【作者】 张有；

【导师】 王成彪； 王贵和；

【作者基本信息】 中国地质大学（北京） ， 地质工程， 2009， 博士

【摘要】 随着城市建设的不断发展,大量带有地下室的高层建筑物、地下车库、地铁、地下商场等地下建筑物、构筑物的抗浮问题变得越来越突出,在解决抗浮问题中摩擦型地锚得到了广泛应用。虽然有关抗浮地锚的理论研究已取得长足发展,但由于影响地锚承载力的因素较多,这也使得合理进行地锚设计存在一定的难度。因此,本文对实际工程中的抗浮地锚进行现场试验测试,并采用可以考虑土体应变硬化-软化与体积剪胀模型的数值分析方法进行验证,在此基础上对层状土体中拉力摩擦型地锚和群锚的受力特性进行了深入的研究分析。本课题研究成果无论在理论还是在工程应用上,有具有重大的意义。主要研究工作如下:通过现场试验,抗浮地锚进行等级荷载张拉时,随着荷载的逐级增加,地锚锚头位移以及沿地锚不同部位的受力也逐渐增加;并且在不同等级荷载情况下,随着深度地锚各部位的轴力逐渐减小,从而说明抗浮地锚受拉时,荷载传递是由锚头向底部传递。通过数值分析,得到了与现场试验结果相近的规律,验证了数值分析方法的合理性和有效性。本文对成层土体中的摩擦型地锚进行了受力分析,随着地下水位的升高,地锚锚固力将会降低;锚固在基础底板下的垂直地锚,在开挖深度大于5m后,锚固力受超固结比的影响而趋于定值。将层状土体简化成单层土体来计算地锚的锚固力其误差不大。但在层状土体中的地锚宜采用双层保护,以免水泥浆体开裂,造成钢绞线锈蚀,影响地锚的长期锚固力。地锚的拉拔力随SPT-N值、覆土深度、锚固段长度及地锚直径的增加而提高,其中在受力范围内又以增加地锚锚固段长度的效果最佳。对群锚研究而言,由数值分析发现,对于2×2排列的群锚,水平间距为2D(D:地锚直径)时,群锚效应系数有75%~80%;当水平间距大于6D后,群锚效应系数可达98%以上,甚至不受群锚效应的影响。群锚周围土体的屈服区域随覆土深度增加而增加,增加地锚的水平间距能减少地锚拉拔力受群锚效应的影响。比较2×2与3×3排列群锚的群锚效应与水平间距的关系中发现,在相同的水平间距下3×3排列的群锚受群锚效应的影响比2×2排列群锚显著。更多还原

【Abstract】 With the development of city construction, buoyancy effects of buildings, such as tall building, subway, underground supermarket and so on, are getting more and more serious; at the same time, anchors are widely employed to withstand uplift forces. During the last many years various researchers have proposed approximate techniques to estimate the uplift capacity of soil anchors. The majority of past research has been experimentally based and, as a result, current design practices are largely based on empiricism. In contrast, very few rigorous numerical analyses have been performed to determine the ultimate pullout load of anchors because of many factors involved in this procedure. To evaluate the uplift behavior of shaft tension anchors in layered soils and frictional anchor groups, a constitutive model for a strain hardening–softening and volumetric dilatancy model was quoted, a series of triaxial CID and CU tests on clay and sand were performed to obtain the parameters needed for the soil model. In addition, filed tests on a single shaft anchor and an anchor group were conducted in layered soils. Thus, study results will prove very useful for future research and design of anchors in practice. The following conclusions can be drawn:As to tension anchor, with the increasing of loading, the head displacement and the force of anchors were also increased. Under the same loading level, the normal forces of the anchor decreased as the embedment depth increased. The uplift load was transmitted from top to the bottom along the bounded length. The load-displacement relations and ultimate loads calculated from numerical analyses produced good agreement with those measured by field tests not only for the single anchor but also for the anchor group.As to the anchor in layer soil, the higher elevations of ground water table the less anchorage capacity. For a vertical anchor which wad anchored on foundation mat, the effect of over consolidation ratio on anchorage capacity was not evident, when depth of excavation was greater than 5m. There is not much distinction on anchorage capacity between an anchor installed in a pure soil and a layer soil, if their average SPT blow counts are equal. However, when an anchors was located in a layer soil, the friction stress occurs discontinue behavior, the double protection should be used in fixed length for keeping long term anchorage capacity. Whether SPT blow count, overburden depth, fixed length or diameter of an anchor increased, the anchorage capacity also increased. Increasing fixed length should be the optimum method to increase the anchorage capacity.When a 2×2 anchor group with spacing of 2D (D: anchor diameter), efficiency of the anchor group was calculated to be only 75%~80%. There is no interference when spacing was 6D, and the efficiency of an anchor group could more than 95%. The yielding zone of the anchor groups increase as overburden depth increase. The efficiency of anchor groups can be eliminated as the anchors spacing are increase horizontally. It can be found that from the numerical results, the efficiency of 3×3 anchor group is greater than that of 2×2 anchor group.更多还原