共查询到20条相似文献,搜索用时 15 毫秒
1.
An analytical method has been proposed to predict the ultimate uplift capacity of single vertical piles embedded in sand considering
arching effect. The present analysis takes into consideration of various pile and soil parameters such as length ( L), diameter ( d) of the pile, angle of internal friction of soil ( ϕ), soil pile friction angle ( δ) and unit weight of soil ( γ). A modified value of coefficient of lateral earth pressure in uplift has been developed considering the arching effect of
soil. A comparative assessment of the uplift capacity of piles predicted by using proposed theory and the existing available
theories is made with the existing field and model test results. It has been observed that the present model considering the
arching effect predicts the results closer. 相似文献
2.
In this article, the shear behavior of discontinuities caused by bedding planes of weakness between two different rock types
with high strength difference is investigated. The effect of roughness and compressive strength of joint wall in such discontinuities
are studied. The designed profiles consist of two regular and three irregular artificial joints molded by three types of plaster
mortars with different uniaxial compressive strengths. Firstly, it is demonstrated that the shear behavior of discontinuities
with different joint wall compressive strengths (JCS) is different from rock joints with identical wall compressive strengths
by showing that Barton’s empirical criterion is not appropriate for the former discontinuities. After that, some correlation
equations are proposed between the joint roughness coefficient (JRC) parameter and some surface statistical/fractal parameters,
and the normal stress range of Barton’s strength criterion is also modified to be used for such discontinuities. Then, a new
empirical criterion is proposed for these discontinuities in such a way that a rational function is used instead of JRC log 10(JCS/ σ
n) as i
0( σ
c/ σ
n) a/[ b + ( σ
c/ σ
n)
a
] by satisfying the peak dilation angle boundary conditions under zero and very high normal stress (physical infinite normal
stress causing zero peak dilation angle). The proposed criterion has three surface parameters: i
0, a, and b. The reason for separation of i
0 from JRC is indicated and the method of its calculation is mentioned based on the literature. The two remaining coefficients
( a and b) are discussed in detail and it is shown that a shows a power-law relationship with b, introducing the coefficient c through b = c
a
. Then, it is expressed that a is directly related to discontinuity surface topography. Finally, it is shown that the coefficient c has higher values in irregular profiles in comparison with regular profiles and is dominated by intensity of peak dilation
angle reduction (majorly related to the surface irregularity and minorly related to roughness). The coefficient c is to be determined by performing regression analysis on experimental data. 相似文献
3.
The paper pertains to the development of a simple semi-empirical model for predicting the uplift capacity of piles embedded
in sand. Various pile and soil parameters such as length ( L), diameter ( d) of the pile and angle of friction (ϕ), soil–pile friction angle (δ) and unit weight (γ) of the soil which have direct influence
on the uplift capacity of the pile are incorporated in the analysis. A comparative assessment of the ultimate uplift capacity
of piles predicted by using the proposed theory and some of the available theories are made with respect to each other and
with reference to the measured values obtained from model tests in the laboratory. For this purpose experimental data have
been collected from the literature and also from model tests conducted as a part of the present investigation. The study shows
the proposed model has an excellent potential in predicting the uplift capacity of piles embedded in sand that are consistent
with model pile test results. 相似文献
4.
The ultimate uplift resistance of a group of multiple strip anchors placed in sand and subjected to equal magnitudes of vertical
upward pullout loads has been determined by means of model experiments. Instead of using a number of anchor plates in the
experiments, a single anchor plate was used by simulating the boundary conditions along the planes of symmetry on both the
sides of the anchor plate. The effect of clear spacing ( s) between the anchors, for different combinations of embedment ratio ( λ) of anchors and friction angle ( ϕ) of soil mass, was examined in detail. The results were presented in terms of a non-dimensional efficiency factor (ξ γ), which was defined as the ratio of the failure load for an intervening strip anchor of a given width ( B) to that of a single strip anchor plate having the same width. It was clearly noted that the magnitude of ξ γ reduces quite extensively with a decrease in the spacing between the anchors. The magnitude of ξ γ for a given s/ B was found to vary only marginally with respect to changes in λ and ϕ. The experimental results presented in this study compare reasonably well with the theoretical and experimental data available
in literature. 相似文献
5.
This study presents shear wave splitting analysis results observed at ISP (Isparta) broadband station in the Isparta Angle,
southwestern Turkey. We selected 21 good quality seismic events out of nearly 357 earthquakes and calculated splitting parameters
(polarization direction of fast wave, ϕ and delay time between fast and slow waves, δt) from mainly SKS and a few SKKS phases of the selected 21 seismic events. Then, we compared calculated splitting parameters
at ISP station (56° ≤ ϕ ≤ 205°; 0.37 s ≤ δt ≤ 4 s) with those previously calculated at ANTO (Ankara) and ISK (İstanbul) stations (27° ≤ ϕ ≤ 59°; 0.6 s ≤ δt ≤ 2.4 s and 26° ≤ ϕ ≤ 54°; 0.6 s ≤ δt ≤ 1.5 s) which are located at 230 and 379 km away from ISP station in central and northwestern Turkey, respectively. The
backazimuthal variations of the splitting parameters at ISP station indicate a different and complex mantle polarization anisotropy
for the Isparta Angle in southwestern Turkey compared to those obtained for Ankara and İstanbul stations. 相似文献
6.
By applying the Griffith stress criterion of brittle failure, one can find that the uniaxial compressive strength (σ c) of rocks is eight times the value of the uniaxial tensile strength (σ t). The Griffith strength ratio is smaller than what is normally measured for rocks, even with the consideration of crack closure.
The reason is that Griffith’s theories address only the initiation of failure. Under tensile conditions, the crack propagation
is unstable so that the tensile crack propagation stress (σ cd) t and the peak tensile strength σ t are almost identical to the tensile crack initiation stress (σ ci) t. On the other hand, the crack growth after crack initiation is stable under a predominantly compressive condition. Additional
loading is required in compression to bring the stress from the crack initiation stress σ ci to the peak strength σ c. It is proposed to estimate the tensile strength of strong brittle rocks from the strength ratio of
R = \fracs \textc | s \textt | = 8\fracs \textc s \textci . R = {\frac{{\sigma_{\text{c}} }}{{\left| {\sigma_{\text{t}} } \right|}}} = 8{\frac{{\sigma_{\text{c}} }}{{\sigma_{\text{ci}} }}}. The term
\fracs \textc s \textci {\frac{{\sigma_{\text{c}} }}{{\sigma_{\text{ci}} }}} accounts for the difference of crack growth or propagation in tension and compression in uniaxial compression tests.
\fracs c s ci {\frac{{\sigma_{c} }}{{\sigma_{ci} }}} depends on rock heterogeneity and is larger for coarse grained rocks than for fine grained rocks. σ ci can be obtained from volumetric strain measurement or acoustic emission (AE) monitoring. With the strength ratio R determined, the tensile strength can be indirectly obtained from
| s \textt | = \fracs \textc R = \fracs \textci 8. \left| {\sigma_{\text{t}} } \right| = {\frac{{\sigma_{\text{c}} }}{R}} = {\frac{{\sigma_{\text{ci}} }}{8}}. It is found that the predicted tensile strengths using this method are in good agreement with test data. Finally, a practical
estimate of the Hoek–Brown strength parameter m
i is presented and a bi-segmental or multi-segmental representation of the Hoek–Brown strength envelope is suggested for some
brittle rocks. In this fashion, the rock strength parameters like σ t and m
i, which require specialty tests such as direct tensile (or Brazilian) and triaxial compression tests for their determination,
can be reasonably estimated from uniaxial compression tests. 相似文献
7.
New empirical models were developed to predict the soil deformation moduli using gene expression programming (GEP). The principal soil deformation parameters formulated were secant ( Es) and reloading ( Er) moduli. The proposed models relate Es and Er obtained from plate load-settlement curves to the basic soil physical properties. The best GEP models were selected after developing and controlling several models with different combinations of the influencing parameters. The experimental database used for developing the models was established upon a series of plate load tests conducted on different soil types at depths of 1–24 m. To verify the applicability of the derived models, they were employed to estimate the soil moduli of a part of test results that were not included in the analysis. The external validation of the models was further verified using several statistical criteria recommended by researchers. A sensitivity analysis was carried out to determine the contributions of the parameters affecting Es and Er. The proposed models give precise estimates of the soil deformation moduli. The Es prediction model provides considerably better results in comparison with the model developed for Er. The simplified formulation for Es significantly outperforms the empirical equations found in the literature. The derived models can reliably be employed for pre-design purposes. 相似文献
8.
Probabilistic analyses provide rational means to treat the uncertainties associated with underlying parameters in a systematic
manner. The stability of a 734-m-high jointed rock slope in the west of Norway, the Oppstadhornet rock slope, is investigated
by using a probabilistic method. The first-order reliability method (FORM) is used for probabilistic modeling of the plane
failure problem in the rock slope. The Barton–Bandis (BB) shear strength criterion is used for the limit state equation. The
statistical distributions of the BB criterion parameters, for which comprehensive data were collected and statistically analyzed,
are determined by using distribution fitting algorithms. The sensitivity of the FORM model for the BB criterion is also investigated.
It is found that the model is most sensitive to the mean value of the residual friction angle ( ϕ
r) and least sensitive to the mean value of the slope angle ( β
f). It is also found that the standard deviation of joint compressive strength (JCS) causes the greatest difference in the
reliability index, which has the least sensitivity to the change in the mean and standard deviation of joint roughness coefficient
(JRC). 相似文献
9.
Arching is a well known phenomenon, which effects stress developments which were investigated and compared using analytical
and numerical solutions. Marston’s ( 1930) solution was extended to a generalised 3-dimensional rectangular stope and later modified for square and circular stopes
for comparison with FLAC results. Aubertin et al. ( 2003) & Li et al. ( 2003) models were improved significantly by placing the backfill within narrow stopes as lifts or layers in numerical modelling
where the normal stress variation with depth were found to be more realistic. The FLAC results were compared with analytical
solutions which were developed by previous researchers and modified by the authors to evaluate the arching effects in backfilled
placed in narrow and circular stopes. It appeared from the investigation herein that δ = 0.67 ϕ and K = K
o condition gives a very close match with the numerical model solutions obtained from FLAC. Many laboratory tests were conducted
to find out friction angles for four Australian mines, which were between 30 and 49 degrees. 相似文献
10.
Site-specific geotechnical data are always random and variable in space. In the present study, a procedure for quantifying the variability in geotechnical characterization and design parameters is discussed using the site-specific cone tip resistance data ( qc) obtained from static cone penetration test (SCPT). The parameters for the spatial variability modeling of geotechnical parameters i.e. ( i) existing trend function in the in situ qc data; ( ii) second moment statistics i.e. analysis of mean, variance, and auto-correlation structure of the soil strength and stiffness parameters; and ( iii) inputs from the spatial correlation analysis, are utilized in the numerical modeling procedures using the finite difference numerical code FLAC 5.0. The influence of consideration of spatially variable soil parameters on the reliability-based geotechnical deign is studied for the two cases i.e. ( a) bearing capacity analysis of a shallow foundation resting on a clayey soil, and ( b) analysis of stability and deformation pattern of a cohesive-frictional soil slope. The study highlights the procedure for conducting a site-specific study using field test data such as SCPT in geotechnical analysis and demonstrates that a few additional computations involving soil variability provide a better insight into the role of variability in designs. 相似文献
11.
In this paper an experimental study was planned on rock mass model with three joint sets under triaxial and true-triaxial
stress states to assess the influence of joint geometry and stress ratios on deformational behaviour of rock mass. The physical
models were composed of three continuous orthogonal joint sets in which joint set-I was inclined at angle θ=0°, 20°, 40°,
60°, 80° and 90° with x-axis, joint set-II was produced at staggering s=0.5 and joint set-III was kept always vertical. Thus, rock mass models with medium interlocked smooth joints (ϕ
j
=36.8°) were simulated under true triaxial compression (σ 1>σ 2>σ 3). Modulus of rock mass shows anisotropy with joint inclination θ which diminishes with increase in σ 2/σ 3 ratio. The rock mass at θ=60° shows the highest modulus enhancement (599.9%) whereas it is minimum (32.3%) at θ=90°. Further
two empirical expressions for estimation of deformation modulus were suggested based on experimental results, which were developed
by incorporating two basic concepts, e.g. Janbu’s coefficients and joint factor, J
f. 相似文献
12.
The thermo-elastic behavior of a natural epidote [Ca 1.925 Fe 0.745Al 2.265Ti 0.004Si 3.037O 12(OH)] has been investigated up to 1,200 K (at 0.0001 GPa) and 10 GPa (at 298 K) by means of in situ synchrotron powder diffraction.
No phase transition has been observed within the temperature and pressure range investigated. P– V data fitted with a third-order Birch–Murnaghan equation of state (BM-EoS) give V
0 = 458.8(1)Å 3, K
T0 = 111(3) GPa, and K′ = 7.6(7). The confidence ellipse from the variance–covariance matrix of K
T0 and K′ from the least-square procedure is strongly elongated with negative slope. The evolution of the “Eulerian finite strain”
vs “normalized stress” yields Fe(0) = 114(1) GPa as intercept values, and the slope of the regression line gives K′ = 7.0(4). The evolution of the lattice parameters with pressure is slightly anisotropic. The elastic parameters calculated
with a linearized BM-EoS are: a
0 = 8.8877(7) Å, K
T0( a) = 117(2) GPa, and K′( a) = 3.7(4) for the a-axis; b
0 = 5.6271(7) Å, K
T0( b) = 126(3) GPa, and K′( b) = 12(1) for the b-axis; and c
0 = 10.1527(7) Å, K
T0( c) = 90(1) GPa, and K’( c) = 8.1(4) for the c-axis [ K
T0( a): K
T0( b): K
T0( c) = 1.30:1.40:1]. The β angle decreases with pressure, β P(°) = β P0 −0.0286(9) P +0.00134(9) P
2 ( P in GPa). The evolution of axial and volume thermal expansion coefficient, α, with T was described by the polynomial function: α( T) = α 0 + α 1
T
−1/2. The refined parameters for epidote are: α 0 = 5.1(2) × 10 −5 K −1 and α 1 = −5.1(6) × 10 −4 K 1/2 for the unit-cell volume, α 0( a) = 1.21(7) × 10 −5 K −1 and α 1( a) = −1.2(2) × 10 −4 K 1/2 for the a-axis, α 0( b) = 1.88(7) × 10 −5 K −1 and α 1( b) = −1.7(2) × 10 −4 K 1/2 for the b-axis, and α 0( c) = 2.14(9) × 10 −5 K −1 and α 1( c) = −2.0(2) × 10 −4 K 1/2 for the c-axis. The thermo-elastic anisotropy can be described, at a first approximation, by α 0( a): α 0( b): α 0( c) = 1 : 1.55 : 1.77. The β angle increases continuously with T, with β T(°) = β T0 + 2.5(1) × 10 −4
T + 1.3(7) × 10 −8
T
2. A comparison between the thermo-elastic parameters of epidote and clinozoisite is carried out. 相似文献
13.
A semi-analytical equation for the modeling of stress–strain relationship for heterogeneous carbonate rocks exhibiting large
axial strains (ε af > 1%) is formulated. The equation is derived by modifying the stress–strain model based on Haldane’s distribution proposed
by Palchik ( 2006) for carbonate rocks exhibiting ε
af ≤ 1%. The developed exponential model is used to relate normalized axial stress ( σ
a/ σ
c) over the whole pre-failure strain range to current axial strain ( ε
a) and failure strain ( ε
af). For carbonate rocks exhibiting ε
af > 1%, the value of pre-calculated parameter δ involved in the stress–strain model is not constant, but dependent on the failure strain value ( ε
af). The normalized stress–strain model can be used to calculate the failure strain in terms of uniaxial compressive strength
and stress–strain measurement at one point only. The advantages of the failure strain model and ways of its use in engineering
practice are discussed. 相似文献
14.
The thermoelastic behavior of a natural clintonite-1 M [with composition: Ca 1.01(Mg 2.29Al 0.59Fe 0.12) Σ3.00(Si 1.20Al 2.80) Σ4.00O 10(OH) 2] has been investigated up to 10 GPa (at room temperature) and up to 960°C (at room pressure) by means of in situ synchrotron
single-crystal and powder diffraction, respectively. No evidence of phase transition has been observed within the pressure
and temperature range investigated. P– V data fitted with an isothermal third-order Birch–Murnaghan equation of state (BM-EoS) give V
0 = 457.1(2) ? 3, K
T0 = 76(3)GPa, and K′ = 10.6(15). The evolution of the “Eulerian finite strain” versus “normalized stress” shows a linear positive trend. The
linear regression yields Fe(0) = 76(3) GPa as intercept value, and the slope of the regression line leads to a K′ value of 10.6(8). The evolution of the lattice parameters with pressure is significantly anisotropic [β( a) = 1/3 K
T0( a) = 0.0023(1) GPa −1; β( b) = 1/3 K
T0( b) = 0.0018(1) GPa −1; β( c) = 1/ K
T0( c) = 0.0072(3) GPa −1]. The β-angle increases in response to the applied P, with: β P = β 0 + 0.033(4) P ( P in GPa). The structure refinements of clintonite up to 10.1 GPa show that, under hydrostatic pressure, the structure rearranges
by compressing mainly isotropically the inter-layer Ca-polyhedron. The bulk modulus of the Ca-polyhedron, described using
a second-order BM-EoS, is K
T0(Ca-polyhedron) = 41(2) GPa. The compression of the bond distances between calcium and the basal oxygens of the tetrahedral
sheet leads, in turn, to an increase in the ditrigonal distortion of the tetrahedral ring, with ∂α/∂ P ≈ 0.1°/GPa within the P-range investigated. The Mg-rich octahedra appear to compress in response to the applied pressure, whereas the tetrahedron
appears to behave as a rigid unit. The evolution of axial and volume thermal expansion coefficient α with temperature was
described by the polynomial α( T) = α 0 + α 1
T
−1/2. The refined parameters for clintonite are as follows: α 0 = 2.78(4) 10 −5°C −1 and α 1 = −4.4(6) 10 −5°C 1/2 for the unit-cell volume; α 0( a) = 1.01(2) 10 −5°C −1 and α 1( a) = −1.8(3) 10 −5°C 1/2 for the a-axis; α 0( b) = 1.07(1) 10 −5°C −1 and α 1( b) = −2.3(2) 10 −5°C 1/2 for the b-axis; and α 0( c) = 0.64(2) 10 −5°C −1 and α 1( c) = −7.3(30) 10 −6°C 1/2for the c-axis. The β-angle appears to be almost constant within the given T-range. No structure collapsing in response to the T-induced dehydroxylation was found up to 960°C. The H P- and H T-data of this study show that in clintonite, the most and the less expandable directions do not correspond to the most and
the less compressible directions, respectively. A comparison between the thermoelastic parameters of clintonite and those
of true micas was carried out. 相似文献
15.
The Indian summer monsoon rainfall is known to have considerable spatial variability, which imposes some limitations on the
all-India mean widely used at present. To prepare a spatially coherent monsoon rainfall series for the largest possible area,
fourteen subdivisions covering the northwestern and central parts of India (about 55% of the total area of the country), having
similar rainfall characteristics and associations with regional/global circulation parameters are merged and their area-weighted
means computed, to form monthly and seasonal Homogeneous Indian Monsoon (HIM) rainfall series for the period 1871–1990. This
paper includes a listing of monthly and seasonal rainfall of HIM region. HIM rainfall series has been statistically analysed
to understand its characteristics, variability and teleconnections for long-range prediction.
HIM rainfall series isfound to be homogeneous, Gaussian distributed and free from persistence. The mean (R) rainfall is 757
mm (87% of annual) and standard deviation ( S) 119 mm, with a Coefficient of Variation (CV) of 16%. There were 21 dry (K, -< R S) and 19 wet ( R
i R + S) years during 1871–1990. There were clusters of frequent negative departures during 1899–1920 and 1965–1987 and positive
departures during 1942–1961. The recent three decades show very high rainfall variability with 10 dry and 6 wet years. The
decadal averages were alternatively positive and negative for three consecutive decades, viz., 1871–1900 (positive); 1901–1930
(negative); 1931–1960 (positive) and 1961–1990 (negative) respectively. Significant QBO and autocorrelation at 14th lag have
been found in HIM rainfall series.
To delineate the changes in the climatic regime of the Indian summer monsoon, sliding correlation coefficients (CCs) between
HIM rainfall series and (i) Bombay msl pressure, (ii) Darwin msl pressure and (iii) Northern Hemisphere surface air temperature
over the period 1871–1990 have been examined. The 31-year sliding CCs showed the systematic turning points of positive and
negative CCs around the years, 1900 and 1940. In the light of other corroborative evidences, these turning points seem to
delineate ‘meridional’ monsoon regime during 1871–1900 and 1940–1990 and ‘zonal’ monsoon regime during 1901–1940. The monsoon
signal is particularly dominant in many regional and global circulation parameters, during 1951–1990.
Using the teleconnections of HIM series with 12 regional/global circulation parameters during the recent 36-year period 1951–86 regression models have been
developed for long-range prediction. In the regression equations 3 to 4 parameters were entered, explaining upto 80% of the
variance, depending upon the data period. The parameters that prominently enter the multiple regression equations are (i)
Bombay msl pressure, (ii) April 500 mb Ridge at 75°E, (iii) NH temperature, (iv) Nouvelle minus Agalega msl pressure and (v)
South American msl pressure. Eleven circulation parameters for the period 1951–80 were subjected to Principal Component Analysis
(PCA) and the PC’s were used in the regression model to estimate HIM rainfall. The multiple regression with three PCs explain
72% of variance in HIM rainfall. 相似文献
16.
The ratios M
R = E/ σ
c for 11 heterogeneous carbonate (dolomites, limestones and chalks) rock formations collected from different regions of Israel
were examined. Sixty-eight uniaxial compressive tests were conducted on weak-to-strong (5 MPa < σ
c < 100 MPa) and very strong ( σ
c > 100 MPa) rock samples exhibiting wide ranges of elastic modulus ( E = 6100–82300 MPa), uniaxial compressive strength ( σ
c = 14–273.9 MPa), Poisson's ratio ( ν = 0.13–0.49), and dry bulk density ( ρ = 1.7–2.7 g/cm 3). The observed range of M
R = 60.9–1011.4 and mean value of M
R = 380.5 are compared with the results obtained by Deere (Rock mechanics in engineering practice, Wiley, London, pp 1–20,
1968) for limestones and dolomites, and the statistical analysis of M
R distribution is performed. Mutual relations between E, σ
c, ρ, M
R for all studied rocks, and separately for concrete rock formations are revealed. Linear multiple correlations between E on the one hand and σ
c and ρ on the other for Nekorot and Bina limestone and Aminadav dolomite are obtained. It is established that the elastic modulus
and M
R in very strong carbonate samples are more correlated with ρ− σ
c combination and ε
a max, respectively, than in weak to strong samples. The relation between M
R and maximum axial strain ( ε
a max) for all studied rock samples (weak-to-strong and very strong) is discussed. 相似文献
17.
Porous cordierite ceramics were prepared from a mixture of coal fly ash and basic magnesium carbonate at 1100-1350℃. Porosity, flexural strength and thermal expansion coefficient of the samples sintered at 1300℃ were estimated to be 26%, 65 MPa and 4.21×10^-6/℃, respectively. The kinetics of the formation progress was investigated by stepwise isothermal dilatometry (SID) accompanied with XRD, SEM and porosity measurement. It was found that the isothermal shrinkage data from SID could be well analyzed to get kinetic parameters according to the erapirical rate equation developed by Makipirtti-Meng, dY/dt=nk(T)Y(1-Y)(Y/1-Y)^(1/n),where Y is the fractional shrinkage during the sintering process and n is a dimensionless component. The apparent activation energy △E values for 900-1000℃ and 1050-1 150℃ were 1294 and 1778 kJ/mol, respectively. 相似文献
18.
This paper presents the analyses of twelve prestressed concrete (PSC) instrumented test piles that were driven in different bridge construction projects of Louisiana in order to develop analytical models to estimate the increase in pile capacity with time or pile setup. The twelve test piles were driven mainly in cohesive soils. Detailed soil characterizations including laboratory and in situ tests were conducted to determine the different soil properties. The test piles were instrumented with vibrating wire strain gauges, piezometers, pressure cells that were monitored during the whole testing period. Several static load tests (SLTs) and dynamic load tests were conducted on each test pile at different times after end of driving (EOD) to quantify the magnitude and rate of setup. Measurements of load tests confirmed that pile capacity increases almost linearly with the logarithm of time elapsed after EOD. Case pile wave analysis program was performed on the restrikes data and was used along with the load distribution plots from the SLTs to evaluate the increase in skin friction capacity of individual soil layers along the length of the piles. The logarithmic linear setup parameter “A” for unit skin friction was calculated of the 70 individual clayey soil layers and was correlated with different soil properties such as undrained shear strength (Su), plasticity index, vertical coefficient of consolidation (cv), over consolidation ratio and sensitivity (St). Nonlinear multivariable regression analyses were performed, and three different empirical models are proposed to predict the pile setup parameter “A” as a function of soil properties. For verification, the subsurface soil conditions and setup information for additional 18 PSC piles collected from local database were used to compare the measured versus predicted “A” parameters from the proposed models, which showed good agreement. 相似文献
19.
The variation and distribution of temperature and water moisture in the seasonal frozen soil is an important factor in the
study of both the soil water cycle and heat balance within the source region of the Yellow River, especially under the different
conditions of vegetation coverage. In this study, the impact of various degrees of vegetation coverage on soil water content
and temperature was assessed. Soil moisture ( θ
v) and soil temperature ( T
s) were monitored on a daily basis. Measurements were made under different vegetation coverage (95, 70–80, 40–50 and 10%) and
on both thawed and frozen soils. Contour charts of T
s and θ
v as well as a θ
v– T
s coupling model were developed in order to account for the influence of vegetation cover and the interaction between T
s and θ
v. It was observed that soil water content affected both the overall range and trend in the soil temperature. The regression
analysis of θ
v versus T
s plots indicated that the soil freezing and thawing processes were significantly affected by vegetation cover changes. Vegetation
coverage changes also caused variations in the θ
v– T
s interaction. The effect of soil water content on soil temperature during the freezing period was larger than during the thawing
period. Moreover, the soil with higher vegetation coverage retained more water than that with lower coverage. In the process
of freezing, the higher vegetation coverage reduced the rate of the reduction in the soil temperature because the thermal
capacity of water is higher than that of soil. Areas with higher vegetation coverage also functioned better for the purpose
of heat-insulating. This phenomenon may thus play an important role in the environmental protection and effective uses of
frozen soil. 相似文献
20.
Minimum energy geometries and electron density distributions, ϱ( r), for ∼40 polyatomic oxide molecules containing first and second row M-cations have been calculated at the Hartree-Fock level with a 6-311++G** basis set. The nature of the bonded interactions
in these molecules is examined in terms of the relative electronegativities, χ
M
, of the M-cations and the properties of the electron density distribution, ϱ( r
c
), evaluated at the bond critical points, r
c
, along each MO bond. As ϱ( r
c
) and the Laplacian of ϱ( r
c
) increase, χ
M
increases indicating an increase in the covalent character of the bonded interactions between M and O. The ratios of the curvatures of ϱ( r
c
) indicate that the NO bond is predominantly covalent, that the CO and SO bonds are of intermediate type and that the remaining
MO bonds are indicated to be predominantly ionic in character. A comparison of the critical point properties of ϱ( r
c
) and χ
M
indicates that the minimum energy MO bond length is an important determinate of the properties of ϱ( r
c
) and the character of the MO bonds.
On the other hand, values of the local energy density, H( r
c
), indicate that the LiO, BeO, NaO, MgO and AlO bonds are predominantly ionic and that the BO, CO, NO, SiO, PO and SO bonds
are predominantly covalent in character. The χ
M
-values provided by the properties of ϱ( r
c
) indicate that the covalent component of a bond increases with decreasing bond length, coordination number and increasing
bond strength. Each MO bond seems to represent a unique entity and to possess a distinct set of ϱ( r
c
) properties, the distinction being greater for the more electronegative cations.
The bonded radius of the oxide ion, r
b
(O), and the χ
M
-values determined from ϱ( r
c
) correlate with values determined from promolecule electron density distributions. In addition, r
b
(O) and χ
M
-values determined from experimental electron density distributions for crystals correlate with values determined from procrystal
electron density distributions. The number of critical points and bond paths are modeled rather faithfully by procrystal and
promolecule electron density distributions, despite the neglect of the binding forces in their constructions.
Received: October 15, 1996/Revised, accepted: February 10, 1997 相似文献
|