问题 问答题 简答题

试分析影响土的击实试验结果准确性的因素。

答案

参考答案:

(1)现场取样时,土样的代表性不够(尤其是含粗粒土的);或室内未坚持四分法分取土样;

(2)击实时,击锤以一定的初速度下落或未至要求高度便下落,以及最后一层土层的量过多或过少,这些都使得土体获得的击实功与标准不符;

(3)配置的土样含水量不合理,因而导致不能正确绘制击实曲线;

(4)击实点数过少(小于5个点);不绘击实曲线及错绘曲线等错误做法等。

单项选择题 共用题干题
阅读理解

阅读理解。

     The doctor pointed to some bones on his desk. "They are a man's foot bones," he said. "They

were found inside the cave, and I have been examining them. The C14 test shows that they are

about 12,000 years old."

     "What is the C14 test?" I asked. "It's a way of finding the age of some things that had been

done long ago. The 'C' means carbon and carbon is found in all living things. It is also found in

the remains of things that lived and died thousands or millions of years ago. Plants and animals

take carbon into their bodies from the air. It stays in their remains."

     "Well, there are two kinds of carbon, called carbon 12(C12) and carbon 14 (C14). Both are

taken in together, but in living things C12 is one trillion (1012) times more plentiful (大量的) than

C14. The two kinds are different in one important aspect."

     "C14 is radioactive:it gives out rays of energy at a fixed frequency (频率). As it does so, it

changes to C12  in 5,600 years. Then in the next 5,600 years, half of the remaining C14 becomes

C12 and so on. We say that C14 has a half-life (半衰期) of 5,600 years."

     "You must have found some C14 in these bones, then," I said.

     "Yes, I did. But the C12 is now four million times more plentiful. About a quarter of the C14 

 is left. That means nearly enough, that two half-lives have passed." The doctor picked up one of the

brown toe bones. "It's 12,000 years since this toe was broken. Perhaps the man was playing football

outside-with no boots on."

1. The word "remains" in paragraph two means ______.

A. things left by ancient people

B. dead bodies

C. newly-found ancient places

D. caves where ancient people lived

2. Carbon 14 is a natural element (元素) ______.

A. but it kills quickly          

B. and we all have some in us

C. found only in bones          

D. but it disappears after 5,600 years

3. It is true that only ______.

A. C14 has a half-life                    

B. old bones have a half-life

C. radioactive materials have a half-life    

D. a living thing has a half-life