[求助]怎样做Top Down Construction，有照片？

bobcat

怎样做Top Down Construction，有照片？请分享。Thanks a lot。。。

topdown

Error in chinese typing (简体拼音) so i write in english. sorry.
Top down construction is one of the construction methodology  for deep excavation. The system start with the perimeter CBP or diaphragm wall installation. The depth of penetration and reinforcement cage for the wall is calculated by geotechnical engineer using FEM software like Plaxis, the most common commercial software. Reinforcement is required due to the lateral force from soil retained. In some case due to  high ground water level,  jet-grouted column or soil-cement mixing  should be used to provide water-tightness. The boredpile for superstructure also proceed at the same time. Immediate after the completion of the bored pile, steel column was erected on top of each pile at its formation level, which would be used as support to the basement slabs during the construction process .
Depend to the site/archi general layout /soil condition, normally the first casting slab/plate (will use as working platform) always set at 3-4 m below existing ground level. These mean the upper part of DW/CBP are in cantilever action. Then, the logistic should be planning well including temporary steel ramp, steel platform, void/opening for soil to move out, placing of tower crane, casting sequence… After the completion of first plate, basement excavation can be started from there. As a means to expedite the progress in the basement construction, the "double-bit" method was adopted. The method employed in this project was to have the excavation for the 2/3-level be done at a same time, making an excavated depth of about 7m. At the bottom of the excavated, then cast the slab of the 3-level basement. And from the slab, usual floor form would be erected and cast the 2-level basement slab after on. The 4/5-level basement would be repeated using the same principle.
The removal of spoil was done in two ways. First, spoils were collected into steel bucket approximately 2 cu m. in size by the use of loaders, and lifted to ground level by the crawler crane. The other way was by the use of the bucket of excavating machine to transfer the spoil from the working pit to the ground level. The excavating machine was located at slab platform, which was also supported by the strut frame. Since the vertical access positions (opening) were located around the work platforms as to convenient the removal of spoil. As a consequence, spoil produced from the bottom site had to be collected on these locations in order to make removal easier. To make this possible, significant amount of spoil were required to be transported horizontally using loading machines at the bottom of the pit until they reached the collecting points. In addition, this had to be done in limited working space with rows of strut in between that made the spoil removal process rather interrupting.
The excavation for the formation level was become complicated due to the limited headroom at average 3.1 m. The numbers of mini-sized excavating machines need to be lowered into the pit for further excavation. Temporary shores were installed in certain positions to stabilize the sides for pilecap/center core wall constructing due to the depth of the excavation exceed 5.0 m. The casting of base slab followed after the construction of pilecap. The floor system in the base slab was of flat slab design with dropped panel around column heads. Average slab thickness was 600mm and no ground beam was provided.

Top-down is one of the construction methodology for deep excavaton use at malaysia. we still can use other system like DW/CBP with ground anchor, DW/CBP with Kingpost/steel framing, deep soil-cement mixing, sheet-pile wall, lagging wall and....
need to consider many factor on using which type of system, ground water level, cantilever action, deep of excavation, soil condition, working sequence/time frame, space availbale, adjacent building, lrt line, underground utility ....

Not to upload photo because public will known my ID. Only very few contractor doing these type of deep basement at malaysia.

单眼皮男孩84

我公司有一场工在sri hartamas那边， 你有空去看看应该会获益良多

davidmy

逆作法施工技术是高层建筑物目前最先进的施工技术方法。

原理：先沿建筑物地下室轴线或周围施工地下连续墙或其他支护结构，同时建筑物内部的有关位置浇筑或打下中间支承桩和柱，作为施工期间于底板封底之前承受上部结构自重和施工荷载的支撑。然后施工地面一层的梁板楼面结构，作为地下连续墙刚度很大的支撑，随后逐层向下开挖土方和浇筑各层地下结构，直至底板封底。同时，由于地面一层的楼面结构已完成，为上部结构施工创造了条件，所以可以同时向上逐层进行地上结构的施工。如此地面上、下同时进行施工，直至工程结束。

分类：逆作法可以分为全逆作法、半逆作法、部分逆作法、分层逆作法。

工艺特点

（1）可使建筑物上部结构的施工和地下基础结构施工平行立体作业，在建筑规模大、 上下层次多时，大约可节省工时1/3。
（2）受力良好合理，围护结构变形量小，因而对邻近建筑的影响亦小。
（3）施工可少受风雨影响，且土方开挖可较少或基本不占总工期。
（4）最大限度利用地下空间，扩大地下室建筑面积。
（5）一层结构平面可作为工作平台，不必另外架设开挖工作平台与内撑，这样大幅度削减了支撑和工作平台等大型临时设施，减少了施工费用。
（6）由于开挖和施工的交错进行，逆作结构的自身荷载由立柱直接承担并传递至地基，减少了大开挖时卸载对持力层的影响，降低了基坑内地基回弹量。
（7）逆作法存在的不足，如逆作法支撑位置受地下室层高的限制，无法调整高度，如遇较大层高的地下室，有时需另设临时水平支撑或加大围护墙的断面及配筋。由于挖土是在顶部封闭状态下进行，基坑中还分布有一定数量的中间支承柱和降水用井点管，目前尚缺乏小型、灵活、高效的小型挖土机械,使挖土的难度增大。但这些技术问题相信很快会得到解决。

davidmy

PHOTO for TOP-DOWN CONSTRUCTION

http://personal.cityu.edu.hk/~bs ... ent/introindex.html