Ekuqondeni kobunjiniyela benhlabathi kunqunywa umthamo wokuthwala omkhulu womhlabathi kanye nomthwalo ovumelekile wenhlabathi.
Amandla okuthwala omkhawulo wenhlabathi yilawo afinyelelwa ngesikhathi kuvela ukwehluleka kwenhlabathi. Ukwehluleka kwenhlabathi kwenzeka lapho umthwalo isisekelo esisebenza ngawo enhlabathini weqa amandla aso okugunda. Kuleso simo, ngaphansi komthwalo wesisekelo P kuvela izindawo ezinomelana okuncane kakhulu ACD kanye BCE – izindawo zokushibilika sl. 1, lapho inhlabathi ikhishwa eceleni futhi ngesikhathi esifanayo kuvela ukuphakama kwenhlabathi ngaphezu kobuso bomhlaba eduze kwesakhiwo DG no EF, kuyilapho isisekelo uqobo sicwila.
Sl. 1. Ukuqhekeka komhlabathi ngaphansi komthwalo wesisekelo
Amandla okushefa enhlabathi ayanda ngokujula kwesisekelo t, ngoba ngenxa yesisindo sezendlalelo eziphezulu kuncipha amathuba okucindezelwa eceleni. Ngakho-ke, izisekelo ezijulile zivame kancane ukubangela ukuwohloka komhlaba, kanti izisekelo ezingajulile ziyingozi ngokuwohloka. Ngokufanayo, izisekelo ezibanzi zivame kancane ukubangela ukuwohloka komhlaba, ngoba izindawo zokushelela zijule kakhulu.
Umthwalo ovumelekile womhlabathi yilowo ongavunyelwa ukuba usebenze emhlabathini kangangokuthi kungabangeli ukuphuka komhlabathi ngaphansi kwezimo ezimbi kakhulu ezingase zibe khona. Umthwalo ovumelekile womhlabathi unqunywa ngokusekelwe kumthamo wokuthwala wokugcina womhlabathi ngokusebenzisa isici sokuphepha. Ubukhulu besici sokuphepha buxhomeke ezintweni eziningi, phakathi kwazo ezibaluleke kakhulu ukunemba kwezici ezingokomzimba zomhlabathi, amathuba oshintsho lwamanani ezinto zokumelana kwangaphakathi komhlabathi ikakhulukazi ukuhlanganisana, inani lakho elingahluka kakhulu ngaphansi kwethonya lamanzi emhlabathini, bese kuba nomthelela wezinye izici ezingaba khona, njengezimo zomthwalo (ithuba lomthwalo osheshayo nowa-dynamic), ukujula kokwakhiwa kwesisekelo, kanye nobubanzi besisekelo.
Umthamo womhlabathi wokuthwala umthwalo unganqunywa ngokusekelwe ekuqhekekeni komhlabathi, okunikeza umthamo wokugcina wokuthwala. Ngaphansi komthamo wokugcina wokuthwala komhlabathi kuqondwa inani lomthwalo elibangela ukuqhekeka. Kukhona izindlela ezimbili zokunquma umthamo wokugcina wokuthwala ngokusekelwe ekuqhekekeni komhlabathi, okuyi isixazululo sezibalo kanye nomthwalo wokuhlola.
Isixazululo sezibalo
Ososayensi abaningi bazamile ukuthola isisombululo sezibalo sokunquma amandla okuthwala omkhawulo womhlabathi, ngokusekelwe ekwazini izici ezithinta lokhu kanye ngaphansi kwemibono ehlukahlukene yezimo zokwehluleka. Izici ezithintayo ziyizici ezingokomzimba zomhlabathi, ezinqunywa ngokuhlolwa kwelabhorethri kumasampula omhlaba angaphazamisekanga, isimo samanzi angaphansi komhlaba, ukujula kwesisekelo, ubukhulu nesimo sendawo elayishiwe, kanye nendlela yokulayisha, okungukuthi ukulayisha okufanayo noma okungalingani, okumaphakathi noma okunezikhundla ezingalingani zomthwalo womhlaba. Imibono ngezimo zokwehluleka isuselwa emfundisweni ye-plasticity nasemfundisweni ye-elasticity. Nokho izindlela zesimanje zokunquma amandla okuthwala omhlaba zisekelwe emfundisweni ye-plasticity, ehlanganiswa neminye imibono eyenziwe yaba lula.
Lapha sizoveza izindlela ezimbalwa ezaziwayo zokubala zokunquma umthamo womthwalo wokugcina, okungukuthi umthwalo ovumelekile wenhlabathi.
Ifomu likaPrandtl-Caquota
Uma ifayini yesisekelo i_AB_ isisekelwe ekujuleni t ngaphansi kobuso bomhlaba, kuleli zinga kuba khona ingcindezi yokuxhumana po ngenxa yomthwalo wesisekelo kanye nengcindezi eseceleni p=γt ngenxa yesisindo somhlabathi ongaphezu kwezinga lefayini yesisekelo kuze kufike ebusweni bomhlaba (sl. 2).
Ngaphansi kwesenzo esiqondile sesisindo sesisekelo, ngesikhathi sokudlula komkhawulo wokuthwala umthwalo womhlabathi kuvela izindawo zangempela zokushelela AC no BC, ezakha i-engeli α = 45° + ϕ/2 nendawo elayishiwe. Lezi zindawo zokushelela zakha iprizimu yomhlabathi esebenzayo ABC.
Umd. 2. Izindawo zokushibilika ezisesimweni se-logarithmic spiral ngaphansi komthwalo osebenza maphakathi esisekelweni ngokuka-Prandtl-Caquotu
Ngaphansi kwengcindezi yeprizimu yomhlabathi esebenzayo kwakheka ama-prizimu asemaceleni omhlabathi angenzi lutho ADD1 no BEE1, wona ezama ukuwaphoqa phezulu ezindaweni zokushelela DD1 no EE1, nge-engeli engu 45°-ϕ/2 nomugqa oqondile ovundlile. Phakathi kwendawo yengcindezi yomhlabathi esebenzayo neyomhlabathi engenzi lutho kukhona indawo yokushelela kwe-radial ACD noma BCE, lapho, uma umkhawulo wokulingana weqiwa, ukushelela kwenzeka ezindaweni zokushelela ezigoqekile. U-Résal ubale ukuthi izindawo zokushelela endaweni yokushelela kwe-radial zisesimweni se-spirali ye-logarithmic enesigxobo ku A noma B, okuyisibalo sayo esingu r=r0 eπ tg_ϕ_
Ukuze kunqunywe umthwalo womkhawulo wenhlabathi, kwenziwa le mibono elandelayo:
- ukuthi isisekelo sibushelelezi, okungukuthi ukungqubuzana phakathi kwefayini yesisekelo nomhlabathi kuyashiywa ngaphandle;
- ukuthi amandla eshearing enhlabathi emigqeni D1M no E1N awekho, noma ayashaywa indiva;
- ukuthi isisindo somthamo wenhlabathi ngaphansi kwesansi sesisekelo γ=0, okusho ukuthi umthelela wesisindo senhlabathi ngaphansi kwezinyawo zesisekelo awunakwa, endaweni yokulingana kwepulasitiki.
Ifomu lika-Prandtl-Caquota lithi:
Amandla okuthwala omkhawulo womhlabathi yi
Uma sibeka:
umthamo omkhulu wokuthwala womhlabathi oboshiwe ngu qf = γtm + cm1.
Ngezilinganiso ezihlukene ze-engeli yokungqubuzana kwangaphakathi kwenhlabathi, amanani ka m no m1 anikezwe kuthebula 1.
Tabl. 1. Amanani ama-coefficients m no m__1 ezinani ezahlukene ze-engeli yokungqubuzana kwangaphakathi kwenhlabathi
Umthwalo womhlabathi ovunyelwe ngu qa = pdozv = qf/F lapho F kuyisici sokuphepha. Ukuze kusetshenziswe ifomula kaPrandtl-Caquot kwamukelwa F = 4, ngakho qa = qf/4.
Ifomula ka-Terzaghiev
UTerzaghi wanikeza ifomula ye-semi-empirical yokubala amandla okuthwala okuphelele kwenhlabathi ngaphansi komthelela wemithwalo yesimo sebhande, isikwele kanye nepuleti eliyindilinga. Wabheka isisekelo esimiswe ekujuleni Df ngaphansi kobuso bomhlaba, ngobubanzi B (fig. 3), futhi wamukela ukuthi kukhona ukungqubuzana phakathi kwesisekelo AB nenhlabathi, okuphikisana nokucindezelwa kwenhlabathi eceleni, nokuthi izindawo zokushelela AB no BC zakha i-engeli yokungqubuzana kwangaphakathi nobuso obuthwele umthwalo.
Sl. 3. Amandla okugcina omhlabathi ngokusho kukaTerzaghi
Ngenxa yalokho, inhlabathi ekwikhilini lomhlabathi ABC, ehlanganiswe phakathi kwesisekelo AB nezindawo zokushelela AC no BC ihlala esimweni sokulingana oku-elastic futhi iziphatha njengengxenye yesisekelo. Iprizimu ABC ayikwazi ukucindezelwa kuze kube yilapho izingcindezi ezinhlangothini zayo AC no BC sezilingana nengcindezi yomhlabathi eyipasivhu yamaprizimu asemaceleni, okusho ukuthi, lapho isimo somkhawulo wokulingana sidlulile, ingcindezi yomhlabathi ephumayo q isebenza nge-engeli ϕ maqondana ne-normal endaweni yokushelela, okungukuthi, iqonde mpo (umfanekiso 3). Njengoba ngaphansi komthelela womthwalo ikhili lihamba liye phansi mpo, inkinga yokulingana emhlabathini incike ekunqumeni ingcindezi yomhlabathi eyipasivhu. Kodwa njengoba ukubalwa okunembile komthamo wokuthwala womhlabathi ngale ndlela kuyinkimbinkimbi, uTerzaghi wanikeza isixazululo esenziwe lula. Ifomula kaTerzaghi yokubala umthamo wokuthwala womhlabathi wokugcina _q_f ithi
- Ngesisekelo sesimo somucu
qf = cNc + γ1 DfNq + 0,5 γ2 BNγ
lapho c kuyihlangano yenhlabathi
γ1 isisindo somthamo wenhlabathi ngenhla kwesisekelo sesisekelo
Df ukujula kokusungula isisekelo ngaphansi kobuso bomhlaba kuya ezansi kwesisekelo
γ2 isisindo somthamo wenhlabathi ngaphansi kwesisekelo
B ububanzi besisekelo.
Nc, Nq, Nγ yizici zokuthwala umthwalo, ezincike ku-engela yokungqubuzana kwangaphakathi kwenhlabathi. amanani alezi zici anikezwa ngala mafomula alandelayo:
Nq iyisici ngenxa yesisindo sesendlalelo somhlabathi eseceleni kuze kufike ekujuleni kwesisekelo: Nq = tg2 (45° + ϕ/2) eπ tg_ϕ_
Nc iyisici esibangelwa ukuhlanganisana: Nc = (Nq – 1) ctg_ϕ_
Nγ iyisici ngenxa yesisindo sayo somkhono womhlabathi ngaphansi kwekhanda lesisekelo, okungukuthi ngaphansi kobubanzi bekhanda AB. Inani lalesi sici uBrinch Hansen uliphakamisa njengelilinganiselwe: Nγ ≈ 1,8 (Nq – 1) tg_ϕ_
Sl. 4. Ukwabiwa kwezingcindezi ezitholwa inhlabathi lapho isisekelo silayishwe ngomthwalo oqondile ophakathi nendawo
Ngenxa yomehluko omncane wesisindo sevolumu senhlabathi kuvame ukwamukelwa γ1= γ2= γ. Ngokwalinganiso elingenhla amandla okuthwala kwenhlabathi ancike (sl. 4) ku: ukubumbana kwenhlabathi yesisekelo c, umthwalo wenhlabathi eduze kwesisekelo _γ1 D_F, isisindo sayo senhlabathi yeprizimu eshelelayo esebenzayo enobubanzi B.
Nokho, nakuba ukusatshalaliswa kwengcindezi etholwa inhlabathi ngenxa yomthelela wokubumbana c nokujula kwesisekelo Df kufana kuyo yonke ububanzi, okungukuthi kuwunxande, ukusatshalaliswa kwengcindezi etholwa inhlabathi ngenxa yomthelela wobubanzi B kungunxantathu, okungukuthi izingcindezi ezinkulu zitholakala maphakathi nesisekelo, bese zehla ziye emaphethelweni lapho zilingana noziro.
Fig. 5. Umfanekiso we-factor yokuthwala ngokuvumelana ne-engeli yokungqubuzana kwangaphakathi kwenhlabathi ngokukaTerzaghi
Ngemibandela ehlukene ye-engeli esuka ku-0 iye ku-40°, uTerzaghi wakha amashadi ezici zokuthwala umthwalo (sl. 5). Nokho izici zokuthwala umthwalo Nc, Nq no-Nγ (imigqa eqinile esithombeni 5) zingamukelwa kuphela esimeni somhlabathi ominyene futhi oqinile. Uma umhlabathi ukhihlithekile noma ucindezeleka kakhulu, khona-ke kufanele zamukelwe izici zokuthwala umthwalo N’c, N’q no-N’γ (imigqa enemigqa ephukile ku-sl. 5), ezinikeza amanani 2/3 okumelana nokungqubuzana. Ngaphezu kwalokho, kulesi simo kufanele kuthathwe amanani 2/3 wokubambisana c atholwe elabhorethri, ukuze kuleso simo sibe no-qf = 2/3 cN’c + γ1 DfN’q + 0,5 γ2 BN’γ.
2. Okwesisekelo esiyimo yedonsele elingunxande
qf = 2/3 (1+0,3 B/L) cN’c + γ1 DfN’q + 0,5 γ2 BN’γ lapho L kuyibude besisekelo
3. Ngokwesisekelo somhlabathi esinomumo wesikwele
qf = 2/3 1,3 cN’c + γ1 DfN’q + 0,4 γ2 BN’γ
4. Okwesisekelo sesisekelo esiyindilinga
qf = 2/3 1,3 cN’c + γ1 DfN’q + 0,6 γ2 rN’γ lapho r kuyiradiyasi yesisekelo sesisekelo.
Ekubalweni komthwalo ovunyelwe wenhlabathi kuthathwa i-factor yokuphepha F: qa = qf/F. Inani le-factor yokuphepha lisuka ku-2 liye ku-3 ngokwezimo zenhlabathi nomthwalo.
Ukusetshenziswa kwamaphethini ezibalo
Ukusetshenziswa kwamafomula ezibalo ukuthola umthwalo ovumelekile wenhlabathi kudinga ulwazi lwezici ze-geomechanical zenhlabathi, okungukuthi ukuhlangana nokungqubuzana kwangaphakathi ekujuleni kwesisekelo kanye nesisindo somthamo wenhlabathi ngenhla nangaphansi kwesisekelo. Uma inhlabathi yesisekelo itholakala ngaphansi kwezinga lamanzi angaphansi komhlaba, kufanele kubhekwe nokuphakama okusekela phezulu ekunqumeni isisindo somthamo wenhlabathi.
Emithwalweni emikhulu yomhlabathi nasezinhlelweni ezinkulu, lapho inani elitholakele lomthwalo ovunyelwe womhlabathi elisekelwe ezimisweni zezibalo lisetshenziswa ngokuphelele, ukubalwa komthamo wokuthwala komhlabathi kufanele kuhambisane nokubalwa kokuhlala phansi. Umthamo wokuthwala womhlabathi obalwe ngamukelwa kuphela uma ukubalwa kokuhlala phansi kuthole ukwehla okuncane kunokuvunyelwe ngalolo hlobo lwesakhiwo. Uma kwenzeka ukubalwa kuthole ukuhlala phansi okukhulu kunokuvunyelwe, inani elibalwe lomthwalo ovunyelwe womhlabathi kusetshenziswa izindlela zokubala alimukelwa, kodwa indlela yokusungula isisekelo kufanele ishintshwe ukuze kutholakale ukuhlala phansi okuncane, ngaphakathi kwemikhawulo yokuhlala phansi evunyelwe kuleso sakhiwo.
Sl. 6. Ukujula okusebenzayo kokusungula D__f
Ezinkambisweni zezibalo zokunquma umthamo wokuthwala womkhawulo wenhlabathi akuzange kubhekwe ukungqubuzana kwegobolondo lesisekelo, nakho okusebenza njengokumelana nomphumela womthwalo, uma isisekelo sithinta ngokuqinile inhlabathi ezinhlangothini. Ukumelana kokungqubuzana kwegobolondo akufanele kubhekwe, ngoba ukungqubuzana kwangempela kwegobolondo kukhona kuphela ezinqwabeni ezishayelwa emhlabathini, kanti ezinyaweni zesisekelo ukungqubuzana kwegobolondo kuncane, ngoba izinyawo zenziwa emigodini esele imbiwe ngaphambili.
Ukusetshenziswa kwamaphethini ezibalo lapho kunganakwa ukuma kwesisekelo kunikeza imiphumela eseduze kakhulu ezisekelweni zohlobo lwebhande, okusho ukuthi lapho ubude besisekelo bungaphezu kokuphindwe kabili kobubanzi baso. Ngokuvivinywa kutholakele ukuthi ezinqabeni zesisekelo ezinomumo oyisikwele noma oyindilinga ukuphuka kwenzeka emthwalweni womkhawulo ophakeme ngo 10-30% kunalowo obalwa ngamaphethini ezibalo. Izisekelo ezinomumo wothathu zinikeza umthamo wokuthwala omncane kunowebhande, kanti umthamo omncane kakhulu unikezwa izisekelo ezinomumo wendandatho, uma zingagcwaliswanga.
Ukujula kokusungula Df kubalwa njengokujula okusebenzayo kokusungula kusukela emhlabathini wesisekelo kuya phansi kwesisekelo (Sl. 6). Ezisekelweni ezingaphansi kwezindawo ezingaphansi komhlaba, ukujula okusebenzayo kokusungula Df kwehlukile ekujuleni kokusungula nasezingeni lobuso bomhlaba. Ezimweni ezinjalo, ekubaleni umthwalo womkhawulo nowovunyelwe wenhlabathi kufanele njalo kuthathwe Df, ngoba ngenhla komhlabathi wesisekelo kunomoya ongamelani nokucindezelwa kwenhlabathi eceleni ngaphansi kwesenzo somthwalo wesisekelo P.