Foundations

All structures designed to be supported by the earth, including buildings, bridges, earth fills, and earth, earth and rock, and concrete dams, consist of two parts. These are the superstructure, or upper part, and the substructure element which interfaces the superstructure and supporting ground. In the case of earth fills and dams, there is often not a clear line of demarcation between the superstructure and substructure. The foundation can be defined as the substructure and that adjacent zone of soil and/or rock which will be affected by both the substructure element and its loads.

所有支承在地基上的结构物，包括建筑物、桥梁、土堤以及土坝、土石坝、混凝土坝都是由两部分组成的。它们是上部结构，或者说上面部分，和介于上部结构与支承地基之间的下部结构构件。就土堤和各种坝而言，在上、下部结构之间通常没有一条明显的划分线。“基础”这个名词可以被定义为下部结构及其邻近的土和/或岩石，这些土或岩石既受到下部结构构件的影响，也受到荷载的影响。

The foundation engineer is that person who by reason of experience and training can produce solutions for design problems involving this part of the engineered system. In this context, foundation engineering can be defined as the science of applying the principles of soil and structural mechanics together with engineering judgment to solve the interfacing problem. The foundation engineer is concerned directly with the structural members which affect the transfer of load from the superstructure to the soil such that the resulting soil stability and estimated deformations are tolerable. Since the design geometry and location of the substructure element often have an effect on how the soil responds, the foundation engineer must be reasonably versed in structural design.

基础工程师是能够根据经验和所受的训练对涉及这一部分工程系统的设计问题提出解决方案的人员。由于这个原因，基础工程则可以定义为运用土力学与结构力学原理和工程判断来解决交界面问题的科学。基础工程师所直接关心的是影响上部结构向地基传递荷载的那些结构构件，以使地基稳定性及预估变形量都在容许范围以内。由于下部结构构件的设计几何尺寸及位置常常会对地基有影响，因此基础工程师必须具有足够的结构设计方面的知识。

Foundations for structures such as buildings, from the smallest residential to the tallest high-rise, and bridges are for the purpose of transmitting the superstructure loads. These loads come from column-type members with stress intensities ranging from perhaps 140 MPa for steel to 10 MPa for concrete to the supporting capacity of the soil, which is seldom over 500 kPa but more often on the order of 200 to 250 kPa.

从最小的居住房屋到最高的高层建筑以及桥梁等结构物的基础都是用来传递上部结构荷载的。这种从柱型构件传下的荷载的应力大小，钢柱约在140 MPa 左右，混凝土柱约为 10 MPa左右。而土的承载能力则很少超过 500kPa，比较常见的是在200 到250 kPa 左右。

Almost any reasonable structure can be built and safely supported if there is unlimited financing. Unfortunately, in the real situation this is seldom, if ever, the case, and the foundation engineer has the dilemma of making a decision under much less than the ideal condition. Also, even though the mistake may be buried, the results from the error are not and can show up relatively soon and probably before any statute of limitations expires. There are reported cases where the foundation defects such as cracked walls or broken mechanical fixtures have shown up years later also cases where the defects have shown up either during construction of the superstructure or immediately thereafter.

对于任何合理的结构物只要有足够的经费，总是可以建造得很安全。不巧的是，如果在实际中有这种情况的话，也是非常少见的，基础工程师总需要在比理想情况差很多的窘境下作出决定。此外，即使错误可以被掩埋，但错误造成的后果不会被掩盖，并且能够较快地显示出来—而且可能是在一些法规所规定的期限到期之前出现失效。已经有过这样事例报道，基础的缺陷（例如引起墙体开裂或机械装置损坏）是在几年之后才显示出来的，但是，在有的事例中，基础的缺陷是在上部结构施工中或紧随其后显示出来的。

Since the substructure is buried, or is beneath the superstructure, in such a configuration that access will be difficult should foundation inadequacies develop after the superstructure is in place, it is common practice to be conservative. A one or two percent overdesign in these areas produces a larger potential investment return than in the superstructure.

由于下部结构是埋藏在地下或者是在上部结构的下面，所以在这样的部位，当上部结构就位之后，如果基础上的缺陷扩展，那么检修将很困难，因此通常在设计上都比较保守。在这些部位保守设计1% 或2%则会在投资上取得比在上部结构中更大的潜在收益。

The designer is always faced with the question of what constitutes a safe, economical design while simultaneously contending with the inevitable natural soil heterogeneity at a site. Nowadays that problem may be compounded by land scarcity requiring reclamation of areas which have been used as sanitary landfills, garbage dumps, or even hazardous waste disposal areas. Still another complicating factor is that the act of construction can alter the soil properties considerably from those used in the initial analyses/design of the foundation. These factors result in foundation design becoming difficult to quantify that two design firms might come up with completely different designs that would perform equally satisfactory. Cost would likely be the distinguishing feature for the preferred design. 

设计人员总是面临如何进行既安全又经济的设计，而同时又需要与必然存在的工地的自然土壤的不均匀性作斗争这个问题。现在这个问题又因为土地稀少，而要利用那些曾被用作垃圾填充的，甚至危险废料处理区的土地而复杂化。还有另一个复杂因素是施工作用会改变土性，使其相对它在基础的初步分析/设计时发生显著的变化。这些因素都使基础设计变得难以用数量来表示，以至于两个设计单位会提出完全不同的设计，但其使用效果可能同样令人满意。造价很可能是区分设计方案是否被选的主要因素。

This problem and the widely differing solutions would depend, for example, on the following:

(1) What constitutes satisfactory and tolerable settlement; how much extra could, or should, be spent to reduce estimated settlements from say 30 to 15 mm?

(2) Has the client been willing to authorize an adequate soil exploration program? What kind of soil variability did the soil borings indicate? Would additional borings actually improve the foundation recommendations?

(3) Can the building be supported by the soil using

(a) Spread footings- least cost.

(b) Mats-intermediate in cost.

(c) Piles or caissons-several times the cost of spread footings.

这个问题以及很多不同的解决方案取决于下列各项：

1.满意和容许的沉降量为多少？如果将预估的沉降量从 30 mm 减少到15mm 应该多花费多少钱？

2.业主是否愿意授权进行一项充分的勘察计划？从钻孔情况得到的土层变化程度是怎样的？增加钻孔是否能切实改进基础设计方案？

3.房屋能否用下列基础支撑：

a.扩展基础－造价最低；

b.筏板基础－造价为中等；

c.桩或沉箱－造价为扩展基础的数倍。

(4) What are the consequences of a foundation failure in terms of public safety? What is the likelihood of a lawsuit if the foundation does not perform adequately?

(5) Is sufficient money available for the foundation? It is not unheard of that the foundation alone would cost so much the project is not economically feasible. It may be necessary to abandon the site in favor of one where foundation costs are affordable.

(6) What is the ability of the local construction force? It is hardly sensible to design an elaborate foundation if no one can build it, or if it is so different in design that the contractor includes a large "uncertainty" factor in the bid.

(7) What is the engineering ability of the foundation engineer? While this factor is listed last, this is not of least importance in economical design. 

4.基础事故会在公共安全方面造成什么后果？如果基础达不到要求是否会引起诉讼？

5.是否有足够的经费用于基础？曾经有过这种情况，即由于基础的造价过高而使工程在经济上不可行。因此，需要放弃某一场地而去另选基础造价能为业主所能承受的场地。

6.当地施工单位的能力如何？如果设计一个复杂的基础而没人能够施工，或者因为设计的非常独特，以致承包商在投标中包含了很多的“不确定性”因素，这都是不明智的。

7.基础工程师处理工程问题的能力如何？此项目列于最末，但是在经济设计中并不是一条最不重要的因素。

The foundation engineer must look at the entire system: the building purpose, probable service-life loading, soil profile, construction methods, and construction costs to arrive at a design that is consistent with the client/owner's needs and does not excessively degrade the environment. This must be done with a safety factor which produces a tolerable risk level to both the public and the owner.

基础工程师应着眼于整个系统：建筑物的用途，使用年限内可能承受的荷载，土层剖面，施工方法及造价，以便使设计与业主需要相适应，并且不会对周围环境有过多的影响。这就必须使所选取安全系数产生的风险水平能够被公众和业主所接受。