The Study On The Land Subsidence With The Affect Of High-rise Buildings In Tianjin Binhai New Area

Land subsidence is a Environmental geological phenomenon which is caused by the natural and human and it is permanent environmental and resource loss. Mid-twentieth century, as the needs of industrialization, groundwater resources has been extracted extremely, the groundwater level continued to decline significantly and the phenomenon of land subsidence happened, it has caused enormous economic losses so the Governments and experts started on the ground subsidence analysis and research. Currently with global warming and sea level rising, global coastal cities security is threatened, so the phenomenon of the land subsidence is caused the Attention of worldwide again.With the high-rise building continuously building in the Shanghai Pudong New Area, the land subsidence that has been controlled is developing rapidly. In Tianjin Binhai New Area, as same as Shanghai Pudong New Area, a large number of dense high-rise buildings are building and planned. At the same time, it is also distribute thick layer of marine soft soil, so with the development of the urban construction, the land subsidence caused by the high-rise building gradually appeared. The land subsidence caused by the high-rise building is a new directions and new problems of the hazards study on urban land subsidence. And the study for Tianjin Binhai New Area will guide the planning and construction of Binhai New Area, it can benefit Binhai New Area sciencely, rapidly, sustainable developing.Around the problem that Binhai New Area is coming, research works has been done as the follow:(1) The settlement data of Binhai New Area was collected, the recent land subsidence of Tang-gu, Han-gu and Da-guang were analysised and concluded in detail. The result proved that the prevention and control of land subsidence situation remains grim in Tianjin Binhai New Area.(2)Fitted the characteristics of the Tianjin Binhai New Area stratum, Toyoura sand and Kaolin clay composed the pile bearing stratum and soft soil around the pile separately. The course of construction was simulated by loading one of the pile groups in-flight.(3)The theoretical calculation and finite element software were used for analysis the results of centrifuge experiments and some result were added. Innovative research results obtained as follow:(1)During the high-rise building construction of Binhai New Area, uplift will occurred in somewhere of surface.Contrast the measured settlement curves during the period construction loads imposed by hydraulic equipment and the deduced curves based on the past period of 100g in-flight, the partial uplift was found, it is analysised by the principle of soil compaction effect in soft soil and the finite element software, the partial uplift is mainly happened during the period of the time of the building construction, the location changed with the period of construction, the approximate range of uplift is about 2.0-5.0 fold breadth of building from the center of the building, at the same time the uplift part is effected by the border of building nearby.(2) The land subsidence distribution in plain face of the high-rise buildings is obtained, and in cross section it is mainly happened in mine soft soil.During the high-rise building construction, uplift will occurred, the subsidiary stress caused by the loading of high-rise building decide that the land subsidence fade down with the distance increasing from the building, also with the marine soft soil consolidate by its sole weight, the piles and the soil interact each other, the settlement of soft soil around the piles is restrained by the piles, based on the three factors, the land subsidence distribution in plain face of the high-rise buildings in Binhai New Area is complex.During the period of high-rise building construction, the settlement in the marine soft soil occupy 70%-77.8% of total.(3)As the high-rise building construction, the regularity of excess pore water pressre and earth pressure is obtained.The sphere of influence of excess pore water pressure caused by study high-rise building is greater than 37.5m from the center of the building. In the marine soft soil, the excess pore water pressure increases along the depth and decreases with increasing distance from the building. The excess pore water pressure in 27.0m is 2.2-4.0 times bigger than 8.5m.The subsidiary stress caused by the old building fade down with the distance increasing, so it cause the engineering properties of soil differences, when a new high-rise building is setup around an old one, because the engineering properties of soil closer old buildings is better. So the excess pore water between adjacent buildings is smaller than the corresponding position which located the other side of the new building, and also the settlement is smaller than the other side.Fitted with the low permeability and the excess pore water pressre increasing along the depth, with the influence of study prototype buildings, the observation points in the middle of the two Buildings considerate 11.81 years, the degree of consolidation gets 97.6%, and the soil need 7.8cm settlement happen to finish the final settlement. Land subsidence caused by the high-rise building has the long duration characteristics.