Ukucindezela okuqondile kumelwa njengendlela eyisisekelo yokuthuthukiswa komhlabathi esetshenziselwa emihlanganweni ehlukahlukene ye-geotechnical kanye nobunjiniyela bezisekelo ukuze kuthuthukiswe izimo zomhlaba ngokusebenzisa ukusetyenziswa kokucindezela okuqondile kanye nengcindezi. Le ndlela yomsebenzi ibandakanya ukujolisa okuphumelelayo kwemithwalo yomhlabathi ukuze kuncishiswe izizinda, kukhuphuke amandla okubamba, futhi kuthuthukiswe khona yonke imisebenzi yokuthwala - lezi zinto ezibalulekile ekulungiseleleni izindawo zohlelo lwezisekelo ezijulile ezifana nokufaka izinsiza, izindonga ze-diaphragm, nezinye izakhiwo eziphakeme. Izindlela zokucindezela okuqondile zibalulekile kakhulu lapho izimo zomhlabathi zikhombisa ubunzima obuphansi bokuqala noma izakhiwo zokugcina ezikahle ezingase ziphazamise ubuqotho kanye nokuthwala okuphakade kokufakwa kwezisekelo. Umehluko oyinhloko phakathi kokucindezela okuqondile nezindlela zokukhukhumala ubandakanya ukuncika ekucindezelweni okuqhubekayo kunokuba kube ukungqubuzana okwenziwe ngezinto eziphathekayo ukuze kufinyelelwe ekujoliseni komhlaba. Ukucindezela okuqondile kusebenzisa imishini ekhethekile esindayo okufaka phakathi ama-roller aqondile, abacindezeli abashile, kanye nezindawo zokucindezela eziphuzi ezisebenzisayo amandla anembile okuhamba phansi ukuze ziqinisekise amasendlalelo emhlabathini nokwenza kube nemifino namathoni. Le ndlela ibonakala ikhululekile ezindaweni eziyinqaba, ezizindaweni ezisemthethweni, nakwezelwandle lapho ukuphathwa kwezinto eziphathekayo kubalulekile ukuze kuvinjezelwe ukuphazamiseka kwezinto ezikwi-ndaweni ezithile noma emisebenzini ekhona. Onjiniyela bakhetha izindlela zokucindezela okuqondile ngokusekelwe ekuhlukanisweni komhlabathi, okuqukethwe kwamanzi, kanye nezinga elidingekayo lokuhlola - lezi zinto zibonakalayo zinomthelela ngqo ekukhetheni kwemishini yokucindezela kanye nezindlela zokusebenza. Ukucindezela okuqondile kufinyelela emiphumeleni emihle ekuhlinzekweni kwe-subgrade, ekwakhiweni kwe-embankment, nasekuzinzeni kwezingxenye zomhlabathi ezinamandla okuphuthumako lapho ukufaniswa kwezwa kuhlale kusemqoka ekwakhiweni kwezisekelo. Izicelo zokucindezela okuqondile ziqhubeka kulesi sikhungo sobunjiniyela bezisekelo nezimboni zokwakha ezibanzi. Ukuthwala izindawo ngaphambi kokufaka izinsiza kunciphisa ama-differentials wokuhlala futhi kuthuthukisa ukusatshalaliswa komthwalo phakathi nezinsizakalo zokudlidliza. I-engineering ye-landfill, ukuvulwa kwemizila, ama-embankments ezitimela, nezinhlelo zezimboni zonke zithola inzuzo ekuthuthukiseni amandla okubamba kanye nokunciphisa ukuthwala ngokuhambisana phakathi nezinhlelo zokucindezela okuqondile ezanele. Ezimweni zomhlabathi ezinamandla - i-silt, i-clay, kanye nemithonyama engafakiwe kakhulu - ukucindezela okuqondile kusebenza njengesixazululo sokuthuthukiswa komhlabathi esiyinkanyezi uma kuqhathaniswa nezindlela zokuhlaziya ezinzima. Le ndlela iqhakambisa ukuhlinzekwa kwezakhiwo zezakhiwo ezinzima zokwakha ngokwakha izici zomhlaba ezilungile ngaphambi kokufaka izinsiza, ama-micro-piling, noma ezinye izindlela ezikhethekile zokufaka izisekelo ziqale. Ukuqedwa kwezinsizakalo zokucindezela okuqondile kudinga uchwepheshe, ukuchaza elastiki ze- site, ukusho izinga lokuhlola elikhethwe ngokwehlukaniswa komhlabathi kanye nezinhlelo zokwakha, kanye nokuqinisekiswa kokwaziswa okuphephile ngokuqhubekayo ngokuhlola in-situ density. Abaphathi bemishini kufanele baqonde ukuphathwa kwe-cumpaction phakathi kwezinhlobo ezahlukene zomhlabathi nezimo zamanzi ukuze kube nezimbangela ezihambisanayo eziphelele endaweni yomsebenzi. Izinkontileka zokucindezela okuqondile zivame ukuhlanganiswa nezinhlelo zokuthuthukiswa komhlaba ezibanzi nezinhlelo zokulungisa izisekelo, okwenza ukuba kube nengxoxo phakathi kwamaphoyisa wemishini, abeluleki bezinhlaka ze-geotechnical, kanye nabakhi bezisekelo kuphumelele ngempumelelo yomsebenzi kanye nokuhlangabezana nezimfuneko zokwakhiwa.
Izakhiwo ezinqamlekileyo zedwala zimela indlela yokuzinzisa umhlaba ebalulekile ngaphakathi kwemigomo yokucindezela engashintshi, eyenzelwe ukusabalalisa imithwalo egxilile emakhakheni amakhulu angaphansi komhlaba futhi ithuthukise amandla okuphatha ezimeni ezinzima zomhlaba. Lo msebenzi uhlanganisa ukufakwa nokufakwa ngok precision kwezinhlelo zedwala ezinqamlekileyo ezilungiselelwe njengezinto zokwakha emiphakathini yokwakha izisekelo. Lezi zinqamlekileyo zakhiwe ukuhambisa imithwalo ye-superstructure kahle ezindaweni zembewu nezinto ezisemhlabathini, ukuvimbela ukwehla okungaphezulu nokwenza kube nezakhiwo eziqhubekayo. Le ndlela ibaluleke kakhulu ezinhlelweni ezijulile zokwakha izisekelo lapho izixazululo zokudonsa zendabuko zingenzeki, futhi lapho ukuthuthukiswa komhlaba ngokusabalalisa imithwalo engashintshi kudlula emalini nasempumelelweni kunezindlela zokuzinzisa ezahlukene. Inqubo yokufaka idinga ukuphathwa kahle komhlaba kanye nokuhlola izinzuzo zomhlaba ukuze kuqondwe izici zomhlabathi, amandla okuphatha, kanye nezimo ezingaphansi komhlaba ezizothonya ukujula, isakhiwo, kanye nezincazelo zokwaziqinisekisa zokuqinisa ama-blokki. Izinsiza ezikhethekile zibalulekile ekuphumeleleni, kuhlanganisa izinhlelo zemishini ezicindezelayo ukuze kuzuze ukucindezela komhlaba okufanele obala nasenkingeni ze-blokki, imishini yokuhamba eqinile yokulungiselela izisekelo, kanye nezinsiza zokubeka ngokunembile ukuze kuqinisekiswe ukuhleleka kahle nokusabalalisa imithwalo. Abachwepheshe bokuthuthukiswa komhlaba basebenzisa izinqubo zokuhlola nezokubheka ezithuthukisiwe ukuze balandele imikhondo yokwehla futhi baqinisekise ukuthi ubuqotho bokucindezela buhambisana nezincazelo zokwakha yonke into ngesikhathi sokwakha. Izakhiwo ezinqamlekileyo zedwala zisebenza ezinhlelweni ezihlukene zokuthuthukiswa kwezinsiza, ikakhulukazi ekwakheni imboni, ezisekelweni zokwakha izakhiwo zezimali, ezindaweni zokufinyelela ezakhiwe, kanye nokwakhiwa kwezindiza ezindaweni zokuhamba. Indlela yokucindezela engashintshi iletha izinzuzo ezinkulu ezindaweni ezinomhlabathikazi omncane, kufaka phakathi umhlabathi onamandla amancane, okubumbene, nemigqa engazinzile engenasidingo sokudonsa okuyisiphithiphithi okungase kubangele ukukhathazeka kwemvelo noma umonakalo kwezindawo eziseduze. Lezi zinqamlekileyo zakha amapulatifomu emithwalo ezinzile asekelayo izinguquko zesakhiwo esizayo futhi anikezela ngezindlela zesisekelo ezilinganiselwe ezikhathini ezinde. Le ndlela iphinde ibonakale ikhululekile kakhulu emsebenzini wezisekelo ezilungiswayo, lapho izakhi ezikhona zidinga ukuxhaswa noma ukuqiniswa ngaphandle kokuphazamiseka okukhulu ezindaweni eziseduze. Izinhlelo zamanje zezakhiwo ezinqamlekileyo zedwala zifaka imigaqo yokwakha ethuthukile eqonda ukwehla okubangela, ukweqa kwemithwalo, kanye ne-geology enzima engaphansi komhlaba eyaziwa kakhulu ekuthuthukiseni amadolobha nasemakhaya ezimbonini. Umkhakha wezobunjiniyela bezisekelo uqhubeka nokwazisa ukuthuthukiswa okusekelwe emabhulokhi njengenketho efanele ezindaweni zokwakha ezijulile ezijwayelekile, ikakhulukazi lapho izimo zomhlaba ziveza izinselelo ezinsizeni zokudonsa zendabuko noma lapho ukusindisa nezifundo zemvelo kudlulela kumasu wokwabelana imithwalo engashintshi. Abakhi abaphatha lezi zinhlelo badinga ukufinyelela kumishini yokucindezela ethile, izinsiza zokubheka, kanye namaqembu anolwazi akwazi ukuhlela imisebenzi yokuthuthukiswa komhlaba eyinkimbinkimbi ngenkathi behlola amazinga aphezulu okusebenza kwansuku zonke.
Ama-plates anezinto zensimbi ezisetshenzisiwe akhombisa indlela ebalulekile yokuzinza komhlaba emkhakheni wezezimali ze-geotechnical kanye nomsebenzi wezisekelo ezijulile, anikeza ukuqinisekiswa kokucindezela okuhleliwe kwezingqimba zembile ukuze kuthuthukiswe amandla okuphatha kanye nokuzinza jikelele komhlaba. Le ndlela yokwakha eyakhayo ihlanganisa ukufakwa okuhleliwe nokucindezelwa kwezingxenye zama-plates zensimbi eziphephile phezulu kwezingqimba zembile ezilungiselelwe, ukudala izindawo ezinxenxa ukuthi zidakwe kangcono emandleni okuphatha emhlabeni onobuthi noma onenkinga. Le nqubo ibalulekile emisebenzini lapho ukufaka ama-piles okujwayelekile noma izindlela zokucindezela ezisebenzayo zingafaneleki noma lapho kuthuthukiswa komhlaba okucacile kudingeka ngaphambi kokwakha izinhlelo zesisekelo zezindlu, izinsiza, noma izikhungo zemboni. Ukwenza kahle ama-plates anezinto zensimbi kusebenzisa izingxenye zensimbi ezakhiwe zokumelana nezinsizakalo zokucindezela ezithile ngenkathi kugcinwa ukuthambekela kwezilinganiso nemithetho yokwabiwa komthwalo. Lezi zingcezu zisebenza njengohlelo lokwabiwa komthwalo olugcwalisa kancane izingqimba zembile eziphansi ngokusebenza k فشار ایستایی (static pressure), okuhluke kakhulu ezindleleni zokucindezela ezisemkhathini wokushaya. Le ndlela idinga ukuhlela ngokucophelela nedatha yeziqu zomhlaba ukuze kutholakale ubukhulu obufanele be-plates, izincazelo zezinto, kanye nezinga lokucindezela ngokuhambisana nesakhiwo, okujwayelekile kokwaziswa, kanye nemfuneko ethile yokuphatha emsebenzini. Izinsiza ezisetshenziswa kule ndawo zifaka phakathi ama-presses e-hydraulic, izinsiza zokuhlola umthwalo osemhlabeni, nezinsiza zokuhlola ukuze kuqinisekiswe ukusebenza kahle kokucindezela nokwenza uqinisekise ukuthi umhlaba oqinisiwe uhambisana nezincazelo zokusungula. Abakhiqizi basebenzisa izindlela ezihlelelekile ezibhekelelayo izinga lezingqimba zembile, izimo ze-subsurface, kanye nezimfuno zokwabiwa komthwalo ukuze kuthuthukiswe inqubo yokucindezela. Ama-plates anezinto zensimbi akhombisa ukusebenza kahle ikakhulukazi ekubhekaneni nezimo ezimbi zomhlaba njengezindawo ezithambile, umhlaba we-organic, ama-silts aphansi, kanye nezingqimba eziyizingxenye ezihlukahlukene lapho izindlela zesisekelo ezijwayelekile zingaba yindleko noma zingashintshi. Indlela yokucindezela okuhleliwe ihlinzeka ngezinsizakalo endaweni ezibucayi lapho umsindo nodaka kufanele kuhlale kuncishiswe, okwenza ifaneleke kakhulu emisebenzini yokuba ngaphakathi emadolobheni, ukulungiswa kwezindawo zezinkumbulo, kanye nokwakhiwa eduze kwezakhiwo ezikhona. Izinhlelo zokuthuthukisa umhlaba zifaka ngaphakathi kwezisetshenziswa ezithambile, ukwakhiwa kwezinkundla zendlela, kanye nezindawo zokuzinza ezingaphakathi zokwakha ama-piling aphase. Le ndlela ivumela ukulawula ngokucophelela ub глубины (depth) kanye nenani lokucindezela, ivumela abajikeli ukuthi bakhe izingqimba ezakhiwe ezinezakhiwo ezibhalwe phansi. Ukukhetha ama-sistimu e-plates anezinto zensimbi kuncike ezindaweni eziningi ze-geotechnical okuhlanganisa amandla okuphatha umhlaba, umhlaba wokuhlala, isikhathi sokwakha, kanye nemikhawulo yokufinyelela endaweni. Ukuklama okusemthethweni kwendawo kubandakanya ukubala izinsiza zokucindezela ezidingekayo, ukuthola ubukhulu benhlangano kanye namakholi, kanye nokubeka imihlahlandlela yokuhlola ngokusebenzisa ukuhlolwa kokuhamba kwe-plates kanye nokuhlola ukuhamba. Le ndlela yokuthuthukisa umhlaba ihlanganisa kahle ezinhlelweni eziphelele zezezimali zezisekelo, ikakhulukazi uma ihlanganiswa nezinye izindlela zokuthuthukisa umhlaba ezifana nama-stone columns, izinqubo zokugqugquzela, noma izinhlelo ezijulile zamapile ukuze kuthuthukiswe izinsiza ezinkulu.
Amabhokisi agcwele amanzi, isigaxa, noma igilavu ayinikeza indlela eyisisekelo yokucindezela okuqhubekayo phakathi kokuzinzisa umhlaba kanye nezinhlelo zokuthuthukiswa komhlaba kwedwangu elijulile. Le ndlela ifaka imithwalo yokucindezela eyonciphisa emhlabeni ezindaweni zokusebenza ngebhokisi elinezinsiza ezilodwa, ngokuhlanganyela yehlisa ukuhamba komhlaba futhi ithuthukise amandla okuphatha ngaphambi kokufakwa kwemiphetho noma eminye imisebenzi yokwakha. Le ndlela iyasiza kakhulu ku-geotechnical engineering lapho kudingeka ukuphatha umhlaba othambile, imfucuza ephefumulayo, noma umhlaba obuyiselwa obungekho phansi obudinga ukuphucula ukufaka imithwalo enkulu. Ngokucindezela umhlaba ngalesi sikhathi ngalezi zinsiza, abakhiqizi bafinyelela i-consolidation eyinhloko kanye ne-consolidation yesibili eyengeziwe, benza i-pre-loading yomhlaba futhi yehlisa ukuhamba ngemuva kokwakha okungashintsha ubumsulwa benkumbulo noma kudale ukuhamba okunokuphambuka. Ukuqhutshwa kokucindezela okuqhubekayo okusekelwe kumabhokisi kubandakanya ukufaka amabhokisi agcwele amanzi, isigaxa, noma igilavu ezindaweni zomsebenzi, ngokuhleleka okwenziwe ngocwaningo lwe-geotechnical kanye nemodeli yokubikezela ukuhamba. Amabhokisi agcwele amanzi anikeza inzuzo yokulawula kalula, avumela abaphathi ukuthi bandise imithwalo ngokuhamba kwesikhathi njengoba ukuhlanganiswa komhlaba kuqhubeka futhi izilinganiso zokuhamba zikhombisa ukuhlinzekelwa okwanele. Amabhokisi agcwele isigaxa noma igilavu anikeza izixazululo zokuhlala ezinzima lapho ukuzinza kokuphatha kubalulekile noma uma ukufinyelela kwemishini kungcwatshwa ngenxa yamazinga endawo. Umsebenzi wokwakha unama-sistimu wokuhlola ukuhamba, kuhlanganisa amaphuzu okuhamba, izinsiza zokwenziwa, nezinsiza zokuthola idatha ezizenzekelayo, okwenza ukuba kube lula ukuhlaziya impendulo yomhlaba ngesikhathi esifanele nokuthuthukisa isikhathi sokulayisha kanye nomthamo. Le ndlela yokubala iqinisekisa ukuthi ukuhlanganiswa okuqhubekayo kuqinisekisa ukujabuliswa kwezindinganiso ezichaziwe ngaphambi kokuhamba ukuya kwe-pile driving, drilling, noma eminye imikhuba yokwakha. Izicelo phakathi kokwakhiwa kwamafasitelana ajulile ziwumkhakha omkhulu futhi onesizotha, ikakhulukazi ezindaweni zokuxhumana, izihlahla zezimoto, izikhungo zezimboni, kanye nezinhlelo ezinkulu zokwakha lapho ukuthuthukiswa komhlaba kwenzeka ngaphambi kokufakwa kwezigaxa ezihambayo, izigaxa ezibhorisiwe, noma ukufaka i-diaphragm wall. Le ndlela ibonakala ikahle ezindaweni ezinamathala athokozisayo, izilonda ezithambile, umhlaba obhalayo, kanye nesimo esiyingqayizivele lapho ukuhamba okwehlukahlukene kukhombisa ingozi yokusebenza kwendawo ephezulu. Kuxhumene nokucindezela okukhululekile, izindlela zokuvungama, noma i-jet grouting, ukucindezela okuqhubekayo okusekelwe kwimibhokisi kudala izinhlelo zokuthuthukiswa komhlaba eziphelele ezihlangabezana nezimo eziningi zomhlaba kanye nezithiyo zokwakha. Ukuhlanganiswa kwemishini nezinhlelo ezinkulu zokusebenza—kuhlanganisa ukuqinisekisa ukuhamba ngokuhlola ngokubhobhodla, ukuhlolwa kwamakhono, kanye nokuhlaziywa kokuhamba—kuqinisekisa ukuthi iziphakamiso zokwakha ziyahambisana nokuziphatha komhlaba, kunciphisa izidingo zezimali zokuzenzela futhi kuthuthukise umnotho wemisebenzi. Ukukhetha phakathi kokugcwalisa amanzi, isigaxa, kanye negilavu kuxhomeke esikhathini somsebenzi, ukufinyelela endaweni, ukutholakala kwezinto, kanye nezidingo zokubuyiselwa kwendawo ngemuva kokwakhiwa. Amabhokisi agcwele amanzi, evame ukusebenzisa izinhlelo zokuhlala ezitholakalayo noma izinsiza ezikhethekile, ahlala enza kube lula ukususa kanye nokususa ngempumelelo okuncane emvelweni, okwenzela kube kuhle kokuthuthukiswa kwesikhashana phakathi nezigaba zokwakha. Izinto zempucuko nogilavu zinikeza izixazululo ezinkulu zokuphakamisa lapho imibhokisi ihlala lapho noma uma ukulayisha kufanele kuqhubeke phakathi kwezikhathi ezide zokuhlanganyela. Ukuhlanganiswa nokuthengwa kwezimali kanye nezinkampani ezikhethekile kuqinisekisa ukutholakala kwesikhathi semibhokisi enzelwe kahle, izinsiza zokuhlola, kanye nobuchwepheshe obudinga ukuqhubeka kahle phakathi kwemisebenzi eyinkimbinkimbi ezidinga ukulawulwa okuqinile kokuhamba.
Amathafa al-load anama-supports akhombisa isixazululo esiyisisekelo se-geotechnical sokwakha izindawo ezizinzile zokuthwala phezulu kumafoundation aphakanyisiwe nezingqimba zokweseka ezakhiwe kahle. Le nhlobo yomsebenzi ibandakanya inqubo ephelele yokuklama, ukufaka, nokulungisa amathafa athwala imithwalo adlulisa imithwalo yesakhiwo ngezinqubo zokweseka ezikhethekile zibe ezindaweni ezikwazi ukuthwala. Le ndlela ihlanganisa izindlela zokuqinisa ezimile nezinto ze-foundation ezijulile ukuze kufezwe ukusabalala kwemithwalo nokulawula ukwehla, ikakhulukazi ezindaweni zomhlabathi eziyinkinga lapho ama-foundations ajulile ajwayelekile engakwazi. Ukwakhiwa kwamathafa al-load anama-supports kuqala ngokuqapha okuningiliziwe kwe-geotechnical endaweni yokwakha ukuze kubonakale amafayela omhlabathi, kutholakale izinga lempahla yokuthwala, futhi kuqageliswe ukuziphatha kokwehla. Izindlela zokuqinisa ezimile, kuhlanganise nama-vibratory rollers nama-plate compactors, zilungisa indawo ye-platform ukuze ihambisane nezidingo zobukhulu obusobala ngenkathi kugcinwa ubumsulwa bezakhiwo ezisemaphethelweni. Imishini yokushaya ama-pile ibeka isisekelo, i-impact hammers kanye ne-vibratory pile drivers zakha indlela yemithwalo ukusuka phezulu kothafa olu-layisha ngaphakathi kwezinto ezisekelayo zibe phezulu ezindaweni ezizinzile. Imishini eyakhelwe ngokukhethekile efaka ama-kelly bar attachments, ama-pile caps, kanye nama-load distribution plates ikhulisa ukudluliswa kwemithwalo kahle. Lapho izimo zomhlabathi zikhombisa izidingo ezingeziwe zokuthuthukiswa, izinto ezilawulwayo ezinomsebenzi ophansi, izisekelo ezinzile ze-cement, noma amasistimu wombhede ophakanyisiwe ayengeza inqubo yokulungisa ithafa. Imishini esetshenziswa ekwakhiweni kwamathafa al-load iyahluka ngokuya ngohlobo lomhlabathi, isikali se-platform, izithiyo zendawo, nezidingo zokuthwala imithwalo. Ama-compactors akhulu aphakamisa ukwenziwa okudingekayo ukuze kuqinisekiswe ukuzinza kwamathafa nokuphumelelayo kokudluliswa kwemithwalo. Izinsiza zama-piling ezigcwele ama-drilling attachments ne-rotary heads zikwenza kube lula ukufaka izakhiwo ezisekelayo, ngenkathi izinhlelo zokukhipha amanzi zilawula ukungenelela kwamanzi phansi ekwenziweni kokuqinisa nokusebenza kokuthwala. Imishini yokuphatha izinto efana namakhanter kanye namadhozi isekela ukusabalala kwezinto ngokuqondile nokusebenza kokulinganisa i-platform. Imishini yokulandelela ngesikhathi sangempela efana nama-settlement plates nama-inclinometers ilandelela ukusebenza phakathi kokwakhiwa nokuphila kwensiza. Izinhlelo zisebenzela ezakhamizini zezimboni, izindawo zokuhweba, amaphrojekthi wezokwakha, nezindawo zokulungiswa ezidinga ama-platform akhiwe ngaphezulu komhlabathi ofanele noma owezinyaweni ezingafanele. Ama-foundations etanki, indlela zamabhuloho, ukufakwa kwamandla avuselelwayo, kanye nokuthuthukiswa kwezindawo eziyingozi kuvame ukusebenzisa izixazululo zamathafa al-load ezakhiweni ezikhethekile. Ochwepheshe be-geotechnical baklama lezi zinhlelo ezifundeni ezinezinsila ezinkulu, izinqubo ze-organic, noma izendlalelo ezibucayi lapho ama-foundations ajwayelekile engase abangele ukusabalala noma ubungozi bokugcina obungkolile. Indlela ehlanganisiwe yendlela yokuqinisa ezimile nohlelo lwe-foundation ezijulile iletha izixazululo ezimnandi nezithembekile zokuhlangabezana nezidingo zokwakha, izimiso zokwakha, nezilindelo zokusebenza ezide ngenkathi kuncishiswa isikhathi sokwakha nezingozi zokusebenza.