Effects of excavation and construction sequence on behavior of existing pile groups

In congested urban areas, new structures are regularly constructed next to high-rise buildings. At different stages of excavation for the new structures, settlement and tilting of the adjacent piled buildings may be occurred. Thus, attention here will be focused on the interaction behavior between deep excavation and adjacent piled foundations. Accurate prediction of soil movement and pile response plays an important role in preventing damages to adjacent buildings. Finite-element models are employed to compute the pile group responses. The parametric study has been performed by varying pile group configurations, center-to-center pile spacing, and new building load. Two, four, and six capped head pile groups next to excavation sites have been examined. In this paper, discussion centers on settlement and tilting of the pile groups nearby an excavation in fully saturated sand. The influence of pile group configuration and new building loads are systematically investigated. New building can be constructed in the excavated area after completion of the excavation. The effect of new building construction sequences is also investigated. Results provide confirmatory evidence that, excavation depth has the most significant effect on pile settlement and pile cap tilting. High pile cap tilting and small pile group settlement are apparent in case of two piles near the excavation. For the four pile group, the induced tilting of pile cap decreases as spacing between the piles increases. Due to construction of the new building, the settlement is exacerbated but the tilting is moderated.


Introduction
Excavation works inevitably have side effects on the nearby bridges and high-rise buildings, which are supported by pile foundations.During the excavation works, special care should be paid to nearby adjacent structures and utilities.Existing structure foundations and soil conditions are significantly affected by the adjacent construction activities.Thus, understanding effect of excavation on adjacent piled buildings has been improved with increasing demands for underground spaces in geotechnical engineering.Excavation causes horizontal and vertical soil movements.The vertical soil movements induce settlement and tilting on adjacent pile foundations.A clearly noticeable settlement and tilting may be observed when the piles are located closer to the excavation.Support system design and soil properties can play a significant role in limiting damage to adjacent structures.Although stiff excavation support system may provide a safety factor against structural damage, it may yield soil movements and deformations.Excavation in fully saturated sand introduces flow of water, which has an impact on stability of the excavation bottom as well as the adjacent buildings.Building-excavation interaction can be investigated by using finite element method.Numerical runs have been performed on capped head pile groups consisting of two, four, and six piles near an excavation to look at the group effect with different number of loaded piles.In the USA, 223 Page 2 of 12 buildings failures caused by adjacent excavation activates constitute account for around 4% of the 225 documented building failures between 1989 and 2000 [1].There are many examples where pile foundations have been damaged by an adjacent excavation.Field investigations revealed that excavation-induced settlement and tilting had caused damage to a large number of buildings supported by pile foundations.For example, a 9-story office block founded on piles was tilted and demolished in 1991 [2].Moreover, a high-rise building collapsed in China in 2009 [3][4][5].Tilting and damage to buildings adjacent to excavation in a thick layer of sand were explored by [6].The damage potential index given by [7] was reasonable with observations in the field.Many studies have been performed to investigate excavation-induced horizontal displacement and bending moment in existing piles via numerical analyses [8][9][10], centrifuge tests [11][12][13] and actual full-scale test [14].Side effects of shallow and deep excavations on existing pile foundations were demonstrated by [2].Extensive three-dimensional numerical analyses such as [15][16][17][18][19] have been carried out in order to predict the pile deformation mechanism, differential settlement, drift in the building, and changes in axial load distribution during construction of an adjacent excavation.Pile vertical response was significantly affected by the load applied on the pile before the excavation [20].In addition, soil settlement below the pile base and reduction in the pile capacity were observed due to excavation in soft soils [21].Movement of soil around a loaded pile caused by the adjacent excavation was examined by [22] using PLAXIS 3D finite element software.The pile settlement due to adjacent excavation can be determined using an analytical model in simplified conditions (i.e., there is no load transfer between soil springs) [23].In dry sand, pile settlement and mechanisms of stress transfer due to an adjacent excavation were investigated using three-dimensional numerical analyses [24].Moreover, centrifuge tests and numerical analyses have been performed by [25] to investigate impact of nearby twin excavations on behavior of an existing single pile.Some studies have been carried out to examine pile settlement in dry sandy soil due to adjacent excavation.However, the settlement and tilting of a pile group combined with applied working load adjacent to supported deep excavation in saturated sand have not been extensively studied.
Although interaction of excavation and adjacent piled foundations has received attention in research, most of the previous researches focused on pile response due to the adjacent excavation.Numerical analyses in this study have been performed to evaluate effects of excavation and new building construction sequence on adjacent piled structures.Excessive settlement and tilting of piled structures may result from adjacent deep excavation in sand below the water table.The aim of this study is to analyze settlement and tilting behavior of a capped pile groups during and after the excavation.
After completion of the excavation, new structure can be constructed in the excavated area.Furthermore, load of the new building is increased with advancement of the construction.Thus, this study will capture the effect of new building applied load on performance of the adjacent pile groups.

Three-dimensional numerical analysis
Finite-element method is a very popular technique for applications in geotechnical engineering.The finite-element method can reflect the complex ground movements and deformations caused by an excavation.Finite-element program PLAXIS 3D (CONNECT Edition V20) [26] was employed in the numerical analysis.Figures 1, 2, 3, 4, 5 show typical excavation geometry, pile group configurations, distances, and dimensions for all the tests that were selected in the analysis.Because of symmetry plane, just half width of the excavation has been modeled in order to accomplish this study with minimum mesh generation in a reasonable time.In this model, the excavation length and width were 24 and 10 m, respectively.In common engineering practice, ratio of diaphragm wall penetration depth to excavation depth was varied between 0.5 and 2.0 [27,28].Therefore, the ratio was designed as 1.0 in this study.As shown in the figures, five levels of struts were installed at 1.0, 4.0, 7.0, 10, and 13 m below ground surface.Moreover, struts were constructed 0.5 m above level of the excavation in all stages.Horizontal spacing of the struts was 8.0 m.Responses of pile groups subjected to initial working loads and adjacent to deep excavation work in Berlin sand has been investigated in this analysis.

Finite-element mesh and boundary conditions
Figure 6 presents a 3D view of the finite-element mesh and boundary conditions employed in this analysis.The mesh width (x) was 24 m, and the mesh depth (z) was 45 m.The mesh length in the lateral direction (y) was 70 m in order to capture the influence zone of settlement trough nearby the excavation [29].In addition, the boundaries were far enough away to prevent any restriction to the analysis.Mesh sensitivity analysis was carried out in order to determine a suitable mesh size.Fine mesh-size with a relative element size factor about (0.7) was chosen.Additionally, mesh becomes finer with a relative element size factor about (0.35) for the plates and embedded piles as large shear strain variations were expected.Moreover, the soil elements are relatively small near the excavation and gradually increase in size as they move away from it to maintain a logical balance between the results accuracy and computational cost.Based on a numerical parametric analysis, the mesh refinement degree was chosen by the criterion that the variation of computed pile group settlement was less than 10% if size of the current mesh was halved.Therefore, a good balance has been achieved between analyzing costs and accuracy.Vertical loads from the new building were applied as uniformly distributed axial loads on a 1.0 m thick concrete raft.The uniformly distributed axial load was applied on the raft and increased gradually from 50 kN/m 2 to 200 kN/ m 2 .Soil elements in the mesh were the 10-node tetrahedral elements.The tetrahedral soil elements provided a secondorder interpolation of displacements.Moreover, the 10-node tetrahedral element can be crossed by the pile at any place.In addition, 6-node plate element was employed to model behavior of the pile cap, diaphragm wall, and raft of the new building in the excavated area.Moreover, soil-wall interaction was simulated using 12-node interface elements.The interface element consists of a pair of nodes to ensure that it is compatible with the 6-noded triangular side of plate element or soil element [26].Three degrees of freedom (ux, uy, uz) are available for translation in each node in the interface element and differential displacements can occur.Struts were simulated in the analysis using fixed end anchor elements.The fixed end anchors were considered to be point elements in PLAXIS 3D.Embedded piles with 3-node line elements, which are available in PLAXIS 3D were employed to simulate the bored piles.The embedded piles interact with soil by means of special interface elements and behave like volume piles.To reduce effects of the undesirable meshdependent, specific volume around the embedded pile based on the pile diameter (elastic zone) is assumed in the analysis.Embedded pile model is capable of modeling the soil-pile interaction under lateral load and able to reproduce behavior of laterally loaded pile with rough shaft surface in numerical analysis [30].Estimation of pile group behavior by employing the current embedded pile model was described by [31].Moreover, validation and formulation of the embedded pile element can be found in [26,32,33].These validation studies show a reasonable agreement with the calculations and field measurements for bored piles.The details about the elements and interface properties can be found in [26].In total, mesh in Test G1 consisted of 33,727 nodes and 19,450 soil elements with average element size about 3.19 m.The model bottom boundary was fixed by pin supports in all directions, while roller supports restrained soil deformations in directions normal to vertical planes.However, the model top surface was free in all directions.Ground water level was initially at the ground surface, which developed a hydrostatic initial pore-water pressure profile.Free drainage was permitted on the mesh top boundary only.A multi-stage excavation with final depth of 15 m was modeled in the numerical analysis.During the excavation process, the water table inside the excavation pit was lowered to the excavation level with each stage.In this study, excavation was sufficiently slow that the flow field reached a steady-state situation in every excavation step.Moreover, the same steady state water pressure was developed on both passive and active sides below diaphragm wall.However, water pressure on the passive side was set to zero at the excavation level.This is a reasonable assumption for slow excavations in high permeable soils.

Constitutive model and model parameters
The hardening soil model with small-strain stiffness (HS Small), available in PLAXIS 3D, was used to simulate the nonlinear behavior of soil.The most important feature of this constitutive model is the difference between Young's modulus values under loading and unloading conditions.In addition, this soil model incorporates strain dependent stiffness modulus, simulating different soil reactions from small strains to large strains.Thus, the HS small model could significantly enhance the reliability of deep excavation analysis by providing more accurate displacements after each excavation stage [34,35].The soil parameters in Table 1 are derived from reference solution by [34,36].High quality experimental data are available for validation of berlin sand parameters.Comparing numerically simulated experimental data with real measured data allowed researchers to validate the soil parameters in the HS small model.Validation and verification of the Hs small model and soil parameters are available in [34].In this study, the main interface parameter is the strength reduction factor (R inter ).The interface parameters can be obtained from the soil layer properties and the strength reduction factor by applying the following two equations: where c i and ϕ i are interface cohesion and friction angel, c soil and ϕ soil are effective cohesion and effective internal friction angel of the soil.An interface strength reduction factor (R inter ) of 0.95 gives a reasonable simulation of sand deformations [33].
(1)  Elevated pile group was chosen to avoid soil-cap interaction and contribution of the cap in load carrying capacity.The elevated pile group reflects the worst-case scenario encountered in engineering practice.The piles were rigidly connected to a 1.0 m thick pile cap, and the cap was subjected to initial uniformly distributed load.For comparison purpose, all tests had the same pile cap thickness to avoid contribution of the cap rigidity in this study.The concrete used for the pile groups, diaphragm wall, and raft had a unit weight of 25 kN/m 3 .For all model groups, pile diameter (d p ) was 0.7 m and the pile cap projected 0.35 m beyond the face of the piles.In addition, pile load test was numerically simulated for pile group configuration in Test G3, The ultimate load-carrying capacity of pile group (i.e., failure load) was established to be 8293 kN, based on the failure criterion proposed by [37] for large diameter bored piles.By taking a safety factor (FOS) as 2.5, the initial applied load on the pile cap of four pile groups before excavation is 3317 kN.In the same way, the initial applied load on the pile cap of two and six pile groups before excavation are 1659 kN and 4976 kN, respectively.These loads are considered to ensure that each individual pile in all groups has the same head load prior to the excavation so that results could be compared.A realistic elastic modulus of 30 GPa was used in simulation of concrete diaphragm wall, pile cap, and raft.The excavation was supported by a 1.0 m thick diaphragm wall and many struts.The diaphragm wall, cap, and raft material behaviors were assumed to be linear elastic with Poisson's ratio of 0.2.Steel pipes, having a thickness of 2.5 cm, outer diameter of 60 cm, and axial rigidity of EA = 9.03 × 10 6 kN were used as struts.

Numerical modeling procedures
In the current study, bottom-up excavation method was adopted.Staged construction provides an accurate simulation of various loading, construction and excavation processes.Firstly, the finite element model was established with the initial stress and boundary conditions with the at-rest earth pressure coefficient of 0.43.The K o procedure considered only self-weight of the soil so that vertical stresses were generated in equilibrium with this soil self-weight without external loads.The numerical modeling procedures are summarized for the purpose of this research as follows: 1. Generation of the initial stresses using K o procedure and boundary conditions were set up.

Two-pile group (tests G1 and G2)
Test G1 was performed with two bored piles arranged in one row parallel to the diaphragm wall at 3 m away from the diaphragm wall.In Test G2, two piles were arranged in one line perpendicular to the diaphragm wall with front and rear piles at 3.0 and 5.1 m away from the diaphragm wall, respectively.In both tests, the pile length was 12 m and the center-to-center pile spacing was three times of the pile diameter (d p = 0.7 m). Figure 7 shows settlement of the pile group with advancement of the excavation.To obtain generalized results, pile group settlement (Δ) and excavation depth (H e ) are normalized by the pile diameter (d p ) and pile length (L p ), respectively.The normalized pile group settlement is presented in percentage.The general trend of the settlement is consistent with findings of [24].For simplicity, only the results after excavation depth reaches 4.5, 7.5, 10.5, 13.5, and 15 m are included in the figure.The piles and diaphragm wall were wished-in-place, which means that pile behavior was closed to bored pile and installation effects were ignored.This assumption is suitable for structural elements that cause a limited disturbance of the surrounding soil during installation.Displacement is set to zero before the excavation begins.Hence, settlement due to initial working loads and diaphragm wall installation are not included in the presented results to exclude deformations before excavation.The pile group settlement is measured at center of the pile cap with reference to its original elevation.In test G1, settlement of the two piles with advancement of the excavation are essentially identical because of the symmetrical pile configuration.In both tests, variations of pile group settlement with excavation depth are similar.Upon completion of the excavation, settlements of 2.90% and 3.06% (d p ) are induced in the pile group in tests G1 and G2, respectively.It is thus concluded that, increasing of excavation depth leads to increasing pile group settlement at a rising rate.This is because soil stiffness and normal stress acting on pile shaft are significantly reduced with advancement the excavation.Moreover, this settlement is induced to maintain vertical load equilibrium.
Figure 8 shows variation of pile group tilting for different excavation depth.Tilting is represented in percentage and calculated by dividing the differential settlement between two edges of the pile cap by the horizontal distance between them.Tilting toward the excavation is regarded as positive and tilting away from the excavation is regarded as negative.Pile group tilting is a consequence of the side effects of the adjacent excavation.In Test G1, advancement of excavation induces totally negative pile group tilting.Initially, rear pile experiences lower settlement than those of front pile till H e /L p = 0.8 and then the rear pile experiences higher settlement than those of the front pile in Test G2.Upon completion of the excavation, a tilting of 0.12% is induced in the pile group in both tests.For both tests, the pile group tilting ranges from 0.001 to 0.118%, which not exceeds the allowable tilting of existing building (0.2% by [38,39]).However, tilting caused an increased moment due to the eccentricity of the weight of the building.In addition, some structures experienced architectural and functional problems due to this tilting.
The models were tested with a variety of new building loads in order to investigate their influence.Effects of loading sequence of new building on settlement and tilting of the two-pile groups are plotted in Figs. 9 and 10.During construction of the new building in the excavated area, soil moves down.Accordingly, additional pile group settlement is induced, which is due to new building loads.Settlement of the pile group before new building construction is less than that induced after the construction.Upon completion of the new building construction (i.e., P new building = 200 kN/ m 2 ), settlement in the existing pile group in Test G1 is about 3.87% (d p ).However, the settlement in Test G1 is about 2.90% (d p ) after completing the excavation.In Test G2, the pile group settlement increases by 8% (i.e., from 3.06 to 3.29% d p ) after applying vertical load of 50 kN/m 2 on raft of the new building.The settlement in Test G2 increases by 21% (i.e., from 3.29 to 3.97% d p ) when the new load increases from 50 kN/m 2 to 200 kN/m 2 .This increase is due to the increased vertical soil movements.It infers that safety of the existing piled structures is significantly affected by the construction of new building in the excavated area.With reference to Figs. 8 and 10, it is inferred that the provision of new building reduces tilting in the pile cap.A closer examination at green field settlement and mechanism of soil shear failure can explain this phenomenon.The term "greenfield settlement" refers to settlement with absence of adjacent piles and building.Before applying new building load, adjacent piled structures significantly tilted away from Fig. 8 Effect of excavation depth on pile cap tilting for two-pile groups Fig. 9 Effect of new building load on pile group settlement for twopile groups Fig. 10 Effect of new building load on pile cap tilting for two-pile groups the excavation (negative tilting) to follow the greenfield settlement at location of the pile group.Applying load of the new building forces the piled structures to slightly tilt toward the excavation (positive tilting) due to vertical soil movements and mechanism of soil shear failure.This explains why the negative tilting of the pile cap is reduced with the advancement of new building construction.Effect of this construction plays a key role in the tilting in both tests.After completion of new building construction, the pile cap tilting is about 0.094%, which is about 80% of that induced after completing the excavation in Tests G1.In the same manner, the pile cap tilting is about 0.088% after completion of new building construction, which is about 75% of that induced after completing the excavation in Tests G2.

Four-pile group (tests G3, G4, and G5)
Three model Tests, G3,G4, and G5 were performed to give a better insight in the response of a 2 × 2 pile group with 12 m pile length subjected to initial working load and adjacent to an excavation.To confirm results with different pile spacing, the effect of center-to-center pile spacing in a capped head four-pile group has been evaluated by performing these three tests.The front pair of piles were located at 3 m away from the diaphragm wall.In Test G3, the center-to-center pile spacing was three times of the pile diameter (d p = 0.7 m).However, tests G4 and G5 were carried out with the same pile configuration as Test G3 except that the center-to-center pile spacing was 3.15 m in Test G4 and 4.2 m in Test G5.The normalized pile group settlement is plotted against the normalized excavation depth in Fig. 11.During the excavation, settlement of the pile group is very similar in Tests G4 and G5.However, settlement of the pile group in Test G3 is a little high than that of Tests G4 and G5.
Tilting of the pile cap in Tests G3, G4, and G5 is depicted in Fig. 12.Initially, pile cap tilting is positive and increases with the increase in excavation depth.Further advancement of excavation induces negative pile cap tilting in the three tests.In addition, tilting of the pile cap in Test G4 is very close to that of Test G3.Thus, increasing the center-to-center pile spacing from 3 to 4.5 of the pile diameter (d p = 0.7 m) is insignificant on the pile cap tilting.Obviously, the pile group centroid shifts farther away from the diaphragm wall in test G5.Hence, the pile cap tilting in Tests G3 and G4 are significantly larger than that in Test G5 upon completion of the excavation.Based on the computed results, the maximum pile cap tilting decreases from 0.1 to 0.09% and from 0.09 to 0.05% when center-to-center pile spacing increases from 2.1 to 3.15 m and from 3.15 to 4.2 m, respectively.Some previous studies like [17,29] found that the induced settlement increases with excavation depth.A similar general trend of pile settlement and tilting during the excavation are also observed in the present study.
Figure 13 shows the influence of new building load on settlements of the four-pile groups.The pile group settlement is exacerbated due to construction of the new building.For example, the pile group settlement in Test G3 increases by 5% (i.e., from 3.44 to 3.62% d p ) due to applying a vertical load of 50 kN/m 2 on the new building raft.This settlement increases by 6% and 20% when the load increases from 50 to 100 kN/m 2 and from 50 to 200 kN/m 2 , respectively.
Figure 14 shows the effect of increase of new building load on the pile cap tilting.The figure clearly shows that the magnitude of pile cap tilting decreases with increasing new Fig.11 Effect of excavation depth on pile group settlement for fourpile groups Fig. 12 Effect of excavation depth on pile cap tilting for four-pile groups Fig. 13 Effect of new building load on pile group settlement for fourpile groups building load.The increase in the new building load to 100 kN/m 2 causes a decrease of pile cap tilting by 6% for Test G3, 8% for Test G4, and 12% Test G5 of that induced due to applying load of 50 kN/m 2 .A further increase in the load to 200 kN/m 2 results in a decrease in tilting ranging from 15 to 33% of that induced after applying 100 kN/m 2 .

Six-pile group (tests G6 and G7)
Tests G6 and G7 were carried out with six piles in order to further examine the group effect by using a relatively great number of piles.Test G6 was performed with 2 × 3 capped piles (piles arranged in 2 rows parallel to the diaphragm wall), whereas test G7 was performed with 3 × 2 capped piles (piles arranged in 3 rows parallel to the diaphragm wall), See Figs. 4 and 5.The pile length was 12 m in both tests.In these two tests, front piles were located at 3.0 m away from the diaphragm wall and the center-tocenter pile spacing was three times of the pile diameter (d p = 0.7 m). Figure 15 illustrates settlement of the pile groups with advancement of the excavation in both tests.Generally speaking, Tests G6 and G7 have the same settlement of pile group at the start and the end of excavation, while a minor difference in the settlement is observed at 7.5, 10.5, and 13.5 m excavation depth.After completing the excavation works in both tests, the pile group settlements in Tests G6 and G7 are 3.68% (d p ) and 3.67% (d p ), respectively.
Figure 16 shows variations of pile cap tilting in Tests G6 and G7 for different excavation depth.These variations are similar in shape as clearly seen in the figure .As the excavation depth reaches 10.5 m the (i.e., H e /L p = 0.88), pile cap tilts away from the excavation and tilting is reversed in Test G7.Tilting becomes clearly noticeable upon completion of the excavation in both tests.The calculated pile cap tilting is about 0.11% and 0.10% in Tests G6 and G7, respectively.
The induced pile group settlements during construction of the new building are presented in Fig. 17.As expected, construction of the new building induces additional settlement in the existing pile groups.The pile group settlement increases as new building load goes up.This increase is due to larger vertical soil movements.Upon completion of new building construction (i.e., P new building = 200 kN/m 2 ), settlement in the existing pile groups in Tests G6 and G7 are about 4.64% (d p ) and 4.56% (d p ), respectively.
Figure 18 represents the pile cap tilting at different new building loads.Obviously, pile cap tilting is reduced because of the increase in load of new building in both tests.In test G7, the pile cap tilting decreases from 0.090 to 0.085% when the new building load increases from 50 to 100 kN/m 2 .In the same way, the tilting decreases from 0.085 to 0.072% when the load increases from 100 to 200 kN/m 2 , as shown in Fig. 18.
After all, it is apparent that maximum settlement of the pile group appears at the end of new building construction.However, maximum pile cap tilting appears at end of the excavation.Moreover, similar trend of the pile responses are also observed in all tests.The pile group settlement increases almost linearly with increasing load of the new building in all tests.In addition, tilting of the pile cap continuously decreases with increasing the new building load.Based on the simulated results except test G1, initially tilting is positive and further advancement of excavation induces negative pile cap tilting.This observation may be attributed to the interaction between rear and front piles in Tests from G2 to G7.Moreover, this tilting trend can be illustrated by closer look at the greenfield ground surface settlement (concave type settlement).Maximum surface settlement takes place at a distance away from the diaphragm wall in the concave type settlement.If the pile group is situated between the diaphragm wall and position of the maximum ground surface settlement, pile group is tilted away from the excavation (negative tilting) and rear piles experience higher soil movements.On the contrary, the presence of the pile group at larger distance from the wall provides pile cap tilting toward the excavation (positive tilting).For comparison purpose, pile group settlement and tilting at the end of excavation are plotted for different groups in Figs.19 and 20, respectively.During the excavation works, magnitude of pile group settlement of the two piles is lower than that of the four and six piles.Loses in pile shaft resistance increases by increasing number of piles in a group during the adjacent excavation.So the magnitude of pile group settlement at end of the excavation can be reduced by decreasing number of capped piles due to increasing group effects.It can be noticed that, settlement of the pile group in Tests G6 and G7 is slightly higher than that in test G3.Thus, much larger soil deformations is induced by excavating adjacent to six-pile group.Front piles reduce the effects of excavation on the rear piles in Tests from G2 to G7.The maximum magnitudes of pile cap tilting is 0.118%, which is obtained after completing the excavation in Test G2.In test G6, tilting of the pile cap is slightly higher than that in test G3.It seems fair to suggest that low values of pile cap tilting can be obtained in the case of four piles with large center-to-center pile spacing as test G5.
Finally, a Comparison of pile group settlements after construction of the new building is presented in Fig. 21.To produce plastic equilibrium, vertical downward movement of the raft is observed after applying the load in the excavated area.Thus, the settlement of pile group increases when the magnitude of new building applied load increases.Tilting of the pile cap at end of the new building construction in all tests is shown in Fig. 22.The pile cap tilting in test G1

Summary and conclusions
The present study presents results of seven pile group configurations adjacent to an excavation in sand below the ground water table for the construction of a new building.It has attempted to demonstrate the effect of excavation and new building construction on behavior the adjacent pile groups.Results provide good remarks for reasonable prediction of pile group response.Settlement and tilting induced by deep excavation and construction sequence of new building in the vicinity of adjacent piled building are presented in this research.Based on results of the present study, following general conclusions can be drawn: 1. Pile group configuration must be carefully considered in soil-structure interaction prediction.Increasing the excavation depth results in a significant increase in pile group settlement due to the reduction in soil stiffness and normal stress acting on the pile shaft during the excavation.In addition, the magnitude of settlement and tilting depends on the pile group configurations.2.An increase in the pile group settlement is observed due to increasing loads of the new building in the excavated area due to the increased vertical soil movements.3. Decreasing number of the capped piles results in a decrease in the induced settlement due to decreasing reduction in the pile resistance after completing the adjacent excavation.4. The pile cap experiences higher tilting in the case of two capped head piles.5.In all cases, maximum pile cap tilting occurred at end of the excavation.The induced pile cap tilting can be reduced by increasing spacing between the existing piles.For the four-pile group, the maximum pile cap tilting decreases from 0.1 to 0.05% when center-to-center pile spacing increases from 2.1 to 4.2 m. 6.Before construction of the new building, the adjacent piled structures significantly tilted away from the excavation (negative tilting) to follow the greenfield settlement at location of the pile group.The construction of the new building forces the piled structures to slightly tilt toward the excavation (positive tilting) due to vertical soil movements and mechanism of soil shear failure.This explains why the tilting of the pile cap is reduced with the advancement of the new building construction.Thus, construction of the new building slightly enhanced the overturning foundation stability.

Fig. 1 Fig. 2
Fig. 1 Typical geometry of pile group configuration in Test G1 Fig. 2 Typical geometry of pile group configuration in Test G2

Fig. 5 Fig. 6
Fig. 5 Typical geometry of pile group configuration in Test G7

2 .
Construction of the wished-in-place pile group (piles and pile cap).3. Application of initial axial working load on the pile cap. 4. Construction of wished-in-place diaphragm wall. 5. Excavation down to level-1.5 m. 6. Installation of struts at level-1.0 m. 7. Excavation down to level-4.5 m. 8. Installation of struts at level-4.0 m. 9. Excavation down to level-7.5 m. 10.Installation of struts at level-7.0 m. 11.Excavation down to level-10.5 m. 12. Installation of struts at level-10.0 m. 13.Excavation down to level-13.5 m. 14.Installation of struts at level-13.0 m. 15.Excavation down to level-15.0m. 16.Construction of the raft and application of new building load on it.

Fig. 7
Fig. 7 Effect of excavation depth on pile group settlement for twopile groups

Fig. 14 Fig. 15 Fig. 16 Fig. 17
Fig. 14 Effect of new building load on pile cap tilting for four-pile groups

Fig. 18 Fig. 19 Fig. 20
Fig.18 Effect of new building load on pile cap tilting for six-pile groups