Bearing Capacity Factors Nq Research Articles

Pullout behavior of a bearing polymeric strap under monotonic and cyclic tensile loads

Soil-reinforcement interaction consists of three factors including frictional resistance, shear strength of the soil and passive resistance. In the ordinary polymeric strap (PS) reinforcement, only frictional resistance contributes to pullout resistance. In this study, in order to develop passive resistance in the soil, a number of angles as transversal elements were attached to PS reinforcement, which is called bearing polymeric strap (BPS). The post-cyclic pullout behaviour of the BPS is evaluated using a large-scale pullout apparatus adopting multistage pullout (MSP) test and one-stage pullout (OSP) test procedures. The results show that a spacing-to-high ratio of angles equal to 3.33 gives the maximum pullout resistance. MSP tests were performed on the BPS with an optimum arrangement to evaluate the influence of various factors including cyclic tensile load amplitude, load frequency and number of load cycles, and also the influence of vertical effective stress on the pullout resistance and the peak apparent coefficient of friction mobilized at the soil-BPS interface. Moreover, for BPS system with a single isolated transverse member, the bearing capacity factor Nq was calculated using equations based on three failure modes and it was found that the Nq calculated in the punching shear failure mode makes the best prediction.

An exercise on the bearing capacity of strip foundations

This paper deals with the exact solution of the bearing capacity of strip foundations on weightless cohesive−frictional soil considering the inclination of the (a) foundation base, (b) ground surface and (c) loads on the foundation base and on the ground surface. It will be seen that the upper bound and the lower bound solutions coincide unless extreme conditions are considered. New definitions for the bearing capacity factors Nq and Nc will then be provided.

Upper bound solutions of vertical bearing capacity of skirted mudmat in sand

The mudmat is an important foundation form for deep water oil and gas engineering in the sub sea production system. The mudmat has a wide application prospective because of its shallower buried depth and convenient construction in the ocean. The existence of skirts, which are set up at the bottom of the mudmat in order to adapt to the requirements of the foundation slip resistance, increases the difficulty in the vertical bearing capacity calculation of the mudmat. The mudmat is simplified to a skirted strip foundation in this paper, and the mechanisms have been proposed according to the surcharge soil assumption. The upper value of the vertical bearing capacity of the mudmat is obtained by the upper bound theorem of the limit analysis. The soil damage rate as a new empirical parameter concerning the combined action between the skirts and the inner soil of the foundation has been defined. The value of the soil damage rate indicates the range of soil failure. The relationship between the soil damage rate and the aspect ratio is determined for the mudmat using a two-dimensional simplified analysis. The relationship of the bearing capacity factors Nq and Nγ with the friction angle is also discussed under the different soil damage rates.

BEARING CAPACITY OF STRIP FOOTING ON REINFORCED LAYERED GRANULAR SOILS

In this study a limit equilibrium method is proposed to determine the bearing capacity of strip foundations on geosynthetic reinforced sand soils. A two-layered granular soil was foreseen to represent the loose in situ soil and the compacted fill above the reinforcement. First the modified bearing capacity factors Nq and Nγ were derived for the two layered granular reinforced soil. The bearing capacities were also calculated for different reinforcement geometries and soil properties using Finite Element analyses. The bearing capacities obtained from Finite Element and Limit Equilibrium analyses were compared, it was seen a good agreement. Therefore, it was concluded that the new limit equilibrium method proposed in this paper for reinforced two-layered soils can be successfully used in calculating the bearing capacities of geosynthetic reinforced soils.

Vertical bearing behaviour of the composite bucket shallow foundation of offshore wind turbines

A composite bucket shallow foundation (CBSF) has been proposed by Tianjin University to adapt the offshore soft geological conditions of China for wind turbines. Vertical bearing capacity modelling and observation tests regarding the CBSF are performed. The test results are accompanied by numerical simulations to provide a better understanding of the failure mechanism of the CBSF. The upper limit of the vertical bearing capacity of the bucket foundation is derived through the upper bound theorem of classical plasticity theory according to the failure mechanism. The soil damage rate is specified as a new empirical parameter in the formula and is defined as the rate between the thickness of the soil that is broken inside the foundation and the radius of the foundation, which indicates the range of soil failure. Furthermore, the range of the soil damage rate is obtained through vertical bearing capacity model tests. The relationship of the bearing capacity factor Nq and Nγ with the friction angle is also discussed under the specific soil damage rates.

Interactional Properties between Drag Anchor and Installation Line

During penetrating of a drag anchor in seabed soils, complex interaction happens between the anchor and installation line. It is important to clarify the properties of the drag force and drag angle at the shackle of the anchor, which are especially meaningful to the design and theoretical analysis of drag anchors. The interactional properties between the drag anchor and installation line are theoretically and experimentally investigated in the present work. Based on mechanical models for the embedded line and drag anchor, analytical expressions that can predict the drag force at the shackle for both cohesive and noncohesive soils are derived. Theoretical methods are also developed to predict not only the evolution but also the exact value of the drag angle at the shackle during anchor penetration. All the analytical methods are examined by comparing the predicted drag force and drag angle with available experimental data. A detailed parametric analysis is also performed to explore the effects of different parameters on the drag force and drag angle and to determine reasonable values of several key parameters, including the lateral soil pressure factor K, the angle of interface friction δ, and the bearing capacity factor Nq.

Model Test Research of Surcharge Contribution to Ground Bearing Capacity

To investigate the influence of surcharge on bearing capacity, model tests were performed. In the tests, 5 kPa and 10 kPa surcharge was applied on silt respectively. The bearing capacity factor Nq is smaller than theoretical solution, and is only of 60.3% and 80.5% of theoretical solution. Model test show that the ground failure mode is not general shear failure mode in condition of ground under surcharge. In bearing capacity calculation, if bearing capacity factor theoretical solution which is from general shear failure mode is applied, the result will be overestimate.

A Simple Limit Equilibrium Approach for Calculation of Ultimate Bearing Capacity of Shallow Foundations on Two-Layered Granular Soils

The bearing capacity of shallow foundations in a non-homogeneous soil profile has been a challenging task in geotechnical engineering. In this paper, a limit equilibrium method is used for calculating bearing capacity factors of shallow foundations constructed on a two-layered granular soil profile. The main objective has been to determine the ultimate bearing capacity computed from equivalent bearing capacity factors Nq and Nγ and comparing that with numerical analysis using finite element methods. It will be shown that the data obtained form the developed method are well comparable with those obtained from FE approach, specially when the difference between shear strength parameters of layers is low which is a practical case for sedimentary soil profiles and also for artificially compacted soils. A computer program has been developed to investigate the influence of various parameters on bearing capacity factors.

A limit equilibrium solution for bearing capacity of strip foundations on sand

A limit equilibrium analysis is used in this paper to obtain the bearing capacity of a strip foundation on sand. Bearing capacity factors Nq and Nγ are determined for a practical range of friction angles, using a minimization procedure. The dilatancy angle Ψ of the sand coupled with the apparent friction angle ϕ allows the use of a modified friction angle ϕ*, which is in turn employed in the analysis. Comparisons with previous published data indicate that the proposed analysis gives adequate results. It is also shown that consideration of a dilatancy angle Ψ < ϕ leads to a bearing capacity value that is lower than that obtained for the case with Ψ = ϕ.Key words: limit equilibrium, bearing capacity, sand, dilatancy, strip footing, Nq and Nγ factors.

Bearing Capacity of Expanded‐Base Piles in Sand

The results of loading tests are used to develop empirical correlations between the point‐bearing resistance of expanded‐base piles and the results of standard penetration tests. The resistance is shown to be proportional to depth for piles having shaft lengths not exceeding 10 base diameters. The results also show that there is no significant difference between the point resistance of piles in relatively homogeneous soils and piles founded in a bearing stratum overlain by soft, compressible soil at the same overall depth/base diameter ratio measured from ground surface. Values of the bearing capacity factor Nq were calculated by dividing the point resistance at failure by the effective overburden pressure at the level of the maximum cross section of the base. Nq was found to decrease dramatically with increasing effective overburden pressure, indicating that ambient stress level must be considered in bearing capacity analysis. The results show no evidence of a critical depth below which point resistance is constant; rather point resistance continues to increase with depth, but at a reducing rate.