Thisarticle originally appeared在八月/ 9月2020年9月的基础钻井杂志

该档案馆位于明尼阿波利斯历史悠久的仓库区的北环邻居，是270,000平方英尺的公寓楼，由六级高于等级和3级以下的等级停车场。312以下的等级停车位将提供公共停车场和服务于198家公寓的建筑物;在这个快速增长的时髦邻域内提供比其他住宅更多的停车位。

北循环名称是指曾经为该地区提供过的街道线。从历史上看，北圈是一个装满仓库和铁路轨道的工业区，多年来一大块铁路围场位于项目现场的北侧。从大约1885年开始，该网站用于各种商业企业。过去的居住者包括肝脏，铁匠，零售店，酒店，马车商店，塔架纸厂，糖果厂，藏皮和毛皮邮政，仓库等。当普通区域在20世纪60年代跌倒时，档案馆成为一个表面停车场，仍然是一个停车场，直到建设开始。

On the east and west sides of the site are located vintage brick buildings, both constructed in 1886, with three levels above grade and a full basement. The Foster House building is on the east of the project site and the Chicago House Hotel is on the west. Both structures are built tight to the lot lines with the Foster House extending approximately 9 inches over the property line and into the site. Figure 1 shows an overview of the site during excavation.

The large railroad yard was replaced by the Federal Reserve Bank Facility in 1997. Construction of the Federal Reserve included a large open excavation extending to an elevation approximately equal to the lowest parking level ofThe Archive。这种挖掘以距离存档延伸的近似45°角的近似45°角切割基岩。图2显示了该挖掘的范围，归档站点位置由红色轮廓表示。在此建设中，福斯特房屋被转换为支持美联储银行的机械建筑。

manbet万博app岩土工程

一般土壤剖面由10到13英尺of urban fill comprised of silty sand, poorly graded sand, sandy lean clay, and miscellaneous debris over bedrock. The bedrock stratigraphy consists of a layer of Platteville Limestone varying between 8 to 12 feet thick over a 2 to 4-foot-thick layer of Glenwood Shale, sitting on St. Peter Sandstone. The Platteville Limestone has RQD values from 0 to 90 with an average of 37 and the Glenwood Shale is known to deteriorate if exposed for an extended time period.

Design

With parking at a premium in this area of downtown, and some nearby competing residential buildings touting approximately ½ of a parking space for every unit, The Archive desired to stand out, by maximizing the available parking for tenants. Incorporating three below grade levels, places the lowest floor a few feet above the water table, thus maximizing the depth of excavation.

Usingtraditional temporary retention and cast-in-place below-grade wallswould have reduced the footprint of the building enough to remove one row of parking for all three levels. Therefore, the project team decided the temporary support of excavation (SOE) system would become the permanent below-grade wall to provide as much space as possible. The depth to bedrock prevented the use of sheet piles as the permanent foundation system and the limitations on the use of permanent tiebacks beyond the property line prevented the use of a soil nail system. A drilled system would be required, systems such as drilled soldier piles, secant walls, and diaphragm walls were explored. A drilled soldier pile system was proposed based on the cost and ability to meet project timelines.

克服兵桩系统克服的障碍之一是永久暴露的面向外观的外观。对于档案，壁支撑土的上部将暴露在滞后的喷射子。稳定的基岩将被曝光和覆盖着岩网。页岩和砂岩的高度将在岩石面上施加喷射。

The shotcrete levels were reinforced with epoxy coated rebar and headed studs were welded to the webs of the piles to transfer the load. The shotcrete was placed at the back flange of the piles and the rock was excavated to the back flange of the piles. This was done to allow air flow to pass between the lower floors in the web of the piles, reducing the demand on the mechanical systems. Figure 3 shows a close up of the exposed face.

“The Federal Reserve Bank would not allow tiebacks to cross the property line, limiting the tieback length on the north wall to only an 18-foot horizontal dimension.”

通过挖掘尽可能深入并将临时支撑到永久性系统中，档案能够每单位创建1.5个停车位。其中一些空间将被用作公共停车场以产生收入。

The design of the soldier piles had to consider both the temporary condition during construction and the permanent condition when it becomes part of the permanent structure. For the temporary SOE, the soldier piles used temporary tiebacks for lateral support. The design called for the tiebacks to remain in-place until the floor diaphragms were cast and grouted to the piles, whereby the floor diaphragms provide lateral support for the piles.

The Federal Reserve Bank would not allow tiebacks to cross the property line, limiting the tieback length on the north wall to only an 18-foot horizontal dimension. To achieve resistance in such a short horizontal length, the tiebacks would have to be bonded into the bedrock within the theoretical failure plane. Knowing the quality of the bedrock gave us confidence we would be able to provide adequate support in this condition. However, as shown by historical photos (Figure 2.), extensive rock excavation had occurred north of the site. Thus, there was a risk the bonded length of the tie-backs could extend into soils, rather than bedrock. To account for this, the tiebacks were installed at the lowest elevation the piles could support in a cantilevered condition and drilled in at a 45° angle to run parallel with the previously excavated rock surface.

On the east side, tiebacks were not allowed to be installed under the Foster House. While this building has a basement with strip footings bearing directly on the limestone bedrock, the planned excavations would remove the soil pressure on one side of the building, producing an unbalanced soil load that needed to be resisted by the shoring. The Foster House building only extends about two thirds of the site along this wall and the remainder of the wall had direct soil loading applied to the shoring.

在不使用重件的情况下构造31英尺深的挖掘将是困难的。探索了割割墙和内部支架等选项，并决定是成本持有的障碍和阻碍性。最终设计成为钻石桩，原位土壤混合和后张紧的组合。

建筑师能够在寄养房屋和士兵桩的后面之间提供三英尺的空间。这种空间的覆盖层土壤与基岩仰角混合的土壤，产生了2,000 psi土水泥基质。HollowBar Tiedowns被安装在寄养房屋上的土壤混合中央，并张紧以提供倾覆的抗性。由于距离窄，重件的张紧施加到岩石表面的大约17ksf的轴承压力。然后，士兵桩设计为20英尺高的悬臂元件，抵抗覆盖覆盖土的剪切力（不是时刻）和来自基岩的一些局部侧向压力。图4显示了墙壁系统的示意图，图5显示了土壤混合和图6显示完成的壁。

由于在土壤混合和张紧之前钻出桩并用瘦混合物灌浆，因此预计瘦杆将填充岩石中的一些现有骨折，并通过轴承和侧电阻提供交替的负载路径桩，以帮助抵抗张紧力。

监测墙壁的偏转，如果满足偏转限制，计划围绕着偏转限制，如广泛的角支撑。墙壁上的墙壁和偏转仍然小于桩顶部的1英寸的通知限制，在现有的建筑基础水平上转化为小于½英寸。

在芝加哥家庭酒店的西侧芝加哥房屋酒店允许重叠，大大简化了设计。临时连接位于脚踏高度低于脚梯下方，要求士兵桩到悬臂上方大约14英尺上方的负载。图7显示了芝加哥房屋酒店的挖掘，显示了桩之间的岩石的碎裂。

Construction

存档是一个设计版本项目，挖掘开始，因为结构和建筑设计正在进行中。下层楼层被设计为张紧板块，柱子靠近周边的柱子，悬臂悬臂悬挂在士兵桩墙上。结果，除了支撑柱负载的三个桩外，焊料桩壁不需要携带大量轴向载荷。

Coordination was required to place the temporary tiebacks at elevations that did not interfere with the floor slabs, columns, or formwork for casting the floor slabs. With the tiebacks installed based on progress plans, a conflict was discovered in the field along the south wall where there were interferences with some columns and the temporary tiebacks. The entire team helped with the solution, the structural engineer was able to move some of the columns that were not yet cast. Temporary corner bracing was installed to remove some of the conflicts, such as shown in Figure 8. The remaining conflicts were solved by changing the forming system for the columns and shortening the bearing ends of the wales.

Conclusion

The Archive used an innovate application of drilled soldier piles as the permanent foundation wall and post tensioned soil mixing to maximize the structure footprint, while saving cost over a conventional wall system.

项目团队

Developer: Solhem Companies and TE Miller Development
建筑师：动量设计组
结构工程师：Ericksen Roed＆Associates
General Contractor: Ironmark Building Company
Drilling and Shoring Contractor: Bolander
manbet万博app岩土工程师：Bmanbet体育滚球raun Intertec Corporation
Shoring Engineer：Bmanbet体育滚球raun Intertec Corporation