根(gen)(gen)據不同(tong)土質情況，采用(yong)(yong)不同(tong)的挖土順(shun)序(xu)，分(fen)層(ceng)開挖，使挖土對稱(cheng)均(jun)勻，刃腳均(jun)勻受力，沉井(jing)均(jun)勻、豎直(zhi)平穩下沉。采用(yong)(yong)剛(gang)性(xing)導管法進行水下混凝土封底時，混凝土坍落度宜為150－200mm。封底需用(yong)(yong)的導管根(gen)(gen)數及間距應由導管作(zuo)用(yong)(yong)半徑和封底面積(ji)確(que)定(ding)。沉井(jing)下沉前，應根(gen)(gen)據設計(ji)單位(wei)提供(gong)的地質資料(liao)決定(ding)是否需要增補施(shi)工(gong)勘探，為編制施(shi)工(gong)技術方案提供(gong)準確(que)依據。施(shi)工(gong)前，應詳細調查施(shi)工(gong)期間內的洪汛(xun)、凌汛(xun)、河床沖涮、通(tong)航及漂流物等情況，并根(gen)(gen)據調查情況制定(ding)具體措施(shi)，確(que)保安全。

沉(chen)(chen)(chen)(chen)(chen)井(jing)下(xia)(xia)沉(chen)(chen)(chen)(chen)(chen)至設計標高后(hou)，應(ying)進行(xing)沉(chen)(chen)(chen)(chen)(chen)降觀測，沉(chen)(chen)(chen)(chen)(chen)井(jing)法施工，待(dai)8h內累(lei)計下(xia)(xia)沉(chen)(chen)(chen)(chen)(chen)量不大于10mm時，方可(ke)進行(xing)封底(di)(di)(di)。沉(chen)(chen)(chen)(chen)(chen)井(jing)封底(di)(di)(di)時影響沉(chen)(chen)(chen)(chen)(chen)井(jing)防水(shui)(shui)后(hou)果的(de)(de)要害，封底(di)(di)(di)有拍攝封底(di)(di)(di)和不排水(shui)(shui)封底(di)(di)(di)。（即干(gan)封底(di)(di)(di)和水(shui)(shui)下(xia)(xia)封底(di)(di)(di)）兩種方式。在刃腳遇到障礙物(wu)的(de)(de)情(qing)況(kuang)(kuang)下(xia)(xia)，必須先清(qing)除后(hou)再下(xia)(xia)沉(chen)(chen)(chen)(chen)(chen)。清(qing)除方法是(shi)人工排除，在不能排水(shui)(shui)的(de)(de)情(qing)況(kuang)(kuang)下(xia)(xia)，由潔水(shui)(shui)工進行(xing)下(xia)(xia)切割(ge)或者水(shui)(shui)下(xia)(xia)。水(shui)(shui)量大而沉(chen)(chen)(chen)(chen)(chen)井(jing)斷面(mian)又大時，應(ying)先挖(wa)超前(qian)小井(jing)，以(yi)供排水(shui)(shui)。為消(xiao)除降雨和施工用(yong)水(shui)(shui)流進沉(chen)(chen)(chen)(chen)(chen)井(jing)基(ji)坑，在沉(chen)(chen)(chen)(chen)(chen)井(jing)基(ji)坑內也應(ying)設泵抽水(shui)(shui)，基(ji)礎施工沉(chen)(chen)(chen)(chen)(chen)井(jing)，這(zhe)樣井(jing)內，井(jing)外同時排水(shui)(shui)，對挖(wa)土下(xia)(xia)沉(chen)(chen)(chen)(chen)(chen)，肅清(qing)障礙物(wu)、糾偏(pian)、干(gan)封，確保(bao)工程(cheng)質量都有利益。

下(xia)(xia)沉(chen)(chen)通過(guo)粘土(tu)(tu)膠(jiao)結層或(huo)(huo)沉(chen)(chen)井(jing)自(zi)身重力偏輕下(xia)(xia)沉(chen)(chen)困難時(shi)，可(ke)采(cai)用(yong)(yong)井(jing)外高壓(ya)射水、降低(di)井(jing)內(nei)(nei)水位等方法下(xia)(xia)沉(chen)(chen)。在結構受(shou)力容許的(de)條(tiao)件下(xia)(xia)，亦(yi)可(ke)采(cai)用(yong)(yong)壓(ya)重或(huo)(huo)接高沉(chen)(chen)井(jing)下(xia)(xia)沉(chen)(chen)。在灌(guan)注過(guo)程中，沉(chen)(chen)井(jing)施工，應注意(yi)隨著混(hun)(hun)凝(ning)土(tu)(tu)面的(de)升(sheng)高而隨時(shi)提升(sheng)導管(guan)(guan)，使導管(guan)(guan)埋深始終與導管(guan)(guan)內(nei)(nei)混(hun)(hun)凝(ning)土(tu)(tu)下(xia)(xia)落(luo)深度相適應，單根(gen)導管(guan)(guan)的(de)小埋深一般在o．6～1．5m范(fan)圍內(nei)(nei)，根(gen)據(ju)不(bu)同灌(guan)注深度選定。多根(gen)導管(guan)(guan)的(de)小埋深則(ze)根(gen)據(ju)導管(guan)(guan)的(de)不(bu)同間(jian)距選定，一般在o．6～1．6m范(fan)圍內(nei)(nei)。根(gen)據(ju)不(bu)同土(tu)(tu)質情況，采(cai)用(yong)(yong)不(bu)同的(de)挖土(tu)(tu)順序，分層開挖，使挖土(tu)(tu)對稱均(jun)勻(yun)，刃(ren)腳均(jun)勻(yun)受(shou)力，沉(chen)(chen)井(jing)均(jun)勻(yun)、豎直平穩下(xia)(xia)沉(chen)(chen)。