mphamvu za mgwirizano, zomwe zili zamphamvu kuposa mphamvu ya mphamvu yokoka ya tinthu tating’ono ndipo zimawamatira pa malo okhudzana. Chifukwa chake tinthu tating’ono sitimagwa pansi motsatira mzere, koma timakhalabe titamamatirana pamwamba pa wina ndi mnzake ndi pafupi ndi wina ndi mnzake (chith. 3_a_), motero kupanga kapangidwe ka unyolo ndi ukonde (chith. 3_b_), ka nthenga (chith. 3_c_) ndi zina zotero, zomwe zimatchedwa kapangidwe ka mulingo wapamwamba. Kapangidwe kameneka kali ndi porousness yayikulu, yomwe imatha kufika 60-80% ya kulemera konse, zomwe sizingakhale mu nthaka yosamangika.
Chith. 3. Kapangidwe ka dothi lolumikizidwa
Porosity ndi koefishienti ya porosity
Porosity ya nthaka imatanthauzidwa ndi chiŵerengero cha voliyumu ya mipata poyerekeza ndi voliyumu yonse ya nthaka (chith. 4).
Chith. 4. Porosity ndi coefficient ya porosity ya nthaka
Ngati tilongosola ndi
- Vp = kuchuluka kwa ma pores m’nthaka
- Vm = volume of solid particles
- V = voliyumu yonse ya nthaka,
porosity ya nthaka n ndi, mwa tanthauzo,
n = VP / V = VP / (VP + Vm),
kapena mu % ya voliyumu yonse ya nthaka
n = 100 * VP / (VP + Vm) %.
Coefficient ya porosity ya nthaka imatanthauzidwa ndi chiŵerengero cha voliyumu ya mipata ku voliyumu ya tinthu tating’ono tolimba:
e = VP / Vm.
Kuchokera pa fomula ya porosity n tili ndi:
nVP + nVm = VP, kuchokera apo Vm = VP(1-n) / n.
Poyika mtengo umenewu m’njira ya e timapeza
e = n / (1-n).
Kuchokera pa equation imeneyi timapeza
e - ne = n; n = e / (1 + e).
Coefficient ya porosity imasonyeza kachulukidwe ka nthaka. Ngati coefficient e ndi yayikulu, m’menemo kachulukidwe ka nthaka kamakhala kochepa, ndipo mosiyana. Ngati nthaka yowumuka ikakhala pansi pa katundu ndikuchepa, pogwiritsa ntchito coefficient ya porosity isanachitike ndi pambuyo pa kuchepa kungadziwike kukula kwa kuchepa Δ_h_.
Tiyeni tiwone gawo la nthaka yosasunthika yokhuthala h (chith. 5_a_). Ngati gawo limeneli litanyamula katundu, lidzakhazikika pansi ndi kutalika Δ_h_, kotero kuti makulidwe ake chifukwa cha katunduyo achepa kufika ku h1. Choncho
Δ_h_ = h – h1.
Popeza kutsika kwa nthaka yosakakamizika kumachitika chifukwa cha ma pore, chifukwa tinthu tolimba n’zosakakamizika pafupifupi, komanso madzi, ngati ma pore a nthaka adzazidwa nawo pang’ono kapena kwathunthu, kutsika kumeneku kungasonyezedwe mwachidule pa chith. 5_b_.
Sl. 5. Kutsika Δh kwa gawo la nthaka lotsetsereka lomwe lili ndi makulidwe h pansi pa katundu
Ngati tichita chizindikiro cha h0 ngati kutalika koyerekeza kwa gawo la tinthu tolimba opanda ma pore, lotchedwa kutalika kochepetsedwa, ndiye tingasonyeze kukhazikika Δ_h_ poyerekezera ndi kutalika kochepetsedwa h0 ndi ubale uwu:
Ngati tingaganize za nthaka yokhala ndi m’lifupi ndi kutalika kofanana ndi unit imodzi, ndiye kuti kutalika h, h1 ndi h0 zimayimira ma voliyumu, ndipo ndiye kuti
kumene e ndi coefficient ya porosity isanakwane, e1 pambuyo pa kutsika. Kuchokera pa zimenezi kumapezeka kutsika
Δ_h_ = h0 (e-e1).
Kukhalira pansi kungasonyezedwe mogwirizana ndi kutalika kwa gawo h asanayambe kukhalira pansi ngati tisinthe mtengo wa kutalika kochepetsedwa h0:
h0 = h – nh = h (1-n) = h / (1+e),
popeza n = VP / V = VP / h_,_ kumene VP = nh.
Choncho zimapezeka
Mitundu ina ya nthaka ili ndi average zotsatirazi za porosity n ndi coefficient ya porosity e:
Chinyezi cha nthaka
Mitundu ya madzi m’nthaka
Madzi a m’nthaka amaoneka ngati madzi m’ma pores pakati pa tinthu toulimba, otchedwa madzi a pore, kenaka ngati madzi a adsorbed pa tinthu toulimba ndiponso ngati madzi a constitutive.
Madzi a m’ma pores amapangidwa ndi madzi aulere pakati pa tinthu tating’ono tating’ono tolimba, mmene kuyenda kwake kumatsatira lamulo la Darcy, kenako madzi a mphamvu yokoka, omwe amasuntha chifukwa cha mphamvu yokoka kuchokera pamwamba kupita pansi m’mbali zonse, koma kuyenda kwake sikutsatira lamulo la Darcy, madzi a capillary omwe amasuntha chifukwa cha mphamvu za capillary ndiponso madzi a kupsinjika kwa pamwamba, omwe amasungidwa ndi kupsinjika kwa pamwamba m’ngodya pakati pa tinthu tolimba ta nthaka ndipo amatchedwanso madzi a m’ngodya za pores. Madzi onsewa angachotsedwe kwathunthu mwa kuumitsa nthaka pa kutentha kwa 110oC.
Madzi a adsorbed ndi amene amakulunga tinthu toulimba, ndipo amamangiriridwa nawo ndi mphamvu za ma molekyulu. Ichi ndi chotchedwa filimu ya madzi, makulidwe ake amakhala 6-80 µµ (1µµ=10-6 mm, milimikron). Mphamvu ya madzi a adsorbed pa tinthu tating’ono ting’ono ndi yochepa kwambiri, komabe ngati tinthuzo n’ting’ono kwambiri mphamvu yake imakulirakulira, chifukwa malo onse a tinthu amawonjezeka ndipo motero chiŵerengero cha madzi a adsorbed poyerekeza ndi tinthu toulimba mu voliyumu imodzi ya nthaka chimawonjezeka. Madzi amenewa angachotsedwe pang’ono okha mwa kuyanika pa 110oC.
Madzi a constitutive ndi omwe amaphatikizika mwa mankhwala mu makhiristo a mchere wa tinthu toulimba ta nthaka. Madzi amenewa ndi ochepa kwambiri ndipo sangathetsedwe mwa kuumitsa nthaka. Choncho, madzi amenewa angatengedwe ngati mbali yofunikira ya tinthu lolimba.
Kuchuluka kwa madzi m’nthaka
Malinga ndi tanthauzo, kuchuluka kwa madzi mu nthaka kapena chinyezi cha nthaka ndi chiŵerengero cha kulemera kwa madzi omwe ali mu nthaka poyerekeza ndi kulemera kwa zigawo zake zolimba. Malinga ndi kuchuluka kwa madzi mu nthaka, pali milandu itatu: nthaka yodzaza kwathunthu ndi madzi, nthaka yodzaza pang’ono ndi madzi ndi nthaka youma kwathunthu.
Nthaka yodzaza kwathunthu ndi madzi
Ngati titchula ndi n porosity ya nthaka, γs kulemera kwa voliyumu kwa tinthu tonse, γw kulemera kwa voliyumu kwa madzi, ndiye kuti chinyezi cha nthaka yodzaza wZ chingafotokozedwe ndi chiganizo chotsatirachi
Nthaka yodzaza pang’ono ndi madzi
Ngati titchula Ww kulemera kwa madzi omwe ali m’nthaka, ndi Wd kulemera kwa tinthu tolima kapena kulemera kouma kwa nthaka, ndiye chinyezi cha nthaka w
w = Ww / Wd , kapena mwa peresenti ya kulemera kowuma kwa nthaka: w = 100 Ww / Wd.
Pankhaniyi, chinyezi cha nthaka chingafotokozedwe ndi digiri ya chinyezi Sr yomwe imayimira chiŵerengero cha kulemera kwenikweni kwa madzi mu nthaka poyerekeza ndi kulemera kwa madzi omwe ali mu nthaka yomweyi akanakhala ngati mipata yonse itadzazidwa ndi madzi, ndiponso poyerekeza ndi kulemera kwa madzi a nthaka yodzaza ndi madzi:
kutanthauza kuti kwa _γ_w = 1,00 Sr = w*γs / e.
Malire a mtengo wa mlingo wa chinyezi ndi awa:
- kwa nthaka youma kwathunthu w = 0; Sr = 0
- kwa nthaka yodzaza kwathunthu w = e/γs; Sr = e/γs * γs / e = 1,0.
Sl. 6. Chitsanzo cha nthaka chosakhuta kwathunthu ndi madzi
Mlingo wa kukhuta (omwe nthawi zina umatchedwanso kukhuta kapena mlingo wa chinyezi) umawonetsedwanso ndi chiŵerengero cha kuchuluka kwa malo opanda kanthu odzazidwa ndi madzi poyerekezera ndi kuchuluka konse kwa malo opanda kanthu (chith. 6):
Sr = V2 / V1
komwe V2 ndi kuchuluka kwa ma pores odzaza ndi madzi, V1 ndi kuchuluka kwathunthu kwa ma pores odzaza ndi madzi, mpweya ndi gasi. Ngati w ndi chinyezi cha nthaka mu % ya kulemera kowuma kwa nthaka Wd, ndiye tili ndi
V2 * γW = w Wd, pomwe V2 = w Wd / γw.
Kumbali ina, tili ndi kuti V1 = V – Vd, ndipo popeza Vd * γs = Wd, ndiye kuti
Vd = Wd / γs ndi V1 = V – Wd / γs.
Choncho, mlingo wa kukhuta kwa nthaka Sr udzakhala
kapena mu peresenti ya kulemera kouma kwa nthaka
Nthaka youma kwambiri
Pankhaniyi w = 0. Madzi onse a m’ma pores achotsedwa, pamene madzi omamatira achotsedwa pang’ono chabe, ndiko kuti, filimu ya madzi ikadalipo, koma makulidwe ake achepetsedwa.