Dynamic Soil Stress Research Articles

Full-scale field testing on a highway composite pavement dynamic responses

A series of full-scale field tests were conducted to observe the composite pavement’s dynamic responses subjected to heavy traffic load. The tire contact pressure beneficially influences the dynamic strains and the dynamic stresses of pavement. A typical “M” shape is observed for the distribution of dynamic responses cross lane. The range of dynamic soil stress on roadbed ranges at 20–50kPa, and a non-linear model is presented for the dynamic stress attenuation along subgrade depth. Furthermore, the increasing of truck speed decreases the dynamic responses of composite pavement. This is owing to the viscoelastic property of HMA layer and the resonant frequency. At a lower moving speed, the dominant frequency of heavy truck loading is close to the dominant frequency of HMA layer. This would amplify the vibrations of pavements and consequently result in larger mechanical responses. The experimental findings would be helpful to understand the dynamic performance of composite pavement subjected to heavy traffic load.

Design method of pile-slab structure roadbed of ballastless track on soil subgrade

Pile-slab structure roadbed is a new form of ballastless track for high speed railway. Due to lack of corresponding design code, based on the analysis of its structure characteristics and application requirements, it is proposed to carry out load effect combination according to ultimate limit state and serviceability limit state, and the most unfavorable combination of each state is chosen to carry through design calculation for pile-slab structure. Space model of pile-slab structure can be simplified as a plane frame model, by using the orthogonal test method, and the design parameter of pile-slab structure is optimized. Moreover, based on the engineering background of Suining-Chongqing high-speed railway, the dynamic deformation characteristics of pile-slab structure roadbed are further researched by carrying on the indoor dynamic model test. The test results show that the settlement after construction of subgrade satisfies the requirement of settlement control to build ballastless track on soil subgrade for high-speed railway. Slab structure plays the role of arch shell as load is transmitted from slab to pile, and the vertical dynamic stress of subgrade soil is approximately of “K” form distribution with the depth. The distribution of pile stress is closely related to soil characteristics, which has an upset triangle shape where the large dynamic stress is at the top. Pile compared with soil shares most dynamic stress. Pile structure expands the depth of the dynamic response of subgrade and improves the stress of subgrade soil, and the speed of train has limited effect on dynamic response. These results can provide scientific basis for pile-slab structure roadbed used on soil subgrade.

Comparison of Seismic Responses of Geosynthetically Reinforced Walls with Tire-Derived Aggregates and Granular Backfills

AbstractThis paper reports the seismic responses of geosynthetically reinforced walls with two types of backfills using shake table tests. The backfills are tire-derived aggregates (TDA) and poorly graded sand, respectively. Mechanically stabilized earth (MSE) walls with reinforced TDA backfill have not been fully tested under seismic conditions. In this study, two geosynthetically reinforced walls are tested on a one-dimensional shake table. A section of reduced-scale MSE wall (1.6 m high, 1.5 m deep, and 1.5 m long) is built in a box that is anchored on a shake table that can generate earthquake excitations obtained from actual field recordings. Layers of geogrid are used as reinforcement. The geosynthetic reinforcement is based on static external and internal stability design. In each test, the segmental MSE wall is instrumented with accelerometers, linear variable differential transformers, linear potentiometers, and dynamic soil stress gauges to record the accelerations, wall vertical deformations, h...

Dynamic Response Analysis on Efficacy of CFG-Pile in Different Height Embankment

In order to analyze the effect of embankment height to dynamic stability, Cross-section in the Beijing-Shanghai high-speed railway is chosen and the numerical simulation calculation method is applying. Distributing rules of dynamic displacement and dynamic stress of the subgrade surface and ground surface, attenuation rules of dynamic response and dynamic stress ratio between pile and soil on the vertical section were studied. It shows that the dynamic stress of pile and soil generally attenuates in depth and attenuation of dynamic stress ratio between pile and soil mostly concentrates into the scope of 10 meters beneath the ground. Moreover, with the increment of embankment height and attenuation of dynamic stress in direct proportion to the depth, the dynamic stress transferring to ground surface decrease and the dynamic displacement of ground surface minish. As a result, the scheme of CFG-pile with 3m scheme is superior to that of 2m scheme for enhancing dynamic stability and reducing dynamic displacement and stress in low embankment. It will be instructive to control design and construction for the low embankment in Beijing-Shanghai high-speed railway.

The Effect of CFG-Pile Caps and Cushion to Stability of Embankment

Subgrade diseases are exposed more and more serious with raising speed of existing railway in wide range. Dynamic numerical simulation had been done to analyze the effect of CFG-pile caps and cushion in composite foundation with CFG-pile in low embankment of Beijing-Shanghai high-speed railway. Distribution rules of dynamic displacement and dynamic stress of the subgrade surface and ground surface on the cross section, attenuation rules of dynamic response and dynamic stress ratio between pile and soil on the vertical section were studied. It shows that the dynamic stress of pile and soil generally attenuates in depth and attenuation of dynamic stress ratio between pile and soil mostly concentrates in the scope of 10m beneath the ground and dynamic stress caused by train load is undertaken by the pile. Moreover the scheme of CFG-pile with no pile caps and rigid cushion scheme is superior to that of pile caps and flexible cushion scheme for enhancing dynamic stability and reducing dynamic displacement and stress in low embankment. It will be instructive to control design and construction for the low embankment in Beijing-Shanghai high-speed railway.

Study on dynamic response of saturated soft clay under the subway vibration loading I: instantaneous dynamic response

In this paper, the results of the instantaneous dynamic response of saturated soft clay under the subway vibration loading are presented. Based on the assumption of soil as viscoelastic medium, wave equation under forced vibration of three-dimensional anisotropy is derived, and time–space domain semi-analytical solution is given through Laplace and Fourier transform and their inverse transform using MATALB. Taking Shanghai metro line No. 2 for example, the dynamic monitoring is conducted with embedded earth pressure gauges and pore piezometers around the tunnel, and the horizontal response amplitude of dynamic stress of soil around the tunnel is calculated by the method presented in this paper with the laboratory Global Digital System test apparatus to determine the related calculation parameters. Then, a comparative analysis is made between calculation result and continuous field monitored data, and it is found that the attenuation trend of the two cases agree well with each other both in the horizontal and vertical direction, which indicates that the method presented in this study is reasonable.

Real-Time Diagnosis Method of Compaction State of Subgrade during Dynamic Compaction

Abstract Dynamic compaction (DC) has become a popular method for deep improvement of subgrade. Dynamic settlement is often used as the termination index of DC. However, the index is external and experiential and cannot directly reflect the compaction state of a soil mass. In this regard, this paper presents a method for a real-time diagnosis of compaction state of subgrade, which is based on the analysis of dynamic pore pressure and dynamic soil stress induced by the impact of tamper weight. A field test was conducted to measure the dynamic pore water pressure and soil stress in a road subgrade under DC for expressway widening. After a certain number of compactions, the amplitudes of dynamic stress and pore pressure were stabilized and correlated well with both the compaction degree of soil and the dynamic settlement of ground. The dynamic response of the subgrade under different impact number reflects the variation of stiffness and strength of soil. With the findings the method for determining the optimum compaction number and the optimum single impact energy was presented.