Combined with fiber Bragg grating(FBG)sensing technology,four glass fiber reinforced polymer(GFRP)anti-floating anchors and four steel anti-floating anchors were tested for on-site destructive failure to investigate t...Combined with fiber Bragg grating(FBG)sensing technology,four glass fiber reinforced polymer(GFRP)anti-floating anchors and four steel anti-floating anchors were tested for on-site destructive failure to investigate the anchoring performance and the bonding characteristics between GFRP anti-floating anchor and concrete floor.The test results show that bending GFRP anchor will be broken at the common boundary between vertical anchorage section and bending section during the pullout process,and the spring-back load provided by the rupture contributes to a decrease of bearing capacity and an inflection point on the load-slip curve.The loaddisplacement curve of the straight anchor GFRP anti-floating anchor is smoother and has better predictability than the same type of steel anchor.Additionally,different forms of GFRP anti-floating bolt have different bondslip constitutive relations.By introducing the sliding-slip correction factor of bending bolt,constitutive models describing the rising-section of sliding-slip relation of bending and straight-anchored GFRP anti-floating bolt are established respectively.The model can fit the test results rightly.展开更多
The "Anti-floating Technical Standard for Construction Engineering" (JGJ476-2019) issued by the Ministry of Housing and Urban-rural Development on March 1, 2020 contains specific regulations and requirements...The "Anti-floating Technical Standard for Construction Engineering" (JGJ476-2019) issued by the Ministry of Housing and Urban-rural Development on March 1, 2020 contains specific regulations and requirements for crack control design of anti-floating anchor bolts. Among them, the anti-floating design grade is Grade A, which is designed according to the principle of no cracks, and the anchoring slurry should not generate tensile stress under the standard combination of load effect. The anti-floating design grade is Class B, which is designed according to crack control. The tensile stress in the anchoring slurry should not be greater than the axial tensile strength of the anchoring slurry under the standard combination of load effect. In order to ensure the safety of the design, while achieving the principles of clear and definite theoretical concepts and taking into account of economy, this paper analyzes and discusses the basic concepts, stress process, design principles and methods of the prestressed anti-floating anchor rod, and at the same time gives the matters needing attention and relevant suggestions in the design process.展开更多
With the continuous development of today's construction industry, the construction of underground engineering is becoming more and more common. Especially with the accelerating process of urbanization, more and mo...With the continuous development of today's construction industry, the construction of underground engineering is becoming more and more common. Especially with the accelerating process of urbanization, more and more construction projects and underground projects begin to develop in the direction of ultra-deep and multi-layered. However, under the influence of groundwater, the underground building engineering structure will be subject to greater buoyancy, and this buoyancy will increase with the buried depth of the underground building structure, which will lead to the floating of the bottom plate and wall. In serious cases, there will even be building overturning, which will bring a great security threat to the construction engineering. In order to ensure the anti- floating ability of underground engineering, the anti-floating design and control measures are analyzed in this paper. It is hoped that this analysis can lay a good foundation for the improvement of anti-floating performance of underground construction engineering, so as to ensure the quality and safety of the overall construction engineering.展开更多
Accurately predicting the overlying pressure is crucial for determining an appropriate cover depth of underwater box tunnels to avoid the uplifting failure.Based on the project of box jacking crossing the Beijing-Hang...Accurately predicting the overlying pressure is crucial for determining an appropriate cover depth of underwater box tunnels to avoid the uplifting failure.Based on the project of box jacking crossing the Beijing-Hangzhou Grand Canal in Suzhou,the characteristics of overlying pressure variation during tunneling are investigated.The monitoring results reveal that the fluctuation of overlying pressure is weakened during the rapid tunneling process.A modified analytical model for vertical earth pressure is conceived,in which the active and passive limit states for multi-layered soils are both considered.The probable range of overlying pressure obtained by the proposed model is suitable to cover the actual values.The anti-floating behavior of underwater box tunnels for two different working conditions is discussed by calculating the minimum cover depth.Using the calibrated analytical models,a parametric study is conducted to explore the influence of injection pressure,hardened slurry unit weight,soil internal friction angle,soil cohesion,and tunnel geometry.It is found that the injection pressure during the construction process is crucial for determining the necessary cover depth,and the change of box tunnel height makes it easier to trigger the variation of minimum cover depth.展开更多
With the development of global urbanization,the utilization of underground space is more critical and attractive for civil purposes.Various shapes of shield tunnels have been gradually proposed to cope with different ...With the development of global urbanization,the utilization of underground space is more critical and attractive for civil purposes.Various shapes of shield tunnels have been gradually proposed to cope with different geological conditions and service purposes of underground structures.Generally,reducing the burial depth of shield tunnel is conducive to construction and cost saving.However,extremely small overburden depth cannot provide sufficient uplift resistance to maintain the stability and serviceability of the tunnel.To this end,this paper firstly reviewed the status of deriving the minimum sand over-burden depth of circular shield tunnel using mechanical equilibrium(ME)method.It revealed that the estimated depth is rather conservative.Then,the uplift resistance mechanism of both circular and rectangular tunnels was deduced theoretically and verified with the model tests.The theoretical uplift resistance is consistent with the experimental values,indicating the feasibility of the proposed equations.Furthermore,the determination of the minimum soil overburden depth of rectangular shield tunnel under various working conditions was presented through integrated ME method,which can provide more reasonable estimations of suggested tunnel burial depth for practical construction.Additionally,optimizations were made for calculating the uplift resistance,and the soil thickness providing uplift resistance is suggested to be adjusted according to the testing results.The results can provide reference for the design and construction of various shapes of shield tunnels in urban underground space exploitation.展开更多
基金the National Natural Science Foundation of China(Nos.51708316 and 51778312)the China Postdoctoral Science Foundation(No.2018M632641)+1 种基金the Shandong Provincial Key Research and Development Program(Nos.2017GSF16107 and 2018GSF117008)the Shandong Provincial Natural Science Foundation(Nos.ZR2016EEQ08 and ZR2017PEE006)。
文摘Combined with fiber Bragg grating(FBG)sensing technology,four glass fiber reinforced polymer(GFRP)anti-floating anchors and four steel anti-floating anchors were tested for on-site destructive failure to investigate the anchoring performance and the bonding characteristics between GFRP anti-floating anchor and concrete floor.The test results show that bending GFRP anchor will be broken at the common boundary between vertical anchorage section and bending section during the pullout process,and the spring-back load provided by the rupture contributes to a decrease of bearing capacity and an inflection point on the load-slip curve.The loaddisplacement curve of the straight anchor GFRP anti-floating anchor is smoother and has better predictability than the same type of steel anchor.Additionally,different forms of GFRP anti-floating bolt have different bondslip constitutive relations.By introducing the sliding-slip correction factor of bending bolt,constitutive models describing the rising-section of sliding-slip relation of bending and straight-anchored GFRP anti-floating bolt are established respectively.The model can fit the test results rightly.
文摘The "Anti-floating Technical Standard for Construction Engineering" (JGJ476-2019) issued by the Ministry of Housing and Urban-rural Development on March 1, 2020 contains specific regulations and requirements for crack control design of anti-floating anchor bolts. Among them, the anti-floating design grade is Grade A, which is designed according to the principle of no cracks, and the anchoring slurry should not generate tensile stress under the standard combination of load effect. The anti-floating design grade is Class B, which is designed according to crack control. The tensile stress in the anchoring slurry should not be greater than the axial tensile strength of the anchoring slurry under the standard combination of load effect. In order to ensure the safety of the design, while achieving the principles of clear and definite theoretical concepts and taking into account of economy, this paper analyzes and discusses the basic concepts, stress process, design principles and methods of the prestressed anti-floating anchor rod, and at the same time gives the matters needing attention and relevant suggestions in the design process.
文摘With the continuous development of today's construction industry, the construction of underground engineering is becoming more and more common. Especially with the accelerating process of urbanization, more and more construction projects and underground projects begin to develop in the direction of ultra-deep and multi-layered. However, under the influence of groundwater, the underground building engineering structure will be subject to greater buoyancy, and this buoyancy will increase with the buried depth of the underground building structure, which will lead to the floating of the bottom plate and wall. In serious cases, there will even be building overturning, which will bring a great security threat to the construction engineering. In order to ensure the anti- floating ability of underground engineering, the anti-floating design and control measures are analyzed in this paper. It is hoped that this analysis can lay a good foundation for the improvement of anti-floating performance of underground construction engineering, so as to ensure the quality and safety of the overall construction engineering.
基金supported by the Natural Science Foundation of Jiangsu Province of China (Grant Nos.BK20230500 and BK20210721)the Young Talent Fund of Association for Science and Technology in Shaanxi,China (Grant No.20240722).
文摘Accurately predicting the overlying pressure is crucial for determining an appropriate cover depth of underwater box tunnels to avoid the uplifting failure.Based on the project of box jacking crossing the Beijing-Hangzhou Grand Canal in Suzhou,the characteristics of overlying pressure variation during tunneling are investigated.The monitoring results reveal that the fluctuation of overlying pressure is weakened during the rapid tunneling process.A modified analytical model for vertical earth pressure is conceived,in which the active and passive limit states for multi-layered soils are both considered.The probable range of overlying pressure obtained by the proposed model is suitable to cover the actual values.The anti-floating behavior of underwater box tunnels for two different working conditions is discussed by calculating the minimum cover depth.Using the calibrated analytical models,a parametric study is conducted to explore the influence of injection pressure,hardened slurry unit weight,soil internal friction angle,soil cohesion,and tunnel geometry.It is found that the injection pressure during the construction process is crucial for determining the necessary cover depth,and the change of box tunnel height makes it easier to trigger the variation of minimum cover depth.
基金support from National Major Scientific Instruments Development Project of China(Grant No.5202780029)Program of Distinguished Young Scholars,Natural Science Foundation of Chongqing,China(Grant No.cstc2020jcyjjq0087)Research on resilience prevention,control and adaptation strategy of flood disaster in megacities under changing environment(Grant No.2021-ZD-CQ-2).
文摘With the development of global urbanization,the utilization of underground space is more critical and attractive for civil purposes.Various shapes of shield tunnels have been gradually proposed to cope with different geological conditions and service purposes of underground structures.Generally,reducing the burial depth of shield tunnel is conducive to construction and cost saving.However,extremely small overburden depth cannot provide sufficient uplift resistance to maintain the stability and serviceability of the tunnel.To this end,this paper firstly reviewed the status of deriving the minimum sand over-burden depth of circular shield tunnel using mechanical equilibrium(ME)method.It revealed that the estimated depth is rather conservative.Then,the uplift resistance mechanism of both circular and rectangular tunnels was deduced theoretically and verified with the model tests.The theoretical uplift resistance is consistent with the experimental values,indicating the feasibility of the proposed equations.Furthermore,the determination of the minimum soil overburden depth of rectangular shield tunnel under various working conditions was presented through integrated ME method,which can provide more reasonable estimations of suggested tunnel burial depth for practical construction.Additionally,optimizations were made for calculating the uplift resistance,and the soil thickness providing uplift resistance is suggested to be adjusted according to the testing results.The results can provide reference for the design and construction of various shapes of shield tunnels in urban underground space exploitation.
