Uma enquma isilinda enhlabathini eboshwe bese esibeka ngaphansi kwesenzo sengcindezi evamile P (sl. 1), esilindeni kuzovela izingcindezi ezintsha, okungukuthi ingcindezi eqondile yokucindezela σ kanye nengcindezi evundlile yokusika. Uma ingcindezi P siyikhulisa kancane kancane, ngemva kwesikhathi esithile kuzovela esilindeni imifantu etshekile, bese khona manjalo kuzovela ukuphuka kwesilinda. Ngesikhathi sokuphuka isilinda isuswa endaweni yayo ngaphansi kwesenzo sengcindezi P futhi ngaphezu kwendiza yokusika yokumelana okuncane N-N.
Isith. 1. Umthelela wengcindezi kusilinda esikhishwe enhlabathini ehlanganisiwe
Ukumelana komhlabathi okwakuvinjwe yisilinda ngokumelene nesenzo samandla P ngesikhathi sokuphuka kubizwa ngokuthi ukumelana kokugunda komhlabathi, kanti i-engeli α yokuthambeka kwendiza yokumelana okuncane kakhulu maqondana ne-horizontali ibizwa ngokuthi i-engeli yendiza yokumelana okuncane kakhulu kokugunda komhlabathi.
Ukumelana nokugunda kwenhlabathi ehlanganisiwe kuhlanganiswa izakhi ezimbili ezisemqoka zokumelana: ukungqubuzana kwangaphakathi phakathi kwezinhlayiya eziqinile kanye nokubambisana (cohesion) okubopha izinhlayiya eziqinile. Amandla okugunda omhlabathi athathwa njengalingana nengcindezi enkulu yokugunda ngesikhathi sokuphuka futhi aboniswa ngesibalo
τf = c + σ tg_φ_
lapho: τf amandla okushelela enhlabathi [kp/cm2],
c ukuhambisana komhlabathi [kp/cm3],
σ ingcindezi evamile yenhlabathi [kp/cm3],
φ i-engela yokungqubuzana kwangaphakathi kwenhlabathi.
Ifomula engenhla yanikezwa nguFulansi uCoulomb ngonyaka 1785. Ngokwale fomula, enhlabathini ethile ukubambisana c kuhlala kungashintshi futhi kuzimele kwengcindezi ejwayelekile, kanti ukumelana nokungqubuzana σ tg_ϕ_ kulingana ngqo nengcindezi σ. Eqinisweni ukubambisana e akuhlali kungashintshi enhlabathini ethile, kodwa nalo ngezinga elithile lincike engcindezini ejwayelekile σ, ngoba ngaphansi kwale ngcindezi ubukhulu befilimu yamanzi emboza izinhlayiya eziqinile buyancipha futhi ngaleyo ndlela ukubambisana kuyanda. Ifomula kaCoulomb isebenza emhlabathini ongeneka kalula, lapho ngaphansi kwengcindezi ejwayelekile amanzi asemigodini ekhishwa ngaphandle kokumelana, okuyisimo somhlabathi onamatshe kanye nesihlabathi, kodwa akuyona isimo somhlabathi oboshiwe, ongavumeli kahle ukudlula kwamanzi, yingakho amanzi asemigodini ekhishwa ngobunzima futhi asala njengamanzi emigodini acindezelekile ngaphansi komthwalo P.
Izindleko ezisebenzayo nezingenakulinganiswa emhlabathini
Isith. 2. Ukucindezeleka okusebenzayo nokungathathi hlangothi enhlabathini
Uma sibeka isampula yenhlabathi phansi kwesitsha, ngokwesibonelo isihlabathi esomile, bese siyisilayisha ngomthwalo othile, ngokwesibonelo amahlahla omthofu anesisindo W, wonke lo mthwalo walesi sisindo uzothwalwa izinhlayiya eziqinile zenhlabathi. Ingcindezi ethile ebusweni besampula p0 = W/A ku-kp/cm3, lapho A kuyindawo yesigaba esinqamulelayo sesampula, izobangela ukuhlala kwesampula, okungukuthi ukuncipha kwe-porosity yayo, kodwa futhi izobangela izinguquko kwezinye izakhiwo zomzimba zesampula njengokwanda kwamandla okushefa, ukwanda kwemoduli yokucindezeleka nokunye. Ingcindezi ekhona ezindaweni zokuthintana phakathi kwezinhlayiya ibizwa ngokuthi ingcindezi esebenzayo noma ingcindezi ye-intergranular σ’. Uma sekufinyelelwe ekuhlanganeni, okungukuthi lapho isampula seyiyekile ukuhlala ngaphansi komthwalo p0, ingcindezi esebenzayo ilingana nengcindezi ephelele ethile ekhona ekujuleni lapho inhlabathi ibhekwa khona. Kulesi simo ekujuleni, ngaphansi kobuso besampula esithombeni 2 σ’ = W/A + hzγ lapho γ kuyisisindo somthamo wesampula.
Kodwa-ke uma isampula esitsheni, esikhundleni sokuyilayisha ngosibhamu somthofu, siyilayisha ngamanzi kuze kube ukuphakama h, inqobo nje uma amanzi egcwalise zonke izimbotshana zesampula, ingcindezi yekholomu yamanzi ngaphezu kwesampula hγw, lapho γw kuyisisindo sevolumu samanzi, ngeke ibangele ukuhlala phansi kwesampula nokuncipha kobukhulu bayo bezimbotshana futhi ngeke yandise amandla ayo okucheba kanye ne-modulus yokucindezeleka. Ngakho-ke ingcindezi ye-hydrostatic hγw ibizwa ngokuthi ingcindezi engathathi hlangothi. Ingcindezi engathathi hlangothi, echazwa ngo u, idluliselwa ngesampula kuzo zonke izinkomba ngamandla alinganayo. Le ngcindezi ngeke ibangele ukwanda kwamandla okucheba, ngoba amanzi ngokwawo awanawo nhlobo amandla okucheba.
Ngakho-ke ingcindezi esebenzayo σ’ idluliselwa ngezindawo zokuthintana phakathi kwezinhlayiya eziqinile zenhlabathi, kanti ingcindezi engathathi hlangothi u idluliselwa ngamanzi asema-pores. Uma ingxenye engezansi yesiqukethe igcwele isampula lomhlabathi eligcwele amanzi elinesisindo sevolumu γz, kanti ngaphezu kobuso besampula kuze kufike ezingeni N isiqukethe sigcwaliswe ngamanzi anesisindo sevolumu γw, khona-ke ingcindezi iyonke σ kunoma yiliphi iphuzu lesampula izoba σ = σ’ + u.
Ebuhleni obungu-hz, ngaphansi kobuso besampula ukucindezeleka okusebenzayo kuzoba σ = σ’ - u
lapho σ = h γw + h γz
u = (h + hz) γw.
Ngakho-ke kuzoba σ’ = hz γ’
γ’ isisindo sevolumu yenhlabathi ecwilisiwe emanzini.
Isibalo esijwayelekile samandla okushefa enhlabathi
Uma umhlabathi obophelelekile uwuthwala ngomthwalo P, lo mthwalo uzodala ukwehla kwenhlabathi futhi okokuqala umoya uzophushwa uphume ezimbotsheni ngaphansi kwawo, ukuze ngokushesha ezimbotsheni kusale amanzi kuphela. Njengoba ngenxa yokungavumeli kahle amanzi emhlabathini obophelelekile amanzi engenakucindezelwa aphume ngokushesha, ahlala njengamanzi acindezelekile ezimbotsheni futhi ekuqaleni athwale wonke umthwalo wangaphandle P. Ngokuhamba kwesikhathi, ngaphansi komthelela womthwalo P amanzi aqala ukuphushwa aphume ezimbotsheni bese kuba nokusondelana kwezinhlayiya eziqinile, ezithwala manje ingxenye yomthwalo P. Khona-ke sinakho τf =c + (σ - u) tg_ϕ,_ lapho σ kuwukucindezeleka okuphelele okuvela emthwalweni P, u kuyizingcindezi zamanzi ezimbotsheni.
Ukucindezela kwamanzi embotsheni u kuncike ezintweni eziningi, njengokuhamba kwesikhathi sokuhlanganiswa, ukungena komhlabathi, ubukhulu bomthwalo womhlabathi njll. Amandla okushefa omhlabathi ancike ekucindezelweni kwamanzi embotsheni futhi aba makhulu kakhulu lapho u=0, lapho kuvela khona ukuhlanganiswa komhlabathi.
Umsebenzi we-colloidal wenhlabathi
Izakhi zokumelana kwangaphakathi komhlabathi ukubambisana nokuthi ukungqubuzana zingahluka futhi zincike kakhulu ebukhulu bezinhlayiya eziqinile zomhlabathi nasezimpahleni zawo zepulasitiki. Ukuze kunqunywe umthelela wokubambisana maqondana nokumelana kokungqubuzana kwangaphakathi komhlaba onobumbano, u-Skempton wethula umqondo womsebenzi we-colloidal womhlaba _K_P, ovezwa ngesilinganiso somkhombandlela we-plasticity IP maqondana nenani lezinhlayiya ezincane kuno 0,002 mm ngo-% wesisindo somzimba wonke. Lapho kwamukelwa lo mqondo olandelayo (sl. 3):
Sl. 3. Ukusebenza kwe-colloid komhlaba
Ku-KP < 0,75 kukhona ubumba obungasebenzi,
ku-KP = 0,75 – 1,25 zingubumba ezivamile,
for Kp > 1,25 yobumba olusebenzayo.
Njengoba i-KP ikhula, umthelela wokuhlangana ukhula uma uqhathaniswa nokungqubuzana kwangaphakathi komhlaba ohambisanayo.
Ukuzwela komhlabathi
Uma enhlabathini ehambisanayo sikhipha isilinda sobubanzi 3—3,4 cm nobude ~ 5 cm bese siyasifaka ngaphansi komthwalo oqondile, ngesikhathi sokuphuka kwesilinda sizothola amandla okucindezela enhlabathi isesimweni esingaphazamisekile σ__ₙ:
σn = P/A ku-kp/cm2,
lapho A kuyisiphambano esinqamulelayo sesilinda.
Ngemva kokuphothulwa kokuhlolwa isampula ephukile siyisusa bese sakha kabusha isilinda esinobukhulu obufanayo, sisebenzisa isikhunta sesilinda esifanayo, kanti umswakama waso uhlala lowo owawukhona ngesikhathi sokuhlolwa kwangaphambilini. Bese ngokushesha ngemva kokwenziwa kwesilinda esixovwe kabusha kuphindwa ukuhlolwa ngaso, ukuze kutholakale amandla okucindezela omhlabathi esesimweni esiphazamisekile σ__ₚ.
Ukuzwela (sensitivitet) S__ₜ kuwubudlelwano phakathi kwamandla okucindezela esimweni esingaphazamisekile namandla okucindezela esimweni esiphazamisekile: St = σn/σp,
Ngokomgomo owodwa, ukuzwela S__ₜ kuhlolwa kanje:
- ku S__ₜ = 1 — 2 ukuzwela kobumba kuncane,
- ku S__ₜ = 2 — 4 kukhona ukuzwela okumaphakathi kobumba,
- ku S__ₜ = 4 — 8 kukhona ukuzwela okukhulu kobumba,
- ukuthi S__ₜ > 8 iwubumba oluzwela kakhulu.
Emvelweni kwenzeka ukuthi ngenxa yesenzo somshini, isibonelo ukuzamazama komhlaba, inhlabathi yobumba ilahlekelwe ngokuzumayo ukuqina kwayo, bese ikuthola futhi uma isimile. Lesi sici sibizwa ngokuthi i-thixotropy yenhlabathi. Obunye ubumba bunazo ngezinga elithile izici ze-thixotropy. Kuyaziwa izimo zokushibilika kwemithambeka emigedeni ngenxa yokuphuma kwebumba eline-thixotropy eNorway, eSweden naseFinland, lapho ngophenyo kwatholakala ukuthi kwakungekho ushintsho emswakameni webumba phakathi nale nqubo, okungukuthi, ukuthi umswakama webumba wawuhlala ungashintshi ngaphambi nangemva kokuphuma.