1. 什么叫水土资源
2 土壤侵蚀、水土流失与水土保持
水土资源是生物赖以生存与繁衍的重要的自然资源，与生物群落有着千丝万缕的联系，要探究水土资源与生物群落的互为促进作用，必须掌握土壤侵蚀 、水土流失、水土保持等一些最基本的概念；熟悉水土流失成因、水土流失特性以及水土流失状况；了解土壤侵蚀、水土流失与水土保持相互间的内在联系。
2.1 术语释义
2.1.1土壤侵蚀 (soil erosion)：在《中国大网络全书·水利卷》（1992.3）中对土壤侵蚀的定义为：土壤及其母质在水力、风力、冻融、重力等外营力作用下，被破坏、剥蚀、搬运和沉积的过程。这一定义与国际上是相近的。土壤流失（Soil loss）与土壤侵蚀基本上是同义语，土壤侵蚀侧重于过程，而土壤流失则重于结果。在国际学术文献中，目前更多地与水连用，称为水土流失。
2.1.2水土流失（water and soil loss）：在《中国水利网络全书·第一卷》（1990.12）中对水土流失的定义为：在水力、重力、风力等外营力作用下，水土资源和土地生产力的破坏和损失，包括土地表层侵蚀及水的损失，亦称水土损失，这是广义的水土流失。从宏观上讲，水土流失包括“土壤侵蚀”一词的含义，且在生产上已习惯称呼水土流失。狭义的水土流失，基于侵蚀主体，特指水力侵蚀；基于受侵主体，特指土壤侵蚀。
2.1.3水土保持(water and soil conservation)：在《中国大网络全书·农业卷》（1990.9）中对水土保持的定义为：防治水土流失，保护、改良与合理利用山丘区和风沙区水土资源，维护和提高土地生产力，以利于充分发挥水土资源的经济效益和社会效益，建立良好生态环境的事业。
2.2 土壤侵蚀与水土流失
2.2.1相关概念
2.2.1.1 土壤侵蚀类型
按外营力种类划分：一种土壤侵蚀类型的发生往往是由一种或两种外营力导致的。依据外营力的种类，将土壤侵蚀划分为水力侵蚀、风力侵蚀、重力侵蚀、冻融侵蚀、混合侵蚀等类型。在各种土壤侵蚀类型中，水力侵蚀和风力侵蚀为面上侵蚀，是主要侵蚀类型；重力侵蚀、冻融侵蚀等为点上侵蚀，是次要侵蚀类型。
按发生时间划分：按人类在地球上出现的时间，将土壤侵蚀划分为古代侵蚀和现代侵蚀。现代侵蚀包括自然因素和人为因素的双重作用。
按侵蚀速度划分：按侵蚀速度比对成土速度（成土速率），将土壤侵蚀划分为正常侵蚀和加速侵蚀。
2.2.1.2 土壤侵蚀量（the amount of soil erosion）：是指土壤在外营力的作用下产生位移的物质量。
2.2.1.3 土壤侵蚀强度 （intensity of soil erosion）：是指各种土壤侵蚀类型在单位时间内单位面积上的土壤侵蚀量或在单位时间内的土壤侵蚀深（厚）度。表示为土壤侵蚀速度（土壤侵蚀模数），单位 (t/km2.a 、t/hm2.a)或（mm/a）。
2.2.1.4 允许土壤侵蚀量（土壤容许流失量）：是指小于或等于成土速度的年土壤侵蚀量。即在长时期内能保持土壤肥力和维持土地生产力基本稳定的最大土壤流失量。由于不同地区的成土速度不同，因此允许土壤侵蚀量也不同。小于允许土壤侵蚀量的侵蚀，属正常侵蚀（微度侵蚀）；大于或等于允许土壤侵蚀量的侵蚀，属加速侵蚀（水土流失），在土壤侵蚀强度上分为轻度侵蚀、中度侵蚀、强度侵蚀、极强度侵蚀、剧烈侵蚀。
确定允许土壤流失量值是一项较为复杂的工作，目前各国确定的指标还有待完善，需要积累成土速度和土壤侵蚀对土壤生产能力影响等方面的资料。在美国规定各类地区的允许土壤流失量值为4～11.2t/hm2.a。中国也在不断积累资料的基础上，确定了不同地区的允许土壤流失量值为2～10t/hm2.a。
2.2.1.5 土壤侵蚀速率：是指有效土层厚度与年度侵蚀深度的比值，单位为年。用以评价一个地区的土壤抗侵蚀能力，反映出土壤侵蚀潜在危险程度。
2.2.1.6 侵蚀土壤程度：是指土壤遭受侵蚀的过程中所达到的不同阶段，并不直接反映现状侵蚀强度的大小。诊断侵蚀土壤程度，是根据土壤剖面中的表土层（A层）、心土层（B层）及母质层（C层）的丧失情况加以判别。侵蚀土壤程度反映土壤肥力和土地生产力现状，为土地利用改良和防治土壤侵蚀提供科学依据。
土壤侵蚀强度反映了土壤流走的状况，而侵蚀土壤程度则反映了侵蚀留下的状况。
2.2.2中国水土流失现状
根据全国第二次水土流失遥感调查，20世纪90年代末全国水土流失总面积356万km2，占国土总面积的37.08%。其中水力侵蚀165万km2；风力侵蚀191万km2，包括水力侵蚀、风力侵蚀交错区水土流失面积26万km2。在水力侵蚀面积中,不同强度等级的面积为：轻度83万km2，中度55万km2，强度18万km2，极强度6万km2，剧烈3万km2；在风力侵蚀面积中，不同强度等级的面积为：轻度79万km2，中度25万km2，强度25万km2，极强度27万km2，剧烈35万km2。
2.2.3水力侵蚀地区的水土流失特性
水力侵蚀是水土流失的一种主要类型。山东全省水土流失面积35987km2，其中水蚀32432 km2，占90.12%；风蚀3555 km2，占9.88%。显然，水土流失以水力侵蚀为主。
2.2.3.1 水力侵蚀特点：水力侵蚀的特点是以水为动力冲走土壤。既有土的流失（即土壤侵蚀），也有水的流失。
2.3.3.2 水力侵蚀形式：按水土流失的发生发展过程，将水力侵蚀划分为面蚀和沟蚀两种形式。
面蚀：是指地表径流冲刷坡面表层土壤的一种侵蚀现象。它是土壤侵蚀中最常见的一种形式。面蚀起源于溅蚀，发生在坡面，呈面状，可分为层状面蚀、鳞片状面蚀、沙粒化面蚀和细沟状面蚀。
沟蚀：是指由片状水流汇集于沟槽，形成切入地表及以下沟壑，冲刷破坏土壤及其母质的土壤侵蚀形式。沟蚀起源于面蚀，发生在沟壑，呈线状。面蚀产生的细沟，以沟头前进、沟底下切和沟岸扩张三种方式，分别向长、宽、深三个方向发展，形成侵蚀沟。根据沟蚀程度及表现形态，自上而下可分为浅沟侵蚀、切沟侵蚀和冲沟侵蚀。
2.2.3.3 水土流失成因
影响水土流失的因素有自然的、也有人为的，有有利的、也有不利的。人类自在地球上出现以来，就不断对自然界施加影响，使自然侵蚀过程受到人为因素的干扰。在水力侵蚀地区，降雨（外营力）、土壤、地形（地形为地面起伏的形状，地貌为地球表面的形态。地理学上二者等同，测绘学上地形是地貌和地物的总称）、植被四项自然因素直接影响水土流失，人为因素则通过改变自然因素影响水土流失。不合理的人类活动是土壤侵蚀加速的主导因素。
自然因素中降雨是侵蚀的动力，动力的大小决定着侵蚀的强弱；土壤既是被侵蚀的对象又是影响径流的因素，腐殖质含量高，胶结物质多，团粒结构稳定的土壤，抗蚀性强；地形中不同的坡度、坡长、坡形及坡面糙率决定着坡面径流的汇集和能量的转化；地表植被能够防止雨滴击溅表土，并以其根系直接固持土体，且枯枝落叶及其形成的物质能够改变地表径流，促进土壤渗蓄。
水力侵蚀地区的水土保持科技工作者应注重对流体动力学的研究，了解地表径流的流速、流量，熟悉其发生、发展和消亡规律，掌握降雨、地形、植被、土壤对地表径流的影响。
2.3 水土流失和水土保持
水土流失（Soil and Water Losses ）和水土保持（Soil and Water Conservation）是两个相对的概念，虽然未在国际经典辞书上找到专门简明释意条目，但根据一些国际学术专著，它们的意义也是比较明确的。
水土流失是指土壤侵蚀（包括水、风等营力）造成水土资源和土地生产力的破坏和损失。水土保持的含义则是为防治水土流失、保护和合理利用水土资源、提高土地生产力而采取的全部措施的总称。
与土壤流失或土壤侵蚀相比，在应用水土流失概念时，水不仅是作为引起土壤侵蚀的营力，同时也是作为农业生产的资源要素。从农业生产角度讲，土壤侵蚀不仅造成土壤及其养分的流失，也造成土壤水分和水资源的流失或损失。水的损失在国外一些国家的水土保持文献中是指植物截留损失、地面及水面蒸发损失、植物蒸腾损失、深层渗漏损失、坡面径流损失。在我国，水的损失主要指坡地径流损失。水的损失在干旱、半干旱地区加重了干旱，加重了干旱对农业、林业、牧业等生产事业的危害。
3 生态系统与水土资源
水是生命之源，土是生存之本。水和土是人类赖以生存和发展的基本条件，是不可替代的基础资源。地球上真正能被人类直接利用的水资源，仅占全球水贮量的0.3%。当今世界水资源短缺，我国人均水资源拥有量仅占世界平均水平的1/4左右,是世界水资源极度缺乏的国家之一。水资源的匮乏已经制约了中国生态环境建设，影响了中国经济和社会的可持续发展；土地资源是人类生产活动最基本的自然资源和劳动对象。人类对土地的利用虽然反映了人类文明的发展，但也造成了对土地资源的直接破坏，主要表现为不合理的人类活动引起的土壤退化。这之中水土流失是祸首，是当今世界面临的严重问题。
3.1 水资源
水土流失减少水资源可利用量。
水土保持是江河治理的根本，是水资源利用和保护的源头和基础，是与水资源管理互为促进、紧密结合的有机整体。水土保持措施一是坡面渗蓄、工程拦蓄天上水，使地表淡水向土体深层转化，并保持在地下，在无雨时节，上游山丘区的地下水因靠高差形成的势能，能够转换为下游平原区的地表水。二是减少水库、江河淤积，使水利工程延长寿命，增加效益，减轻防洪负担。三是避免点源和非点源（面源）污染通过径流汇入受纳水体，减轻水体富营养化及其它形式的污染。这一切都有利于水资源的开发利用和水环境的保护，都是建设景观水利、营造亲水空间的基础。
3.2 土地资源
水土流失对土地资源的破坏表现在外营力对土壤及其母质的分散、剥离以及搬运和沉积上。由于雨滴击溅、雨水冲刷土壤，把坡面切割得支离破碎，沟壑纵横。上游土壤经分散、剥离，砂砾颗粒残积在地表细，小颗粒不断被水冲走，沿途沉积，下游遭受水冲砂压。如此反复，细土变少，砂砾变多，土壤沙化，肥力降低，质地变粗，土层变薄，土壤面积减少，裸岩面积增加，最终导致弃耕，成为“荒山荒坡”。
我国人口众多，可开发利用的土地资源十分有限，能够耕种的土地则尤为珍贵，而每年却因土壤退化损失耕地46.6～53.3万hm2，因自然灾害丧失耕地约10万hm2，成为世界上水土流失最为严重的国家之一。耕地面积在逐年减少，人口却每年增加1400万，这两个逆向增长如继续下去，人地矛盾将更加突出。由于水土流失与土壤退化日趋严重，生物的生存空间日益缩小，已经带给我们极大的危害，影响了经济社会的可持续发展。为了民族的生存、人民的幸福和国家的繁荣昌盛，全社会每个成员都应当高度重视水土流失这个头号环境问题，珍惜、保护和合理利用好水土资源，防止人为活动造成新的水土流失。
水土保持是国土整治的根本。保护珍贵的土地资源免受外力侵蚀，既是水土保持的基本内涵，也是土地资源利用和保护的主要内容。从保护土地资源、减轻土壤退化的角度上讲，水土保持对土地资源的利用和保护有着积极的促进作用，是土地资源利用和保护的基础。
古今中外大量事实表明，人类不合理的开发建设活动必然导致严重的水土流失，导致生态环境恶化，最终引发人类生存与发展危机。随着经济社会的发展和人类开发建设活动规模的不断扩大，人为破坏生态所造成的水土流失问题越来越严重，对生态环境的影响也越来越大。因此，必须坚持“预防为主”的方针，始终把预防监督放在水土保持工作的首位；在此基础上，综合治理自然水土流失，不断改善生产条件和生态环境。只有这样，才能从源头上控制住人为水土流失，才能抓住水土保持的根本，才能使水土保持生态环境建设既经济、又有效，达到了事半功倍的效果。
3.3 生态系统与水土资源
生态系统的平衡往往是大自然经过了很长时间才建立起来的动态平衡。一旦受到破坏，有些平衡就无法重建了，带来的恶果可能是人的努力无法弥补的。因此人类要尊重生态平衡，维护生态平衡，而绝不可轻易地去破坏它。
水和土地都是不可替代的珍贵的地质资源。水土流失对水土资源的破坏，使生物生存的环境恶化，物种减少。水土流失威胁城镇，破坏交通，危及工矿设施和下游地区生产建设和人民生命财产的安全， 1998年长江、嫩江、松花江流域暴发特大洪水灾害,使1.8亿人受灾，因水死亡4150人，直接经济损失2550.9亿元；近年来北方地区连续遭受沙尘暴袭击以及发生在首都北京（2004年7月10日）和济南等地区的城市积水，追根溯源，都与水土流失相关，都是水土流失的恶果。
水土流失流走的是沃土，流下的是贫瘠。在水土流失严重地区，地力衰退，产量下降，形成“越穷越垦、越垦越穷”的恶性循环。目前全国农村贫困人口90%以上都生活在生态环境比较恶劣的水土流失地区。
水土流失是我国面临的头号环境问题，是我国生态环境恶化的主要特征，是贫困的根源。要解决这一问题，争取继续生存、继续发展的权利，必须调整好人类、环境与发展三者之间的关系，特别是要调整好经济发展的模式。保持水土，根除灾害，时不我待，刻不容缓，应该呼吁全社会都来关心。
水土保持既是生态环境建设的主体，也是生态环境建设的基础，处在生态环境建设的前沿。生态系统的稳定性在很大程度上取决于自然界中的水土资源条件；经济社会发展引起生态环境的变化，主要取决于对水土资源的利用。正基于此，水土流失才成为我国的头号环境问题，水土保持才被作为我国必须长期坚持的一项基本国策。
2. soilworks直径60贯穿怎么标注
画好对称轴的情况下，智能尺寸——点击第一个点到对称线的距离（不直接点直线的长度）,鼠标移动到对称轴的另一侧就会显示“对称情况下的乱猛总长”，然后点击一下鼠标左键，即可形成尺寸。在尺寸前放一个直径符号就行。
1、第一步：打开一个2D草图。
2、第二步：点击菜单栏中的“草图”，找到“智能尺寸”。
3、第三步：点击“智能尺寸”，选择一条需要标注尺寸的边。
4、第四步：标注完成，点击左上角的“√”。
5、第五步：修改标注尺寸，左键双击标注中的数字。
6、第六步：知陪局修改搭让左边窗口的“标注尺寸文字”，输入需要修改的数字。这样尺寸就修改完成了。
3. FastDNA03 SPIN kit for Soil 实验操作步骤说明 怎样去除腐植酸
试剂准备：
1. 使用前先在SEWS-M Wash Solution中加入100 ml 100%的乙醇，混匀。在瓶子上做好标记，密闭储存于室温条件。
提取步骤：
1. 在样品处理管E中加入至多500 mg的土壤样品
2. 将978 μl的Sodium Phosphate Buffer加入到样品处理管E中
3. 再加入122 μl的 MT Buffer
（为了得到良好的样品处理效果，请在加入土壤样品及两个缓冲液后，在样品处理管中仍能保留有250 – 500μl 空间）
4. 将样品置于FastPrep® 仪器上，样品处理条件一般为，时间：40秒，速度：6.0
（如果样品需要额外的处理时间，请在间隔期将样品处理管在冰上孵育至少2分钟，以免样品过热）
5. 14,000 x g离心5~10分钟
（如果把离心时间延长到15分钟，可以更好地使样品量较大的；或者细胞壁结构较复杂的细胞的碎片沉降到管底）
6. 将上清转移到一个干净的2.0 ml离心管中。加入250μL的PPS溶液（蛋白质沉淀溶液），用手摇晃10次，使之充分的混合。
7. 14,000 x g离心5分钟，将上清转移到一个干净的15ml管中
(此处也可使用2Ml管，但使用大管子能获得更好的混合和DNA绑定效果)
8. 重悬硅珠（Binding Matrix）溶液，将1.0 ml重悬液加入该15ml管中。
9. 使用振荡器或者手动震荡2分钟，将DNA绑定在硅珠上。将管子置于管架上，静置3分钟，使硅珠沉淀下来。
10. 小心地移除500μl的上清液，避免吸取到沉淀下来的硅珠。
11. 将硅珠在剩余的上清液中重悬。转移约600μl的重悬液至SPIN™ Filter中，14,000 x g离心1分钟。弃去接液管中的废液，将15ml管中剩余的重悬液转移到SPIN™ Filter再次离心弃去废液。
12. 加入500 μl事先准备好的SEWS-M溶液，用枪头轻轻吹打，小心地重悬沉淀。
13. 14,000 x g离心1分钟，弃去废液。
14. 不加其他溶液，将SPIN™ Filter 14,000 x g离心2分钟，除去残留的SEWS-M溶液。弃去接液管，更换一个新的、干净的离心管。
15. 将SPIN™ Filter置于室温下晾干5分钟
16.轻轻地用50-100 μl 的DES溶液（或者无菌/无DNA酶的水）重悬SPIN filter上的硅珠
（为了避免过度稀释纯化出的DNA，请尽量减少DES溶液的量，55˚C孵育5分钟能帮助提高纯化产物的得率）
17. 14,000 x g离心1分钟使溶解的DNA转移到接液管中。弃去SPIN™ Filter
（得到的纯化产物可直接用于PCR等其他下游的操作，4°C使用前保存或者-20°C长期保存。）
技术优势
1. 能有效的处理土壤样品中一些很难处理的组分如： 真细菌孢子（eubacterial spores）、内芽孢（endospores）、格兰仕阳性菌（gram positive bacteria）、酵母（yeast）、线虫（nematodes）、海藻（algea）、真菌（fungi）等。
2. 样品处理过程中使用的 MT Buffer和Sodium Phosphate Buffer可在整个提取过程中有效的保护核酸，并最大限度的降低RNA污染。
3. 基于硅珠的纯化方法，可有效地去除腐植酸、多元酚等PCR抑制物
4. 纯化所得的DNA可直接用于PCR、酶切都后续实验之中。
5. 对腐植酸含量特别高的样品，附加额外的处理方法。
注：对于去除腐植酸的方法
在使用以下任何一种方法之前，请预先准备5.5M的异硫氰酸胍（Guanidine Thiocyanate）溶液
方法A：
1.当操作到土壤DNA提取试剂盒的第九步时，使用14,000 x g (~约5秒)的短时离心替代硅珠的自然沉降，移除上清。
2.用1ml事先准备好的异硫氰酸胍溶液洗涤、重悬硅珠。
3.14,000 x g (~约5秒)短时离心该离心管，除去上清。
4.重复上述的洗涤步骤，直到硅珠恢复到原先的颜色。
5.最后一次洗涤之后，用1ml的异硫氰酸胍溶液重悬硅珠，将600µl重悬液转移到SPIN filter里，14,000 x g离心1分钟。
6.移除接液管中的废液，将剩余的重悬液转移至SPIN filter里，14,000 x g离心1分钟，弃去废液。
7.从提取试剂盒操作说明的第十二步开始继续操作。
方法B：
1.将下列成分混合于1.5ml的离心管中，组成腐植酸洗涤液：
978 μl Sodium Phosphate Buffer
122 μl MT Buffer
250 μl PPS
2.充分混匀后，全速离心1分钟，将上清转移到一个新的离心管中（容量大于或等于2ml）
3.加入等体积的5.5M的异硫氰酸胍溶液、混匀。
4.完成了土壤试剂盒操作说明中的第九步后，将500μl的腐植酸洗涤液加入SPIN filter
5.14,000 x g离心1分钟，弃去废液。
6.重复上述的洗涤步骤，直到硅珠恢复到原先的颜色。
7.从提取试剂盒操作说明的第十二步开始继续操作
4. soil mite 是什么动物或微生物啊
土壤螨
来自动物学词典（Zoology Dictionary）
5. 英语 真土 怎么说
真土的英文：Genuine soil
soil读法 英[sɔɪl]美[sɔɪl]
n.土答态地；土壤；污物，粪便
v.弄污
例句
1、This soil is good for growing things.
这种土壤适宜种植庄稼。
2、She makes her living from the soil.
她依靠土地谋生。
短语
1、heavy soil 难耕地
2、hungry soil 瘠土
3、light-coloured soil 浅色土壤
4、packed soil 压得坚实的土壤
5、poor soil 贫瘠的土地
(5)神马电影soil6扩展阅读
词语用法
1、soil的意思是“泥土,土壤,土地”,本意指可生长植物的“土壤”“土地”,属地球表面的一部分,也可作“领土”“故土”解,还可引申为“滋生地”“脏东西”,是不可数名词。
2、soil作“某种土壤”解时是可数名词。
3、soil主要用作及物动词,作“(使)…弄脏”解,接名词、代词作宾语。偶尔可毁档用作不及物动词,这时主动形式含有被动意清余源义。
4、soil的过去分词soiled常用作形容词作定语。
词汇搭配
1、proctive soil 肥沃的土壤
2、rich soil 沃土
3、sandy soil 沙土
4、soft soil 软土
5、workable soil 可耕作的土地
6、foreign soil 异国他乡
6. I had set foot on African soil为什么不直接I set foot on African soil
这是时态的问题，
用had set 是辩则过去完成时。had +过去分词 是过去完成时，具体用法如下：
用set是一般现在时或过去时 set- set-set set的过去式和过去分词都与原形一样
have、has+过去分词 是现在完成时，具体用法如下
现在完成时：携告棚1.表示从过去某一事件发生到现在或将继续持续下去2.过去发生的事对现在造成的影响3.表示现在已经完成的动作4.构成 主语+have/has +动词友升的过去分词.过去完成时用法讲解
1、概述
过去完成时表示过去某一时间或动作以前已经发生或完成了的动作。它表示动作发生的时间是“过去的过去”。表示过去某一时间可用by, before等构成的短语，也可用when, before等引导的从句或通过上下代表示。
His eyes shone brightly when he finally received the magazine he had long expected. 当她终于收到她盼望已久的杂志时，她兴奋得两眼闪光。
By the time he was twelve, Edison had begun to make a living by himself.12岁时，爱迪生就开始自己谋生。
2、构成
过去完成时由“助动词had+过去分词”构成。其否定式、肯定式、疑问式如下表：
肯定式 否定式 疑问式
I(we) I(We) you
You had read it. had not read it Had they read it?
He(She, They) He(She ,They) he
注意：had not 常简略为hadn't。
They asked me to have a drink with them and said it was at least ten years since I had enjoyed a good drink. 他们请我和他们一起喝酒，并说我自上次喝酒到现在至少十年了。
We had learnt 30 lessons by the end of last month.到上个月末为止，我们已经学了30课。
He said we hadn’t seen each other since I left Beijing.自从我离开北京，我们还没见过面。
3、过去完成时的用法
过去完成时的主要用法和现在完成时一样。不同的是，过去完成时把时间推移到了过去某一时间之前，与现在无关。
（1）过去完成时表示在过去某一时间或动作以前已经完成了的动作。这个过去的时间状语有by, before等介词短语或when, before等引导的从句。
Helen had left her keys in the office so she had to wait until her husband came home. 海伦把钥匙忘到办公室里了，因此她不得不等她丈夫回来。
When we got to the cinema, the film had already begun.当我们到达电影院时，电影已经开始了。
He told me that he had visited the Great Wall before.他告诉我他以前参观过长城。
By the end of the match, they had kicked 2 goals, and we had kicked 4.比赛结束时，他们踢进了2个球而我们踢进了4个球。
When Jack arrived he learned Mary had been away for almost an hour.杰克到达后得知玛丽走了近一个小时了。
（2）表示动作在过去某一时间之前开始，一直延续到过去的这一时间，而且还可能继续下去的动作，常和for, since构成的短语或引导的从句连用。
The news came as no surprise to me. I had known for some time that the factory was going to shut down. 听到这个消息我并不感到吃惊。工厂要倒闭这件事我早就知道了。
By the time I left the school, he had taught the class for 3 years.到我毕业时，他已经教那个班三年了。
He said he had made great progress since he came here.他说自从他来这里他已经取得了很大进步。
（3）用于表示与过去事实相反的虚拟条件从句或as if从句中表示与过去事实相反
If he had seen you yesterday, he would have asked you about it.假如他昨天看到你，他就会问你这件事了。
I should have called you if I had known your telephone number.假如我过去知道你的电话号码，我就给你打电话了。
He described the scene as if he had been there.他描绘的景色如同他去过那里一样。
Had I known that you wanted the book, I would have sent it.如果我知道你要这本书，我会送来的。
（4）表示假设的宾语从句
放在像said，told，asked，thought，wondered等过去时动词的后面，表示在这些动作发生之前已经发生了的事情。
My friend told me that he had passed the exam.我的朋友告诉我，他已通过了考试。
He asked me whether I had seen the film the night before.他问我头一天晚上是否看过那部电影。
She wondered who had left the door open.她想知道谁敞着门的。
（5）用在 "It was the first/second/third…time that…”句型中
在此句型中，主句用了一般过去时，that引导的定语从句要用过去完成时。
This was the first time they had met in thirty-nine years. 这是39年里他们第一次见面。
It was the first time we had spoken together. 这是我们第一次在一起说话。
（6）intend, mean, hope, want, plan, suppose, expect, think等动词的过去完成时可以表示一个本来打算做而没有做的事
这种结构也可以表示过去未曾实现的设想、意图或希望等，含有某种惋惜。
I had intended to call on you yesterday, but I had an unexpected visitor.我本来昨天打算要去看你，但我来了个不速之客。
We had meant to tell her the news but found that she wasn’t in.我们本想把这个消息告诉她的，但发现她不在家。
（7）过去完成时常用结构有“hardly, scarcely, barely … when, no sooner… than等副词的句子里。
She hardly had gone to bed when the bell rang.他刚睡下铃就响了。
No sooner had they left the building than a bomb exploded.他们刚刚离开大楼，一颗炸弹就爆炸了。
（8）当before , after, as soon as 等引导的从句里的动作与主句的动作紧接时，由于这些连词本身已经说明了两个动作发生的先后关系，因此两个动作均可用一般过去时表示。
We had breakfast after we did morning exercises.做完早操之后，我们吃早饭。
The train started to move just before we reached the station.我们到车站时火车刚开动。
As soon as they got there, they started to study.他们一到那里就开始学习了。
7. If there had not been a hard layer of rock beneath the soil 这句话为什么要用过去完成时呢
这是表示与过去事实相反虚拟绝扒语气在条件状语从句中的动词形式【had+过去分词】， 不是过去完成时， 尽管形式一样
不信你接着看后面的主悄握句，里面的动启宏庆词形式就是【would + have + 过去分词】
【希望帮助到你，若有疑问，可以追问~~~
祝你学习进步，更上一层楼！(*^__^*)】
8. Soil Nailing
Introction. Soil nailing consists of reinforcing the soil mass by the introction of a series of thin elements called nails to resist tension，bending and shear forces. The reinforcing elements are made of steel round cross-section bars. Nails are installed sub-horizontally into the soil mass in a pre-bored hole，which is grouted. Figure 13. 1 shows typical applications in slopes and excavations.
Figure 13. 1 Typical applications for an existing slope or an excavation
Origin. Soil nailing is a shotcrete support tunnelling method developed in the late 1960s( Figure 13. 2) ，which consisting of the use of a flexible lining that enables soil deformation around the excavation which has been reinforced by means of bolting or nailing. An active zone is formed around the excavation and the lining is consequently subjected to reced loading. This technique contrasts with the traditional tunnelling technique where a rigid lining was employed to prevent soil deformation and was subjected to full loading from ground pressures.
Figure 13. 2 Conceptual differences between rigid and flexible tunnel lining
Experience in resials and saprolitic soils. The soil nailing construction sequence is similar to the Brazilian practice with tieback walls. They are constructed from the top with excavation stages ranging from 1 to 2 m. Thousands of such structures have been constructed throughout Brazil to stabilize slopes in resial soils，as reported by Ortigao et al.
The Geotechnical Engineering Office ( GEO) of Hong Kong extensively uses soil nailing to stabilize man made slopes in resial and saprolitic soils. The only types of soils that soil nailing cannot be applied are very loose sands and very soft clays.
Construction method and soil nailing application. Soil nailing walls have been employed to stabilize natural slopes or excavations. In this case，the reinforcement is installed in stages as the excavation progresses， typically in 1 to 2 m deep excavation stages. The maximum excavation depth in each stage depends on the soil type and the inclination of the slope，which must be kept stable ring the stage of excavation，until the reinforcement is in place and starts to mobilise its effects.
Installation of nails. Nails should be installed soon after excavation by driving or drilling. Nail driving has been in use for years for stabilizing the faces of tunnels in soils. Short nails， usually up to 3 m in length，are driven by percussion employing hand operated pneumatic hammers. This technique has been applied in temporary walls but should not be applicable to permanent structures e to lack of corrosion protection.
Nail driving is inadequate in soils containing boulders，in most hard resial soils and in all permanent structures， because the steel bar is unprotected against corrosion. Another disadvantage is the resulting lowsoil-nail friction，which ranges from 30 to 40 kPa in sands and with even lower values in clays.
The most common technique is similar to the installation of soil anchors，i. e. ，by drilling a 50 to 100 mm diameter hole，introcing a 20 to 32 mm diameter steel bar，followed by lowpressure grouting. This process leads to reasonably high unit soil-nail friction in which values greater than 100 kPa can easily be obtained in most soils.
Nail head details. Figure 13. 3 presents details of the nail heads for vertical or near vertical walls. In this case，the torque applied to the bolt and nut system applies a small loading of the order of 5 kN to each nail in order to maintain contact of the facing against the soil.
Figure 13. 3 Nail heads details for vertical or near vertical walls
In the stabilization of inclined slopes in which small diameter nails ( less than 20 mm in diameter) are used，a second type shown in Figure 13. 4a is frequently preferred. The steel bar is laterally bent at right angles to anchor the mesh and shotcrete.
Figure 13. 4b shows details of the nail head extensively used in Hong Kong for inclined slopes. The nail head is embedded in a cast-in-place concrete plate excavated in niche behind the slope face.
Figure 13. 4 Nail head details for inclined slopes
The slope facing. Shotcrete is the standard type of facing in soil-nailed structures，contrary to most tieback walls where standard concrete is utilized. Shotcrete can be applied through dry or wet mix. For small jobs，such as soil nailed walls，the dry mix is preferred.
The thickness of the facing varies between 50 to 150 mm with one or two steel meshes embedded in the shotcrete. Thinner facings are generally used on inclined slopes; thicker，for vertical permanent excavations.
In the last years there has been a considerable progress in the use of steel fibre reinforced shotcrete ( SFRS) ，which presents advantages in relation to the use of mesh reinforcement.
Fibres are high tensile strength steel elements having 30 － 50 mm in length and 0. 5 mm in diameter with hooked ends that are mixed in the concrete as an aggregate with a dosage in the range of 35 to 60 kg / m3. It can be used in either dry or wet sprayed concrete mix. Fibres have no effect in the compressive strength of the concrete，but increase ctility，enabling to take into account flexural tensile strength. The final SFRS proct is a homogeneous material with increased crack and corrosion resistance. SFRS saves labour for mesh placement and saves total concrete volume in relation to mesh-reinforced shotcrete. SFRS complies with soil or rock surface irregularities，saving total concrete volume，as compared to the use of a steel mesh. It is expected that SFRS will replace most steel meshes today employed for slope stabilization and soil nailing.
Comparison with tieback walls. Although there are some similarities in the construction technique between a soil nailed and a tieback wall，significant conceptual differences exist，as shown in Figure 13. 5. Anchors are pre-stressed with high loads that may vary between 150 to 400 kN，while on nails only a very small pre-tension of the order of 5 to 10 kN is applied to ensure contact of the facing against the soil behind.
Anchors have a free length，in contrast to nails which transfer load by friction against the soil along their entire length.
Figure 13. 5 Comparison between tieback and soil nailed wall Tmax—Maximum tension force
The concrete facing of a tieback wall is in general 200 to 300 mm thick，being designed to support high anchor loads. On the other hand，loads on the facing applied by nails are much smaller leading to thinner facings.
Most tieback walls in Brazil are designed with a vertical facing to avoid problems that may occur when pouring concrete in inclined formwork. Shotcreting，on the other hand，can be accomplished in any direction. It is，therefore，possible to take advantage of the existing slope and to design inclined soil nailed wall. This may rece excavations.
The length of nails is 60% to 120% of the depth of a vertical excavation. Soil anchors tend to be longer.
Most failures in resial soils take place in shallowdepths，and soil nailing together with deep and surface drainage can be a very economical solution. However，there are a fewcases in which the failure surface is so deep that it may be more appropriate to employ long soil anchors.
Comparison with reinforced walls. Soil nailing is conceptually very similar to geosynthetic reinforced walls or the reinforced earth technique. The main difference is in the construction process. Soil nailed walls are constructed from the top down， whereas geosynthetic or reinforced earth walls are constructed upwards. This leads to a different pattern of soil displacements，as shown in Figure 13. 6.
Figure 13. 6 Comparison between soil nailing and reinforced earth
Advantages of soil nailing. Soil nailing presents the following advantages that has contributed to the widespread of this technique in several countries:
·Economy: economical evaluation of a fewprojects has led to the conclusion that soil nailing is definitely a cost-effective technique as compared with a tieback wall. Cost of soil nailing may be 50% of a tieback wall.
·Rate of construction: fast rates of construction can be achieved if adequate drilling equipment is employed. Shotcrete is also a rapid technique for placement of the facing.
·Facing inclination: as mentioned before，the use of shotcrete easily accommodates an inclined facing，with benefits to overall stability. Backwards inclination of the facing also reces shotcrete losses e to rebound.
·Deformation behaviour: observation of actual nailed structures demonstrated that horizontal deformation at the top of the wall ranges from 0. 1% to 0. 3% of the wall height for well designed walls.
·Design flexibility: a flexible soil nailed wall can be incorporated with soil anchors in order to limit deformation in the vicinity of existing structures or foundations.
·Design reliability in saprolitic soils: saprolitic soils frequently present relict weak surfaces which can be undetected ring site investigation. Soil nailing across these surfaces may lead to an increased factor of safety and increased reliability，as compared with other stabilization solutions.
Limitations of soil nailing. Soil nailing technique mobilizes soil strength and the soil mass deforms，leading to displacements in the surroundings of the wall. This can bring unacceptable deformation to a sensitive structure in the vicinity of the wall. Placement of the shotcrete requires that the excavated face be free-standing for a period of time. Corrosion protection requires careful attention in aggressive environments.
Examples of soil nailing.
In 1984，at Icaraf Beach，a 35 m high vertical cut in gneiss saprolites was constructed for the construction of a high apartment building. A tieback wall with soil anchors supported the lower 18 m of the cut. The upper wall consisted of a soil-nailed structure inclined 75° backwards with 6 to 9 m long，25 mm diameter，steel bar nails in 90 mm diameter boreholes. The spacing was 1. 5 m in both vertical and horizontal directions. The shotcrete facing was 150 mm thick，reinforced with two steel meshes.
At the end of the construction a fewcracks were observed at the crest of the slope. They were filled with cement grout and no additional signs of deformation were observed.
Slope stabilization in phyllite at the abutment of a railway bridge. Figure 13. 7 shows a 26 m high railway bridge abutment that was stabilized by nailing. Local soils consisted of severely structured phyllites with bedding planes dipping in the direction of the slope. Soil wedge failures occurred and led to the decision to stabilize it by 25 mm diameter steel bar nails in 75 mm diameter boreholes. Vertical spacing was 2 m and horizontal spacing was 2. 5 m. Nail length varied from 10 to 25 m. The shotcrete facing was inclined backwards at an angle of 75° and its thickness was 50 mm.
Figure 13. 7 Slope stabilization by nailing at a railway abutment in phyllites，Sao Paulo，Brazil