石灰改良土在铁路工程中的应用

从铁路第五期提速施工的实际角度出发，详细介绍了石灰改良土从改良机理、试验、施工到检测的全过程。以解决目前铁路工程建设施工中石灰改良土的施工控制难点。     

Forecast formula for strength of cement-treated clay

A simple formula with no fitting parameters is proposed, with which the strength of cement-treated soil can be calculated at any curing time with the known cement-water ratio (the ratio of the cement mass to the mass sum of the water in the soil and the water in the cement paste) of the cement-treated soil and the corresponding strength at a certain short curing time. The results obtained with this formula basically reflect the law whereby the strength of cement-treated soil increases with the curing time. To further facilitate the use of this formula, the conversion relation of the cement-water ratio to the cement-mixed ratio and the water-cement ratio of the cement paste were presented. In such a way, the strength of cement-treated soil can be predicted directly using the common proportioning parameter of the cement-treated soil. In addition, with the known long-term (within 180 d) target strength of the cement-treated soil, its short-term strength can also be speculated through this formula, on whose basis a formulation design for cement-treated soil may be conducted as well.     

Effects of porosity,dry unit weight,cement content and void/cement ratio on unconfined compressive strength of roof tile waste-silty soil mixtures

One of the conventional ways to improve the mechanical behavior of soils is to mix them with cementing agents such as cement, lime and fly ash. Recently, introduction to alternative materials or sub-products that can be adopted to improve the soil strength is of paramount importance. Therefore, the present study aims to investigate the effects of porosity (η), dry unit weight (γ_d) of molding, cement content (C) and porosity/volumetric cement content ratio (η/C_iv) or void/cement ratio on the unconfined compressive strength (q_u or UCS) of silty soil–roof tile waste (RT) mixtures. Soil samples are molded into four different dry unit weights (i.e. 13 kN/m³, 13.67 kN/m³, 14.33 kN/m³ and 15 kN/m³) using 3%, 6% and 9% cement and 5%, 15% and 30% RT. The results show that with the addition of cement, the strength of the RT–soil mixtures increases in a linear manner. On the other hand, the addition of RT decreases q_u of the samples at a constant percentage of cement, and the decrease in porosity can increase q_u. A dosage equation is derived from the experimental data using the porosity/volumetric cement content ratio (η/C_iv) where the control variables are the moisture content, crushed tile content, cement content and porosity.     

掺石灰改良膨胀土的室内试验研究

针对膨胀土路基的改良问题,进行了一系列室内土工试验,对石灰以及石灰改良后膨胀土的基本物理性质、胀缩特性、击实特性、力学特性等进行了室内对比试验分析,结果表明,石灰改良膨胀土试样的强度主要取决于试样的含水率、掺灰率.     

Design and calibration of a laminar soil box suitable for a low-capacity shake table using free-field tests on Ganga sand

The present study concentrates on design, commissioning and calibration of a uniaxial laminar soil box suitable for use on a low base-shear capacity shake table available at IIT Kanpur, India. The box is designed to simulate the behavior of soil deposits subjected to earthquake motions, with minimal boundary effects due to reflection of waves at the boundary. The 1.1 m × 1.6 m × 0.765 m box is comprised of a series of individual lamina supported independently on multiple roller bearings guided through a guide channel. The outer frame connected to the guide rods is designed in such as way that it can transfer the self weight of each lamina out of the shake table. A series of free-field tests are carried out on dry Ganga sand sample to calibrate the box. Dynamic response parameters, such as acceleration, displacement, stress-strain behavior, strain-dependant modulus and damping ratio of the sand at various depth are investigated. Large strain and subsequent increased inelasticity is observed towards the top of the sand bed. The experimental results are further compared with equivalent-linear SHAKE analysis and nonlinear finite element ground response analysis of the free-field soil using OpenSees for assessing the performance of the laminar box.     

Durability analysis of seashore saline soil bound with a slag compound binder

In this paper, a slag compound binder (hereinafter referred to as the SM binder) was used to bind seashore saline soil. Compressive tests, scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction analytical tests were carried out to measure the unconfined compressive strength, observe the microstructure, analyze the composition of hydration products and evaluate the binding mechanism of the saline soil/SM binder mixture. The results showed that calcium silicate and calcium aluminate hydrates were produced after the hydration of the cinder components in the SM binder. Part of the calcium aluminate hydrate reacted with the gypsum to form ettringite, while the other part reacted with the Cl^? and SO₄^2? in the saline soil to produce Kuzel’s salt. Na⁺ also participated in the hydration reaction and produced zeolite-like substances. These hydration reactions led to the rapid binding of the soil sample. As the surface of the saline soil particles also contained active SiO₂ and A1₂O₃, the Ca(OH)₂ reacted with them to form calcium silicate and calcium aluminate hydrates in a continuously alkaline environment. Such reactions contributed to the third-stage binding of the saline soil, leading to a gradual increase in the strength of the soil samples during the middle and late stages of binding.     

Rate dependence on mechanical properties of unsaturated cohesive soil with stress-induced anisotropy

The strain rate during shearing has been shown in experimental studies to strongly affect the mechanical behaviour of soil. For saturated soil, sufficient knowledge has been obtained to achieve equilibrium conditions for the pore water pressure. Nevertheless, little is known about unsaturated soil. Therefore, this study used a hollow cylindrical torsional shear apparatus to investigate the rate dependence on the deformation and strength properties of unsaturated soil. First, unsaturated specimens were anisotropically consolidated with different directions of major principal stress to assess the rate dependence of the anisotropic behaviour. Then, the shear stress was removed to produce an isotropic stress state. Shearing was applied using the specimens to evaluate the strain rate effects on the mechanical properties of unsaturated cohesive soil. The results indicate that the secant shear modulus increased with the strain rate in both constant suction (CS) and constant water content (CW) conditions. The shear strength did not change with the strain rate under a CW condition, but it decreased with the strain rate under a CS condition.     

石灰改良膨胀土路基填筑质量控制浅析

结合长晋高速公路改良膨胀土路基施工实例,阐述了膨胀土的特性及危害,提出了改良膨胀土掺灰工艺控制要点,着重介绍了石灰改良膨胀土质量控制和检测方法以及石灰剂量衰减的规律。     

如何使石灰稳定土基层达到较高的强度

针对石灰稳定土的特性,从石灰的选择、土质的选择、石灰剂量的选择、含水量、石灰土密实度、石灰土龄期、石灰土冰冻稳定性规律等方面提出了使石灰稳定土基层达到较高强度的措施,以提高路面质量。     

The effects of curing time and temperature on stiffness,strength and durability of sand-environment friendly binder blends

Agricultural-industrial wastes, like rice-husk ash (RHA) and carbide lime (CL), have great potential applications in such earthworks as the stabilization of slopes and pavement layers and the spread footings and bed of pipelines, particularly in the regions near where the waste is produced. Present research evaluates the potential use of RHA mixed with CL as a binder, improving strength, stiffness and durability properties of a uniform sand. Two different curing temperatures, 23 °C and 40 °C, and curing periods, 7 and 28 days, of compacted sand-RHA-CL blends (distinct dry unit weights and contents of RHA and CL) were evaluated to determine the importance of these changes on the reactions between the materials. The experimental program aims to assess the following parameters: initial shear modulus (G₀), unconfined compressive strength (q_u), and accumulated loss of mass (ALM). Studies have been carried out to quantify these parameters as a function of a novel index called porosity/volumetric binder content (η/B_iv). The results showed higher values of G₀ and q_u, as well as a small rate of ALM with reduction of porosity and with rise of the environment friendly binder content. The latter is achieved either by increasing eith the RHA or the CL content. The curing temperature acts as a catalyser, accelerating the pozzolanic reactions between RHA and CL. Longer curing periods also benefit reactions between materials by enhancing their geotechnical properties. An analysis of variance (ANOVA) was carried and the results showed the dry unit weight, RHA content and curing type are significantly effect the strength results. It was also possible to verify that curing for 28 days at 23 °C and for 7 days at 40 °C are statistically equivalent in terms of strength. The G₀ results after weathering cycles tended to decrease in specimens at a 40 °C curing temperature and increase in specimens at a 23 °C curing temperature.     

Behaviour of model footing on bamboo mat-reinforced sand beds

Soil reinforcement is one of the most common and cost-effective methods among ground-improvement techniques. Recently, sustainable and natural materials for soil reinforcement have attracted the attention of soil engineers. Bamboo is considered to be one of the most effective materials for soil reinforcement due to it’s excellent mechanical and engineering properties. This paper discusses the results of laboratory model studies conducted on sand beds reinforced with traditionally woven bamboo mats. An improvement in the bearing capacity of about 2.5 times was seen when the reinforcement was placed at the optimum depth. The effective spacing of the reinforcement between two layers of bamboo mats was found to be equal to the optimum depth value, i.e., 0.3B. An improvement in the bearing capacity of about seven times was observed when four layers of reinforcement were placed at a spacing of 0.3B. The results obtained from the present study reveal the excellent capacity of bamboo mat for soil reinforcement.     

Bottom ash as a backfill material in reinforced soil structures

The paper describes the interface behaviour of bottom ash, obtained from two thermal power plants, and geogrid for possible utilization as a reinforced fill material in reinforced soil structures. Pullout tests were conducted on polyester geogrid embedded in compacted bottom ash samples as per ASTM D6706-01. Locally available natural sand was used as a reference material. The pullout resistance offered by geogrid embedded in bottom ash was almost identical to that in sand. In order to study the influence of placement condition of the material on pullout resistance, test were conducted on uncompacted fill materials. Pullout resistance offered by geogrids embedded in uncompacted specimen reduced by 30–60% than that at the compacted condition.     

Utilization of carbide slag-activated ground granulated blastfurnace slag to treat gypseous soil

Treating gypseous soils with lime or cement may induce remarkable swelling, resulting in the deterioration of pavement subgrade or other foundation layers. To mitigate this swelling, two industry by-products, carbide slag (CS) and ground granulated blastfurnace slag (GGBS), were utilized in this study. The CS was used to activate the GGBS, which was used to treat an artificial gypseous soil with different binder contents and CS:GGBS ratios, compared to ordinary Portland cement. The treated soils were soaked after a 7-day curing period. A series of tests was performed to examine the properties of the treated soils, including swelling, strength, water content, X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). It was found that the CS-GGBS-treated soils experienced slightly higher swelling (0.2%–1.0%) than the cement-treated soils (0.1%–0.3%) during the 7-day curing period. However, the following soaking process significantly increased the swelling of the cement-treated soils (>5.0%), caused cracks on the specimen surface, and reduced the strength, whilst the swelling of the CS-GGBS-treated soils after soaking was much lower (<0.3%), no cracks were observed, and the decrease in the soaking-induced strength was much less. The XRD, SEM, and MIP results indicated that the formation of ettringite was primarily responsible for the swelling. For the CS-GGBS-treated soils, the activation of GGBS and the formation of ettringite at an early age (within 7 days) rapidly consumed the Ca(OH)₂ in the CS; and hence, the further formation of ettringite after soaking was very limited. For the cement-treated soils, the cement hydration continuously supplied Ca(OH)₂ for the ettringite formation until completion, resulting in longer and higher swelling after soaking.     

Test method for minimum and maximum densities of small quantities of soil

The minimum and maximum void ratios are required to establish the relative density of sandy soil. Undisturbed simple shear test specimens are often too small to provide enough material to employ the Japanese Standard JIS A 1224:2009 Test Method. An alternative test method for evaluating the dry minimum and maximum densities of soil is proposed for those cases when a test specimen does not provide enough material to use the standard-size mold. The alternative test method was applied to soil from 42 small test specimens. Soil from test specimens of the same material were subsequently mixed to produce eight soil composites for which their minimum and maximum densities could be determined using both the standard and alternative methods. The minimum and maximum void ratios determined by both methods for the composite soil are in good agreement. Moreover, trends in the dataset are consistent with those from previous studies on sand and non-plastic fine-grained soil.     

冻融及不同温度下石灰改良盐渍土动力参数研究

为研究季冻区石灰改良盐渍土路基稳定性,室内试验分析了冻融及低温环境下的动力参数变化规律.以哈肇公路沿线盐渍土为研究对象,采用英国GDS动三轴试验系统(GDSTAS),对不同动荷载频率、围压、温度及冻融循环次数下的石灰改良盐渍土动剪切模量和阻尼比进行试验测定,结果表明:转折点动剪切模量可以反映动剪切模量的变化趋势;温度降...     

Geo-mechanical behavior of clay soils stabilized at ambient temperature with fly-ash geopolymer-incorporated granulated slag

Geopolymer is a cementitious material that can replace ordinary Portland cement in several geotechnical engineering applications, such as soil stabilization, with the advantages of much lower harmful emissions and energy consumption. This paper presents a rigorous evaluation of the geo-mechanical behavior of different types of clay soils treated with geopolymer, including the influence of soil characteristics and mineralogy. Two natural clay soils in addition to a commercially available kaolin clay were used for this investigation. Laboratory experiments were performed including unconfined compressive strength (UCS) and consolidated undrained (CU) triaxial compression tests under different confining pressures. The UCS and triaxial tests indicated that the addition of geopolymer considerably increased the yield stress and initial stiffness of all examined clays. With the increase of geopolymer content, the stress–strain behavior of treated clays was found to develop progressively from ductile response into a post-peak brittle fashion. The CU tests also demonstrated that the addition of geopolymer changed the initial characteristics of remolded clays from quasi-over-consolidated to heavily over-consolidated, rendering high yield surface and more effective shear strength parameters (i.e., cohesion and friction angle). Moreover, although the overall qualitative stress–strain and stress path responses of the clays were similar, significant quantitative differences were observed, particularly in terms of the attainable yield strength, stiffness, and shear strength. These differences can be attributed mainly to the heterogeneity associated with the soil mineralogy and the corresponding differences in the interaction between the clay/non-clay minerals and geopolymer.     

Influence of soil reinforcement on the uplift bearing capacity of a pre-stressed high-strength concrete pile embedded in clayey soil

This paper presents a field study on the uplift bearing capacity of a pre-stressed high-strength concrete (PHC) pile embedded in clayey soil, and on the soil around the PHC pile that was treated with cement paste. The PHC pile was inserted into a pile hole filled with cemented soil by its own weight (by gravity), and the soil compaction effect of a conventionally driven pile induced by the installation process was avoided. The test results showed that: the pile head displacement needed to fully mobilize the uplift bearing capacity of the test piles was about 0.1 D (pile diameter); the ultimate skin friction of the PHC pile–cemented soil interface was much larger than that of the cemented soil–soil interface; the PHC pile and the cemented soil around the pile behaved as an integral pile in the load transfer process; and the measured ultimate bearing capacity of the test piles was 0.91–0.94 times the American Petroleum Institute (API)’s proposed values for piles under compression and 0.79–0.80 times the values calculated with the effective stress method for piles under compression.     

Application of generalized regression neural network method for corrosion modeling of steel embedded in soil

In this work, a generalized regression neural network (GRNN) model is used to predict the corrosion potential values and corrosion current densities of ASTM A572-50 steel specimens embedded in nine soils with different physiochemical properties, i.e., pH, moisture content, resistivity, chloride content, sulfate and sulfite contents, and mean total organic carbon concentration. Experiments were conducted, and the corrosion current densities and corrosion potential values of the steel specimens embedded in the different soils were measured. The results obtained with the GRNN model agreed very well with the results of the experiments, suggesting that the proposed model is capable of predicting the corrosion activity of steel specimens embedded in different soils.     

Model test assessment of the generation of underground cavities and ground cave-ins by damaged sewer pipes

Ground cave-ins caused by damaged sewer pipes have been frequently reported in metropolitan areas and have caused severe socioeconomic losses. In this study, model experiments were conducted to determine how damaged sewer pipes generate ground cave-ins or cavities, with a focus on the influence of the soil type and density. Digital images of the model ground were captured to evaluate the internal deformation of the model grounds. Additionally, the vertical displacement at the surface, the size of the cavity, and the weight of the discharged soil were measured in each test. The results indicate that uniform soil with no fines content was more vulnerable to ground cavities than well-graded soil with fines content. Loose soil led to a ground cave-in with significant deformation over the entire model ground, whereas deformation was concentrated only on the ground cavities in the dense soil ground.     

Feasibility of using electrokinetics and nanomaterials to stabilize and improve collapsible soils

Loess as a subcategory of collapsible soils is a well-known aeolian deposit generally characterized as a highly-porous medium with relatively low natural density and water content and a high percentage of fine-grained particles.Such collapsible soil sustains large stresses under a dry condition with natural water content.However,it can experience high and relatively sudden decreases in its volume once it reaches a certain water content under a certain load and therefore,the natural condition of the soil might not be suitable for construction if the possibility of the exposure of the soil to excessive water exists during the lifetime of the project.This research presents the utilization of an innovative method for stabilization and improvement of Gorgan loessial soil.This method uses electrokinetics and nanomaterials to instigate additives to move through soil pores,as an in situ remedial measure.To assess the acceptability of this measure,the deformability and strength characteristics of the improved collapsible soil are measured and compared with those of the unimproved soil,implementing several unsaturated oedometer tests under constant vertical stress and varying matric suction.The result emphasizes the importance of the matric suction on the behavior of both improved and unimproved soils.The test results indicate that the resistance of the soil was highly dependent on the water content and matric suction of the soil.The oedometer tests on samples improved by 3% lime and 5% nanomaterials show considerable improvement of the collapse potential.Results also reveal that stabilized samples experience notably lower volume decrease under the same applied stresses.