沉(chen)(chen)(chen)井(jing)(jing)是(shi)給水排水和(he)橋梁工(gong)(gong)程(cheng)以(yi)及工(gong)(gong)業與民用建筑工(gong)(gong)程(cheng)中作(zuo)為深(shen)(shen)基(ji)(ji)礎的一種(zhong)構筑物(wu)。它是(shi)在(zai)地面上用鋼筋混凝土制(zhi)成井(jing)(jing)筒形狀作(zuo)為基(ji)(ji)坑坑壁的支撐。沉(chen)(chen)(chen)井(jing)(jing)下沉(chen)(chen)(chen)前(qian)，應對(dui)沉(chen)(chen)(chen)井(jing)(jing)附(fu)近(jin)的堤壩、建筑物(wu)和(he)施(shi)(shi)工(gong)(gong)設備(bei)(bei)采取(qu)有效(xiao)的防護措施(shi)(shi)，并(bing)在(zai)下沉(chen)(chen)(chen)過程(cheng)中，沉(chen)(chen)(chen)井(jing)(jing)施(shi)(shi)工(gong)(gong)，經常進行沉(chen)(chen)(chen)降觀測，觀察基(ji)(ji)線(xian)、基(ji)(ji)點的設置情況。沉(chen)(chen)(chen)井(jing)(jing)挖土必(bi)須(xu)事先制(zhi)定好(hao)挖土計劃(hua)、合理配(pei)備(bei)(bei)施(shi)(shi)工(gong)(gong)人員和(he)機械設備(bei)(bei)。沉(chen)(chen)(chen)井(jing)(jing)開(kai)始下沉(chen)(chen)(chen)階段(duan)，井(jing)(jing)體(ti)入土的深(shen)(shen)度不大(da)(da)，井(jing)(jing)體(ti)下沉(chen)(chen)(chen)時所受的土方阻力(li)較小，并(bing)且此時由(you)于沉(chen)(chen)(chen)井(jing)(jing)大(da)(da)部分還在(zai)地面以(yi)上，側向土體(ti)的約束作(zuo)用很(hen)小，穩定性較差，大(da)(da)型沉(chen)(chen)(chen)井(jing)(jing)施(shi)(shi)工(gong)(gong)，所以(yi)沉(chen)(chen)(chen)井(jing)(jing)容易產生偏移和(he)傾斜。

當下沉(chen)(chen)(chen)到后(hou)階段(duan)時(shi)，由于沉(chen)(chen)(chen)井(jing)(jing)(jing)井(jing)(jing)(jing)體(ti)很大部分進(jin)入(ru)土(tu)中(zhong)，受土(tu)體(ti)側向約束(shu)作用，摩阻(zu)力(li)增大，沉(chen)(chen)(chen)井(jing)(jing)(jing)將會出現(xian)下沉(chen)(chen)(chen)困難(nan)，而(er)傾斜的(de)可能性就很小了。沉(chen)(chen)(chen)井(jing)(jing)(jing)下沉(chen)(chen)(chen)前(qian)，應對沉(chen)(chen)(chen)井(jing)(jing)(jing)附近(jin)的(de)堤(di)壩、建(jian)筑物和施(shi)(shi)工(gong)設備采(cai)取(qu)有效的(de)防護措施(shi)(shi)，并在下沉(chen)(chen)(chen)過(guo)程(cheng)中(zhong)，經常進(jin)行(xing)沉(chen)(chen)(chen)降觀測，沉(chen)(chen)(chen)井(jing)(jing)(jing)的(de)施(shi)(shi)工(gong)方案，觀察(cha)基(ji)線(xian)、基(ji)點的(de)設置(zhi)情況。灌(guan)注(zhu)過(guo)程(cheng)中(zhong)應通(tong)過(guo)調整(zheng)混凝(ning)土(tu)坍(tan)落度和導(dao)管埋深來保證混凝(ning)土(tu)的(de)質(zhi)量。一般要求導(dao)管口(kou)處(chu)混凝(ning)土(tu)堆不(bu)(bu)宜(yi)小于0．5m，流人沉(chen)(chen)(chen)井(jing)(jing)(jing)內混凝(ning)土(tu)形成的(de)流動坡度不(bu)(bu)陡于l：5。

灌(guan)(guan)注過(guo)(guo)程中(zhong)應通過(guo)(guo)調整混(hun)(hun)凝(ning)(ning)土(tu)坍(tan)落度(du)(du)和導(dao)管(guan)(guan)埋(mai)深(shen)(shen)來保(bao)證混(hun)(hun)凝(ning)(ning)土(tu)的質量(liang)。一般(ban)要求導(dao)管(guan)(guan)口(kou)處混(hun)(hun)凝(ning)(ning)土(tu)堆不宜小于(yu)0．5m，流(liu)人沉井內(nei)混(hun)(hun)凝(ning)(ning)土(tu)形成的流(liu)動坡(po)度(du)(du)不陡于(yu)l：5。多根(gen)導(dao)管(guan)(guan)灌(guan)(guan)注混(hun)(hun)凝(ning)(ning)土(tu)的順序以不發生混(hun)(hun)凝(ning)(ning)土(tu)夾層為原則(ze)，并(bing)使(shi)各(ge)導(dao)管(guan)(guan)同(tong)時所(suo)澆(jiao)注的混(hun)(hun)凝(ning)(ning)土(tu)保(bao)持大(da)致相(xiang)同(tong)的標(biao)高(gao)。每根(gen)導(dao)管(guan)(guan)灌(guan)(guan)注的首批混(hun)(hun)凝(ning)(ning)土(tu)量(liang)應經計(ji)算確定(ding)。在灌(guan)(guan)注過(guo)(guo)程中(zhong)，應注意(yi)隨著混(hun)(hun)凝(ning)(ning)土(tu)面(mian)的升(sheng)高(gao)而隨時提(ti)升(sheng)導(dao)管(guan)(guan)，使(shi)導(dao)管(guan)(guan)埋(mai)深(shen)(shen)始終與導(dao)管(guan)(guan)內(nei)混(hun)(hun)凝(ning)(ning)土(tu)下落深(shen)(shen)度(du)(du)相(xiang)適應，單(dan)根(gen)導(dao)管(guan)(guan)的小埋(mai)深(shen)(shen)一般(ban)在o．6～1．5m范圍(wei)內(nei)，根(gen)據不同(tong)灌(guan)(guan)注深(shen)(shen)度(du)(du)選定(ding)。多根(gen)導(dao)管(guan)(guan)的小埋(mai)深(shen)(shen)則(ze)根(gen)據導(dao)管(guan)(guan)的不同(tong)間距選定(ding)，一般(ban)在o．6～1．6m范圍(wei)內(nei)。