Study On Engineering Characteristics And Settlement Deformation Laws Of Macau Coastal Soft Soil

Macau has a small area and a high population density,so it must expand the limited land through reclamation.The Macau reclamation area is located in the Pearl River Estuary.The thickness of the coastal sedimentary soft soils distributed on the seabed is generally between 6 and 15m.It has the characteristics of high water content,low bearing capacity,strong structure,large deformation after loading,and obvious time effect.Therefore,insufficient bearing capacity,excessive settlement deformation and uneven settlement are the main problems of soft soil foundation after land reclamation,and will directly affect the engineering safety and durability of the upper building（structure）.Macau is still continuing to carry out large-scale land reclamation projects,and has accumulated some engineering construction experience in many years of reclamation.Combined with engineering practice,the research summarizes the engineering characteristics and long-term settlement laws of the coastal soft soil of Macau,which is helpful to better understand the impact of the coastal soft soil of Macau on the construction and post-construction effect of the project,and is also very important to ensure the safety of engineering construction in reclamation areas.In this paper,combined with the geotechnical investigation results,indoor geotechnical test data and the foundation treatment case of the Macau reclamation area,the engineering characteristics and settlement deformation laws of the coastal sedimentary soft soil in Macau are studied.Though analyzing the geotechnical test results of the undisturbed soft soil samples in a large number of engineering examples,the soil properties and statistical indicators of the coastal soft soil in Macau are obtained.Long-term in-situ testing and deformation monitoring were carried out on the soft soil foundation reinforced by drainage consolidation method to analyze the deformation characteristics in loading process and after unloading.Though comparing the results which are calculated using multiple settlement prediction methods such as the layered sum method and curve fitting method,appropriate calculation models and parameters are proposed.The main research contents and conclusions are as follows:（1）Macau coastal soft soil has high water content,large pore ratio,fine grain size,large clay content,with some structural strengths.Its compressibility is high,permeability is weak,drainage is slow,sedimentation age is late.The strength obtained by the direct shear test is 10%lower than that of the silt layer in Yangshan Port and 20%lower than that of the silt layer in Wenzhou.（3）The rebound index C_s,the secondary consolidation coefficient C_a and the compression index C_c have good linear relationship.The value of C_s/C_c is between 1/8-1/9,and the value of C_a/C_c is between 0.027-0.037.The unconfined compressive strength value q_uand the triaxial unconsolidated undrained shear strength value have a good linear relationship with the cohesive force C_uu,and the ratio of the two is about 2.0.The triaxial tests reveal that the Macau marine soft soil is strain-hardening,and the pore pressure varies with the compressive stress.（2）The settlement of Macau coastal soft soil is greatly affected by the loading amount and loading time,and has a positive correlation with the loading amount and loading time.When the loading remains unchanged,the settlement gradually increases with the extension of the loading time,but the settlement rate gradually decreases.When the loading cycle is the same,the settlement increases gradually along to the loading increase.When the loading amount is constant,the deposition rate in the same loading period is"from fast to slow".As time increases,the deposition rate gradually stabilizes.（3）In the design stage of Soft foundation treatment in Macau Reclamation area,the layer-wise summation method is recommended to estimate the settlement,while the hyperbolic method is recommended to estimate the final settlement and degree of consolidation.In the absence of long-term monitoring data,based on the research results of this paper,it is suggested that the settlement empirical coefficient m_s in the layer-wise summation method should be 1.17.（4）Through the soft ground treatment in Macau east fill area,the engineering geological properties of the foundation are improved obviously,and the strength of the foundation is improved obviously.The monitoring data of the loading period and the dead-load period play a guiding role in controlling the loading rate and unloading time.