Effect of Inter-Column Spacing on Soil Stresses due to Vibro-Installed Stone Columns: Interesting Findings

This paper reveals the interesting relation between the inter-column spacing and the corresponding alteration of soil state of stresses due to the vibro-installation technique. This relation is inferred from analyses for load settlement records of various field load tests, performed for stone columns arrangements with different inter-column spacing values. In order to have adequate confidence in the findings, a well-documented case history, involving three columns patterns along with their relevant field and laboratory test results, is utilized for this study. Moreover, a well-tested finite element model, capable of simulating both elasto-plastic and time dependent soil deformations as well as pore water pressure building and dissipation, is employed in the analysis. Instead of determining the soil response to the test load, based on known initial soil stresses and material properties, the analysis is inversely posed to determine the soil initial stresses, based on the recorded settlements and the post-installation material properties. The alteration in the soil state of stress is represented by the increase in the post-installation horizontal to vertical stress ratio, K*, as a function of the inter-column spacing. It is found that this alteration experiences a systematic decrease in its magnitude as the inter-column spacing increases.     

Re-appraisal of seismicity and seismotectonics in the north-eastern Algeria Part II: 20th century seismicity and seismotectonics analysis

The main objective of the research work isthe homogenisation of the two recentAlgerian earthquake catalogues for thecommon covered period of time, from 1900 to1990, for the region under considerationlimited by [33^°N–38^°N,4^°E-9.5^°E] and the updatingof the catalogue for the twentieth century(1900–2000). To mitigate the deficiencyof the incompleteness of catalogue, aneffort was made to establish a correlationbetween surface-wave magnitude Ms andbody-wave magnitude m_b in the form ofMs = a + b (m_b). A complete, exact andhomogeneous earthquake catalogue as much aspossible, comprising 870 seismic events,has been compiled. Seismicity analysis ofthe region shows a strong concentration ofseismicity along a band of no more than400 km width oriented mainly in theeast-west direction parallel to the coast.Moreover, earthquakes in this zone arerather associated to strike-slip mechanism.The focal mechanism show a regional stressregime that corresponds to horizontalcompression in NW-SE to N-S direction. As aresult of the review of the seismicity ofnorth-eastern Algeria from the compilationof checked and corrected data and itscorrelation with other geologic andgeophysical investigations based ondocumentary sources, it was possible toconstruct a most complete seismotectonicmap. It leads also to delineate fourseismogenic zones in the Tellian Atlas, aless important zone in the Saharan Atlas, asixth zone at the boundary of both Atlasand finally, a seventh one along thecoastal zone. The seismicity-active faultscorrelation of some of these defined zonesis examined in details with a specialattention to the Saharan Atlas zone, theHodna and Biban zone as well as Soummam andBabor zone where further research workallowed to find some neotectonic featuresconsidered as a significant sign of recenttectonic activity.     

Design of efficient base isolation for hammers and presses

Foundations supporting hammers and presses have to withstand powerful short-period impact loads. When designing these foundations, their vibration amplitudes and the forces transmitted to the supporting piles or soil medium must be reduced to meet serviceability and stability requirements. Mounting systems are often used to achieve this goal. The objectives of this paper are to investigate the efficiency of mounting systems for different foundation configurations and to provide practical guidance for their design. A comprehensive parametric study was conducted and the results were used to establish a set of charts for the design of efficient mounting systems.     

One-dimensional consolidation of soil under multistage load based on continuous drainage boundary

In engineering practice, a rapid loading rate can result in ground failure when the strength of soft soils is relatively low, and a multistage loading scheme is always utilized to deal with this situation. Firstly, under a multistage load and the continuous drainage boundary, an analytical solution of excess pore-water pressure and consolidation degree is obtained by virtue of the superposition formula of excess pore-water pressure, and a more general continuous drainage boundary under arbitrary time-dependent load is developed. Then, a comparison with existing analytical solutions is conducted to verify the present solution. A preliminary attempt on applying the continuous drainage boundary into the finite element model is made, and the feasibility of the numerical model for the one-dimensional consolidation under the continuous drainage boundary is verified by comparing the results calculated by FEM with that from present analytical solution. Finally, the consolidation behavior of soil is investigated in detail for different int erface parameters or loading scheme. The results show that, in land reclamation projects, a horizontal drain should be placed close to the boundary with a smaller interface parameter to improve the consolidation efficiency. The degree of consolidation is also related to the applied time-dependent load and interface parameters.     

Multichannel analysis of surface waves (MASW) for seismic site characterization using 2D genetic algorithm at Bahrah area,Wadi Fatima,Saudi Arabia

The present study deals with the seismic site classification of Bahrah area, Wadi Fatima, to characterize the local site conditions. The dynamic behavior of sediments was studied by the application of surface wave inversion. The multichannel analysis of surface waves (MASW) shallow geophysical technique was utilized for site classification. MASW survey was carried out at 66 sites along with 13 seismic refraction profiles at suitable localities. MASW and seismic refraction profiles were processed and compared with the available borehole data. The integration of MASW techniques with seismic refraction and borehole data progressively enhanced the subsurface visualization and reliability of the shear wave velocity estimation in the subsurface in the study area. The subsurface shear-wave velocity model was achieved by the solution of an inverse problem-based dispersion of surface waves and propagation in a vertically heterogeneous medium. The 2D genetic algorithm was employed for the inversion of dispersion curves to obtain velocity and thickness of subsurface layers. The depth to engineering bedrock and velocity of shear waves in the first 30 m was deciphered and mapped. The depth of bedrock in study area varies from 4 to 30 m, and V _{S 30} ranges from 320 to 800 m/s. The most of study area falls in B and C class categories in addition to few sites of D class according to the NEHRP guidelines.     

Field study on the behavior of pre-bored grouted planted pile with enlarged grout base

This paper presents the results of field tests performed to investigate the compressive bearing capacity of pre-bored grouted planted (PGP) pile with enlarged grout base focusing on its base bearing capacity. The bi-directional O-cell load test was conducted to evaluate the behavior of full scale PGP piles. The test results show that the pile head displacements needed to fully mobilize the shaft resistance were 5.9% and 6.4% D (D is pile diameter), respectively, of two test piles, owing to the large elastic shortening of pile shaft. Furthermore, the results demonstrated that the PHC nodular pile base and grout body at the enlarged base could act as a unit in the loading process, and the enlarged grout base could effectively promote the base bearing capacity of PGP pile through increasing the base area. The normalized base resistances (unit base resistance/average cone base resistance) of two test piles were 0.17 and 0.19, respectively, when the base displacement reached 5% D_b (D_b is pile base diameter). The permeation of grout into the silty sand layer under pile base increased the elastic modulus of silty sand, which could help to decrease pile head displacement under working load.

     

Effect of clayey media parameters on the negative response of a coincident loop1

The aim of this work is to consider the phenomenon of negative response and its detectability in a polarizable half-space formed of Clay-water mixture which commonly exists in water aquifers and which can be used as a simple indicator of the presence of Underground water. We make use of an analytical treatment for the transient voltage induced in a coincident loop lying on a half-space as a basis for our computations. A Cole-Cole model is used to represent the Clay with appropriate parameters. As saturated Clay is characterized by high conductivity and moderate chargeability, it is hardly detectable relative to the practical noise level. However, there are optimum Clay parameters that offer a maximum negative response. It is also observed that for a very short time constant τ in the Cole-Cole model, the amplitude of the negative response decreases with the decrease of the time constant due to the fast decay of the polarization current. Finally, it is found that there is an optimum value for the loop radius which gives the largest value of the negative response and this loop radius depends on the model parameters.     

Seismicity, seismic input and site effects in the Sahel—Algiers region (North Algeria)

Algiers city is located in a seismogenic zone. To reduce the impact of seismic risk in this Capital city, a realistic modelling of the seismic ground motion (SGM) is conducted by using the hybrid method that combines the finite differences method and the modal summation. For this purpose, a complete database of geological, geophysical and earthquake data is constructed. A critical re-appraisal of the seismicity of the zone [2.25°E–3.50°E, 36.50°N–37.00°N] is performed and an earthquake list, for the period 1359–2002, is compiled. The analysis of existing and newly retrieved macroseismic information allowed the definition of earthquake parameters of macroseismic events for which a degree of reliability is assigned. Geological cross sections have been built up to model the SGM in the city, caused by the 1989 Mont-Chenoua and the 1924 Douéra earthquakes. Synthetic seismograms and response spectral ratio is produced for Algiers, and they show that the soft sediments in Algiers centre are responsible of the noticed amplification of the SGM.     

Effect of seabed instability on fixed offshore platforms

Storms, hurricanes, and earthquakes may cause seabed instability, especially if the seabed is weak. The seabed instability, manifested in movement of soil layers, exerts lateral forces that may cause large stresses in offshore foundations. The induced stresses may compromise the stability of the foundation and supported structure. The effect of seabed instability on a fixed offshore structure is examined in this study. The method used accounts for soil nonlinearity, dynamic soil resistance, and pile–soil–pile interaction within the stable soil layer. Dynamic p–y curves, dynamic t–z curves and q–z curves have been used to simulate the soil resistance in the lateral and axial directions. The effect of different parameters that influence the response of offshore structures to seabed instability is evaluated. The parameters considered include the value of soil movement, the sliding layer depth, the wave loading, the pile flexibility, the soil movement profile, and the axial loading at the pile head. The response predicted using the proposed analysis compared well with that calculated using a boundary element solution for a case history of a failed offshore platform.     

五大连池近代火山老黑山火烧山火山喷发过程的考察研究

作者在已有工作的基础上,以当代火山学的研究思路和观点,为恢复五大连池两个近代火山,老黑山火烧山的喷发历史过程进行了野外考察研究工作。老黑山火山锥是由三套不同的碎屑堆积物组成。在锥体的南侧、东侧和西侧以及北测和北西侧有５个熔岩溢出口,按它们形成先后关系,认为有早、中、晚三期熔岩流。本文还对老黑山火山锥上的寄生火山、结壳熔岩与渣状熔岩的分布、流动特点及形成的控制因素进行了分析讨论。最后得出结论：老黑山火山是经多期次喷发活动形成的。火烧山火山锥是一碎屑化泡沫化程度很低的浮岩块和熔岩碎块组成,同老黑山有明显区别。