Select

null

2004, 23 (24): 4099-4099 doi:

[PDF] 121 KB (601)

[HTML]

+

Show Abstract

Select

STUDY ON THE EFFECT OF FREEZING RATE ON THE DAMAGE CT VALUES OF TONGCHUAN SANDSTONE

null

2004, 23 (24): 4099-4099 doi:

[PDF] 292 KB (1008)

[HTML]

+

Show Abstract

In cold regions，seasonal freezing and thawing are characterized by temperatures dropping slowly from positive to negative or rising slowly from negative to positive. However，the day-and-night freezing and thawing are characterized by fast temperature dropping and rising. Thus，it is very important to study the damage CT values of rock subjected to different freezing rates. The damage CT values of three kinds of Tongchuan sandstone are studied subjected to different freezing rates under open circumstances. Freezing and statistic frequency are used to analyze the characteristics of damage CT values，which can be referred to geotechnical engineering in the cold region.

Select

A LABORATORY STUDY ON THE DAMAGE PROPAGATION OF ROCKS UNDER FREEZE-THAW CYCLE CONDITION

null

2004, 23 (24): 4105-4105 doi:

[PDF] 316 KB (1105)

[HTML]

+

Show Abstract

By the computerized tomography(CT) technology，the properties of damage propagation of sandy mudstone，on top and waist of Fenghuo Shan tunnel in Tibetan plateau，are studied under the freeze-thaw cycle condition. The results show that water migration and volumetric expansion 9% are the main factors resulting in the freeze-thaw damage of sandy mudstone，and the extent and range of damages are varied with the amount of water. In other words，the damage propagation is rather fast in the first 6 cycles，and then almost keeps constant with a little water-supply or none. But under the condition of large water supply，the damage is always developing. Whatever condition the rock sample is in，the side region is damaged more easily and severely than the others. Moreover，during freeze-thaw disturbance of loading and unloading，moderate weathering of sandy mudstone providing passage for the water migration and vast water supply increase the speed of damage. This indicates that the stability of soft-rock regions with many joints or cracks is not favorable，when the rock is penetrated by enough water in freeze-thaw process.

Select

FEM ANALYSIS OF TEMPERATURE CHARACTERISTICS OF
VENTILATION ROADBED

null

2004, 23 (24): 4112-4112 doi:

[PDF] 494 KB (955)

[HTML]

+

Show Abstract

Using the enthalpy-based finite element method，the three-dimensional temperature characteristics of roadbeds have been numerically analyzed. The results indicate that the refrigeration efficiency of the ventilation roadbed containing apertured rentiduct is the most favorable among three types of roadbeds.

Select

BACK ANALYSIS OF SLIP SURFACE OF THE 102 LANDSLIDE ON SICHUAN—TIBET HIGHWAY

null

2004, 23 (24): 4119-4119 doi:

[PDF] 295 KB (1117)

[HTML]

+

Show Abstract

The parameters of slip surface prove to be crucial and difficult in the study of landslides，especially for many landslides in loose deposit on the Sichuan—Tibet highway. Based on various field investigations，the mechanisms of landslides in these deposits are similar. Hence，a typical study is given in this paper on the mechanical parameters of the slip surface of the102 Landslide on the Sichuan—Tibet highway，and the procedure to obtain these parameters is described. The original sample from the slip surface of the 102 Landslide was obtained and its mechanical parameters were given by triaxial compression tests and back analysis method. By comparision of the results of two procedures，it is shown that back analysis method can determine more accurately the mechanical parameters of the whole slip surface. It is indicated that back analysis is a feasible and effective approach to examine the parameters of the slip surface.

Select

A NUMERICAL ANALYSIS OF SEISMIC DEFORMATION IN MOGAO-GROTTOES WITH 3D FEM

null

2004, 23 (24): 4124-4124 doi:

[PDF] 1146 KB (1055)

[HTML]

+

Show Abstract

3D finite element method is employed in the prediction and calculation of seismic deformation with the parabola model of horizontal displacement distribution，and the seismic deformation of Mogao Grottoes in Dunhuang as a case study. The results show that 3D finite element method is of high precision，being able to control boundary conditions and adjust computation models. The calculated displacements and strains on the ground surface agree，in order of magnitude，with the actual values observed in earthquake. The influence of fault dimension on the result is also studied，which indicates that the calculated value is stable when fault depth is greater than a certain value，and the reliable earthquake deformation with 3D finite element method can be achieved.

Select

ANN PREDICTIVE MODEL FOR PREDICTING TEMPERATURE FIELD EVOLVEMENT WITHIN VENTIDUCT ROADBED

null

2004, 23 (24): 4131-4131 doi:

[PDF] 320 KB (845)

[HTML]

+

Show Abstract

Ventiduct roadbed is an active cooling foundation to resist thaw. Many numerical analyses have been conducted to study the effectiveness of the ventiduct layout on the frozen soil foundation，with a lot of data on temperature field evolvement. Obviously，these data are helpful for engineers to optimize the design of ventiduct roadbed. For the maximum uses of the data，the artificial neural network (ANN) method is preferable. Thus，an ANN model needs to be established to predict temperature field evolvement within ventiduct roadbed. In the process of model establishment，the restriction space is predigested with the guidance of expert experiences. The whole predigestion consists of three main steps. Firstly，the continuous time region is scattered to dispersed time points. Secondly，the continuous 2D space region is scattered to dispersed space points. Lastly，all the other parameters of scheme design，physical and mechanical properties are retrenched and scattered，such as the ventiduct diameter and spacing，the height of road bank，and the heat exchange parameters of stratum and etc.. The ANN model with improved BP arithmetic is used to predict the temperature field. It is shown that the improved BP neural network can solve ten thousand samples. In the end，an applicable model has been obtained with high efficiency and precision，which can quantitatively predict the temperature field through a continuous period of time. This method，as well as its basic ideas，is significant to predict other quality fields.

Select

A STUDY ON THE CRITICAL DEPTH OF DEEP ENTRY WITH
CATASTROPHE THEORY

null

2004, 23 (24): 4137-4137 doi:

[PDF] 199 KB (1086)

[HTML]

+

Show Abstract

Analysis show that there is a critical depth below which remarkable deformation will occur in the surrounding rock of the entry. The entry deeper than the critical depth is defined as deep entry in this paper. The potential energy function of the surrounding rock system of the entry is gained on the basis of the elastoplastic theory. Then the cusp catastrophic model of the surrounding rock system of the entry is established. Thereby，the method for determining the critical depth is presented for support design of the deep entry，and a practical case is given.

Select

DEFORMATION PROPERTIES OF STRUCTURAL LOESS

null

2004, 23 (24): 4142-4142 doi:

[PDF] 261 KB (1345)

[HTML]

+

Show Abstract

On the basis of a variety of tests on both the intact and artificial structural loess specimens including lateral confined compression test，iso-water-content shear test，triaxial immersion deformation test，and iso-suction triaxial shear test，the collapse and deformation properties of loess are comprehensively studied in the paper，for the purpose of overcoming some disadvantages existing in current studies of structural loess. The test results demonstrate that the structural loess has a collapse surface which is independent of the generalized stress path，and its deformation characteristic has close relation with the loss of structural strength.

Select

STRAIN-SPACE-BASED ELASTO-PLASTIC
CONSTITUTIVE MODEL OF Q1 LOESS

null

2004, 23 (24): 4147-4147 doi:

[PDF] 178 KB (1151)

[HTML]

+

Show Abstract

The stress-strain curves and deformation characteristics of Q1 loess achieved from the fifth tunnel of Luohuiqu are analyzed by means of conventional triaxial tests. Based on the Il¢yushin hypothesis，the strain-space-based elasto-plastic model of Q1 loess is proposed. Comparison of the experimental curve with the computational result of the model demonstrates that this model can simulate the softening and dilatancy characteristics of Q1 loess.

Select

AN EXPERIMENTAL STUDY ON DYNAMIC PROPERTIES OF UNSATURATED LOESS UNDER DYNAMIC TORSIONAL SHEAR

null

2004, 23 (24): 4156-4156 doi:

[PDF] 243 KB (1227)

[HTML]

+

Show Abstract

Some aspects such as the behaviors of pore pressure，dynamic strength，and dynamic deformation of unsaturated loess are studied with the dynamic torsional shear test of loess. The pore air pressure gradually rises with the development of axial strain in the process of the dynamic torsional shear test of loess，but the pore water pressure essentially keeps constant or goes up a little in the latter stage. There are some considerable differences in strength and strain between unsaturated loess and saturated loess. The effects of water content，consolidation pressure，and consolidation pressure ratio on the dynamic characteristics of loess are also analyzed.

Select

IN-SITU TESTING STUDY ON INFILTRATION IN UNSATURATED LOESS

null

2004, 23 (24): 4156-4156 doi:

[PDF] 253 KB (1295)

[HTML]

+

Show Abstract

The seepage of water is relatively simple within saturated soils. However，the temporal and spatial distributions of seepage speed and direction are more complicated in unsaturated soils，which are needed to be determined for calculating the settlement of loess with water increasing or reducing. This paper addresses these problems through in-situ testing study on infiltration in unsaturated loess. The results show that，at the stage of unsaturated infiltration，the saturation degree varies approximately linear with the time at different depths，and the time of infiltrating within shallow layers is also approximately linear related to the depth for a short period. In addition，the soggy angle of loess is found to be slightly larger than 30°.

Select

STRUCTURAL DAMAGE EVOLVEMENT PROPERTIES OF COLLAPSIBLE LOESS

null

2004, 23 (24): 4161-4161 doi:

[PDF] 228 KB (1156)

[HTML]

+

Show Abstract

Based on the stress-strain relation of Q3 loess triaxial compression tests with different stress paths，including conventional axial loading，lateral unloading，and constant mean principle stress with different water contents of 2.0%，8.5%，15.0%，and 18.0%，the initial tangent modulus were obtained. It was shown that the initial tangent modulus of structural loess decreases with increasing lateral consolidation pressure but decreases with increasing water content，and the damage of loess structure subjected to compression stress is more serious than its hardening due to compressing. Because the initial tangent modulus decreases gradually with the increase of compression stress and water content and reflects the structural damage increase of loess，this parameter can be used to define the damage variables by the composite theory. A structural damage ratio of Q3 loess was proposed by the change of initial tangent modulus between the initial tangent modulus of undamaged loess and completely damaged loess. With the consideration of the coupled action of compression and water content，the constitutive model is proposed in terms of the damage ratio，which is a new approach for evaluating the possible collapse settlement of loess foundations.

Select

ANALYSIS OF MICROSTRUCTURE CHANGE FOR LOESS IN THE PROCESS OF LOADING AND COLLAPSE WITH CT SCANNING

null

2004, 23 (24): 4166-4166 doi:

[PDF] 377 KB (1246)

[HTML]

+

Show Abstract

The triaxial shear test，soaking test，and CT scanning during soaking are carried out on intact loess specimens. According to images and data of the CT scanning，the microstructure change of the samples is analyzed by means of damage theory. It is shown when the confining pressure is less than the critical structural strength of the sample，the damage destruction exhibits softening dehiscence. During the course of damage，there is a change from axial dominant density damage to crosswise dominant dehiscence damage. In the area containing a variety of big holes，fractures first appear where the structure strength is weak with low density，and then a variety of small fractures are produced which subsequently change into one single shear surface. For hardening yield damage，the later strength depends on the increase of density and sectional area of the sample. It is found that some physical and chemical changes occur in the collapse process and the big pores in loess do not always contribute to collapsibility.

Select

FORECAST AND ANALYSIS OF REFREEZING IN FENGHUOSHAN PERMAFROST TUNNEL

null

2004, 23 (24): 4170-4170 doi:

[PDF] 546 KB (977)

[HTML]

+

Show Abstract

According to the in-situ measured data of the air temperatures and ground temperatures inside at Fenghuoshan Tunnel on Qinghai—Tibet railway，the thawed range of the permafrost surrounding the tunnel is extensive，which is caused by the hydration heat of the cast-in-place concrete lining，insulation measurement in the inlet，exit of the tunnel during winter construction，and other human activities. Taking water transfer and phase change into account，the finite element formulae of this problem and computation program are derived from the governing differential equations and water transfer equations by Galerkin's method. With the computer program，forecast and analysis on the refreezing of permafrost for Fenghuohan Tunnel is performed. The analytical results show that the vault，left wall，and right wall of Fenghuoshan Tunnel will be refrozen in three years，and the arch bottom will be refrozen in September 30 of the fifth years without insulation. On the other hand，if the tunnel is fitted with insulation with thermal conductivity of 0.03 W/m·K，the vault of Fenghuoshan Tunnel will be refrozen in three years，left wall，right wall and the arch bottom will be refrozen at September 30 of the fifth years. Therefore，insulation material will delay the refrozen of permafrost of Fenghuoshan Tunnel. The thawed range of the permafrost surrounding the tunnel in cold regions caused by construction should be considered，and the time of observation should prolong when their temperatures and stresses are observed in site，otherwise observations will differ largely from the real values in the stable state of the tunnel.

Select

STUDY ON DYNAMIC LOAD DISTRIBUTION ON KEY ROOF BLOCKS
OF UNDER THICK SANDY SOIL STRATUM

null

2004, 23 (24): 4179-4179 doi:

[PDF] 201 KB (1207)

[HTML]

+

Show Abstract

By dynamic simulation model tests，the distribution law of dynamic load of key roof stratum and the law of transmission of dynamic load on key roof blocks，key block A，B and C，are revealed. There are 4 load areas on the key roof stratum，and the mining face is just under the load reducing area of key block B. During the roof structure movement，the load of key block B will reduce by about 50% in about 30 minutes. These results are considerable significance to the understanding of the soil damage mechanism under mining and to the establishment of the theory of dynamic roof structure.

Select

SOME PROBLEMS ASSOCIATED WITH ANALYSIS OF TUNNELS IN LOESS USING BOLT ELEMENTS

null

2004, 23 (24): 4183-4183 doi:

[PDF] 530 KB (773)

[HTML]

+

Show Abstract

The basic idea of New Austrian Tunneling Method is to employ the self-sustaining ability of surrounding rock，and the bolt plus shotcrete system is one of the key technologies. Controversies still exist over the function of bolts and how to reasonably consider their effect. This paper presents an elastic-plastic bolt element and performs numerical simulation of tunnels in loess with bolt elements. The reasonable length of bolts and equivalent increase in values of parameters for surrounding soils are suggested for actual design of tunnel.

Select

AN EXPERIMENTAL STUDY ON DEFORMATION OF RAILWAY EMBANKMENT IN HIGH-TEMPERATURE AND FINE-GRAINED PERMAFROST REGIONS ALONG THE QINGHAI—TIBET RAILWAY

null

2004, 23 (24): 4190-4190 doi:

[PDF] 240 KB (1036)

[HTML]

+

Show Abstract

The Qinghai—Tibet railway under construction traverses a 550 km long continuous permafrost region. The railway embankment constructions within permafrost regions substantially disturb the heat and mass transfer balance between the ground surface and the atmosphere，and cause redistribution of temperature field underneath. Deformation feature of embankment in permafrost regions differs from that in non-permafrost regions. Moreover，deformation feature of embankment is one of the most important factors which influence the stability of embankment. Based on monitoring of temperature and deformation of a segment of railway embankment in high-temperature and fine-grained permafrost regions on the Qinghai—Tibet plateau，the depths of seasonal freezing or thawing with time，the characters of deformation of the embankment，and the ground during an entire freezing-thawing cycle，were analyzed. The results indicate that the permafrost table rose after the embankment completion，and differential deformation occurred in south slope and north slope. Frost-heave deformation occurred on the top of embankment was caused by the deformation of the ground and the embankment body did not see frost-heave deformation. Precipitation had important impact on the deformation of embankment. In the end，some suggestions for reducing deformation of embankment were proposed.

Select

AN EXPERIMENTAL STUDY ON COOLING EFFECT OF THE
PERFORATED VENTILATION PIPES ON
QINGHAI—TIBET RAILWAY ROADBED

null

2004, 23 (24): 4195-4195 doi:

[PDF] 400 KB (1166)

[HTML]

+

Show Abstract

Railway roadbed ventilation，as a positive roadbed cooling technique，has attracted much attention from researchers，which can effectively protect the frozen roadbed and maintain the roadbed stability by raising the permafrost table. At present，the ventilation pipes are generally made by concrete or PVC without holes on the pipe walls，whose cooling effects are realized by airflow and heat transference. But the tightness of pipe walls will reduce cooling effect to some extent. Perforated ventilation pipes can cool the railway roadbed through convection heat transference between airflow and soil around the pipes as well as airflow and heat transference. In order to study the roadbed cooling effect of the perforated ventilation pipes，a comparative experiment has been conducted with both ordinary and perforated ventilation pipes. The short-term observation data have shown that the perforated ventilation pipes，raising higher permafrost tables，are superior to the ordinary ones. Through optimization of roadbed structure the cooling effect will be obviously enhanced. However，the long-term effect of the perforated ventilation pipes depends upon long-term observations and further analyses.

Select

STABILITY ANALYSIS AND RELIABILITY EVALUATION OF
SLOPE OF BLOCK CONSTRUCTION FOR ROCK MASS

null

2004, 23 (24): 4200-4200 doi:

[PDF] 209 KB (1236)

[HTML]

+

Show Abstract

The calculation equations for sliding direction，plane intersection points，area，volume，and safety of key blocks of slope are established by stereographic projection of vector and vector calculation. The equations of failure probability are also given based on the reliability theory. As an example，the equations are used in the stability analysis and reliability evaluation of the five-plane construction rock mass.

Select

AN EXPERIMENTAL STUDY ON REFREEZING CHARACTERISTICS OF LARGE-DIAMETER BORED PILE IN DIFFERENT PERMAFROST AREAS OF THE QINGHAI—TIBET PLATEAU

null

2004, 23 (24): 4206-4206 doi:

[PDF] 378 KB (1072)

[HTML]

+

Show Abstract

It is necessary to understand the effect of cast-in-place bored bridge piles in the construction of the Qinghai—Tibet railway on variations in ground temperature around the piles and further to determine the time required for refreezing after the construction of piles in order to provide scientific support for the subsequent constructions such as those of pile caps，bridge piers and super structures and for evaluation of the time schedule of construction. Aiming at the problem of refreezing of cast-in-place bored piles in permafrost regions of the Qinghai—Tibet plateau，comparative analysis are conducted of monitored data on ground temperatures in two experimental sites：one in a low temperature region with annual average ground temperature below －2.0 ℃，and the other in a high temperature unstable region with annual average ranging from －0.5 ℃ to －1.0 ℃. The preliminary characteristics have been obtained of refreezing after installation of large-diameter concrete piles in the two permafrost regions. Negative temperatures first occurred at depths of 3.5～7.5 m below the ground (－0.027 ℃～－0.32 ℃) and at the bottom of pile (－0.35 ℃) after 8 days since installation of pile in the low temperature region. However，in the high temperature unstable region，negative temperatures (－0.18 ℃) first occurred at the bottom of pile after 18 days. On the basis of ground temperature data，the authors analyzed the refreezing characteristics in different regions and some conclusions have been obtained which can be utilized as a guidance or as a reference in the construction of pile foundations in permafrost regions.

Select

ADJUSTING TEMPERATURE DISTRIBUTION UNDER THE NORTH AND SOUTH SLOPES OF ROADBED BY THE RIPPED-ROCK REVETMENT IN PERMAFROST REGIONS

null

2004, 23 (24): 4212-4212 doi:

[PDF] 455 KB (1247)

[HTML]

+

Show Abstract

From the governing equations used to study forced convection for incompressible fluids porous media，the detailed finite element formulae for heat convection in porous media are achieved by using Galerkin's method to solve the computational problem of temperature fields on the ripped-rock revetment roadbed in Qinghai—Tibet railway. The temperature change of the ripped-rock revetment roadbed and common ballast roadbed with north and south slopes，when their temperature difference is 1.8 ℃，are discussed and compared. It is found that the common ballast roadbed makes the temperature field unsymmetrically distributed，and provides heat energy for the foundation soil. In contrast，the ripped-rock revetment roadbed is able to ensure symmetrical temperature field distribution. At the same time，it continuously provides more energy for the roadbed and foundation soil，and 0 ℃ isotherm far above the native ground surface，which guarantees the active layer (frost-susceptible sub-clay) to be completely frozen during summer-time (on Jul. 15 and Oct. 15)，not to mention，i. e.，winter-time (on Jan. 15). Therefore，it is highly recommended that the ripped-rock revetment roadbed，the common ballast roadbed with the ripped-rock of 10 cm diameter，80 and 160 cm thick，paved on the south and north side slopes，respectively，be adopted as a kind of roadbed structure of Qinghai—Tibet railway with north and south slopes in permafrost regions as it can lead to symmetrical distribution of roadbed temperature field and raise permafrost table greatly with frost-susceptible sub-clay，the active layer before roadbed construction，completely frozen under the roadbed around the year，and then eliminate the disasters that result in uneven settlement with longitudinal cracks within the roadbed.

Select

EFFECT ANALYSIS OF AUTO-TEMPERATURE-CONTROLLED VENTILATION ROADBED

null

2004, 23 (24): 4221-4221 doi:

[PDF] 371 KB (1055)

[HTML]

+

Show Abstract

Auto-temperature-controlled ventilation roadbed is one of positive engineering measures for cooling roadbed. In the engineering measure，an auto-temperature-controlled system is installed at one or two ends of the vent-duct. The system is composed of air temperature responsive unit and control unit，by which the wind door in ventilation duct can be controlled. When the air temperature reaches the designed value，the wind door can be automatically opened or closed. Through the system the effect of the heat flux in summer can be effectively controlled，and natural cold can be effectively used to cool the roadbed to adjust the temperature of permafrost and ensure the long-term stability of railway. In order to verify its engineering efficiency，the system was installed on two sections of ventilation roadbed with different duct diameters in Beiluhe test section in Qinghai—Tibet railway. Through the field tests from April to October，2003，with ground temperature comparison between the ventilation roadbeds with and without the system，the test results showed that，with the application of the system with 30 and 40 cm diameter ducts，the artificial permafrost table were raised by 0.3 and 0.7 m，respectively，and the average temperature under tubes were reduced by 1.2 ℃ and 1.7 ℃，respectively，and the average temperature under roadbed were reduced by 0.5 ℃ and 0.7 ℃，respectively. The time of reaching maximal thawed depth could be advanced for nearly 20 days，and the time for roadbed giving out heat was extended for more than a month. Through thermal calculation，the thermal flux has been decreased nearly half in a month with maximal thermal flux coming into permafrost. Comparison of the cooling effect in auto-temperature-controlled ventilation roadbeds with different duct diameters indicates that the efficiency of duct with 30 cm diameter is slightly higher than that with 40 cm diameter.

Select

INFLUENCES OF REFREEZING PROCESS OF GROUND ON BEARING CAPACITY OF SINGLE PILE AND BRIDGE CONSTRUCTION IN PERMAFROST

null

2004, 23 (24): 4229-4229 doi:

[PDF] 291 KB (1254)

[HTML]

+

Show Abstract

Based on the theory of heat conduction，this paper presents governing differential equations of ground temperature field，boundary conditions，initial conditions and finite element model for single pile in permafrost with the consideration of air temperature，hydrogeological conditions，concrete temperature，initial ground temperature field，and phase-change effect. For a cast-in-place bored pile in a practical bridge structure that was built in the representative humid permafrost in the Qinghai—Tibet plateau，the ground temperature field of refreezing process was calculated. The temperatures along the pile body varied with the depth and refreezing time，which were used to evaluate the variation of bearing capacity of the single pile and influence of temperatures on the plan of bridge construction according to the bridge code. The presented procedure and conclusions achieved can provide a theoretical basis for shortening construction period and laying out bridge construction plan in permafrost regions.

Select

NEW TECHNOLOGY FOR TUNNELING IN PERMAFROST
IN QINGHAI—TIBET PLATEAU

null

2004, 23 (24): 4234-4234 doi:

[PDF] 215 KB (1297)

[HTML]

+

Show Abstract

Great challenges have been encountered in the construction of Fenghuoshan tunnel due to its chilly climatic and plateau conditions，which consist of the following：how to construct the tunnel without harm to frozen soils，how to employ special techniques to adapt to the absence of oxygen in the plateau，and how to avoid the frost heaving in frozen soils. Accordingly，a series of techniques have been adopted to overcome these difficulties，which include a heat insulation layer between the lining and initial supporting of the tunnel，an intact waterproof and drainage system，and special construction technique for concrete at low temperature to alleviate the frost damage. Owing to these techniques，the Fenghuoshan tunnel has been successfully constructed .

Select

COOLING MECHANISM ANALYSIS AND COOLING EFFECT EVALUATION FOR A NEW TYPE OF PILE USED IN FROZEN SOIL FOUNDATION

null

2004, 23 (24): 4238-4238 doi:

[PDF] 419 KB (967)

[HTML]

+

Show Abstract

Based on the idea of‘active cooling’，aiming at problems of frozen heaving and heat diffusion which commonly exist in frozen soil pile foundation，a new type of pile is proposed to overcome the disadvantages of the classical pile used in frozen soil. Pile body within active layer is fluted and refilled with porous materials such as gravels and ballasts. Thus convections occur and thermal exchanges inside porous materials in winter，but heat conduction exists only in summer because cold air is at the bottom of the fluting. As a result，the soil around flutings is cooled and the permafrost tables are raised. This paper analyses the cooling mechanism and feasibility and the temperature field of classical pile，and the new type of pile by numerical simulation. The results of numerical simulation indicate that the new type of pile can promote permafrost growth，accelerate the course of refreezing greatly after fluting via effect of natural convection for dropping temperature，help raising the permafrost table，and consequently enhance pile bearing capacity and its capability for resisting frost heaving and thaw settlement.

Select

APPLICATION OF EARLY STRENGTH ACCELERATOR FOR LIME-FLY ASH STABILIZED SANDS IN DESERT AREA

null

2004, 23 (24): 4244-4244 doi:

[PDF] 195 KB (920)

[HTML]

+

Show Abstract

Through a series of tests，the early strength of lime-fly ash stabilized sands with early strength accelerators，NaOH and Na2CO3，are evaluated. The mechanism of early strength is analyzed，and the mechanical property and temperature contraction performance are also tested. The results indicate that not only the early compressive strength of lime-fly ash stabilized sands on 7th day increases，but also the later properties such as the indirect tensile strength and the temperature contraction performance on 180th day are improved with early strength accelerator. Moreover，the properties with NaOH and Na2CO3 and the different proportion of lime to fly ash are compared. The lime-fly ash stabilized sands with accelerator has perfect road-use performance.

Select

STRUCTURAL PARAMETER OF SOIL UNDER
COMPLEX STRESS CONDITIONS

null

2004, 23 (24): 4248-4248 doi:

[PDF] 165 KB (1067)

[HTML]

+

Show Abstract

Soil structure is the most important factor influencing mechanical characteristics of soil，but the quantitative study of soil structure is a considerably difficult problem. A practical expression of structural parameter，named stress comprehensive soil structure potential(stress-CSP)，is proposed by some scholars， which，however，has its own limitations. In this paper，the shortcomings existing in stress comprehensive structure potential (stress-CSP) are overcome. Based on the reasonable side of stress-CSP，a new structural parameter of soils，referred to strain comprehensive structure potential (strain-CSP)，is proposed，which can be used for complex stress conditions. The limitation of structural parameter applied under complex stress condition is overcome，and its application space is thus extended.

Select

DISCUSSION ON ‘STUDY ON PERMEABILITY EVOLUTION IN FAILURE PROCESS OF INHOMOGENEOUS ROCK’

null

2004, 23 (24): 4252-4252 doi:

[PDF] 148 KB (777)

[HTML]

+

Show Abstract

Select

ANALYSIS ON THE RELATIONSHIP BETWEEN SEEPAGE AND DAMAGE DURING THE FAILURE PROCESS OF ROCKS
——AUTHOR¢S REPLY TO DOCTOR TANG HONGXIA¢S DISCUSSION

null

2004, 23 (24): 4254-4254 doi: