A Closer Look at Prevailing Civil Engineering Practice - European ...
A Closer Look at Prevailing Civil Engineering Practice - European ...
A Closer Look at Prevailing Civil Engineering Practice - European ...
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A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Prevailing</strong> <strong>Civil</strong> <strong>Engineering</strong> <strong>Practice</strong>, Wh<strong>at</strong>, Why and How<br />
Vincent T. H. CHU<br />
so th<strong>at</strong> w<strong>at</strong>er could not enter the excav<strong>at</strong>ion zone.<br />
10. Does microtunneling refer to tunnel size less than 1,000mm<br />
The intern<strong>at</strong>ional definition of microtunneling includes pipe with diameter<br />
up to 1,000mm only. However, in the United St<strong>at</strong>es, it allows for larger pipe<br />
size when defining microtunneling in which pipe with diameters up to 144<br />
inches are also counted within the ambit of microtunneling.<br />
The basic concept of microtunneling has changed gradually owing to<br />
recent technological developments and past experience. For instance, the<br />
use of alignment control system with advanced surveying techniques<br />
allows for longer drives with good control and curved microtunneling. The<br />
use of autom<strong>at</strong>ic lubric<strong>at</strong>ion system enhances lower jacking forces. The<br />
employment of gripper in microtunneling machines helps develop<br />
adequ<strong>at</strong>e loads on cutter discs for cutting rock.<br />
11. Wh<strong>at</strong> are the situ<strong>at</strong>ions which warrant the use of microtunneling<br />
instead of other trenchless methods<br />
There are two main advantages of microtunneling:<br />
(i) Difficult ground conditions<br />
Microtunnels could oper<strong>at</strong>e under a w<strong>at</strong>er head of 30m or more. It is<br />
capable of handling a wide range of soils such as cobble, boulders<br />
and rock without the need of dew<strong>at</strong>ering.<br />
(ii) Surface settlement<br />
Surface settlement could be minimized by using microtunneling. For<br />
example, the use of earth pressure balance method in microtunneling<br />
helps balance the external soil loads and groundw<strong>at</strong>er. Moreover, the<br />
r<strong>at</strong>e of advancement of machine and the r<strong>at</strong>e of excav<strong>at</strong>ion of tunnel<br />
face can be readily controlled so th<strong>at</strong> it reduces the occurrence of<br />
over-excav<strong>at</strong>ion <strong>at</strong> tunnel face and hence the ground settlement.<br />
12. Wh<strong>at</strong> is the difference between single shield and double shield<br />
tunnel boring machine (TBM)<br />
In single shield TBM, it extends and moves forward by thrust cylinders on<br />
the last segment ring installed.<br />
In double shield TBM, it consists of an extendable front shield which<br />
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