Modeling a Weak Foundation in Interaction with Reinforced Sand Piles under a Low-Rise Building

One of the ways to increase the bearing capacity and stability of a water-saturated base by introducing a sand pile vertically reinforced along the contour with geosynthetic material (geogrid SSP 30 / 30-2.5) is experimentally substantiated. This constructive solution is used in low-rise construction. For the theoretical substantiation of the suggested method, it is proposed to model the interaction of a weak foundation and a reinforced sand pile on the basis of the linear theory of viscoelasticity. Calculation of vertical displacements of the pile and comparison with the results of in situ experiments is presented.

A method of calculating the bearing capacity of sand pile composite foundations in a mucky soil layer considering consolidation

In engineering practice, the measured bearing capacity of a sand pile composite foundation in a mucky soil layer is much larger than the design value. Based on the sand pile construction and the load application process, a method of calculating the bearing capacity of the foundation based on the effective stress was proposed. Cavity diameter expansion in sand pile construction was simplified into a planar problem, and the cavity expansion theory was used to establish the expression of the rate of displacement and the horizontal stress increase. Based on the e–p curve and the calculation of the degree of consolidation, the relationships between the horizontal and vertical effective stress and the void ratio were obtained. According to the close relationship between the bearing capacity of the foundation in a mucky soil layer and the water content, an expression describing the relationships between the bearing capacity of the foundation, effective stress, void ratio, and water content was established. For the temporary engineering foundation treatment project, which needs a high bearing capacity but allows large foundation deformation, the design of sand pile composite foundations uses these relationships to take the consolidation effect of mucky soil into consideration, thereby reducing the replacement rate and lowering the construction cost.

Analisis Stabilitas Timbunan pada Tanah Dasar Berbentuk Lereng dengan Metode Elemen Hingga

ABSTRAKAnalisis menggunakan program PLAXIS 2D dengan tinggi timbunan dan kemiringan tanah dasar bervariasi tanpa dan dengan perkuatan rock fill sehingga diperoleh kebutuhan rock fill agar faktor keamanan memenuhi syarat. Hasil analisis dengan kemiringan tanah dasar 1V:8H diperoleh kebutuhan rock fill timbunan lempung dengan tinggi 5m, 10m, 15m dan 20m sebesar 0%; 24,7%; 45,5% dan 59,1% sedangkan timbunan pasir sebesar 14,5%; 43,2%; 62,4% dan 71,4%. Pada kemiringan tanah dasar 1V:6H diperoleh kebutuhan rock fill masing-masing ketinggian timbunan lempung sebesar 5%; 45,8%; 59,3% dan 66.6%, sedangkan timbunan pasir sebesar 33,1%; 62,3%; 71,9% dan 73,2%. Pada kemiringan tanah dasar 1V:4H diperoleh kebutuhan rock fill masing-masing ketinggian timbunan lempung sebesar 48,9%; 66,7%; 75,6% dan 81,3%; sedangkan timbunan pasir sebesar 60,1%; 72,6%; 80,5% dan 84%. Variasi jenis mesh menghasilkan faktor keamanan yang tidak signifikan antar jenis mesh dikarenakan lapisan timbunan yang dimodelkan relatif rapat. Analisis geometri tanah dasar bertangga dengan lurus tidak menunjukkan pengaruh yang signifikan terhadap faktor keamanan.Kata kunci: stabilitas lereng, timbunan, tanah dasar, rock fill, metode elemen hingga, PLAXIS 2D ABSTRACTAnalysis using PLAXIS 2D program with varying heights and slopes of subgrade without and with rock fill reinforcement in order to obtain the need for rock fill so that the safety factor meets the requirements. The results of the analysis with a subgrade slope of 1V: 8H obtained the need for rock fill clay pile with a height of 5m, 10m, 15m and 20m of 0%; 24.7%; 45.5% and 59.1% while the sand pile was 14.5%; 43.2%; 62.4% and 71.4%. At a subgrade slope of 1V: 6H, the required rock fill height for each clay pile is 5%; 45.8%; 59.3% and 66.6%, while the sand pile was 33.1%; 62.3%; 71.9% and 73.2%. At 1V: 4H subgrade slope, the required rock fill height for each clay pile height is 48.9%; 66.7%; 75.6% and 81.3%; while the sand pile was 60.1%; 72.6%; 80.5% and 84%. Variation of mesh types resulted in insignificant safety factor between mesh types because the modeled embankment layer was relatively tight. The geometry analysis of the straight stepped subgrade did not show a significant effect on the safety factor.Keywords: slope stability, embankment, subgrade, rock fill, Finite Element method, PLAXIS 2D

A Method of Calculating the Bearing Capacity of Sand Pile Composite Foundations in a Mucky Soil Layer Considering Consolidation

In engineering practice, the measured bearing capacity of a sand pile composite foundation in a mucky soil layer is much larger than the design value. Based on the sand pile construction and the load application process, a method of calculating the bearing capacity of the foundation based on the effective stress was proposed. Cavity diameter expansion in sand pile construction was simplified into a planar problem, and the cavity expansion theory was used to establish the expression of the rate of displacement and the horizontal stress increase. Based on the e–p curve and the calculation of the degree of consolidation, the relationships between the horizontal and vertical effective stress and the void ratio were obtained. According to the close relationship between the bearing capacity of the foundation in a mucky soil layer and the water content, an expression describing the relationships between the bearing capacity of the foundation, effective stress, void ratio, and water content was established. For the temporary engineering foundation treatment project, which needs a high bearing capacity but allows large foundation deformation, the design of sand pile composite foundations uses these relationships to take the consolidation effect of mucky soil into consideration, thereby reducing the replacement rate and lowering the construction cost.

Size distribution law of earthquake-triggered landslides in different seismic intensity zones

The Ms 8.0 Wenchuan earthquake in 2008 and Ms 7.0 Lushan earthquake in 2013 produced thousands of landslides in the southern region of the Longmen Mountains in China. We conducted field investigations and analyzed remote sensing data to determine the distribution law of earthquake-triggered landslides. The results show a strong negative power-law relationship between the size and frequency of landslides in VII, VIII, and IX seismic intensity zones, a weak power law in the X seismic intensity zone, and a lognormal distribution in the XI seismic intensity zone. Landslide density increases with increasing seismic intensity. A sand pile cellular automata model was built under the conceptual framework of self-organized criticality theory to simulate earthquake-induced landslides. Data from the simulations demonstrate that with increasing disturbance intensity, the dynamical mechanism of the sand pile model changes from a strong power law to a weak power law and then to a lognormal distribution. Results from shaking table experiments of a one-sided slope sand pile show that for peak ground acceleration (PGA) in the range of 0.075 g–0.125 g, the relation between the amount and frequency of sand follows a negative power law. For PGA between 0.15 g and 0.25 g, the relation obeys a lognormal distribution. This verifies that the above-mentioned distribution of earthquake-induced landslides should be a universal law from a physical viewpoint and may apply to other areas. This new perspective may be used to guide development of an inventory of earthquake-triggered landslides and provide a scientific basis for their prediction.

Effect of Density on Skin Friction Response of Piles Embedded in Sand by Simple Shear Interface Tests

This study focuses on a particular phenomenon related to the reduction in sand-pile skin friction with initial relative density increment from medium to dense. Frictional behaviour of sand-pile interface is simulated using a simple shear-type device capable of inducing constant normal stiffness condition. Sand-pile interface sliding and soil deformation components are distinguished quantitatively. The effects of initial relative density of sand, initial normal load, and constant normal stiffness are examined on the magnitude of the pile skin friction and shear displacement at failure. Results indicate that the magnitude of the mobilized shear stress at failure significantly relies on the shear stress state concerning the inflexion point on volume change graph, which is equivalent to the position of peak stress ratio. Good correlations exist between results of this study and field data of several heavily instrumented piles embedded in dense to very dense sands. The presented procedure is a useful framework for establishing more accurate skin friction calculation methodologies and t-z curve developments of axially loaded piles.

Some Alternative Solutions to Fractional Models for Modelling Power Law Type Long Memory Behaviours

The paper first describes a process that exhibits a power law-type long memory behaviour: the dynamical behaviour of the heap top of falling granular matter such as sand. Fractional modelling is proposed for this process, and some drawbacks and difficulties associated to fractional models are reviewed and illustrated with the sand pile process. Alternative models that solve the drawbacks and difficulties mentioned while producing power law-type long memory behaviours are presented.