Ƙayyade iyakokin Atterberg
Za mu bayyana gwaje-gwajen tantance iyakar kwarara, iyakar filastisiti da iyakar raguwar ƙasa, waɗanda su ne mafi muhimmanci a ilimin inji na ƙasa. Dukkan waɗannan gwaje-gwaje ana yi ne a kan samfuran ƙasa mai haɗi da aka taɓarɓare.
Gwajin ƙayyade iyakar kwarara
Don wannan gwajin, ana ɗaukar kusan 200 na ƙasa a cikin yanayin da yake da ɗanɗanon danshi na halitta, ba tare da ƙwayoyin da diamitarsu ta wuce 0,5 mm ba, waɗanda za su iya kawo cikas ga daidaiton sakamakon gwajin. Samfurin ba a yarda a busar da shi a cikin murhun busarwa ba, sai dai a saka shi kai tsaye cikin kwanon ain tare da ruwa mai distil, inda ya kamata ya tsaya na sa’o’i da dama har sai ya jiƙu sosai. Ga ƙasar laka mai alamar filastik IP < 20, jiƙa tana ɗaukar kusan 4 awa, ga ƙasa mai yumɓu IP > 20 zuwa 18 awanni. Daga nan a zuba samfurin da aka jiƙa a kan farantin gilashi, sannan a gauraya shi da kyau da wukar dakin gwaje-gwaje, domin a samu kauri mai ɗimbin laushi da daidaitaccen haɗuwa. Idan an lura da ƙwayoyi da suka fi 0,5 mm girma, a cire su yayin gaurayawa.
Ana zubawa samfurin da aka shirya haka a cikin ƙaramin kwanon tagulla na na’urar Casagrande don ƙayyade iyakar zubewa (sl. 1), wadda a dakunan gwajinmu ake kira Casagrandeova treskalica.
Hoto. 1. Na’urar Cassagrande don ƙayyade iyakar gudun zamiya
Na’urar ta ƙunshi ƙaramin kwano na tagulla, wanda ake haɗa shi cikin na’urar ta hanyar wata na musamman, da matashi mai ɗan taushi daga roba mai tauri, tare da eccentric a saman da kuma makunnin juyawa, inda eccentric ɗin yake tashi zuwa tsayin 1 cm, saboda haka kwanon yana faɗuwa ya buga matashin (hoto 1a). Ana daidaita girman na’urar. Bugu da ƙari, akwai kuma wuka mai siffa ta musamman da aka ƙayyade girma daidai (hoto 1b).
Ana daidaita samfurin da aka ɗibo a cikin ƙaramin kwanon tagulla da wuƙa ta yadda saman samfurin ya zama lebur ƙwarai, kuma samfurin ya rufe ɗan fiye da rabin ɓangaren gaba na kwanon, tare da cewa tsayinsa a saman mafi ƙasan wurin ƙasan kwanon ya kai kusan 12 mm. Sai a saka kwanon a cikin na’ura a kuma yanke rami a tsakiya da wuƙar da aka ƙera musamman domin ya zama madaidaici gaba ɗaya kuma a ga ƙasan tagullar kwanon, abin da ake samu ta hanyar ja da wuƙar a hankali a tsaye ga ƙasan kwanon. Tsawon ramin ya kamata ya kai kusan 40 mm. Nan take sai a juya hannun na’urar da saurin 2 juyawa a sakan ɗaya, ana ƙirga bugun da kwanon ke yi a kan tushe kuma ana lura da ramin, wanda saboda bugun kwanon a kan tushe yake kunkuntarwa, domin sassan samfurin da aka yanke suna motsi suna ƙoƙarin haɗuwa. Ana ci gaba da juya hannun na’urar har sai ramin ya haɗu a tsawon 10 mm. Da zarar an samu haka, sai a daina ƙarin juyawa da hannun, sannan nan take a cire da wuƙa wani adadi na samfurin kusan 2 cm3 daga ɓangaren da ke kusa da ramin da ya haɗu daga bangarorin biyu, a sa a kan gilashin agogo sannan a ƙayyade danshin ƙasa.
Ana maimaita wannan gwaji 3-4 sau ta hanya ɗaya, amma kowane lokaci da danshi dabam, abin da ake samu idan da farko an gauraya samfurin da ƙaramar adadin ruwa, sannan a ƙara ruwa don sauran gwaje-gwajen. Bayan kowanne gwaji da aka gama, ana zuba samfurin a kan farantin gilashi, inda ake ƙara ɗan ruwa a gauraya sosai, domin a samu taro mai daidaito, wanda a kowane lokaci yake ɗan zama mai ruwa fiye da na baya.
Domin a gudanar da gwajin, cakudar da aka shirya bai kamata ya yi kauri sosai ko ya yi ruwa sosai ba, domin yanayin daidaiton ƙasa da ya yi nisa da iyakar zubewa ba ya ba da daidaiton da ake buƙata ga wannan gwaji. A mafi yawan lokuta ana ɗauka cewa idan adadin bugun ya yi ƙasa da 10 ko ya wuce 50, gwajin bai yi nasara ba, amma ana ganin daidaiton gwajin ya fi kyau idan tazarar waɗannan iyakoki ta kasance 10-40 na bugawa.
An lura cewa bisa wata hanya, a duk lokacin da aka gama jujjuya abin riƙewa har zuwa haɗuwar rami a tsawon 1 cm, ana nan take gauraya samfurin da wuka a cikin ƙaramar kwanukan tagulla kuma a sake daidaita saman samfurin a cikin kwanukan, a yanke sabuwar rami, sannan a juya abin riƙe na na’urar. Ana maimaita wannan tsari har sai an samu sau uku a jere adadin bugun guda ɗaya a wajen haɗuwar rami a tsawon 1 cm, wanda adadin ake ɗauka domin ci gaba da aikin tantance iyakar yawo. Sakamakon gwaji ana zubawa a cikin zane mai sikelin semilogarithmic (siff. 2). A kan axis na x ana saka adadin bugun a sikelin logarithmic, yayin da a kan axis na y ake saka adadin ruwa cikin kaso na busasshen nauyin samfurin a sikelin arithmetic. Tunda a kowane gwaji adadin ruwa w ya bambanta, za mu samu maki A, B, C da D, waɗanda ke dacewa da adadin bugun daban-daban, inda adadin bugun yake ƙasa idan adadin ruwa ya fi yawa kuma akasin haka. Ta haɗa waɗannan maki, muna samun layi madaidaici mai karkata, a kan wanda muke neman maki M ga 25 bugun. Adadin ruwa da ya dace da wannan maki ana ɗauka a matsayin iyakar yawo wL.
Hoto 2. Ƙayyade iyakar mikewa
Ƙayyade iyakar filastik
An shirya samfurin ƙasa kamar yadda aka bayyana a sama, amma da ruwa kaɗan, ta yadda ya zama masa roba mai kusan a yanayin mai kauri-roba, sai a tara shi a cikin ƙwallo mai kusan 2-3 cm3, sannan a yi masa mirgina da tafin hannu a kan takardar al’ada ko takardar sha ruwa zuwa silinda mai kaurin 3 mm. Idan ana iya mirgina samfurin zuwa wannan kauri ba tare da karyewa ba, sai a sake tara shi a ƙwallo a mirgina shi ta wannan hanya. Ana maimaita wannan hanya har sai an samu cewa silindar, a kaurin 3 mm, ta fara karyewa. Daga nan a sa silindar da ta karye a cikin farantin agogon gwaji, sannan a ƙayyade yawan ruwa. Wannan adadin ruwa, da aka bayyana a matsayin kaso na busasshen nauyin samfurin, ya yi daidai da iyakar filastik wP.
Tantance iyakar raguwar abu
Fig. 3. Ƙayyade iyakar raguwa
A gauraya samfurin ƙasa da ruwan distil kamar yadda aka bayyana a ƙarƙashin Gwajin ƙayyade iyakar kwarara, ta yadda konsistensinsa ya kasance kusan a iyakar kwarara, lokacin da dukkan ramuka suka cika da ruwa. Sai a ƙera ƙwallo, a bar ta ta bushe da farko a iska, sannan a cikin tanda a 105°C. Wannan mataki-mataki na busarwa ya zama dole domin a guji tsagewa a cikin samfurin da ya bushe, wanda zai iya dagula gwajin. Nan take a farkon gwajin ana auna nauyin W1 na samfurin kuma a ƙayyade ƙarfinsa V1 ta gwajin nutsewa a cikin murjani, sannan a ci gaba da busarwa a iska, daga baya kuma a cikin tanda, tare da ɗaukar samfurin lokaci zuwa lokaci, sanyaya shi a cikin eksikator da auna nauyinsa W2, W3, W4 da sauransu da ƙarfinsa V2, V3, V4 da sauransu. Ta haka za a tabbatar cewa a wani matakin danshi ƙarfinsa ya daina raguwa ko da yake nauyinsa na ci gaba da raguwa saboda busarwa. Idan samfurin a farkon halinsa ya cika da ruwa, wato babu iska a cikin ramukansa, asarar ruwan da busarwa ke haifarwa har zuwa iyakar raguwar girma tana kusan daidai da raguwar ƙarfinsa. Bayan haka a ci gaba da busarwa ba tare da auna ƙarfi ba, har sai samfurin ya bushe gaba ɗaya, wato zuwa daidaiton nauyi. Sai a ƙayyade yawan ruwa a matsayin kaso na busasshen nauyin samfurin ga kowane auna ƙarfi da nauyi, a kuma zuba sakamakon gwajin a kan zane (fig. 3). Ta wannan hanya za a samu maki A, B, C, D da E, waɗanda ake haɗawa, ta yadda yawanci ana samun layi mai kaifi a wajen iyakar raguwar girma. A wurin lanƙwasa S ana samun danshi w wanda ya dace da iyakar raguwar girma _W_S.
Ƙayyade ƙarfin kapilari
Gwajin ƙayyade tsayin tashin ruwa ta hanyar kapilari ana yin sa ta hanyoyi biyu, wato kai tsaye auna tsayin tashin ruwa ta kapilari da kuma auna ta kaikaice ta hanyar kapilarimita.
Gwajin tantance tsayin kapilar ta auna kai tsaye
Daga cikin samfurin da aka dame, a ɗauki kusan 300 pondi na ƙasa, a busar da shi a 105°C, sannan bayan ya huce a murƙushe shi ya zama ƙura ƙwarai, ba tare da murƙushe ƙwayoyin ba. Ana zuba ƙurar da aka samu a cikin bututun gilashi mai diamita ø 25 mm, tsawon 1,5 - 2,5 m, buɗe daga ɓangarori biyu, wanda ƙarshen ƙasansa a baya an rufe shi da audugar gilashi ko wani ɓangare na zane. A buɗaɗɗen ƙarshen sama a zuba ƙurar da aka busar har tsayin kusan 10 cm, sannan mu ɗaga bututun mu bar shi ya faɗi da bugawa kan katakon bene ko wani tushe mai ɗan taushi har sai an ga ƙurar tana zaunawa a cikin bututun. Ana duba zaunawar ƙurar ta hanyar yi wa bututun alamun layi da alli mai mai. Bayan haka sai a ƙara zuba sauran 10 cm na ƙura a kuma maimaita wannan hanya har sai mun cika bututun da ƙura busasshiya mai matsewa ta samfurin ƙasar da muke gwada capillary ɗinsa. Sannan a nitse ƙasan bututun a cikin kwanon gilashi mai dauke da ruwan distil ba tare da gudana ba, tare da sharadin cewa ƙarshen ƙasan bututun bai kamata ya taɓa ƙasan kwanon ba (sl. 4). Muna ɗaure bututun gilashin da katako zuwa ma’auni, ta yadda bututun da ma’aunin su kasance a tsaye. Bayan haka muna sa ido kan hawan ruwa a cikin bututun, wanda ake gane shi a fili ta launi: samfurin bushe yana da launi mai haske, mai ɗan ɗumi kuma duhu. Tazara tsakanin matakin ruwa a cikin kwanon da saman gefen samfurin da ya ji ɗumi tana wakiltar tsayin hawan capillary hk.
Sl. 4. Tantance tsayin hawan capillary na ruwa ta auna kai-tsaye
Ana yin lura, bisa ƙa’ida, bayan 1, 2, 4, 8, 16, 32, 64 da sauransu. Sakamakon lura ana zana su a kan jadawali, inda ma’aunin a kwance ke nuna lokaci a cikin sa’o’i, yayin da ma’aunin a tsaye ke nuna tsayin hawan capillary na ruwa a cikin mm (hoto 5).
A cikin kayan yashi, tashi ta capillary tana farawa da sauri sosai, sannan ta ragu, kuma ana isa ga matsakaicin tsayin tashi da wuri. A cikin kayan yumbu, tashi ta capillary tana farawa a hankali, amma tana ɗaukar lokaci mai tsawo kuma tana kaiwa ga tsayi mafi girma sosai.
Wannan hanyar tantance tsawon kapilar tana ɗaukar lokaci mai yawa, musamman a ƙasan laka. Bugu da ƙari, tsayin hawan kapilar yana dogara da zafin iska da kuma danshinsa, saboda haka ya zama dole a kiyaye waɗannan abubuwa su kasance kusan na dindindin gwargwadon iko.
Hoto 5. Zanen hawan ruwa kapilari a cikin ƙasa, a-yashi; b-laka; c-ƙasa mai yumbu
Gwajin tantance tsayin kapila ta amfani da kapilarimita
Akwai capillarimeter da yawa na ƙira daban-daban, kamar capillarimeter na Beskow, Jürgenson da Engelhardt. Anan za mu bayyana ka’idar aiki da capillarimeter na Beskow, wanda shi ne mafi yawan amfani.
Ana yin wannan gwaji ne a kan samfurori marasa tashin hankali ko masu tashin hankali. Idan samfurin ya kasance mai tashin hankali, sai a saka shi cikin na’ura a yanayin iyakar gudana.
Hoto 6. Kapilarimetar na Beskowa
Kapilarimetar Beskowa ya ƙunshi kwantena biyu (sl. 6), waɗanda aka haɗa a sassan ƙasa tsakaninsu ta hanyar bututun roba mai ƙarfafawa. A cikin kwantena 1 ana sa samfurin ƙasa a kan ƙasan tacewa, yayin da ƙasan nasa kwantena ɗin ke cike da wani ɓangare da ruwan da aka tace, wani ɓangare kuma da mercury, wanda yake a ɓangaren ƙasa yadda zai cika dukan bututun roba da kuma ɓangaren ƙasan kwantena 2. A farkon gwajin matakin mercury a cikin kwantena biyun ɗaya ne. Daga nan sai a saukar da kwantena 2 ƙasa, ta haka ake ƙirƙirar ƙarancin matsa lamba a ƙarƙashin ƙasan tacewar kwantena 1. Idan wannan ƙarancin matsa lamba ya fi ƙarfin capillary a cikin samfurin, iska tana ratsa ta cikin samfurin zuwa ƙasan tacewa sannan matakin mercury a cikin kwantena biyun nan take ya daidaita ta saukar da kwantena 2. Bambancin Hg tsakanin matakin mercury a cikin kwantena ɗaya da ɗaya a lokacin da ƙarancin matsa lamba da ƙarfin capillary suka daidaita, wato nan da nan kafin iska ta fara ratsa samfurin, idan aka mayar da shi zuwa tsayin ginshikin ruwa kuma aka ƙara masa tsayin ginshikin ruwa h a ƙarƙashin samfurin, yana ba da tsayin capillary hk. Tunda mercury ya fi ruwa nauyi sau 13,6, to tsayin ɗaga capillary hk shi ne:
hk = 13,6 Hg + h
Ƙayyade ƙarfin wucewar ƙasa
Gwajin ɗakin gwaje-gwaje na tantance ƙarfin ratsa ruwa na ƙasa ana yin sa ne ta amfani da na’urori na musamman da ake kira permeameters. Akwai nau’o’i daban-daban na permeameters, amma ana iya raba su zuwa rukuni biyu: permeameters masu matsin ruwa na dindindin, don ƙasashe masu babban ƙwaya, da permeameters masu matsin ruwa mai raguwa don ƙasashe masu ƙananan ƙwaya. A dukkan lokuta, gwajin ana yi ne da samfurori marasa gurɓatacce.
Ta hanyar gwajin dakin gwaje-gwaje ana ƙayyade alƙalumin wucewar ƙasa, wanda ana bayyana darajarsa a wata takamaiman zafi, saboda bambancin dankon ruwa a zafuka daban-daban, wanda ke shafar darajar alƙalumin wucewar k. Mafi yawan lokaci ana bayyana alƙaluman k a zafin t =10°C. Saboda haka, idan 10°C, zafin ruwan a lokacin ƙayyade alƙalumin k ya kasance T daban da t = 10°C to ana sake lissafa darajarsa bisa ga dabara:
k10oC = ηt /η10oC * kT
inda ηt da η10oC su ne dankon ruwa a yanayin aikin T, wato a yanayin da aka ɗauka t =10°C.
kT ƙimar da aka samu na ma’aunin shigar ƙasa a yanayin aiki T.
Ƙimar viskoziti ga zafin jiki daban-daban T an ba su a cikin teburin 1.
Gwaji da matsin ruwa na dindindin
Fig. 7. Permeametar mai matsa lamba na ruwa na dindindin
Domin wannan gwajin, ana ɗaukar samfurin ƙasa mara tangarda a cikin silinda na ƙarfe mai diamita D, tsayi h, tare da ƙasan da aka kaifafa, ta hanyar matse shi cikin ƙasa ko cikin wani babban samfurin mara tangarda. Bayan an daidaita saman sama da na ƙasa na samfurin da gefunan silindar, sai a sa samfurin a cikin na’ura (sl. 7) tsakanin matatar sama da ta ƙasa. Matatar ƙasa tana ƙunshe da ragar mai ƙaurin yawa da dutse na matata, domin a ba da damar ruwan ya ratsa samfurin kuma a hana wanke ƙwayoyin ƙasa. Matatar sama ba ta da raga saboda akwai ƙananan yiwuwar wankewar ƙwayoyi. Shigar ruwan zuwa samfurin yana daga matakin N, wanda ake riƙe shi daidai ta hanyar zubawa, ta yadda matsin hydrostatic H ya kasance ɗaya. A ƙarƙashin wannan matsin, ruwa yana ratsa samfurin mai kaurin h kuma ta hanyar bututun da aka haɗa a ɓangaren sama na na’urar yana isa a cikin ma’aunin gilashi M inda yake digo.
Da zarar ruwa ya fara wucewa ta cikin samfurin zuwa cikin ma’aunin gilashi, sai mu kunna agogon dakatarwa kuma mu lura da adadin ruwan q da ke zuwa cikin ma’aunin gilashi a cikin lokacin t. Bisa ga dokar Darcy ne
q = k*A*t*i
inda k shi ne coefficient ɗin permeability a cm/sec, A fadin sassan samfurin, i raguwar matsa lamba ta ruwa, i = H/h.
Daga lissafin da ke sama muna da k= qh/Ath [cm/sec].
Muna karanta adadin ruwan da ya ratsa samfurin a takamaiman tazara na lokaci daga farkon zuwa ƙarshen lura, ta yadda za mu samu adadin ruwa na kowane lokaci da kuma jimillar ruwan da ya ratsa samfurin.
Domin a kawar da ƙaramar iska a cikin samfurin da kuma cikin ruwa, wadda za ta iya haifar da sakamakon gwaji mara daidai, wajibi ne kafin gwaji samfurin ya kasance a cikin yanayin cika da ruwa, kuma a yi amfani da ruwan da aka tafasa ko aƙalla ruwan da ya tsaya na ɗan lokaci wajen gudanar da gwajin.
Maimakon na’urar da aka bayyana a baya wadda ta dogara da matsin ruwa na hydrostatic saboda bambancin matakin ruwa H, akwai kuma na’urori inda aka samar da matsin hydrostatic ta hanyar matsin iska daga 10 zuwa 15 kp/cm2, ana kuma kiyaye shi a daidai ta amfani da compressor.