Apparent Earth Pressure Research Articles

Effect of cross wall on the strut forces for braced excavations in clays

This study evaluates and estimates the effect of cross walls on the strut force for braced excavation in clays by using three-dimensional finite element analysis. A well-documented case history of a braced excavation with cross walls was utilized to validate the numerical analysis. Furthermore, a series of parametric studies were conducted to evaluate the distribution of strut force by considering different schematics of cross walls. The results revealed that implementing cross walls inside the excavation could significantly reduce the wall deformation and strut force along the wall section, particularly for the location near cross walls. In addition, a new empirical method was proposed to estimate the maximum strut force based on the apparent earth pressure for braced excavation with cross walls, which was verified through case histories. Finally, this study concluded that the existence of cross walls in braced excavations could ensure a safer bracing system and excavation design.

A Numerical Study of a Soil-Nail-Supported Excavation Pit Subjected to a Vertically Loaded Strip Footing at the Crest

Soil nailing is a prevalent and cost-effective technique employed to reinforce and enhance the stability of precarious natural or cut slopes; however, its application as a primary support system to prevent collapses or cave-ins during foundation excavation could be more frequent. To better understand the behavior of such a support system, this study simulated a full-scale nail-supported excavation for the foundation pit of a 20-story building to examine the effect of placing a strip footing with various combinations of configurations on the crest of the excavation pit. The results are discussed in terms of the nail axial force, wall horizontal deflection, basal heave, and safety factor against sliding. The results show that the footing width and setback distance are the two most significant factors dominating the wall horizontal deflection. This study also reveals that the maximum axial force is closely related to the apparent active earth pressure, which accounts for the presence of a tension crack, at nail depth. Such a finding allows engineers to assess and mitigate the risks of structural failure more effectively and optimize the design of nail-retaining structures.

Improved inverse analysis methods and modified apparent earth pressure for braced excavations in soft clay

Inverse analysis procedures are used to update project parameters and applied to predict future performance in the later stages. However, the inverse analysis procedure of earth pressure of excavation has received less attention. This paper proposes an improved inverse analysis method and the modified apparent earth pressure model for braced excavations in soft clay. A new procedure for inverse analysis of excavation is suggested based on the quintic spline interpolation function, and a trial algorithm is used to eliminate the errors generated in the inverse process. The proposed inverse solutions are validated by numerical simulations and reported engineering examples and show good agreements. Based on the inverse data and empirical apparent pressure diagram (APD), a modified apparent earth pressure method for braced excavations in soft clay is further suggested. And the relationship between the degree of anisotropy of soft clay and apparent earth pressure coefficients is discussed. The study results provide a reference for dynamic feedback design and adaptive management of the excavation.

Analysis of the Deformation Law of Deep and Large Foundation Pits in Soft Soil Areas

Taking a deep excavation in Suzhou soft soils adopting three support schemes as the background, the excavation performance metrics, including the heave and lateral deformation of diaphragm walls, surface vertical deformation, vertical deformation of surrounding buildings, and earth pressure, are thoroughly investigated based on 15 excavation cases collected in the soft soil area of Suzhou. Based on the analysis of monitoring data, some findings were achieved: the foundation pit deformation is greatly affected by the spatial effect. The existing station can constrain the foundation pit deformation. Benefiting from the combination of various support solutions, the average maximum deflection of the diaphragm wall is 0.10% He. The maximum lateral movement depth of the diaphragm wall (δhm) is mainly located at (He-7, He+12.5). The vertical deformation of the wall top is greatly affected by the excavation exposure time and soil conditions. The heave range of the wall top is (−0.08∼0.26%) He. Under the action of the displacement of the diaphragm wall to outside the pit and the upward displacement of the wall top, the ground surface is uplifted, and the maximum uplift is (0.02∼0.14%) He, ranging from 0.12δhm to 1.13δhm. The maximum surface settlement is (−0.01% ∼ −0.15%) He, ranging from −0.22δhm to −3.11δhm. The form of building heave is mainly affected by the surface heave and the distance from the diaphragm wall (d). When d is within a certain range, there is a heave settlement difference between the adjacent side and the opposite side of the excavation, and the adjacent side undergoes mostly subsidence, while the opposite side undergoes mostly uplift. The peak value of the apparent earth pressure (AEP) envelope is 0.59γHe, which falls within (0.47∼0.78) He. The calculation scheme proposed by Kim can be used to predict the AEP for multiple soil types.

Soil-Structure Interaction of Flexible Temporary Trench Box: Parametric Studies Using 3D FE Modelling

This paper presents the results of two parametric finite-element studies that were carried out using the PLAXIS-3D finite element (FE) computer code. The following objectives and corresponding parameters were considered: (i) to evaluate the soil pressure on the steel trench box shield; the parameters studied were related to soil type and material, and the study considered till, dry sand, wet sand, and sensitive clay soil; (ii) to assess the effect of trench box material and geometry on earth pressure; the parameters studied were related to trench box material (steel versus aluminum) as well as geometry (plate thickness and strut diameter). These studies included simulation of two steel (or aluminum) trench box shields stacked upon each other to cover the total 6 m (20 ft) deep trench. A Mohr-Coulomb (MC) constitutive material model was chosen for FE analysis (FEA). The FEA results were compared to empirical apparent earth pressure diagrams for a sensitive clay. Comparisons showed that the parameters related to the soil and the trench box have a significant influence on earth pressures.

The Calculation Method of Apparent Earth Pressure in Multi-Layered Ground with Clay and Sand

The Calculation Method of Apparent Earth Pressure in Multi-Layered Ground with Clay and Sand

Assessment of apparent earth pressure for braced excavations in anisotropic clay

The evaluation of strut forces is critical to ensure the system stability of braced excavation in urban areas. The most common empirical approach to determine the forces in the struts is the empirical apparent pressure diagram (APD) method. Although the importance of soft clay anisotropy on the stability of excavation systems has been demonstrated by various researchers, there are only limited studies on the influence of anisotropy of soft clay on the forces in the struts. In this paper, extensive plane strain finite element studies have been carried out to analyze the strut forces and the apparent earth pressures for braced excavations in anisotropic clay deposits. The NGI-ADP soil constitutive model was adopted in the finite element analyses to assess the influence of various soil properties and wall stiffness properties on the strut forces. Based on the numerical results, modified design pressure envelopes which consider the anisotropic behavior of clays are proposed for flexible and stiff walls.

Determination of apparent earth pressure diagram for anchored walls in c–φ soil with surcharge

PurposeThe purpose of this study is to present a diagram for the lateral earth pressure of c–φ soils exerted on anchored walls in presence of surcharge.Design/methodology/approachTo this end, two-dimensional plane strain modeling of anchored wall was carried out in Plaxis software. To validate the numerical model, two excavations with different specifications were simulated and the model results were compared with the available results. Subsequently, a parametric analysis was done and based on its results, a diagram was proposed for the lateral earth pressure of c–φ soils including the surcharge effects.FindingsThe proposed diagram without the surcharge and cohesion effects is a trapezoidal with zero value at the ground surface that is linearly approaching the apparent earth pressure of sand according to Terzaghi and Peck (1967) at 0.1H (H: wall height). The surcharge and cohesion effects at the ground level is 4 Ka*q and 0, respectively, and below 0.1H, they are treated as the same way for lateral earth pressure of a retaining wall. It should be emphasized that the apparent pressure diagram for design does not resemble the real distribution of earth pressure against the wall and it is for calculating the values of the anchors loads.Originality/valueThe available diagrams to determine the earth pressure exerted on the anchored walls are related to sandy or clayey soils and do not take the presence of surcharge into account. Thus, the proposed diagram is quite original and different from the previous ones.

Performance of Two Anchored Walls Under Cut and Fill Construction Sequences

Tieback walls are typically designed using apparent earth pressures that are obtained initially by back-calculating earth pressures from measured support loads for excavation only. For construction activities involving both excavation and backfilling aspects, the use of apparent earth pressures might not be adequate. This paper investigates the performance of two tieback walls constructed using a combination of fill and cut construction sequences. Results obtained from data collected using load cells and strain gages along with the soldier piles of both walls, show the correlation of axial loads and bending moments to construction activities. Results show that some load is transferred to the soldier piles during anchor installation, despite using steel casings to prevent this action. Backfilling behind the wall created significant curvature in the soldier piles based on the measured bending moments. Moreover, results evidence that the apparent earth pressure does not reflect the observed bending moments in the walls. However, a beam model including lateral displacement is presented to represent the measured response in both walls. The results unveil differences in anchor loads estimations, evaluates the appropriateness of apparent earth pressures for the design of tieback walls and provides design recommendations.

Monitoring and analysis of results for two strutted deep excavations using vibrating wire strain gauges

As part of the North East Line Mass Rapid Transit Project in Singapore, Contract 704 included the construction of two underground station structures. The excavation for Serangoon Station was in the residual Bukit Timah granite and the excavation for Woodleigh Station was in the residual Old Alluvium material. The temporary retaining structures for both excavations consisted of driven soldier piles and timber lagging supported by steel struts. The excavation for the construction of both stations was monitored in part using vibrating wire strain gauges on the struts. This paper presents the strut monitoring results. A comparison is made with the apparent earth pressure envelopes recommended by Peck. The need to balance continued development with the land constraints in Singapore means that underground structures will continue to be used. The results presented in this paper are relevant in determining the geotechnical parameters for deep excavation retaining walls constructed in these types of materials. It is concluded that the measured earth pressures relate reasonably well to the apparent earth pressure envelopes recommended by Peck.

Behavior of Braced and Anchored Walls in Soils Overlying Rock

This paper presents the results of analyses on the behavior of in situ walls, using the measured data collected from various deep excavation sites with multilayered ground conditions of soils overlying rock in Korea. A variety of in situ wall systems from >60 excavation sites were considered, covering a wide range of wall types, including H-pile, soil cement, cast-in-place pile, and diaphragm. The measured data were thoroughly analyzed to investigate the effects of wall and support types on lateral wall movements as well as apparent earth pressures. A series of 2D finite-element analyses were also performed to provide insights regarding the in situ wall behavior. Based on the results, lateral wall movements and apparent earth pressures are related to primary influencing factors affecting the wall behavior and information is presented in forms to provide tools that can be used for design and analysis.

Tieback Supported Cuts in Overconsolidated Soils

The performance of 11 tieback‐supported cuts is reviewed. The excavations were made in overconsolidated Gulf Coast soils in Texas. Excavation depths ranged from 27 to 64 ft (8.2 to 19.5 m). The measured performance characteristics are compared to observations made on internally braced cuts and other tieback‐supported cuts in overconsolidated soils. Tieback loads are based on measurements made during construction. Apparent earth pressures were computed and compared with published cases. Wall and ground movements beyond the excavations are presented and compared with published experience. Conclusions are presented for behavior and design considerations.

Internally Braced Cuts in Overconsolidated Soils

The performance of five internally braced cuts is reviewed. The excavations are made in overconsolidated Gulf Coast soils in Texas and Louisiana. Excavation depths range from 23 to 60 ft (7.0 to 18.3 m); the braces are prestressed for one cut. Bracing loads are reported on four cuts based on measurements made during construction. Apparent earth pressures are computed and compared with published values. Wall and ground movements beyond the excavations are presented and compared with published findings. Conclusions are presented for behavior and design considerations.

Strut loads in a braced excavation in soft clay : MOORE, PJ UNIV. MELBOURNE, AUS ERVIN, MC CITY ROADS BD. VICTORIA, AUS 7F, 1T, 6R. 2ND AUS-N.Z. CONF. GEOMECH, BRISBANE, 1975, INST. ENGRS, AUS. NAT. CONF. PUBL. NO. 75/4, P94–98

A description is given of a series of model tests in soft clay involving excavation through the clay with the vertical sheeting being supported by spring loaded struts. A method is proposed for calculating the total thrust carried by the struts and comparisons with observations are made. Comparisons are also made between individual observed and calculated strut loads, the latter being determined from a trapezoidal apparent earth pressure distribution.

Foundation, construction and performance for a 34-storey building in St Louis

A high-rise building consisting of a tower and adjoining low structure was constructed in 1968. The tower was founded on piers socketed into bed-rock, and the low structure on an overcompensated mat supported on medium silty clay. The significant aspects of the construction of drilled piers for the tower and the braced excavation for the low structure are described. Field measurements were made in the braced excavation; they consisted of measurements of loads in the struts during and after prestressing, lateral and vertical movements of adjacent streets and buildings, and heave of the bottom of the excavation. Strut loads agreed with Peck's apparent earth pressure envelope, except where the struts were prestressed to a higher load during installation. After construction, some measurements were continued, particularly of the mat foundation settlement and the strains and stresses in one rock-socketed pier supporting the tower. Difficulties with loss of ground during construction of the drilled piers are described, as well as the solution eventually developed. Un ensemble composé d'une tour et d'un édifice adjacent de faible hauteur fut construit en 1968. La tour est fondée sur des pieux ancrés dans le rocher; l'édifice de faible hauteur sur un radier compensé reposant sur une argile limoneuse de consistence moyenne. Les aspects signiticatifs de la construction des pieux forés pour la tour et de l'excavation blindée pour l'édifice de faible hauteur sont décrits. Des mesures in situ ont été effectées dans l'excavation blindée. Elles consistaient en mesures des charges dans les étrésillons pendant et après la précontrainte, des mouvements horizontaux et verticaux des rues et des bâtiments adjacents et du soulèvement du fond de l'excavation. Les charges dans les étrésillons étaient en accord avec l'enveloppe de poussée apparente des terres dévelopée par Peck, sauf là où les étrésillons avaient été précontraintes à une charge plus élevée lors de leur mise en place. Aprés construction, quelques mesures furent continutées, en particulier le tassement du radier et les déformations et contraintes dans un des pieux ancrés dans le rocher supportant la tour. Des difficultés de perte de sols rencontrées pendant la construction des pieux forés sont décrites, ainsi que les solutions mises au point.

Circular Land Cofferdam for Deep Excavation

Site conditions, dewatering, design, construction procedures and observations and stress measurements made during construction of a circular land cofferdam for a 79-ft (24.0-m) deep excavation for construction of a car dumper structure for Oak Creek Power Plant in Oak Creek, Wis., are described. The cofferdam consisted of wood lagging, soldier posts, four levels of concrete ring beams, and a lower caisson section. The concrete ring beams were instrumented with mechanical strain gages. Apparent earth pressure diagram computed from the results of the instrumentation is presented. Design and construction of the caisson section and the dewatering system are also examined.

Guages used in testing materials

As part of the North East Line Mass Rapid Transit Project in Singapore, Contract 704 included the construction of two underground station structures. The excavation for Serangoon Station was in the residual Bukit Timah granite and the excavation for Woodleigh Station was in the residual Old Alluvium material. The temporary retaining structures for both excavations consisted of driven soldier piles and timber lagging supported by steel struts. The excavation for the construction of both stations was monitored in part using vibrating wire strain gauges on the struts. This paper presents the strut monitoring results. A comparison is made with the apparent earth pressure envelopes recommended by Peck. The need to balance continued development with the land constraints in Singapore means that underground structures will continue to be used. The results presented in this paper are relevant in determining the geotechnical parameters for deep excavation retaining walls constructed in these types of materials. It is concluded that the measured earth pressures relate reasonably well to the apparent earth pressure envelopes recommended by Peck.