Contiguous Pile Research Articles

Lateral Response of Contiguous Pile Wall Subjected to Staged Excavation: Physical and Numerical Investigations

In this paper, the lateral response of a contiguous pile wall retaining system under staged excavation is investigated using physical modelling. The effect of pile stiffness on pile wall deformation is studied by changing the diameter of pile. Numerical simulation of the physical response of the pile wall is studied using the finite element program PLAXIS-3D. Results of the finite element (FE) analysis are in good agreement with the experimental results. Sensitivity analysis is carried out to evaluate the effect of unit weight and friction angle of sand on the lateral response of the pile wall. It is found that with increase in the unit weight of sand, the deformation of pile wall increases and with increase in the friction angle of sand, the deformation of pile wall reduces. Experiments were performed on the sand to evaluate the unit weight, friction angle, Young’s modulus and Poisson’s ratio of sand corresponding to the four different values of the relative density (i.e. Dr = 15, 35, 65 and 85%). The response of the pile wall under stage excavation with change in the relative density of sand is studied by performing FE analysis. It is found that with increase in the relative density of sand, the deformation of pile wall reduces. The interpretation of modulus of elasticity of sand from the modulus of subgrade reaction evaluated from the plate load test is also presented. Based on the results of the FE analysis, it is noted that the finite element method (FEM) can be used for the real-time simulation of the lateral response of the pile wall systems.

Undrained limiting pressure behind soil gaps in contiguous pile walls

Finite element limit analysis with plane strain condition is employed to determine the upper and lower bound solutions of the undrained limiting pressure behind soil gaps and the lateral force acting on a pile per unit length in a contiguous pile wall. Computed bound solutions confirm serious limitations of existing studies in predicting these two solutions. Predicted failure mechanisms and the arching effect behind soil gaps are discussed. A closed-form equation of the limiting pressure factor is proposed for a convenient and accurate prediction of the lateral force acting on a pile in contiguous pile walls in practice.

Seepage and pore pressures around contiguous pile retaining walls

Diaphragm and bored pile retaining walls are often used for the construction of basements, metro station boxes and cut-and-cover tunnels in urban areas. While diaphragm and secant pile walls are generally intended (and assumed in analysis) to be effectively impermeable, contiguous piles may allow through-the-wall seepage even when preventative measures have been undertaken. Provided the flow rates can be tolerated or dealt with, through-the-wall seepage should result in a reduction in pore water pressures behind the retaining wall compared with an impermeable construction, giving the potential for reductions in the depth of embedment and wall thickness, and hence cost. However, this potential is rarely realised owing to the difficulty in quantifying with sufficient confidence the hydraulic regime associated with a leaky retaining wall. This paper reports the results of laboratory investigations and numerical analyses carried out to assess the effect of the inter-pile gaps on the pore pressure distribution around a contiguous pile retaining wall. The results show that the pore pressures behind the piles reduce significantly as the pile spacing is increased. Long-term field monitoring confirms that the pore water pressures are much lower than would be expected for an impermeable retaining wall in similar soil. The applicability of a simple expression linking the pile diameter, pile spacing and the effective permeability of an equivalent uniform wall is demonstrated.

Study of the progressive collapse mechanism of excavations retained by cantilever contiguous piles

Abstract An increasing number of catastrophic progressive collapses of deep excavations have occurred throughout the world. However, the mechanism by which partial failures evolve into large-scale progressive collapses has rarely been studied. In this paper, long-strip excavations and square excavations retained by cantilever contiguous piles under partial failure were simulated using the explicit finite difference method (FDM). The results show that a partial collapse can cause sharp increases in the internal forces in adjacent intact piles through the horizontal arching effect. Therefore, the concept of a load transfer coefficient is proposed, which is equal to the ratio of increase of the internal force in an intact pile. The relationship between the maximum load transfer coefficient Tmax and the safety factor of the piles determines whether progressive collapse will occur. Furthermore, the influences of a number of important factors on the load transfer mechanism, such as the capping beam, the extent of partial failure, the soil strength, the excavation depth and the corner effect, were examined. A continuous capping beam can reduce the maximum load transfer coefficient Tmax. Within a certain range of the extent of partial collapse, a larger partial collapse extent will produce larger load transfer coefficients and have a greater influence over a larger area. For the same retaining structure, a higher soil strength will result in larger load transfer coefficients. Moreover, when the lateral stiffness of the retaining piles is lower, the maximum load transfer coefficient will be smaller and the range of influence will be larger. In an excavation with a corner effect, when the number of failed piles is above a certain threshold, the maximum load transfer coefficient decreases with an increasing number of failed piles. Therefore, the progressive collapse evolving toward the corner will terminate when the maximum load transfer coefficient decreases below the safety factor. The corner effect can be recognized as a cause of the natural termination of progressive collapse.

Nature Sides with the Hidden Flaw: Lessons Learned from Failures of Earth-Support Systems

In recent years, the demand for excavations and fills of significant height has increased due to many factors, including requirements for below-grade parking for urban buildings and the need to construct on sites with difficult terrain and topography. Fortunately, substantial advances in engineering techniques and systems are now available for the support of cuts and fills, including mechanically stabilized earth (MSE), soil nailing, contiguous pile walls, diaphragm walls, deep soil mixing, and soil freezing, among others. But despite our increasing knowledge and understanding of soil-support systems, failures still occur with some regularity.

A Singapore case history of temporary removable ground anchor design to TR26: 2010

Contract 937B, design and construction of Tai Seng Facility Building (TSFB), is part of Downtown Line Stage 3 (DTL3) of the Singapore mass rapid transit (MRT) System. The proposed TSFB will provide maintenance, operation and staff facilities for DTL3. It is a 52 m wide and 295 m long underground building which consists of two basement levels and entrance structure at ground level. The depth of excavation for the construction of basement is approximately 20 m. The schedule for completion of this project is very tight and it is critical to optimise the design of earth retaining and support system (ERSS). Contiguous bored pile (CBP) wall retaining system supported by temporary removable ground anchorage and a top-down roof slab is proposed as the ERSS for the excavation and construction of the underground TSFB. Partial top-down construction method is adopted, where the roof slab with large access opening will be cast first. Excavation will proceed and ground anchors will be installed as excavation progress d...

Top-Down 공법이 적용된 흙막이벽의 역해석을 이용한 거동분석

본 연구에서는 흙막이벽 설계시 널리 사용되고 있는 SUNEX 프로그램을 이용하여 Top-Down 공법이 적용된 지중연속벽, 주열식 흙막이벽(CIP벽, SCW벽)의 변형거동을 분석하였다. 해석프로그램에 Rankine의 토압(1857), Terzaghi and Peck의 토압(1967), Tschebotarioff의 토압(1973), 홍원표 윤중만의 토압(1995a)을 적용하여 흙막이벽의 수평변위를 예측하였다. 프로그램 해석결과, 흙막이벽의 수평변위량은 토압의 종류에 따라 큰 차이를 나타내고 있다. 홍원표 윤중만의 토압(1995a)을 적용하여 얻은 흙막이벽의 예측수평변위량이 실측수평변위량과 가장 유사하게 나타났다. 따라서 프로그램 해석시 홍원표 윤중만의 경험토압(1995a)을 적용하면, Top-Down 공법이 적용된 흙막이벽의 변형거동을 비교적 정확히 예측할 수 있다. The behaviors of a diaphragm wall and a contiguous pile wall such as CIP(Case-in-place pile) and SCW(Soil-cement wall), applied to the top-down construction method, were analyzed using the SUNEX program, which is widely used to design earth retaining walls. Four types of earth pressures, as described by Rankine (1857), Terzaghi and Peck (1967), Tchbotarioff (1973), and Hong and Yun (1995a), were applied to the analysis program to predict the lateral displacement of walls. The results show that the displacements of an earth retaining walls vary with the applied earth pressure. The predicted lateral displacement based on Hong & Yun's (1995a) earth pressure is similar to the measured displacement. Therefore, the actual lateral displacement of an earth retaining wall, as applied to top-down construction method, can be accurately predicted by using an analysis program considering Hong and Yun's (1995a) earth pressure.

PERFORMANCE OF CONTIGUOUS PILE WALL FOR DEEP EXCAVATION ON CHAO PHRAYA RIVER BANK

The excellent medical center in Asia, Siriraj Hospital is the largest medical center in Asia is constructed with three basement floors on Chao Phraya River bank and close to the preserved building seated on shallow foundation. The excavation is about -10.85 m. depth below ground surface. The contiguous pile wall was used as the temporary soil protection system and permanent wall with two layers of temporary steel bracing system. The behavior of contiguous pile wall was predicted by Finite Element Method (FEM) with simulation of all construction sequences. The instrument including inclinometer, tiltmeter, piezometer and ground surface settlement were installed in the contiguous pile, preserved building and in the ground, respectively. The performance of the contiguous pile wall was evaluated by instrumentation monitoring compared with FEM analysis and trigger level.

Wall and Ground Movements due to Deep Excavations in Shanghai Soft Soils

An extensive database of 300 case histories of wall displacements and ground settlements due to deep excavations in Shanghai soft soils were collected and analyzed. The mean values of the maximum lateral displacements of walls constructed by the top-down method, walls constructed by the bottom-up method (including diaphragm walls, contiguous pile walls, and compound deep soil mixing walls), sheet pile walls, compound soil nail walls, and deep soil mixing walls are 0.27%H, 0.4%H, 1.5%H, 0.55%H, and 0.91%H, respectively, where H is the excavation depth. The mean value of the maximum ground surface settlement is 0.42%H. The settlement influence zone reaches to a distance of about 1.5H to 3.5H from the excavation. The ratio between the maximum ground surface settlement and the maximum lateral displacement of a wall generally ranges from 0.4 to 2.0, with an average value of 0.9. The factors affecting the deformation of the wall were analyzed. It shows that there is a slight evidence of a trend for decreasing wall displacement with increasing system stiffness and the factor of safety against basal heave. Wall and ground movements were also compared with that observed in worldwide case histories.

Opening ceremony shaft for the Athens 2004 Olympic Games

Key aspects of the analysis, design and construction of the retaining structure for a central circular shaft inside the Olympic Stadium of Athens are described. As part of the opening ceremony of the Athens 2004 Olympic Games, the shaft was used as an invisible underground entrance into the stadium, playing a key role in the ceremony. Given the significant depth and the large diameter of the shaft (both about 25 m), excavating and retaining under extreme time constraints and with presumed high water table constituted a challenge. It was accomplished with recourse to the observational method. The retaining structure comprised 1·2 m diameter contiguous piles capped with a ring beam. The initial design used a form of top-down construction of the final 0·75 m thick permanent concrete lining. Delays in starting the excavation necessitated that a depth of 17·5 m be reached before any permanent lining could be constructed. The paper presents the design of the retaining structure, the developed finite element analysis, and the theoretical predictions during the various excavation stages. A detailed monitoring programme was implemented and utilised in the spirit of the observational method. Comparisons every two days of measured against original (class A), as well as updated, analytical predictions led to the successful completion of the project.

Installation effects of a bored pile wall in overconsolidated clay

In situ embedded retaining walls are used to form basements and cuttings in urban areas throughout the world, particularly where space is restricted. It is generally accepted that the process of installing such a wall may influence the stress state of the soil and hence the post-construction displacements, wall bending moments and prop loads. However, wall installation is a complex three-dimensional problem, and its effects are not well understood. This paper describes a study carried out on a section of contiguous bored pile retaining wall in an overconsolidated clay in Kent, England, using instrumentation to monitor total horizontal stresses and pore water pressures before, during and after wall installation. Reductions in horizontal stress were recorded during wall installation, bringing the ratio of horizontal to vertical effective stress, K, from an initial value of about 1 to about 0·8. Following wall installation there was no further change in horizontal stress over an additional period of 10 months during which no further construction work took place.

A34 Chieveley/M4 junction 13 improvement: design

The project involved the grade separation of the A34 at junction 13 of the M4 motorway and was carried out under a design-and-build contract. Three integral bridges with contiguous pile wall abutments and Y-beam and slab decks were designed for construction in a top-down sequence while maintaining three lanes of traffic in each direction on the M4. This paper describes the design process, including derivation of earth pressures on the integral abutments, analysis of the soil–structure interaction and the global analysis of the structure. Comparison is made between the design methods required by BD 42/00 which embodies CIRIA Report 104 and the recently published CIRIA C580, and matters pertaining to the design of integral bridges with frame and embedded type abutments are identified for discussion.

A34 Chieveley/M4 junction 13 improvement: design

The project involved the grade separation of the A34 at junction 13 of the M4 motorway and was carried out under a design-and-build contract. Three integral bridges with contiguous pile wall abutments and Y-beam and slab decks were designed for construction in a top-down sequence while maintaining three lanes of traffic in each direction on the M4. This paper describes the design process, including derivation of earth pressures on the integral abutments, analysis of the soil–structure interaction and the global analysis of the structure. Comparison is made between the design methods required by BD 42/00 which embodies CIRIA Report 104 and the recently published CIRIA C580, and matters pertaining to the design of integral bridges with frame and embedded type abutments are identified for discussion.

Significance of discontinuity surveying in motorway alignment selection, southern Turkey

A detailed discontinuity survey is an essential part of a route location study, because rock quality and subsurface geological conditions can be determined by examining discontinuity systems. It also helps to prepare a sound subsurface investigation programme in the later stages of an engineering project. Some of the more expensive structural elements of a motorway are tunnels, viaducts, reinforced retaining walls and contiguous piles. Each has special requirements depending on ground stability, cost and environmental aspects. A detailed discontinuity survey enables engineers to select the best route and to optimize the geotechnical design. A case study from the Tarsus-Adana-Gaziantep (TAG) motorway being constructed in southern Turkey displays well the role of a discontinuity survey in engineering geological and geotechnical work. The survey, which was carried out by visual inspection and practical field tests, indicated, on the basis of the consistency of the discontinuity systems in each rock exposure, that the suspected floating blocks were outcrops of in situ rock. Misinterpretation of the actual ground condition caused loss of both time and money.

M25 NORTH-EAST SECTOR, HOLMESDALE AND BELL COMMON TUNNELS: CONSTRUCTIO N.

The two cut-and-cover tunnels on the north-east sector of the M25 motorway at Waltham Cross and Epping formed part of two larger contracts awarded to two contractors for the construction of the M25 between the M11 and A10. The 470M long Bell Common tunnel at Epping is situated in an environmentally sensitive area adjacent to Epping Forest, while the 650 m long Holmesdale tunnel passes through a narrow corridor between residential development. Secant and contiguous piles were adopted for the construction of the Bell Common tunnel walls and, at Holmesdale tunnel, the outer walls were constructed using diaphragm wall techniques. The sequence of construction for both tunnels limited excavation until the roof was complete. This paper describes how each contractor dealt with the general problems of constructing the works, the particular programming and temporary works problems caused by service and traffic diversions, the sequence of construction and the requirement for staged completion to allow access for the mechanical and electrical contractors. See also TRIS 451953 and 451954. (Author/TRRL)

Diaphragm walls and anchorages: A review of the recent ice seminar : Hanna, T H; West, A S Ground Engng, V9, N8, Nov 1976, P26–32

This report reviews conference papers on recent developments in design, construction, research and materials in this area of diaphragm walls and anchorages. The first seminar session presented a general analysis of available methods for designing diaphragm walls and anchorages. Certain disadvantages in presently used methods were pointed out and the design and behavior of individual ground anchors for back retaining walls were discussed. Comments were made on the use of diaphragm walls as load bearing structures, the limit state methods of design, surcharge loading, pulling tests, assessment of ground conditions, and skin friction on piling. A second session considered current design practice applied in differing ground conditions for diaphragm walls, contiguous piles and anchorages. Practice in the application design detail for diaphragm walls and contiguous piling was the subject of the 3rd session, while session IV dealt with practice in the detail design applications of anchorages. Further sessions covered the following topics: the design and control of bentonite/clay suspensions and concrete in diaphragm walls and anchorages; installation techniques and testing procedures for ground anchors; and slurry trench practice for diaphragm walls and cut offs.