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Crack is one of the important factors affecting the engineering characteristics of expansive rock and soil. In order to study the evolution characteristics and cracking mechanism of red beds in Central Sichuan during seepage and swelling, multiple groups of cracking tests are conducted under different initial states with a self-made device. In addition, combining swelling-softening mechanism of expansive rock and numerical analysis, the swelling-cracking mechanism is studied. The following research results are obtained. (1) The evolution process of swelling cracks is divided into three stages: the generation stage, the rapid development stage, and the stabilization stage. In the rapid development stage, the increase in the crack degree accounts for 90% of the whole process. (2) The final crack degree of the sample is related to the initial water content, water absorption method, and clay mineral content. The lower the initial water content, the greater the final crack degree of the sample. The final crack degree under the soaking water absorption method is greater than that under the capillary water absorption method, and the final crack degree of mudstone is greater than that of argillaceous sandstone and sandstone. (3) The development of swelling cracks is controlled by three significant values of water absorption, which are w 1 , w 2 , and w 3 , respectively, representing the beginning of cracking, the starting of the rapid development stage, and the starting of the stabilization stage. Among them, w 2 is of great significance in engineering practice. It shows that the development of cracks has entered a stage of rapid development, and the crack degree in this stage will increase exponentially with water absorption. (4) Uneven water absorption and uneven distribution of clay minerals lead to uneven swelling of expansive rock, which in turn generates swelling stress. Under the combined action of swelling stress and water swelling-softening, the internal structure of the rock is destroyed, leading to the generation and development of the cracks. Due to the different causes of uneven expansion, the mechanical mechanism of cracking and the shape of the resulting cracks will be different.

A high-speed railway must support fast-moving vehicles and have strict low-deformation requirements. However, many high-speed railways encounter the problem of abnormal subgrade deformation caused by expansive rocks. In this study, the Neijiangbei station of the Chengdu-Chongqing high-speed railway in Southwest China, where the subgrade has undergone continuous and stable uplift during the construction and operation periods, was considered as an example. The Jurassic red-bed mudstone widely distributed in this area is a typical expansive rock, and its swelling effect is the main cause behind the uplift of the subgrade. Results of water-absorption tests, disintegration tests, and expansion tests indicate that the red-bed mudstone is characterized by easy disintegration, slow water absorption, and long-term swelling. A decoupling analysis method for the seepage and swelling of red-bed mudstone was proposed to simulate the water infiltration through the fissures and the temporal and spatial changes in the swelling. Using monitoring data, an inversion analysis of the high-speed railway subgrade uplift was conducted, and the subgrade deformation was predicted. The results suggest that the main changed area of the moisture-content field in the rock formation was a small area near the fissure layer. The moisture content of the mudstone increased rapidly in the first few years of infiltration and increased slowly over subsequent decades. Correspondingly, the subgrade uplift increased rapidly in the first few years after excavation owing to the swelling of the mudstone; thereafter, the growth rate decreased, but the subgrade uplift maintained long-term continuous growth for several decades.

The Anqing group clay gravel layer is a special geological body composed of gravel and clay. In excavation projects, involving this soil, such a gravel layer, is prone to slope collapse and instability under the influence of rainfall. To clearly understand the failure mechanism and influencing factors of clay gravel slopes, an indoor artificial rainfall erosion model testing was carried out to analyse the effect of various slope ratios, gravel contents, and rainfall intensities. The slope erosion damage form, runoff rate, infiltration rate, scoured material, and slope stability of the clay gravel slope were studied. The test results show that sloping surfaces of the gentle slope were mainly damaged by erosion, and the degree of damage gradually increased from the top to the bottom of the sloping surface; however, the stability of the surface was good. In the case of the sloping surface layer of the steep slope, large-scale landslides occurred, and the stability of the surface was poor. When the gravel content was small, the surface failure was manifested as a gully failure. When the gravel content was large, it was manifested as a “layer-by-layer sliding” failure. The degree of influence of different conditions on the stable runoff rate was as follows: rainfall intensity>slope ratio>gravel content. The degree of influence of the parameters on the stable infiltration rate was as follows: slope ratio>rainfall intensity>gravel content. On gentle slopes, the total mass of the scoured material was inversely proportional to the gravel content and directly proportional to the rainfall intensity; on a steep slope, the total mass of the scoured material increased with an increase in the rainfall intensity and gravel content. Moreover, the slope ratio was the key influencing factor to decide whether there was gravel in the scoured material.

To reduce the difficulties associated with dynamic constitutive models, a model was established for soil in this study based on hypoelasticity. The stress-strain relationship in soil under a cyclic load was divided into three stages: initial loading, unloading, and reloading. The stress-strain relationship in each stage was ascertained using a hyperbolic equation. On this basis, the physical significance of the parameters in the model and their method of determination were described. The effects of the parameters on the stress-strain relationship were investigated and the integration algorithm of the model was established. Finally, the rationality of the proposed model was verified by conducting triaxial tests under conventional and cyclic loads. The results show that the model is able to adequately demonstrate all the stress-strain relations in the soil under both static and dynamic loads.

In this study, the characteristics of self-absorption cracking and its micro-mechanism in the dry state of red mudstone in central Sichuan in the southwestern region were examined using a self-designed water absorption device combined with the digital speckle correlation method (DSCM), scanning electron microscopy, X-ray diffraction experiments, mercury intrusion experiments, and other methods. The results indicated theta compared with an alkaline environment, an acidic environment resulted in the self-absorption and cracking of mudstone. The maximum water absorption rate of mudstone and fracture rate in a pH of 3 were determined as 15.77 and 18.909%, respectively; whereas for pH = 11, they were 11.71 and 7.111%, respectively. In the acidic environment, the maximum combined displacement value and maximum principal strain value of mudstone self-priming and swelling evolution were both greater than in an alkaline environment. Simultaneously, in the former, the moisture absorption failure characteristics of mudstone exhibited increased swelling strain zones and swelling cores. The three possible mechanisms by which pH affects the expansion of mudstone hygroscopic fissures were proposed: hydration-expansion softening, adsorption-wedge failure, and humidity stress field. However, it was found that the solutions with different pH values may affect these three microscopic mechanisms through the following four physical or chemical processes: mineral dissolution, ion absorption and exchange, particle association, and pore change. The results of this study are expected to be of significance and aid in roadbed design, tunnel support, slope treatment, and other projects in the southwest region.

In the Nanyang section of the midroute of the South-to-North Water Transfer Project, the expansive soil is often used as a filler for high-fill channels. After the channel is stabilized, the expansive soil undergoes creep deformation over time. Studying the creep characteristics of expansive soils in different environments is particularly important for evaluating the safe operation of high-fill channels. In the current study, the creep test of expansive soil under different moisture content and dry density was carried out. It is proposed that the slope of the fitted straight line in the compression curve of the expansive soil can be used to represent the secondary consolidation coefficient of unsaturated expansive soil, and the variation law of the secondary consolidation coefficient under different environmental factors is obtained. The modified Bjerrum calculation method considering the influence of additional load and lateral deformation yields the postexpansion soil settlement curve model to determine the control index range of the project site. Moreover, it is also observed that the secondary consolidation coefficient of unsaturated expansive soil increases with the increase of moisture content and decreases with the increase of dry density. The coefficient of secondary compression of unsaturated expansive soil is linearly related to dry density and moisture content. After the preconsolidation treatment of the expansive soil, when the load level is less than the preload, the secondary consolidation coefficient is smaller, otherwise the secondary consolidation coefficient is larger.

An improved method, which combines in situ measured settlement data, hyperbolic method, and deep lateral displacement rate, is presented in this study to predict the consolidation and stability of the ground, which can be used in conducting staged filling construction on soft subsoil. A case history of a highway embankment construction in a tidal flat with thick mucky clay is studied in Xia Pu, China. Preloading with the prefabricated vertical drain method is adopted to accelerate the consolidation of a subgrade. The field behavior of soft ground under filling load is observed through in situ monitoring sensors in four typical sections. The final ground settlement in each stage is determined using the field monitoring data based on the hyperbolic settlement prediction method. For each stage of graded filling load, the ground settlement with a strain consolidation degree of 95% is defined as the standard settlement, and the corresponding settlement time is set as the standard settlement time. The preloading period is estimated according to the standard settlement time. The deep lateral displacement rate of the ground is monitored to control the stability of the foundation and recommended to guide the embankment construction. Results indicate that the presented method can predict the preloading time of graded filling, reduce the frequency of observation, and ensure the consolidation and stability of the ground.

Large-scale physical model test on expansive soil slope at a shallow depth is conducted with the aim of monitoring moisture content and swelling deformation. In this paper, a wedge-shaped model box with a bevel at the bottom was developed to reflect the actual channel slope in the South-to-North Water Transfer Project. The results provide an improved understanding of the physical behavior and failure mode of a saturated-unsaturated expansive soil slope subjected to moisture content variation. Showing that, after rainfall, the surface soil quickly became saturated, with the deeper soil moisture remaining unchanged. Infiltration depth, speed, and saturation region reduced with the increasing height along the slope. Surface displacement increased from slope foot to slope shoulder, and significantly attenuated towards the depth. Horizontal displacement was about 1/3–1/2 of the vertical displacement. The larger the increment of the soil moisture, the greater the surface deformation. Soil showed dehydration shrinkage with fissures first appearing in the soil surface and expands downward with continuing evaporation. The junction of saturated-unsaturated zone and the wet-dry interface were the areas of stress concentration. Swelling effect led to stress field redistribution in the expansive soil slope, and it was the most important factor causing expansive soil shallow slope failure.

The facing design of soil nail walls against flexure, punching shear, and headed-stud tensile limit states has been rarely studied within the reliability-based design framework. This study...

Fissured expansive soils were widely distributed in the South-to-North Water Transfer Project. Most of the fissures were filled with clay, which controlled the stability of the slope. With the method of layered filling&mdash, bevel cutting&mdash, refilling and a modular design idea, the sample with a filled fissure preparation device for triaxial test was designed. After setting the filled fissures of gray-green clay in the expansive soil, triaxial tests were carried out for the samples with no filled fissures and with filled fissures with inclination angles of 15&deg, 30&deg, and 45&deg, Then, considering the spatial distribution and the strength of the filled fissures in the slope, the stability analysis method for the expansive soil slope with filled fissures was proposed. The stability of a typical slope in Nanyang was analyzed. The results show that the c of expansive soil with filled fissures was about 12 to 15 kPa and the &phi, was 3&deg, to 6&deg, Filled fissures had an attenuation effect on the strength of the expansive soil. The larger the inclination of filled fissures, the more significant the effect of soil strength attenuation. The fissured slope stability was controlled by the filled fissures. The sliding surface was affected by the vertical fissures on the top of the slope and the slow-inclined long-large fissures in the slope, and the shape of the sliding surface was a broken line, which was basically consistent with the actual landslide.

To deeply understand the mechanical behaviors and evolution of nano-scale liquid bridge, the influence of variables such as initial particle spacing, the distance between solid-liquid surface and temperature on three-dimensional kaolinite-water system were analyzed by a combination of experiment, molecular simulation and theoretical equation. Studies have shown that initial distance between solid-liquid surface was the most sensitive to the breakage of liquid bridges, and the critical range was 15–20 A. Due to the obvious stratification of water molecules, the calculated results were larger by Young-Laplace equation. By using surface energy to avoid contact angle and surface tension that are poorly defined on the microscopic level, the revised theoretical results were confirmed to be in good agreement with simulated data. The capillary force of kaolinite particles was mainly attributed to the contribution of negative pore water pressure, and nano-size liquid bridge can be considered to still obey the Young-Laplace equation. This work is crucial for the subsequent research on the water-holding properties of unsaturated soils.

High-speed railway engineering in mountainous areas suffers from occasional poor geological conditions, rugged topography, and complex hydrographic conditions. It is an important means of ensuring its safe operation to conduct real-time remote monitoring and analysis of the subgrade structure condition. Through analysing the stress characteristics of the mountainous subgrade, a complete monitoring system has been built and a corresponding software platform for datum acquisition and analysis has also been developed. After selecting a typical mountainous high-speed railway subgrade located in Hunan Province as the test section, the real-time monitoring of the subgrade structure in a static settling period, joint commissioning period, and an operational period was conducted and the primary condition datum was obtained. It is found that the dynamic response parameters have relatively slow attenuation velocities and the influencing depth of the high-speed train loads was about 4–5 m; when the structural state of the mountainous subgrade is healthy, subgrade deformations are small and, compared with the dynamic response datum of the subgrade in plain areas, the dynamic response of the mountainous high-speed railway subgrade was consistent. However, the long-term dynamic response and deformation of such mountainous subgrades still needs to be monitored, and analysed, continually.

Fissured strong expansive soil swelling behavior is complicated. In this paper, considering the typical filling fissures of strong expansive soils, fissure rate Kr was given as a fissure content quantitative indicator. A prediction model was developed for the prediction of swelling effect on a fissured strong expansive soil using BP neural network approach, the gradient descent and the conjugate gradient algorithm methods were adopted. The actual test and predicted results of the two algorithms network showed high degree of similarity. The BP neural network model described by fissure rate, dry density, initial moisture content and overlying load can meet the precision requirements. The conjugate gradient method when compared with the gradient descent method, has a significantly improved calculation efficiency, the convergence rate is about 30 times lesser than the latter, therefore, conjugate gradient algorithm BP network prediction model for swelling in the actual engineering calculation has obvious advantages.

The mechanical properties of subgrade filling materials are significantly weakened when subjected to water softening effects and dynamic loads, which causes significant changes in the dynamic response of the subgrade. Research on these changes helps engineers to quickly determine the state of health of the subgrade structure to ensure safe operation of traffic projects. For this reason, this paper first presents a subgrade model test system for in situ testing that can simulate water immersion. Using this as a basis, dynamic response tests are conducted on the subgrade under normal and different water-immersion conditions. The rules governing the variation in the dynamic response of the subgrade under different conditions are thereby obtained. The results show that: (1) the range of influence of the water-immersion effect on the dynamic response of the subgrade is concentrated in the main range affected by external loads; (2) the dynamic parameters (acceleration and dynamic pressure) appear to decrease under water-immersion conditions; (3) there is a diffusion effect in the transmission of the dynamic parameters: at locations far from the vibrating center, there are circumstances wherein the dynamic parameters in the deeper parts are larger than those in shallower parts.

Aiming at the problem that the construction process of a water conservancy and hydropower project will affect the stability of the slope and its surrounding buildings, a numerical simulation method is used to carry out a numerical analysis of the displacement and stress diffusion of a junction engineering slope and its nearby transmission tower. The results show that: the deeper the excavation depth of the slope, the greater the rebound of the excavated surface; after excavation, the horizontal displacement of the facing surface of the slope under the support of the continuous wall is small, and the slope can maintain stability. The stress ratio method determines the distance between the excavation surface and the tower foundation, and the slope excavation can be carried out smoothly while ensuring the stability of the tower foundation.

The finite element software and finite difference software are used to complete the dynamic simulation of the excavation process and the influence of the foundation pit on the additional deformation of the subway tunnel. The horizontal displacement occurs around the foundation pit due to the excavation, and at the bottom there is vertical uplift deformation. The deformation of the subway tunnel occurred due to the unloading deformation at the bottom of the foundation pit, and the whole tunnel is deformed to the foundation pit. Moreover, the tunnel deformation near the foundation pit is larger than the tunnel deformation far away from the foundation pit.

Integration algorithm is a key to ensure the better application of the dynamic constitutive model. As for the bounding surface model based on swell–shrink rules in this paper, an explicit integration algorithm based on sub-stepping and error control scheme has be described in detail. For being adaptable to the constitutive model, several modifications have been made. The modified explicit algorithm includes two procedures: the first procedure is the second-order forward modified Euler scheme with sub-stepping and error control; the second procedure is the stress correction. However, due to the shrink rule of the bounding surface, the second procedure is not needed at the unloading phase. Finally, several numerical simulations have been conducted for assessing the performance of the explicit algorithm, which demonstrates that the corresponding algorithm is stable and accurate, and can simulate the mechanical characteristics of the clay pretty well.

Geotechnical investigation and dynamic analysis of gas turbine foundation, coupled with the present turbine foundation design codes and Standards were considered for the analytical design of gas turbine foundation. This work was carried out to establish a calculation method that will consider all the fundamental modes of vibration with calculated mass participation during gas turbine foundation design, with the aim of limiting the vibration response amplitude to a specified machine or human tolerance. This was done by creating a model for calculating fundamental modes of vibration. The dynamic analysis of the foundation was carried out through Finite element and the structural analysis program STAAD Pro 2007 and DYNA5.Pile foundation was found to be suitable for the foundation of the study area, to ensure that the vibrating amplitude and the frequencies are maintained below the threshold that may affect human and the serviceability of the gas turbine machine. The dynamic analysis results meet with the turbine foundation code of standard.

The measured settlement curves of high-speed railway are presented with the characteristic of "small scale, large fluctuations", which is difficult to reach the requirements of curve regression coefficient with 0.92 on specification . This was done by adopting the method of mathematical simulation and hyperbola fitting to study the change rules of correlation coefficient on subgrade simulated settlement curve, under different conditions. From the analysis result, smaller value of parameter a and b, will have great influence on curve correlation coefficient, otherwise, the parameter c becomes the major factor; When c value is greater than 1.5mm, the parameter b becomes the major factor; Considering the premise, it is recommended that in order to observe the total settlement amount for working point

Sand liquefaction is a common seismic hazard of foundation. In order to investigate the hazard evaluation criteria of liquefaction of sand soil foundation, a research was made to study different methods of discriminatin g sand liquefaction with the reference of the results of recent related studies in this area. Through comparisons, the study finds out that the standard penetration test (SPT) is a relative reliable method to determine liquefaction. Moreover, based on the related researches about the estimation and hazard evaluation of sand liquefaction, the procedures and standards of the liquefaction hazard evaluation of sand soil foundation of horizontal ground have been put forward at the end through this study.