问题 问答题 案例分析题

某大桥建设项目位于市区西部,大桥全长1332m,其中主桥长790m,单孔最大跨径110m,一般跨径40~60m,为特大型桥梁,桥梁设计标准为城市Ⅰ级主干道。基础采用钻孔灌注桩,设计最大单桩承载力18000kN。市政工程勘察复杂程度为Ⅱ类。大桥属地震烈度为7度区的特大型桥梁,桥址附近存在棋盘式断裂构造,但全新世以来,未见活动迹象,桥址处未有断裂构造带通过,区域构造对建桥无不利影响。大桥桥位处地势平坦、开阔,不存在边坡效应条件。该处河床总宽735m,在距北岸(港)160m处有一小河洲,河床呈不对称心形复式断面,主河汊为南汊,宽约510m。

简述生态环境影响预测与评价主要包含的内容。

答案

参考答案:

(1)土地利用影响评价土地利用影响评价主要考虑大桥占用土地的基本情况,包括耕地和一些原有的道路,在设计方案时应尽可能利用荒地、滩地,尽量不占用耕地,以减少对农业生产带来的损失,同时,在施工过程中,取土将造成少量土地表层及其植被破坏,表层耕作层被污染或丧失,性质变化,保水保肥性能下降等,因此应当进行合理评价。

(2)植被影响分析工程周围植被最大变化发生在施工过程中,首先是征用土地,破坏绿色植被。其次在施工过程中,工程两侧的植被将遭受施工人员和施工机械的破坏。由于桥梁、路基及防洪堤等施工方式不同,对植被的破坏程度也有所区别。工程建设所有土料主要由当地料场供应。植被破坏主要是取土、施工机械、运输车辆的碾压和施工人员活动的破坏,一般来说,这种破坏是毁灭性的,取土场应根据取土后土地的利用规划,进行植被补偿及恢复;施工区域的植被当外界破坏因素完全停止后将向着受破坏之前的类型恢复,恢复的速度决定于外界因素作用的程度和持续时间长短,一般是工程竣工后二三年植被可基本恢复。

(3)水生生物影响分析工程实施后,可能影响鱼类往返迁移,对水生鱼类的栖息、繁殖的环境产生一定的影响。

问答题
单项选择题

Until recently, mobile radio was to wireless communications what the Yugo was to transportation. With a mixed clientele ranging from truckers using CBs to police armed with walkie-talkies to taxi drivers dispatched by radio, it was viewed as an unglamorous business and a technological backwater.

But specialized mobile radio, as it is known, has been rediscovered. It is now considered one of the biggest prizes in the all-out war for the public airwaves. The reason: high-tech companies have figured out how to profitably rebuild the antiquated dispatching system into an advanced cellular-telephone network that can take on the likes of AT & T and the giant Baby Bells. Upstart Nextel Communications sent shock waves through the industry last week when it agreed to buy Motorola’s SMR frequencies for $1.8 billion.

That could pose a serious threat to cellular hegemony. Although both systems are based on the same basic technology, SMR systems are digital and cover almost 25 times as much area as the average cellular network. SMR handsets won’t work on cellular systems and tend to be bulkier than cellular phones, though they provide more features, like a digital pager service. And while cellular growth has tripled to some 13 million subscribers since 2000, the technology has been losing ground. It is running out of channel capacity so fast, in fact, that 40% of cellular calls in high-density areas like Manhattan and Los Angeles fail to be completed. SMRs have capacity to spare, and service could eventually be priced 10% to 15% less than cellular. Dispatchers predict they will have at least 10 million subscribers by the end of the decade. There are now about 1.5 million users of SMRs.

The addition of another contender to an already crowded field of telephone systems will surely multiply the confusion. By the year 2010, consumers will be able to choose from at least half a dozen vendors of a dizzying array of wireless-communications services, including pagers, voice mail answering machines and cellular phones. Phone and cable television operators, such as Bell South, MCI and Cox Enterprises, are developing so-called personal communications networks, or PCNs, a highly advanced portable-phone system that is expected to cover a wider area, connect to a greater variety of services and be cheaper to operate than conventional cellular.

And many companies that have gambled on the wrong technological standards, and invested billions trying to develop the same markets, will undoubtedly lose a great deal of money before the shakeout is over. "The winners," says Nextel chairman Morgan O’Brien, "will be those who can make the choice for consumers easy." With all the anticipated confusion--mindful of the early years of personal computers--it is likely to be years before anyone calls the purchase of wireless products an "easy" choice.

How did mobile radio systems find its business competitiveness()

A. Its technological features have radically changed

B. It has been rebuilt to cater to various subscribers

C. Its dimensions have been reduced by wide margins

D. It was connected to a greater variety of services