【正文】 The cheapest way of moving earth is to take it directly out of the cut and drop it as fill with the same machine. This is not always possible, but when it canbe done it is ideal, being both quick and cheap. Draglines, bulldozers and face shovels an do this. The largest radius is obtained with the dragline,and the largest tonnage of earth is moved by the bulldozer, though only over short disadvantages of the dragline are that it must dig below itself, it cannot dig with force into pacted material, it cannot dig on steep slopws, and its dumping and 4 digging are not accurate. Face shovels are between bulldozers and draglines, having a larger radius of action than bulldozers but less than draglines. They are anle to dig into a vertical cliff face in a way which would be dangerous tor a bulldozer operator and impossible for a dragline. Each piece of equipment should be level of their tracks and for deep digs in pact material a backacter is most useful, but its dumping radius is considerably less than that of the same escavator fitted with a face shovel. Rubbertyred bowl scrapers are indispensable for fairly level digging where the distance of transport is too much tor a dragline or face shovel. They can dig the material deeply ( but only below themselves ) to a fairly flat surface, carry it hundreds of meters if need be, then drop it and level it roughly during the dumping. For hard digging it is often found economical to keep a pusher tractor ( wheeled or tracked ) on the digging site, to push each scraper as it returns to dig. As soon as the scraper is full,the pusher tractor returns to the beginning of the dig to heop to help the nest scraper. Bowl scrapers are often extremely powerful machines。 early or excessive cracks。其抗拉強度約為抗壓強度的十分之一。 設(shè)計鋼筋混凝土構(gòu)件時顯然需要處理大量的參數(shù)，諸如寬度、高度等幾何尺寸，配筋的面積，鋼筋的應(yīng)變和混凝土的應(yīng)變，鋼筋的應(yīng)力等等。土方設(shè)計這項工作落到了從事道路設(shè)計的工程師的身上，因為土方工程的設(shè)計比其他任何工作更能決定工程造價是否低廉。它能在比較平的地面上挖較深的土（但只能挖機械本身下面的土），需要時可以將土運至幾百米遠(yuǎn)，然后卸土并在卸土的過程中把土大致鏟平。就目前的趨勢而言，安全系數(shù)與所使用的材料性質(zhì)及其組織情況無關(guān)，通常把它定義為發(fā)生破壞的條件與結(jié)構(gòu)可預(yù)料的最不利的工作條件之比值。 概率方法，這種方法采用極限狀態(tài)。但是，應(yīng)該考慮到進行全概率分析的困難。器例子包括結(jié)構(gòu)失穩(wěn)之前的過大變形和位移；早期開裂或過大的裂縫；較大的振動和腐蝕。），由 430馬力的牽引發(fā)動機驅(qū)動。推土機和正鏟挖土機都能做到這點。因此，當(dāng)試算截面選定 后，每次設(shè)計都是對截面進行復(fù)核。 如果拌制混凝土的各種材料配合比恰當(dāng)，則混凝土制成品的強度較高，經(jīng)久耐用，配置鋼筋后，可以作為任何結(jié)構(gòu)體系的主要構(gòu)件。 (2)Number of human lives which can be threatened by this failure。 struck capacity ( 25 m 179。 failure by fatigue。 關(guān)鍵詞：混凝土，土方工程 ， 結(jié)構(gòu)安全度 素混凝土是由水泥、水、細(xì)骨料、粗骨料（碎石或；卵石）、空氣，通常還有其他外加劑等經(jīng)過凝固硬化而成。F 以上的條件下。一般說來，有關(guān)挖土機、裝載機和運輸機械的唯一可靠而又最新的資料可以從制造廠商處獲得。每種機械設(shè)備應(yīng)該進行最適合它的性能的作業(yè)。必須記住翻斗車與自卸卡車之間的區(qū)別。 把對應(yīng)于不乘以荷載系數(shù)的活載和恒載的工作（使用）條 件的應(yīng)力與規(guī)定值（使用極限狀態(tài)）相比較。這些實際困難可以采用兩種方法來克服。 此外，根據(jù)安全系數(shù)的不同用途，可以把結(jié)構(gòu)的計算方法分為： （ 1）容許應(yīng)力法，在這種方法中，把結(jié)構(gòu)承受最大荷載時計算得到的應(yīng)力與經(jīng)過按規(guī)定的安全系數(shù)進行折減后的材料強度作比較。最小的翻斗車的容量大約為 立方米，而最大的標(biāo)準(zhǔn)型翻斗車的容量大約為 179。拉鏟挖土機的缺點是只能挖比它本身低的土，不能施加壓力挖入壓實的土壤內(nèi)，不能在陡坡上挖土，而且挖。在 1935 年，目前采用的利用輪胎式機械設(shè)備進行土方挖運的方法大多數(shù)還沒有出現(xiàn)。澆筑基礎(chǔ)前，應(yīng)將坑底土夯實并用水浸濕 6英寸，以免土壤從新澆的混凝土中吸收水分。 (2) Amortization funds for the duration of the construction。. Special types include the selfloading dumper of up to 4 m 179。 and the articulated type of about m 179。 (3) Cost of physical and material damage due to the failure of the construction。一般情況下，除使用混凝土泵澆筑外，混凝土都應(yīng)在水平方向分層澆筑，并使用插入式或表 面式高頻電動振搗器搗實。那是大部分土方是采用窄軌鐵路運輸，在這目前來說是很少采用的。卸都不準(zhǔn)確。特殊型式的翻斗車包括容量為 4 m179。 （ 2）極限狀態(tài)法，在這種方法中，結(jié)構(gòu)的工作狀態(tài)是以其最大強度為依據(jù)來衡量的。第一種方法對材料和荷載采用不同的安全系數(shù)，而不需要采用概率準(zhǔn)則；第二種方法是引入一些而簡化假設(shè)的近似概率方法（半概率方法）。計算荷載等于分別乘以荷載系數(shù)的活載與恒載之和。的鉸接式翻斗車。正鏟挖土機能挖取豎直陡峭的工作面，這種方式對推土機司機來說是危險的，而對拉鏟挖土機則是不可能的。因此，一個工程師為了使自己在土方挖運設(shè)備方面的知識跟得上時代的發(fā)展，他應(yīng)當(dāng)花費一些時間去研究現(xiàn)代的機械。 水泥的水化作用發(fā)生在有水分存在，而且氣溫在 50176。 (5) Moral and psychological views. The definition of all these parameters, for a given safety factor, allows construction at the optimum cost. However, the difficulty of carrying out a plete probabilistic analysis has to be taken into account. For such an analysis the laws of the distribution of the live load and its induced stresses, of the scatter of mechanical properties of materials, and of the geometry of the crosssections and 7 the structure have to be known. Furthermore, it is difficult to interpret the interaction between t