Evaluation of the effects of EPS composite soil replacement on the dynamic performance of caisson structure using shaking table tests

The seismic performance of a caisson structure under two types of models with a saturated sandy foundation(CSS)and an expanded polystyrene(EPS)composite soil foundation(CES)are studied using shaking table tests.The macro phenomena of the two different foundation models are described and analyzed.The effects of the replacement of EPS composite soil on seismic-induced liquefaction of backfill and the dynamic performance of a caisson structure are evaluated in detail.The results show that the excess pore water pressure generation in the CES is significantly slower than that in the CSS during the shaking.The dynamic earth pressure acting on the caisson has a triangular shape.The response of horizontal acceleration,displacement,settlement,and rotation angle of the caisson in the CES is smaller than that in the CSS,which means the caisson in the CES has a better seismic performance.Furthermore,the out-of-phase phenomenon between dynamic earth thrust and inertial force in the CES is more obvious than that in the CSS,which is beneficial to reduce the lateral force and improve the stability of the caisson structure.

A practical constitutive theory based on egg-shaped function in elasto-plastic modeling for soft clay

An exploratory discussion is presented on the application of egg-shaped function in elasto-plastic constitutive analysis for soft clay.Two main tasks of the paper are:1)to propose a complete yield criterion based on egg-shaped function and supplement its definition in the deviatoric section,and then a yield criterion suitable for 3D stress conditions is obtained;2)to elaborate its numerical implementation based on the drained triaxial tests.During the above discussion,a non-associated flow rule is proposed,in which the stress-dilatancy relationship in most classical theory is replaced by a linear dependence between the stress state parameterηand the rotation angleγof the plastic potential surface.Thereafter,isotropic and kinematic hardening behavior is considered by employing the hardening parameter H,which can be expressed as the function of plastic work Wp.Finally,comparisons between numerical results and test data on Taizhou soft clay are made to verify the effectiveness of the proposed model.

Numerical analysis of the influence of a river on tunnelling-induced ground deformation in soft soil

When tunnels are constructed in coastal cities,they will inevitably undercross a river.Exploring the influence of rivers on tunnelling-induced deformation in costal soft soil is of great significance for controlling excessive settlement and protecting surrounding buildings.This paper presents a case study of twin tunnels undercrossing a river in soft soil in Hangzhou,China.The soft soil of Hangzhou refers to cohesive soil in a soft plastic or fluid plastic state with high natural water content,high compressibility,low bearing capacity,and low shear strength.Considering the influence of the river,the research region was divided into two parts,inside and outside the river-affected area,based on monitoring data of the Zizhi Tunnel.The development law of surface settlement is divided into three stages.In the first and second stages,the surface settlement within and outside the river-affected area showed a similar trend:the settlement increased and the growth rate of settlement in the second stage was smaller within the river-affected area.In the third stage,the surface settlement continued to increase within the river-affected area,while it converged outside the river-affected area.Within the river-affected area,there was an asynchronization of the sinking rate and stability of vault settlements and surface settlements.A numerical model was established by simulating different reinforcements of the tunnel.The numerical model revealed that the ground movement is influenced by the distribution and amount of the excess pore water pressure.The excess pore pressure was concentrated mostly in the range of 1.0H_(t)-3.0H_(t)(H_(t) is the tunnel height)before the tunnel face,especially within the river-affected area.Inside the river-affected area,the dissipation of excess pore water pressure needs more time,leading to slow stabilization of surface settlement.When undercrossing a river,a cofferdam is necessary to reduce excessive ground deformation by dispersing the distribution of excess pore water pressure.

Experimental study of the bearing capacity of a drainage pipe pile under vacuum consolidation

In this study,we propose a drainage pipe pile under vacuum consolidation to integrate foundation treatment and pile foundation engineering in soft soil areas.To study its bearing capacity characteristics and foundation treatment performance,single pile static load tests,vane shear tests,and water content tests were carried out for ordinary piles,perforated piles,and drainage pipe piles under conditions of static and vacuum consolidation.Based on the results,the concept of strong and weak reinforcement areas was proposed and used for bearing capacity prediction.The results showed that the drainage pipe pile did not become silted under vacuum consolidation.The single pile bearing capacity was much higher than that of an ordinary pile,and the pile side friction was exerted mainly in the middle and lower parts.Good results were achieved using the shear strength at the junction of the strong and weak reinforcement areas to estimate the ultimate bearing capacity of a single pile.This study provided important insights into the design and construction of drainage pipe piles in a soft soil foundation.