Experimental Study on Consolidation Characteristics of Compacted Loess

The prediction of foundation settlement is an important topic in loess filling engineering. Based on a filled foundation in Yan’an, China, this study explores the consolidation characteristics of compacted loess with different compaction energy and consolidation pressure through consolidation tests, analyzes the strain-time curve and refines the curve within 2 h, separates the primary and secondary consolidations, and obtains the critical time point between the primary and secondary consolidations. Deformation rate S t ′ and cumulative deformation St were introduced to analyze the S t ′ − St curve at the secondary consolidation stage; the secondary consolidation coefficient was employed to describe the secondary consolidation characteristics of compacted loess. According to the secondary consolidation characteristics, a prediction model of loess settlement considering different compaction energy and fill thickness was proposed, and the applicability of the model was further analyzed. The model will facilitate in guiding the design and construction of loess filling engineering.

Consolidation Behavior and Compression Prediction Model of Coastal Cement Soil Modified by Nanoclay

Coastal cement soil modified by nanoclay (NCS) has particular research significance as a modification approach to improve the high compressibility of coastal cement soil (CCS). At curing ages of 7 days and 28 days, consolidation and SEM tests were performed on 6 groups of NCS samples with a nanoclay content between 0% and 10% and 6 groups of CCS samples with a cement content between 10 and 20%, and a compression prediction model was established based on the test results. Test results show that (1) there is a linear interval for the improvement effect of the increment of cement content on the compression of CCS samples. In this test, the cement content in this interval is between 12% and 18%. CCS with a cement content of 18% is preferred. (2) The improvement effect on the compression of the sample is better with a nanoclay content of 4% and 8%, but poor with a content of 2%. At a consolidation pressure between 100 kPa and 800 kPa, NCS with a nanoclay content of 4% is preferred. (3) Adhesion is better with a nanoclay content of 4%, and the filling effect is better with a content of 8%. (4) The cosine-power function-exponential model is established, and the measured data are fitted, and a prediction model for the compression amount of CCS and NCS is established.

Analysis and Application of the Mechanical Properties of the Karst Collapse Column Fillings

The filling material of the karst collapse column (KCC) is easy to be activated by mining. During this process, the mechanical properties of KCC fillings change, and its water resisting capacity constantly deteriorates and thus often leads to water inrush disaster. In this study, the samples of KCC fillings were taken on-site and then were remolded by the consolidation drainage method. The variation laws of the compressive strength, tensile strength, cohesive stress, internal friction angle, and permeability of the filling samples with respect to the consolidation pressure and moisture content were tested and analyzed. Based on an engineering example, the yield and activation and particle loss of the filling material of the KCC are analyzed. A mechanism for the lagging water inrush of KCC in the process of mining is proposed. The main results of the present study can be concluded concisely as follows. (1) The KCC fillings show obvious soft rock characteristics in the process of uniaxial compression and Brazilian split. The ratio of the uniaxial compressive strength to splitting tensile strength is between 12 : 1 and 8 : 1. The larger the consolidation pressure or the smaller the moisture content, the larger the ratio. (2) With the increase of consolidation pressure or the decrease of moisture content, the uniaxial compressive strength, elastic modulus, splitting tensile strength, cohesive stress, and internal friction angle of the filling material of the KCC increase linearly, while its permeability increases exponentially. (3) When the crack field of the surrounding rocks of the stope is connected with the KCC, its filling material will continue to yield, activate, and migrate under the fluid-solid coupling effect and finally result in the lagging water inrush from the KCC.

Influence of a Dynamic Consolidation Force on In Situ Consolidation Quality of Thermoplastic Composite Laminate

For achieving high quality of in situ consolidation in thermoplastic Automated Fiber Placement, an approach is presented in this research work. The approach deals with the combination of material pre-heating and sub-ultrasonic vibration treatment. Therefore, this research work investigates the influence of frequency dependent consolidation pressure on the consolidation quality. A simplified experimental setup was developed that uses resistance electrical heating instead of the laser to establish the thermal consolidation condition in a universal testing machine. Consolidation experiments with frequencies up to 1 kHz were conducted. The manufactured specimens are examined using laser scanning microscopy to evaluate the bonding interface and differential scanning calorimetry to evaluate the degree of crystallinity. Additionally, the vibration-assisted specimens were compared to specimens manufactured with static consolidation pressure only. As a result of the experimental study, the interlaminar pore fraction and degree of compaction show a positive dependency to higher frequencies. The porosity decreases from 0.60% to 0.13% while the degree of compaction increases from 8.64% to 12.49% when increasing the vibration frequency up to 1 kHz. The differential scanning calorimetry experiments show that the crystallinity of the matrix is not affected by vibration-assisted consolidation.

Bender Element Test and Numerical Simulation of Sliding Zone Soil with Gravels of Huangtupo Landslide

<p>In order to study the effect of the different consolidation pressure, loading-unloading path and gravel content on the shear modulus of the small strain of sliding zone soil, a set of consolidation bender element test device was developed. The device consists of three parts: a consolidation system, a deformation measuring system, and a shear wave testing system. The consolidation system is composed of a traditional consolidation instrument and the plexiglass cylinder box. The sample is cylindrical in shape and has a size of 50 mm×50 mm. The consolidation displacement is measured by a digital display micrometer. Shear wave testing system is a wave velocity measurement system made of piezoelectric ceramic. The experimental results show that the device can control the consolidation pressure and measure the vertical deformation, measure the shear wave velocity of the sliding zone soil in real-time, and then study the variation rule of the small strain shear modulus of the sliding zone soil with gravels. The shear modulus of the sliding zone soil increases with an increase in the consolidation pressure. The shear modulus of the unloading of sliding zone soil is larger than that of loading. Under the loading pressure of 200 kPa and 400 kPa, the shear modulus of the sliding zone soil first decreases and then increases with an increase in the gravel content. In the process of unloading, the shear modulus of the sliding zone soil increases with an increase in the gravel content. </p>

Measurement and Investigation on 1-D Consolidation Permeability of Saturated Clay considering Consolidation Stress Ratio and Stress History

To study the influence of consolidation stress ratio and stress history on 1-D consolidation permeability of saturated clay, one-dimensional consolidation permeability tests were carried out with GDS triaxial device. The results indicated that the permeability coefficient and void ratio of normally and overconsolidated saturated clay decreased with the increase of consolidation stress ratio under different consolidation stress ratios but the same stress history. And the amount of final sample’s compression increased with the increase of the consolidation stress ratio. Under the condition of the same consolidation stress ratio but different stress history, the amount of final compression of the overconsolidated saturated clay was smaller than that of the normally consolidated saturated clay. Besides, the stress difference σdv between consolidation pressure σ and gravity stress σ c z was fitted to the amount of the final sample’s compression, and a good linear relationship between the stress difference σ d v and the amount of the final sample’s compression under each consolidation pressure was obtained. The results showed that it is necessary to consider the influence of consolidation stress ratio and stress history simultaneously on 1-D consolidation permeability of saturated clay. Meanwhile, it can accurately predict the amount of the final sample’s compression after knowing the gravity stress. Moreover, a model prediction analysis was conducted on the saturated clay and recommended to use the modified Kozeny-Carman’s equation to predict the permeability coefficient of Luochuan saturated clay during one-dimensional consolidation.

Determination of Pre-Consolidation Pressure by Different Method

One of the most important soil problems seen on fine-grained soils is the settlement problem. The primary consolidation settlement shows itself over time with the effect of water. Also, the settlement properties of soil change depending on the stress history. In this study, silt mixtures with three different sand percentages were prepared using the slurry sludge preparation method under 50kPa load, and pre-consolidation pressures were calculated by performing the oedometer experiment on the obtained samples. Using the collected oedometer data, the pre-consolidation pressures were calculated and compared by six different methods. As a result, the results equal to the vertical stress values applied for the three mixtures were obtained by Butterfield and Tavenas methods. Sand content was effective in Casagrande, Van Zelst, and Janbu methods, but not in Butterfield, Tavenas, and Shmertman.

INFLUENCE OF DRYING-WETTING CYCLES ON THE COMPRESSIBILITY OF CLAY SOILS IN THE COMMUNE OF HOUEYOGBE

This article presents the results of an experimental laboratory study carried out with the odometer and the Richards press on a class A3 clay soil sample that had undergone drying-wetting cycles. These tests allowed us to analyze in fine the influence of the drying-wetting cycles on the compressibility and suction behavior of the soil object of our study. This study reveals that the drying-wetting cycles have a certain influence on clay soils. Indeed, the compressibility index of the soil increases while the swelling index decreases according to the cycles; the pre-consolidation pressure and the oedometric modulus show a more or less constant variation; the permeability of the soil increases clearly when the number of cycles increases. Soil suction decreases as the number of drying-wetting cycles increases under extreme conditions.

Study on the consolidation properties of soft soil distributed in the North Center coastal area of Vietnam

Consolidation parameters of soft soil play an important role in calculating settlement and soft soil improvement by vertical drainage method (distance, quantity, treatment time). In this study, using oedometer tests, consolidation parameters of some soft soils in the North Central coastal region, Vietnam are clarified. The research results show that the compression index Cc has a strong relationship with the natural water content, liquid limit, dry unit weight, and void ratio of the soil. The consolidation coefficient significantly depends on the applied pressure level, at the over-consolidation stage (normal stress is less than pre-consolidation pressure), the consolidation coefficient is high. By contrast, at the normal consolidation stage (normal stress is greater than pre-consolidation pressure), the coefficient of consolidation is small. The pre-consolidation pressure of soil changes with the distribution depth.