For the construction and safe operation of major infrastructure in coastal cities, the impact of regional land subsidence that has occurred or is slowly proceeding deserves attention. Previous studies have mainly focused on the surrounding land subsidence caused during construction or operation, as well as the superposition effect of land subsidence caused by groundwater extraction. However, research on the different impacts of damage due to land subsidence in the construction and operation of urban infrastructure needs to be carried out according to the actual geological environmental conditions, reflected in parameters such as the soil properties and common loads. Numerical simulation cannot fully reflect the details of reality; however, it can avoid the influence of other conditions to focus on different factors influencing land subsidence and thus highlight the contribution of a single factor influencing land subsidence. Therefore, in this paper, we adopt field measurement data and carry out a numerical simulation analysis of different influencing factors. First, taking the Ningbo Jiangdong subsidence center (now located in Yinzhou District) as an example, area growth, cumulative subsidence and the occurrence and development of the subsidence rate of a typical urban subsidence funnel area are analyzed. Then, taking the Ningbo Chunxiao–Meishan area as an example, based on the physical and mechanical characteristics of the main soil layers in the coastal reclamation area, a numerical analysis of the self-weight/backfill and surcharge consolidation settlement of the soil layer (considering the water permeability/impermeability of the bottom surface) and a numerical analysis of the nonuniform settlement caused by pile foundation engineering are carried out. Finally, the Ximenkou–Gulou area is taken as the analysis object. Numerical simulation of metro tunnel pipeline deformation is carried out considering uniform/nonuniform settlement. The results show that the comprehensive prohibition of groundwater exploitation is beneficial to slow the land subsidence rate, while the sedimentation of silty clay in Layer 4 (muddy clay) is the largest among all the soil layers. Compared with uniform settlement, nonuniform settlement is more likely to cause connection failure between tunnel segments. The above research results can provide references for the prevention and control of land subsidence and thus the safe operation of major infrastructure.

Excavations near an existing tunnel are often encountered in underground construction. The influence of the excavation on the adjacent tunnels is not yet fully understood. This study presented a centrifugal model test about excavation next to existing tunnels in soft soil foundation. The bending moment of diaphragm wall, surface settlement, tunnel deformation, and earth pressure around the tunnel were mainly studied. The influence of tunnel location is further studied by numerical simulation. During the stabilization stage of foundation pit, the diaphragm walls present convex deformation towards foundation pit, and the surface settlement outside the diaphragm wall appears to be the concave groove type. During the overexcavation stage, the diaphragm walls are almost damaged, and the shear bands are nearly tangent to the tunnels. The displacement of the tunnels and the surface settlement rapidly increase. The deformation of the diaphragm wall and the surface settlement are limited by the existing tunnel. The numerical results indicate that the change of tunnel location has little effect on the retaining wall but an obvious effect on the tunnel itself.

As an important and basic course of civil engineering, soil mechanics has a wide range of contents and complex basic concepts, which puts forward higher requirements for students' theoretical level besides theoretical mechanics, material mechanics, structural mechanics and other knowledge. Under the current background of new engineering, applied colleges and universities have put forward new requirements for engineering students. As a basic course of civil engineering, soil mechanics is of great significance to the training of students majoring in civil engineering. Aiming at some problems in soil mechanics education in recent years, based on CDIO mode, combined with the virtual simulation technology of BIM and the connotation of higher soil mechanics, the solutions are put forward in order to provide reference for the teaching reform of soil mechanics in colleges and universities.

Based on the conclusion that the effect of normal pressure on temperature distribution and the effect of temperature on soil–concrete interface friction are negligible, the finite-element model was established to analyse the characteristics of a pile enduring cyclic temperatures, adopting the sequential thermal coupling method. The temperature-induced additional displacements and axial forces along the pile depth were analysed, and the influences of temperature on the additional axial force distribution of the energy pile were analysed with different pile head loads. The analysis results showed that cyclic heating and natural cooling will lead to additional axial pile forces and displacements along the pile depth. It was concluded that loads applied at the energy pile top should not be heavier than the value at which plastic deformation at the pile end soil would be initiated and at which non-linear pile top settlement occurred.

Prestressed pipe piles with ribs are new type of pile foundations; and they have better vertical bearing capacity than ordinary pipe pile. But there are few theoretical researches on their bearing characteristics. Based on field measurement comparative test analysis, the bearing characteristics of ribbed bamboo joint piles are studied by ABAQUS finite element method. The relationship between the vertical compressive bearing capacity of ribbed bamboo joint pile and the parameters such as modulus ratio of pile to soil, the ratio of rib to diameter and the friction coefficient are analyzed. The analysis results show that, the vertical compressive bearing capacity increase of ribbed bamboo joint pile is corresponding to the number of ribs. As the pile-soil modulus ratio increasing, the ultimate bearing capacity of composite pile with rib decreased. With the increase of rib diameter ratio, the ultimate bearing capacity firstly increases and then decreases. As the friction coefficient increasing, the ultimate bearing capacity and bearing capacity enhancement coefficient increase linearly. Based on the calculation and analysis, the effected factors are analyzed, so as to provide theoretical basis for the relevant engineering design.

In order to reveal the seepage characteristics of Ningbo marine soft clay under various hydraulic gradient,confining pressure and void ratio,eight series of constant head seepage tests were performed on both undisturbed and remolded soil samples utilizing the GDS apparatus.Fitting study of the widely used seepage models in academic field was conducted by the test results.It is shown that seepage coefficients of test samples decrease nonlinearly with decreasing void ratio,which behave more obviously on remolded soil samples.Similar seepage behaviors were obtained from both remolded and undisturbed soils as well,and the test results agreed well with fitting lines of the four existing seepage models.A new nonlinear empirical model was proposed,and test data of ten kinds of soils were collected to investigate its rationality and applicability.The comparison research on fitting results shows that the new model is better used than four existing seepage models,and the application of this new model turns to worth further research.

Ground settlement laws and its control measures attract comprehensive attention in urban rail transit construction, particularly in soft soil area with shield tunneling method.Phase 1 of No.1 rail transit project in Ningbo is constructed by earth pressure balance (EPB) tunneling methods.In this paper, the horizontal ground settlement caused by single tunnel construction is studied by site measurement results.Correlation analysis of tunnel depth, grouting quantity, cover earth thickness, construction parameters and maximum settlement value is conducted.In the end, measurement data are linear fitted by least square method.Compared Peck formula with the result, the parameter selection and its applicability in Ningbo district are discussed.The research shows that the maximum width value of horizontal influence area can be up to 60 meters owing to the soft soil layer.Widths of settlement tank have mostly ranged between 15 and 20 meters.The maximum surface settlement has great linear relationship with grouting quantity, driving speed of shield machine and torque of cutter.But the depth of the tunnel has weak interaction with maximum ground settlement.Abovementioned research findings can provide technical support and theoretical guidance for the following rail transit construction in Ningbo.

One-dimensional consolidation equation of unsaturated soils was derived in order to solve this special case of consolidation. The presented equation, not similar to Terzaghi's equation, is a type of absolute nonlinear partial differential equation, and it was solved by finite difference method. An example was analyzed and the case of incompressible fluid consolidation was compared. Finally the experimental results from laboratory tests reported in the literature, was fitted by the presented equation, and the agreement was good. The results show that (1) the process of pore-air pressure dissipation is similar to that of pore-water pressure of saturated soils; (2) the compressibility of pore fluid is not an advantageous factor to quicken the consolidation; (3) the presented equation is effective to analyze the process of consolidation of unsaturated soils which consolidate mainly due to the dissipation of pore-air pressure.

Research on the consolidation behavior for Ningbo soft clay was carried out under different considerations for the weight of soils.On the basis of finite strain consolidation equation derived by considering,the governing equations for numerical analysis were derived by taking the nonlinear compressibility and nonlinear permeability of soils into consideration.Based on the experimental data,the governing equations were solved with the finite element method.It can be found that the calculation results considering the weight of soils simply are very close to the ones considering the weight of soils accurately.However, the dissipation rate of excess pore water pressure is underestimated without considering the weight of soils.Influence of the weight of soils on the dissipation rate of excess pore water pressure is quite obvious in the intermediate stage of consolidation.In this stage,the greater the external load or the thickness of soils is,the greater the influence of the weight of soils is.In finite strain consolidation analysis,the weight of soils can be considered simply but it can not be completely ignored in most cases.

A high-rise building with pile-raft foundation suddenly experienced extraordinary settlements and seriously tilted after 6 years of use in Wenzhou, a city in southeastern China. Some investigations were conducted and several potential causal factors were analyzed to determine the cause of the distress. The results indicated that the inadequate bearing capacity of the pile foundation was the reason for the extraordinary settlement. Inappropriate structure type selection and structural arrangement made the building sensitive to earthquake-triggered loading and prone to tilt. Remedial measures were applied to address the causal factors identified. Because of the low bearing capacity of the pile foundation, unloading was first performed and then the pile foundation was strengthened using steel pipe piles driven by anchor bolts. To address the inappropriate structure type and arrangement, the building was retrofitted to resist earthquakes. Observation results showed that the remedial measures took effect and the settlement (and tilt) of the building was completely controlled. (C) 2014 American Society of Civil Engineers.

To describe the time-dependent behavior of soft clay, this paper extended one-dimensional Nishihara model to three-dimensional stress state based on the framework of Perzyna's overstress theory and modified cam-clay model. The yield criterion of modified cam-clay model was used to describe the plastic properties of soft clay, and the overstress theory was used to describe the strain rate effect. Triaxial rheological tests were carried out on Ningbo soft clay and the rheological characteristics were studied. Based on laboratory results, the parameters of proposed model were determined by curve fitting, which show that this model is suitable for the rheological characteristics of Ningbo soft clay. The analysis of parameters shows that, the value of parameters changes slightly with different deviatoric stress when the confining pressure was constant, but changes notably with the increase of confining pressure. A user material subroutine of the proposed constitutive mode was coded on the platform of the FEM software ABAQUS and verified by triaxial compression of soil column. A plain strain problem was computed to analyze the rheological consolidation properties of soft clay, in which the rheological effect and the finite strain effect were considered.

In the research field of ground water, hydraulic gradient is studied for decades. In the consolidation field, hydraulic gradient is yet to be investigated as an important hydraulic variable. So, the variation of hydraulic gradient in nonlinear finite strain consolidation was focused on in this work. Based on lab tests, the nonlinear compressibility and nonlinear permeability of Ningbo soft clay were obtained. Then, a strongly nonlinear governing equation was derived and it was solved with the finite element method.Afterwards, the numerical analysis was performed and it was verified with the existing experiment for Hong Kong marine clay. It can be found that the variation of hydraulic gradient is closely related to the magnitude of external load and the depth in soils. It is interesting that the absolute value of hydraulic gradient(AVHG) increases rapidly first and then decreases gradually after reaching the maximum at different depths of soils. Furthermore, the changing curves of AVHG can be roughly divided into five phases. This five-phase model can be employed to study the migration of pore water during consolidation.

This paper aims to analyze nonlinear finite strain consolidation with secondary consolidation behavior. On the basis of some assumptions about the secondary consolidation behavior, the continuity equation of pore water in Gibson’s consolidation theory is modified. Taking the nonlinear compressibility and nonlinear permeability of soils into consideration, the governing equation for finite strain consolidation analysis is derived. Based on the experimental data of Hangzhou soft clay samples, the new governing equation is solved with the finite element method. Afterwards, the calculation results of this new method and other two methods are compared. It can be found that Gibson’s method may underestimate the excess pore water pressure during primary consolidation. The new method which takes the secondary consolidation behavior, the nonlinear compressibility, and nonlinear permeability of soils into consideration can precisely estimate the settlement rate and the final settlement of Hangzhou soft clay sample.

In reduced coordinates,a one-dimensional finite strain consolidation equation for saturated soils is derived with threshold gradient.The new equation shows that threshold gradient and variation of permeability coefficient with void ratio should be considered.Using the two empirical relations proposed by Mesri,a new governing equation is obtained.Then three examples are analyzed by applying the partial differential finite element software FlexPDE.The results show that excess pore water pressure slightly increases at the beginning of consolidation progress and then dissipates.This phenomenon is similar to the Mandel-Cryer effect.It will be more significant if threshold gradient is greater or location of soil is deeper.Even though the maximum excess pore water pressure increases when threshold gradient increases,the increment is very small.It is too difficult for us to observe the tiny increments in laboratory and practical engineerings.Therefore,there is no need to consider threshold gradient in vast majority of actual projects.In other words,classical Darcy's law is applicable.This research shows that it is very important to consider threshold gradient,geometric nonlinearity and material nonlinearity in studying the Mandel-Cryer effect so as to further understand the consolidation properties of saturated soils.

Taking threshold gradient and variation of permeability coefficient with void ratio into account, a 1-D finite strain consolidation equation for saturated soils can be derived in reduced coordinate. Using the two empirical relations proposed by Mesri, a new governing equation is obtained. On the basis of test data for Ningbo soft clay, an example is analyzed by applying finite element method. The results show that excess pore water pressure at different depths slightly increases at the beginning of consolidation progress and then dissipates gradually after reaching the maximum. This phenomenon is similar to Mandel-Cryer effect. It will be more significant if threshold gradient is greater or location of soil is deeper. It is worth noting that the increment of excess pore water pressure is too tiny to observe in laboratory experiments and engineering practices. Therefore, there is no need to consider threshold gradient in majority of actual projects. In other words, classical Darcy's law is applicable. Our research shows that it is important to consider threshold gradient, geometric nonlinearity and material nonlinearity in the study of Mandel-Cryer effect.

One-dimensional consolidation rheological tests and triaxial rheological tests were conducted in order to analyze the rheological characteristics and rheological model of Ningbo soft soil.The results of rheological tests showed that the process of rheology was weaken by the lateral confinement in consolidation rheological tests,and the equal-time stress-strain curves deviated to the stress axis;while in triaxial rheological tests,the process of rheology adequately developed,and the equal-time stress-strain curves deviated to the strain axis,which better revealed the rheological characteristics of soft soil.The stress-strain relationship of one-dimensional Nishihara model was extended to three-dimension,and the yield function of modified Cambridge model was used to describe the plastic yield property.The calculation formula of creep strain with const load was developed,with which the triaxial rheological tests datas of Ningbo soft soil were fitted,and the parameters of Nishihara model were determined.Results show that the model is suitable for the rheological law of Ningbo soft soil.

Safety assessment of highway slopes is important to highway design and construction. For the mountain highways, slope problems are concerned by engineers. In Ningbo area, highway slope disasters frequently occur due to heavy rainfalls and frequent typhoons. In the paper, 7 provincial highways through the mountain area in Ningbo are investigated. Based on the investigated data of 90 slopes, the disaster problems are analyzed. Based on analysis of main influencing factors of the slope safety, multiply factor assessment system is proposed to evaluate slope safety, then, the safety of the investigated 90 slopes is discussed. Through engineering analogue, the established assessment system is certified, and results suggest that assessment conclusions of the established assessment system basically tally with that of other assessment methods, the system is easy to be accepted by engineers because it is simple and can be operated conveniently.

When using shield driven method to construct tunnels, mechanical properties of injecting cement paste will change at curing age. And then ground settlement will also change because of changes of mechanical properties of injecting cement paste. Based on the first line of Ningbo rail transit, this paper will discuss the effect of ground settlement caused by changes of elastic modulus and Poisson's ratio of injecting cement paste using finite element simulation (FEM) software. The results show that ground settlement will increase if considering changes of elastic modulus, while ground settlement will decrease if considering changes of Poisson's ratio. If changes of elastic modulus and Poisson's ratio are both considered, we will accurately predict ground settlement .The results also show that elastic modulus and Poisson's ratio at early stage of curing age play an important part in ground settlement prediction.

By analyzing the data of O-cell pile testing,new load transfer models before and after post grouting are proposed.The precise conversion method used to load-settlement curve transformation under the O-cell pile testing method is improved,and the influence of continuity of soil on the settlement is considered.The rationality of the proposed models is shown by the practical engineering.Further analysis shows that the the influence of continuity of soil on the settlement of super-long piles is strong,the ultimate bearing capacity with considering the continuity of soil is less than that without,and the improved method is safer.

Rotated branches pile is a new developed pile based on DX pile and squeezed branch pile.They have similar figures and bearing mechanisms to a certain extent.The former is rotated and the latter is squeezed in pile molding,so the bearing behaviors are different.There are problems in calculating bearing capacity of former pile by using the formula of latter pile for a project in Luoyang,a formula of bearing capacity of rotated branches pile is proposed.