Shear strength behaviour of liquefiable sand of petobo on treated by agarose under direct shear test

Liquefaction process is associated with the loss of the shear strength of the saturated loose sands caused by strong earthquakes. Due to mitigitation of liquefaction hazard, an appropriate mitigation of liquefaction using environmentally friendly methods is critical and becoming increasingly important and unavoidable. The laboratory investigation was carried out to study the shear strength behaviour of liquefiable sand of Petobo treated by agarose on different concentration 1%,3% 5%. A series of direct shear test were conducted under three level of vertical stress 10 kPa, 20 kPa, and 30 kPa on the specimen. It was found that the optimum content of agarose which can be considered is at 1%-3%, using stress ratio (τ/σv) analysis shows that stress ratio decreases with increasing the vertical stress on the same agar content. The implication this result that the application of this method must consider variation of material source and characteristic, and the suitable level of vertical stresses.

Investigation on Compressibility and Microstructure Evolution of Intact Loess During Wetting Process

Loess is widely deposited in arid and semi-arid areas and is characterized by low dry density, developed pore space, and loose structure, which is not commensurate with that high structural strength and shear strength in the dry state. Many natural phenomena and experimental studies show that intact loess is very sensitive to the change of water content, with slight increases in water content causing a rapid reduction in strength. Abundant information is available in the literature for collapsibility of loess; however, the research on the evolution of loess compressibility during wetting is still minimal, which is very helpful to understand the loess collapsible deformation caused by long-term irrigation. In this paper, the evolution of compressibility of intact loess during wetting are studied by oedometer test, and the microstructure and pore size distribution (PSD) is characterized on intact loess specimens with different water content before and after oedometer tests by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) methods. The results show that the compression index (Cc) and secondary compression index (Cα) of intact loess depend on water content and vertical stress and change abruptly after the vertical stress exceeds the yield stress. The Cα/Cc values of the intact loess are not constant, which increased with the vertical stress to peak and then gradually decreased and tend to 0.025. Both wetting and loading can cause microstructural damage to the intact loess, in which loading leads to the collapse of the overhead structure and transformation from a bimodal PSD into a single PSD, and wetting intensifies the collapse of microstructure to form a compacted interlocking structure and promotes the transformation of medium pores into small pores.

Analysis of the Mechanical Response of Asphalt Pavement Under Water-Stress Coupling

In order to study the mechanism of water damage of an asphalt pavement, the FLAC3D program was adopted to model and analyze the mechanical response of a saturated asphalt pavement under instantaneous vehicle load. The results show that the horizontal stress, vertical stress and shear stress of an asphalt concrete pavement increase with the increase of instantaneous load. The surfaces of asphalt pavement structural layers are most vulnerable to damage. The horizontal stress, vertical stress and shear stress decrease sharply with the instantaneous dynamic load decreasing to zero. The horizontal stress reaches maximum value at the interface between the base and the large stone porous mixture (LSPM) layer, while the maximum vertical and shear stresses occur on the surface layer of the saturated asphalt pavement. The deformation decreases almost linearly from the surface of the asphalt pavement to the subgrade, and the pore water pressure was little influenced by the transient load.

In situ stress characteristics of the NE Sichuan basin based on acoustic emission test and imaging logging

This study presents the distribution rule of in situ stress in the northeast Sichuan basin and its relationship with fracture. Sixty-seven sets of core samples of 21 Wells from the terrigenous clastic rock formation (Shaximiao, Qianfoya, Xujiahe) and marine carbonate formation (Jialingjiang, Leikoupo, Feixianguan) in the northeast Sichuan basin were tested by acoustic emission experiment. The in situ stress variation with the depth was established and the corresponding regression analysis was done. The horizontal principal stress direction of terrigenous clastic rock formation and marine carbonate rock formation was obtained by combining the dual diameter data of 6 wells and the imaging logging data of 3 wells. The results show that the vertical stress in the northeast of Sichuan basin has a linear relationship with the depth, and there is little difference between the vertical stress and the overburden weight of rocks. The maximum and minimum horizontal principal stress and horizontal shear stress increase with the burial depth. The divergence degree of horizontal shear stress with depth greater than 3000 m is greater than that of the stratum smaller than 3000 m. The horizontal stress plays a dominant role in the northeast Sichuan basin. With the increase in depth, the influence of tectonic stress field decreases and the vertical stress increases. Impacted by Dabashan and Qinling plate tectonic movement, the direction of in situ stress in marine carbonate strata is nearly east–west. The direction of maximum horizontal principal stress in terrigenous clastic rock formation is basically northwest–southeast. The imaging logging data show that the fracture direction is consistent with the horizontal principal stress direction, and the present in situ stress direction is favorable to the secondary reconstruction of natural fractures, and the fractures keep good opening. The distribution law of in situ stress in northeast Sichuan basin shows σH > σV > σh, indicating that the fault activity in this area is dominated by strike-slip type, the tectonic stress field is dominated by horizontal tectonic stress, in addition that the stress state is conducive to reverse fault activity.

CONSOLIDATION CHARACTERISTICS OF A SILTY CLAY: CONCERNING THE EFFECT OF SOIL DISTURBANCE

In this paper, undisturbed specimen of a silty clay constituting of Phu Bai formation (ambQ21-2 pb) was collected from boreholes in Hue city and surrounding areas. The soil, under both undisturbed and disturbed conditions, was then subjected to standard one-dimensional consolidation tests with 7 loading increments. It is shown from the experimental results that the time to the end of primary consolidation (EOP), determined by Log Time method (tLT) and 3-t method (t3T), decreases with the load increment and under the same vertical stress, the primary consolidation of disturbed silty clay finish at a shorter time than those of the undisturbed one. The coefficient of secondary consolidation (Cα) increases with the vertical stress and reaches the maximum values before decreasing. The obtained values of Cα = 0.005 - 0.020 suggest a relatively low secondary compressibility of the silty clay constituting of Phu Bai formation.

Investigation on the CBM Extraction Techniques in the Broken-Soft and Low-Permeability Coal Seams in Zhaozhuang Coalmine

To enhance the coalbed methane (CBM) extraction in broken-soft coal seams, a method of drilling a horizontal well along the roof to hydraulically fracture the coal seam is studied (i.e., HWR-HFC method). We first tested the physical and mechanical properties of the broken-soft and low-permeability (BSLP) coal resourced from Zhaozhuang coalmine. Afterward, the in situ hydraulic fracturing test was conducted in the No. 3 coal seam of Zhaozhuang coalmine. The results show that (1) the top part of the coal seam is fractured coal, and the bottom is fragmented-mylonitic coal with a firmness coefficient value of less than 1.0. (2) In the hydraulic fracturing test of the layered rock-coal specimens in laboratory, the through-type vertical fractures are usually formed if the applied vertical stress is the maximum principal stress and is greater than 4 MPa compared with the maximum horizontal stress. However, horizontal fractures always developed when horizontal stress is the maximum or it is less than 4 MPa compared with vertical stress. (3) The in situ HWR-HFC hydraulic fracturing tests show that the detected maximum daily gas production is 11,000 m3, and the average gas production is about 7000 m3 per day. This implies that the CBM extraction using this method is increased by 50%~100% compared with traditional hydraulic fracturing in BSLP coal seams. The research result could give an indication of CBM developing in the broken-soft and low-permeability coal seams.

Field Application for Evaluating Vertical Stress of Soil in Multilayered Ground

In the west coast and the coast of Busan, at several locations, an overconsolidated layer exists above the soft ground. For soft ground with an upper overconsolidated clay layer, significant errors exist between the design and the actual settlements in the field. For multilayered ground, although Boussinesq's theory is applied, significant errors still exist. In this study, ground settlements in the overconsolidated clay layer were predicted using the Burmister and Hirai method. Based on comparisons with field measurements, it was confirmed that the accuracy could be increased by more than 90%.

In Situ Stress and Stress Regime in the Onshore Part of the Northeast Java Basin

In situ stress is importance in the petroleum industry because it will significantly enhance our understanding of present-day deformation in a sedimentary basin. The Northeast Java Basin is an example of a tectonically active basin in Indonesia. However, the in situ stress in this basin is still little known. This study attempts to analyze the regional in situ stress (i.e., vertical stress, minimum and maximum horizontal stresses) magnitude and orientation, and stress regime in the onshore part of the Northeast Java Basin based on twelve wells data, consist of density log, direct/indirect pressure test, and leak-off test (LOT) data. The magnitude of vertical ( and minimum horizontal ( stresses were determined using density log and LOT data, respectively. Meanwhile, the orientation of maximum horizontal stress ( was determined using image log data, while its magnitude was determined based on pore pressure, mudweight, and the vertical and minimum horizontal stresses. The stress regime was simply analyzed based on the magnitude of in situ stress using Anderson’s faulting theory. The results show that the vertical stress ( ) in wells that experienced less erosion can be determined using the following equation: , where is in psi, and z is in ft. However, wells that experienced severe erosion have vertical stress gradients higher than one psi/ft ( . The minimum horizontal stress ( ) in the hydrostatic zone can be estimated as, while in the overpressured zone, . The maximum horizontal stress ( ) in the shallow and deep hydrostatic zones can be estimated using equations: and , respectively. While in the overpressured zone, . The orientation of is ~NE-SW, with a strike-slip faulting stress regime.