外文原文
Digging for correctives by flushing and Anchor pile underpinning For Reinforcement in open-end caisson foundation
Abstract : With the practical example, the amount of digging for correctives by flushing and anchor pile underpinning for reinforcement in open-end caisson foundation, the application layer of soft soil reinforcement of the foundation and correcting is a certain lesson.
Keywords : pile foundation material analysis
1 Introduction
Soft Ground deformation is a chief problem in the design of the foundation of building, one of the main problems deformation mainly reflected in the following aspect .
(1) Settlement and Differential settlement was major : engineering measured data showed that the load-bearing walls of the mixed structure, If the load size of foundation is appraised by floors of the building, the natural settlement of the foundation of the three-floor building was typically 150 ~ 200 mm; and the four-floor building changes in the general level of 200 ~ 500 mm; five and six-floor layer may be up to 700 mm .
(2) Large sedimentation rate : Building sedimentation rate is a measure of the foundation level of development and status of an important sign. Soft Ground subsidence rate is generally large, and large sedimentation rate is the largest loading rate at the end of loading. With the development, the settlement rate gradually decreases, and buildings differential settlement of the fastest development period is at about six months to one year for buildings, is also the most vulnerable buildings cracks appeared in the period. Under normal circumstances, if the settlement rate reduced to 0.05 m / d below, it cause to the emergence of isokinetic settlement ,however , long isokinetic settlement will lead to loss of stability in the foundation dangerous .
(3) Settlement stable long time : As the permeability of soft soil is weak, the pore water is not precluded, settlement building stability lasted longer, Buildings built after some years, 10 years, even decades settlement did not completely stable .
A large number of tier buildings at the early 1980s in NingBo, because of constraints of basic cost , the form the basis was used to be the strip foundation or raft foundation instead of pile. Although construction has been nearly 20 years, but the influence of the soft soil characteristics and factors of outside interference effects, (such as the construction of nearby buildings, etc.), a great deal of which give birth to uneven subsidence ,which lead to walls cracking, tilt excessive rate and other issues, and some even become dilapidated buildings. In order to safeguard the people's life and property safety, how to apply for these housing reinforcement or corrective economically and applicatively, it has now become very urgent problem .
2 Digging for correctives by flushing and anchor pile underpinning for reinforcement in open-end caisson foundation
(1) The methods of Buildings corrective Underpinning is great , including corrective methods Load Pressure Correction, Correction anchor piles pressure, the amount of soil corrective, Digging corrective precipitation, the amount of soil pile pressure Correction, Correction immersion ,such as roof or corrective.. The methods of underpinning reinforcement consists the broadening the basis underpinning, pit underpinning, pile underpinning, grouting underpinning, high pressure jet grouting underpinning, Heat reinforcement underpinning, infrastructure and strengthening decompression underpinning for such rigidity. The author come to the conclusion In many of the methods from years of practices : the caisson with the amount of soil corrective flushed with bolt static pile underpinning consolidation is a economical and reliable method in a soft ground on the building reinforcement .
(2) The basic theory of the method :at the small settlement side of the basis of the building, we set up a number of well-sinking, Caisson reserved 4 ~ 6% of punching fan, When the caisson is expected to reach the design elevation with hole through the wall reserved with a high-pressure water gun inserted basis for flushing, Mud water discharges through the caisson, and the discharge of process slurry that is on buildings corrective process. When buildings tilted rate target range, a Jack will be used as a paragraph-by-paragraph pile foundation dug through the pile pressure pore pressure buried, and then pile foundation connected, so as to improve infrastructure and capacity to control the purpose of settlement .
(3) It is noteworthy that corrective work should avoid overkill, it must follow from shallow to deep, from small to large, from lean to the confidentiality. It must have the process : settlement → stability → resettlement → restability，repeated the process in order to achieve the purpose of correcting。Therefore, the corrective must be not seek quick results, not the contrary, as a corrective cause excessive original buildings at the side of the small settlement in favor of the project have also seen examples .
3 Engineering Example
(1) The 5th Building MaYuan New Village in NingBo, which was built in 1982, was 29.2 m long in east-west direction, and 8.4m wide in north-south direction, eaves height of 14.4 m, which is a five-storey brick structure. The processing method is soil compaction using mallets, the basis for the strip foundation. And in May 1998 the building has a total of over 50 cm settlement, coupled with a large pit near the construction of new buildings, House, have serious tilt to the corrective work before the start of measured value tilt tilt to the south 27 cm. caused the ground below the bottom of the outdoor terrace, dislocation pipe plug to tenants brought inconvenience. Concrete reinforcement methods have been : Even tilt to the main north-south, east-west tilt of smaller features, Buildings in the north of 2 m away from the wall to install the 1 m diameter reinforced concrete caisson 6, Caisson depth of 5 m, According to the geological structure is 4 m deep reserved 4 ~ 5 flushing hole, and the basis of the external walls of buildings set around 12 to anchor beam piling Kong. ANCHOR PILE section 250 mm × 250 mm, length of pile 18.9m, consists of nine, entered bearing layer 1.5 m. Construction of the building is not the relocation of the residents under the circumstances .
(2) The key of correction, one is to be carried out by hand daily settlement observation, the settlement Control is in 3 mm / d% more appropriate dayly. Because the settlement is to observe a day of work to be done, such as using traditional Level observation is more cumbersome. So using a simple and intuitive method of observation, First bottom of the housing to facilitate the observation position (usually in the window) ? laying around the level of the building, again in the level of the corresponding location leads to observe the standpipe in the legislation governing installed on the steel ruler and irrigation pipes inside. Because of the level of control is the interchange, dumping around the standpipe water level readings of the building shall be poor due to the settlement. To prevent evaporation of water from the error, so that the water level elevation initial value remains unchanged, standards for the construction must be a settlement with the same water tank connected, and cook Office Box plane calibration mark Before reading the daily water level check box alignment with the calibration at any time to adjust. This daily through the water level readings supplemented by regular standard observation, we can achieve a very high degree of accuracy. The second is dumping, using water cannons, submerged within the building for the length of the general building deep into the 0.6 times, too short is not conducive to the basement stress regulation, easier to make housing cracks, it is neither too long nor conducive to the settlement of economic adjustment. Through these measures, the project only two months on the buildings of the corrective tilt from the former dropped 1.85% to the Correction 0.3%, and buildings in the process of correcting no cracks .
(3) At the same time of correcting, drilled hole at the original foundation slab in the corresponding locatione. Generally NingBo early 1980s, the construction of residential building foundation slab thickness of about 25 cm, Bolt can not meet the anti-static pile punching, bending capacity requirements, it needs to reinforce the existing foundation, Sheer Cliff original foundation slab reinforcement and the new distribution of welded steel, poured into to meet the requirements of the beam anchor .
Static pile bolt should pay attention to three dot, the first hole pile pressure on the need to create the next big small trumpet. General singalong to +50 mm diameter pile next to the mouth +100 mm diameter piles. 2 is piling pressure before the primer hole or pilings, if this works because the original soil compaction using mallets construction basis to the thickness of the brick and stone two-3m, will be directly under the pile pressure is bound to create difficulties pile sinking, to anchor beam and pulled off pile deviation, and other issues. To address this situation the first project primer Kong, is used to drill holes pile on the pressure for drilling and aperture of 200 mm, 3 m deep. As a result of the primer hole measures after it piles pressure to be carried out smoothly. Three envelopes in the pile should not unloading conditions, and the closure of the strength of the concrete piles must meet the C15 above before unloading. By this method, Building the settlement rate from the completion of 0.2 mm / d reduced to 70 days of 0.033mm / d, have achieved the desired results, and is upstanding all in the year .
沉井基础中的冲水掏土纠偏和锚杆静压桩托换加固
摘要：结合实际的例子，在开放式沉箱基础上，挖掘纠偏由冲厕及锚桩基托换增援，应用层软土加固的基础和纠正是有一定的指导作用。
关键字：桩 基础 材料分析
1 引言
软土地基的变形问题是房屋地基设计中的一个主要问题，其变形问题主要反映在以下几个方面：
(1) 主要是沉降和不均匀沉降：工程实测资料表明，对砖墙承重的混合结构，如以楼层数表示地基受荷大小，则3层房屋天然地基沉降量一般为150～200mm；4层变化较大一般为200～500mm；5、6层则可能达700mm。
(2) 沉降速率大：建筑物沉降速率是衡量地基发展程度与状况的一个重要标志。软土地基沉降速率一般均较大，而加荷终止时沉降速率最大。随着时间的发展，沉降速率逐渐衰减，约在半年到一年时间内为建筑物差异沉降发展到 最快时期，也是建筑物最易出现裂缝的时期。在正常情况下，如沉降速率减到0.05m/d以下时能出现等速沉降，但长时间的等速沉降就有导致地基丧失稳定的危险。
(3) 沉降稳定时间长：由于软土渗透性弱，孔隙水不易排除，所以建筑物沉降稳定历时较长，有些建筑物建成后几年、十几年甚至几十年沉降都未完全稳定。
宁波地区一大批80年代初建造的多层民用住宅楼，由于受当时造价的限制基本上均未打桩，基础形式大都采用条基或筏基。虽建造至今已有将近20年时间，但由于上述软土地基的特点及外界干扰因素的影响(如邻近建筑物施工等)使其中有相当一部分房屋产生了不均匀沉降，从而出现墙身开裂、倾斜率过大等问题，有的甚至成为危房。为了保障人民的生命财产安全 ，如何既经济又适用地对这些房屋进行加固或纠偏已成为当前极迫切的问题。
2 沉井冲水掏土纠偏和锚杆静压桩托换加固
(1) 纠正建筑物的支柱的方法是很多的，其中纠偏方法有堆载加压纠偏、锚桩加压纠偏、掏土纠偏、降水掏土纠偏、压桩掏土纠偏、浸水纠偏、顶升纠偏等。托换加固方法有基础加宽托换、坑式托换、桩式托换、灌浆托换、高压喷射注浆托换、热加固托换、基础减压和加强刚度托换等。在众多的方法中笔者从多年的实践中得出用沉井冲水掏土纠偏结合锚杆静压桩托换加固法是一种在软土地基上对建筑物进行纠偏加固的既经济又可靠的好方法。
(2) 该法的基本原理是：在基础沉降小的建筑物一侧，设置若干个沉井，沉井内预留4～6个成扇形的冲孔，当沉井到达预计的设计标高后通过井壁预留孔用高压水枪伸入基础下进行冲水，泥浆水通过沉井排出，而泥浆排出的过程即是对建筑物纠偏的过程。当建筑物的倾斜率达到预定的范围后，即可用千斤顶将桩逐段通过基础中开凿的压桩孔压入土中，再将桩与基础连接在一起，从而达到提高基础承载力和控制沉降的目的。
(3) 值得注意的是，纠偏工作切忌矫枉过正，一定要遵循由浅到深，由小到大，由稀到密原则，须经沉降→稳定→再沉降→再稳定的反复工作过程，才能达到纠偏目的。因为在软土地基上建造的建筑物沉降往往需要经过一段时间才能达到最终稳定，所以纠偏决不能急于求成，不然适得其反，由于纠偏过大造成原建筑物沉降小的一侧又倾斜的工程实例也有所见。
3 工程中的实际例子
(1) 宁波市马园新村五号楼，始建于1982年，该楼东西长29.2m，宽8.4m，檐口标高14.4m，为5层砖混结构。地基土采用重锤夯实处理，基础为条形基础。至1998年5月该楼已累计沉降超过50cm，加上近年该楼附近新建建筑物施工，楼体产生严重倾斜，至纠偏工作开始前，测得倾斜值为向南倾斜27cm，造成底层地面低于室外地坪，管道错位堵塞，给住户带来了不便。具体纠偏加固方法是：针对该楼南北向倾斜为主，东西向倾斜较小的特点，在建筑物北面离墙体2m处设置内径1m的钢筋混凝土沉井6只，沉井深度5m，根据地质构造在深4m处预留4～5个冲水孔，并在建筑物基础外墙四周预设12个地锚梁压桩孔。锚杆静压桩截面250mm×250mm，桩长18.9m，共分9节，进入持力层1.5m。工程施工在楼内居民不搬迁的情况下进行。
(2) 纠偏工作的核心重点，其一是必须每天由专人进行沉降观测，日沉降量控制在3mm/d左右较为适宜。由于沉降观察工作是每天必须做的工作，如用传统水准仪进行观察就显得较为繁琐。因此采用一种简便易行且直观的观测方法，首先在房屋底层便于观察的位置(一般在窗口上)?环绕建筑物铺设水平管，再在水平管相应位置引出观察用立管，在立管处安装上钢尺，并在水管内灌水。由于整个水平管是联通的，卸土前后立管水位读数差即为建筑物各对应点的沉降量。为防止水分蒸发带来的误差，使水位初始值高程保持不变，水准管铺设时必须与一沉降不变的水箱相连，并在箱内水平面处做上刻度记号，每天读数前检查箱内水位是否与刻度对齐，随时进行调节。这样通过每天的水位读数再辅以定期水准观察，就可以达到相当高的准确度。其二是卸土用水枪伸入建筑物内的长度一般为建筑物进深的0.6倍左右，太短不利于基底应力调节，容易使房屋产生裂缝，太长则既不经济又不利于沉降调节。通过以上措施本工程仅用两个月就使建筑物的倾斜率由纠偏前的1.85%下降到纠偏后的0.3%，且建筑物在纠偏过程中无裂缝产生。
(3) 在同一时间进行纠偏也即可在原基础底板的相应部位开凿压桩孔。一般来说宁波地区80年代初建造的住宅建筑基础底板厚度大约在25cm左右，不能满足锚杆静压桩的抗冲切、抗弯能力要求，故需对原有基础进行加固，凿出原基础底板筋与新配钢筋焊接，浇筑成满足要求的地锚梁。
锚杆静压桩施工时要注意三点，一是压桩孔需做成上小下大的喇叭口。一般上口为桩径＋50mm，下口为桩径＋100mm。二是压桩前应进行引孔或探桩处理，如本工程由于原地基土采用重锤夯实施工，基础下块石厚度达2～3m，如直接将桩下压势必造成桩下沉困难、地锚梁拉断以及桩身偏位等问题。针对这个情况本工程先作引孔处理，即先用钻机对压桩孔进行钻孔，孔径为200mm，深3m。由于采用了引孔措施，使其后压桩工作得以顺利进行。三是封桩应在不卸载条件下进行，并在封桩混凝土强度等级达到C15以上时才可卸载。通过以上方法，建筑物的沉降速率由竣工时的0.2mm/d减少到70天后的0.033mm/d，取得了预期的效果，使用一年来情况良好。
