Soil Stiffness Research Articles

The Vertical Behaviors of Dissimilar Pile Composite Foundations over Inclined Bedrock

Pile composite foundations (PCFs) have been commonly applied in reinforcement engineering to adjust the vertical stiffness of foundations, due to the displacement control design criteria for foundations. PCFs that have dissimilar pile lengths, located over inclined bedrock, have shown significantly different vertical behaviors from PCFs with equal pile lengths, placed over a semi-infinite medium. However, the vertical behaviors of dissimilar PCFs over inclined bedrock cannot be predicted with the current theoretical methods, although they have been widely adopted in engineering. An analytical method is proposed in this investigation to analyze the vertical bearing characteristics of dissimilar PCFs over inclined bedrock. A pile–soil system is decomposed into fictitious piles and extended soil, and then a control equation to determine the axial force along the fictitious piles is established, stemming from the compatibility conditions between them. The vertical behaviors of dissimilar PCFs can be obtained by solving the control equation with iterative procedures, and the equation is verified by two field load tests of single piles from the Honghe bridge and a numerical case. Then, the settlement and load transfer behaviors of 3 × 1 dissimilar PCFs and their influence factors are analyzed, and the results are as follows. (1) Obvious differences can be observed concerning the axial force distribution, settlement w, and load-sharing ratio (LSR) of each pile element for different pile–soil stiffness ratios (Ep/Es). (2) The LSR of pile 1 increases from 0.074 to 0.253 for the rigid pile and from 0.062 to 0.161 for the flexible pile condition when the cushion stiffness Kc changes from 1 × 104 kN/m to 3 × 108 kN/m. The non-dimensional vertical stiffness of the foundation, N0/wdEs, increases from 10.21 to 28.95 for the rigid pile condition and increases from 8.69 to 14.44 for the flexible pile condition, when Kc increases from 1 × 104 kN/m to 4 × 105 kN/m. (3) The neutral layer depth of the pile zn, the average settlement w, and the differential settlement wd of each element head decrease with Kc, and no negative friction zone exists (zn = 0 m) for all the pile elements when Kc> 2 × 105 kN/m. (4) The N0/wdEs decreases with the distance between the pile bottom and the inclined bedrock Δ. For the rigid and flexible pile conditions, the N0/wdEs is 22.16 and 13.48 for Δ = 1 m, and 13.13 and 10.10 for Δ = 8 m. The wd reaches 16.7 mm and 4.0 mm for Δ = 1 m and Δ = 8 m, respectively. (5) The N0/wdEs increases almost linearly with an increase in l/d for the rigid pile condition, and it gradually decreases for the flexible pile condition. The developed model can improve the design and analysis of PCFs located over inclined bedrock under vertical loading.

Undrained shear behavior of silty sand with a constant state parameter considering initial stress anisotropy effect

Field observations in sedimentation and erosion-prone areas indicate that most natural sand deposits may contain a certain amount of non-plastic fines and are often under anisotropic stress conditions. A series of triaxial compression tests were performed on clean and silty sand with fines content fc ranging from 0 to 20% at an initial mean effective stress of p0′ = 100 kPa and varying consolidation conditions to understand the impact of initial stress anisotropy on undrained shear behavior. The results indicate that the state parameter ψ is a superior predictor for characterizing the responses of sand-fines mixtures compared to the global void ratio and relative density. A comparison of the behavior of clean and silty sand with a constant ψ (= − 0.03) confirms that the sample with 10% fc exhibits the strongest dilation and greatest shear resistance, irrespective of the consolidation conditions. It is also demonstrated that the initial stress anisotropy with a comparably higher static stress ratio ηs typically diminishes the shear strength of mixtures. However, the influence of initial stress anisotropy on soil stiffness is not unilateral. The sample consolidated to a negative ηs is stiffer than that under isotropic consolidation, while the presence of a positive ηs leads to a decrease in the secant Young's modulus.

An assessment of seismicity and near surface geophysical characteristics of potential solid waste landfill sites in the Eastern Black Sea Region of Türkiye.

This study aimed to assess the suitability of the potential solid waste landfill sites in seven provinces (Samsun, Ordu, Giresun, Trabzon, Gümüşhane, Bayburt and Artvin) in the Eastern Blacksea Region of Türkiye. The earthquake hazard analysis for two major earthquakes which occurred in the region was first carried out. Then, the geophysical methods including seismic refraction tomography (SRT), electrical resistivity tomography (ERT) and Multichannel Analysis of Surface Waves (MASW) were conducted to find out the structural and physical properties of the subsurface which include the layering, soil classification based on VS30 and the groundwater content at 25 locations of 13 in target provinces. The integrated interpretation of whole data sets demonstrates that Işıktepe, Esence, Çamburnu and Kazantaş which are characterized by VP > 1200m/s, VS30 ≥ 400m/s, ρ > 70 Ohm-m, low earthquake hazard and seismicity are more suitable among others. Vezirköprü, Şebinkarahisar, Yenice, Bayburt-Center, Balkaynak and Murgul will be suitable after a geotechnical reclamation due to moderate seismic velocities and electrical resistivity which are 900 < VP ≤ 1200m/s, 200 < VS30 < 400m/s and 10 < ρ ≤ 70 Ohm-m representing stiff and wet soils. In addition, Bafra, Ağalık and Ovacık were considered to be unsuitable due to the presence of thick, water-saturated soft soil and extremely weathered rocks. Finally, this study shows that the joint interpretation of seismicity and geophysical data in potential waste landfill sites, extremely important for the planning and development of a city, can provide the valuable information which will enable to prevent possible deformations, environmental problems and economic losses after waste landfill.

Modelling tunnelling-induced deformation in stiff soils with a hyperelastic–plastic anisotropic model

Modelling tunnelling-induced deformation in stiff soils with a hyperelastic–plastic anisotropic model

The Behaviour of Building Frames on Raft Foundation using Dynamic Analysis

When designing building frames for seismic reasons, the effect of soil flexibility is typically disregarded, and the design is executed using the outcomes of dynamic analysis with a fixed base condition. Because the overall lateral stiffness of the structure decreases as a result of soil flexibility, the lateral natural period lengthens. The building frames situated on the Raft foundation may experience a significant change in seismic response due to this extension of the lateral natural period (T). Therefore, it is imperative to consider the soil's flexibility, also known as soil structure interaction, when doing analysis on the foundation's supporting layer.&#x0D; This paper examines how asymmetric building frames with raft footings behave dynamically when subjected to seismic forces that involve soil-structure interaction. The analysis is performed with SAP 2000*V21 FEM software. The structure is idealized as a three-dimensional space frame, with slabs modeled as a thin shell with four noded plate elements and six degrees of freedom at each node, and beams and columns modeled as two noded line elements. The soil is represented as equivalent springs with one (Winkler) and six (Modified Winkler) degrees of freedom; the stiffness of these springs varies depending on the type of soil and is determined by its dynamic shear modulus and poissons ratio. The Modified Winkler and Winkler raft foundations are modeled as thin shells with four noded plate elements, each with six degrees of freedom, and are criticized so that the element aspect ratios are equal to one.&#x0D; &#x0D; To assess the impact of soil structure interaction on building frames, the response is compared for a range of building frames with and without consideration of soil flexibility in terms of fundamental Natural Period, Seismic Base Shear, and Max. Lateral Displacement. The parametric study for Zone V takes into account the influence of various parameters, including the number of bays, stories, span lengths, and soil types (i.e., soft, medium, and stiff).&#x0D; &#x0D; It is discovered that the fundamental lateral natural period and seismic base shear of the system are significantly altered by the influence of soil flexibility on building frames. As soil stiffness decreases, the lateral natural period and seismic base shear increase as a result of soil flexibility. Additionally, it has been noted that as the number of bays increases, so do the building's base shear and lateral period. As the number of bays and stories increases, so does the maximum lateral displacement. &#x0D;

Seismic Microzonation Map of Chiang Mai Basin, Thailand

The seismic site effect which is controlled by local geological conditions is a key parameter of seismic hazards analysis. This paper presents an observational study of microtremor data to investigate the dynamic characteristics of soil in the Chiang Mai basin (Chiang Mai and Lumphun province), Northern Thailand. The Chiang Mai basin was formed on terrace sediments and alluvium sediments. The horizontal vertical spectral ratio (HVSR) analyses of ambient noise data at 101 sites in the basin were analyzed for an average smoothed HVSR curve to estimate the amplification factor and fundamental resonance frequency of each observation point. We also evaluated the shear wave velocity using the HVSR inversion technique based on the diffuse field assumption. Tests undertaken include a comparison of the HVSR of a significant earthquake that was detected at stations in the basin and a nearby bedrock site. The results indicate that the resonance frequency ranges between 0.15 - 0.4 Hz at sites having large thicknesses of soft sediments. The lowest resonance frequencies occur in the center of the basin, whereas higher resonance frequencies were observed in the areas of the shallowest bedrock in the west and east of the basin. It can be inferred that the western margin of the Chiang Mai basin is a steep slope, while the eastern margin of the basin is a low-angle west-dipping basement. The amplification factor ranges between 3 - 5 times, in the middle of the basin. Most of the Chiang Mai basin area is classified as site D soil (stiff soil) relative to alluvium sediments, and a region of class C soil (very dense soil) conforms to the terrace sediments located on the eastern edge of the basin. The soil classification is based on shear wave velocity (Vs30) determined by HVSR inversion. HIGHLIGHTS HVSR analysis and inversion of HVSR from 101 survey points in Chiang Mai basin The Chiang Mai basin area is at high risk from seismic amplification that amplifies a ground motion between 3 - 5 times in the middle of the basin at a dominant frequency range from 0.15 - 0.4 Hz The lowest Vs30 values location is in the middle of the basin classified as site class E (soft soil), while most of the basin area is classified as site D soil (stiff soil) corresponding to alluvium sediments. The class C soil (very dense soil) area conforms to the terrace sediments located on the eastern edge of the basin GRAPHICAL ABSTRACT

Performance of eccentrically loaded strip footings on geocell-reinforced soil

In this pioneering study, the performance of an eccentrically loaded strip footing on geocell-reinforced sand was assessed with instrumented laboratory model tests in terms of pressure-settlement response, surface displacement profiles, failure mechanisms and ultimate bearing capacity considering load eccentricity, geocell height, geocell material stiffness and the relative density of the soil. The results indicated that strip footings on the geocell-reinforced sand outperformed those on unreinforced soils, with up to a 6.5-fold increase in the bearing capacity and significant improvements in the initial slope of the pressure-settlement curve. Furthermore, the strip footing under centric loading on the geocell-reinforced loose and dense sand exhibited either only punching or local shear failure while load eccentricity on the strip footing could lead to the shear failures including punching, local and general. In this research, both a design chart for predicting failure modes of geocell-reinforced strip footings and a new interpretation method to evaluate ultimate bearing capacity were proposed. Increasing the relative density of the soil and material stiffness enhanced the ultimate bearing capacity of geocell-reinforced strip footings under both centric and eccentric loading conditions, with stiffer materials resulting up to 25% increase. However, increased geocell height had no significant impact on bearing capacity.

The interpretation of advanced triaxial tests for the assessment of small strain stiffness

The measurement of small strain stiffness of soils is affected by the techniques and procedures used in advanced triaxial tests, including the connection between the internal load cell and the sample top platen, the resolution of the instrumentation, the ratio of shearing axial strain rate to preceding creep strain rate. The interpretation of the measured data needs to consider how these factors have affected the measured stress-strain response of a sample. This paper reviews the current practice for performing advanced triaxial tests and discusses the interpretation of data resulting from advanced triaxial tests aimed at measuring the true stiffness of soils. It is concluded that the interpretation of the small strain stiffness of stiff clays affects the shape of the stiffness curve at medium to large strain levels and it is therefore relevant for engineering problems. Suitable specifications as well as a detailed review of the results of the tests are required to ascertain the reliability of the measured stiffness.

A simplified cyclic shear test for pore water pressure build-up of different soils

Pore water pressure (PWP) build-up essentially takes place in loose, water saturated, coarse-grained soils causing the reduction of effective stresses and soil stiffness (soil liquefaction). Considering the same internal structure (soil fabric), stress level, loading amplitude etc. the response of different soils to external disturbance is different. Therefore, the increase of PWP or tendency to soil liquefaction is dependent on the granulometric properties of soils. This paper reveals a simple cyclic shear test that enables the comparison of the sensitivity of PWP build-up to density changes for different sands. The presented test allows a fast installation of a soil specimen and a subsequent constant volume cyclic shearing within a short time period (ca. 30 minutes). The results successfully confirm the repeatability of the method as well as the dependence of the PWP build-up on the initial relative density and saturation degree. It is also shown that the soil fabric has an essential influence on the build-up of PWP. The method aims to allocate an index value to every tested sand and thus to quantify a sensitivity of different sands to density changes with respect to liquefaction.

Influence of the coefficient of uniformity on bio-cemented sands: A microscale investigation

Microbially induced carbonate precipitation (MICP) is a bio-mediated ground improvement technique that can increase soil stiffness and produce cohesion within granular material. Most experimental investigations on MICP-treated soils are performed on idealized granular materials. Evaluating a narrow range of particle sizes dismisses the potential influence of soil fabric on MICP treatment efficiency. Therefore, little is known regarding the influence of soil fabric on the level of improvement achievable post-MICP treatment. We investigate the influence of the coefficient of uniformity (Cu) on the level of improvement that can be obtained from MICP treatment. This study couples unconfined compression testing with microscale observations obtained from x-ray computed tomography (CT) of two sand mixtures with different Cu values. A soil column and CT specimen of each sand mixture were prepared and received the same number of MICPinjections. The shear wave velocity (Vs) of the soil columns was monitored to evaluate the increase in soil stiffness over time. After MICP treatment, the bio-cemented columns were subjected to unconfined compressive strength testing. Results indicate that for a similar mass of carbonate, the soil with a larger Cu experienced a greater increase in Vs but a lower maximum unconfined compressive strength. Through CT imaging, the soil with a smaller Cu was observed to have a more uniform distribution of carbonate within the sand matrix whereas the soil with a larger Cu has more sporadic MICP trends. This study elucidates the influence of soil fabric on the level of improvement that can be achieved through MICP treatment and assesses the reliability of x-ray CT scanning of MICP-treated sands with moderate carbonate content.

Subsoil stiffness effects on the bridge-abutment dynamic behaviour

Integral abutment bridges (IABs) are robust structures that avoid the use of bearings and expansion joints and are relatively maintenance-free compared to conventional bridges. The seismic design code of IABs is not fully developed, and the complex soil-abutment interaction is not well understood. Therefore, research was carried out at the Schofield centre, the University of Cambridge, to understand the backfill-abutment interaction under earthquake loading, aimed at developing design guidelines for the industry. Understanding the mechanics by which the foundation soil stiffness and strength govern the abutment deformation and, thus, the earth pressures generated behind the abutment is essential. Two centrifuge tests have been conducted simulating an abutment with the conventional abutment-deck connection (or semi-integral abutment bridge), where moment restraint is released. In this paper, the dynamic response of the abutment founded on dry and liquefiable sandy soil is compared. Different deformation modes have been observed depending on the relative abutmentsoil stiffness. The abutment experienced minimal base displacement in dry sands. Conversely, the abutment witnessed cyclic rotational ratcheting about the deck level in liquefiable soil. The dry soil test helped identify the zones where soil stiffness and strength loss can be critical. In the case of the saturated test, the water table level was up to one-third of the abutment height, fully saturating the foundation soil while the backfill height was dry. The comparative results highlight the vulnerability of semi-integral abutment walls to liquefaction-induced failure, as witnessed in the 2011 Christchurch earthquakes.

Thin layer interface: An alternative modeling consideration in soil-structure interaction system

The numerical modeling of a soil-structure interaction (SSI) system subjected to lateral loads depends mainly upon the interface behavior. The soil stiffness in relation to the structure is quite low, and the structure generally has a rough surface in contact with the soil. As a result of the slipping and rolling of soil grains caused by friction, a thin layer of shear zone forms in soil with the application of lateral loads. A thin layer interface is represented by the shear zone. As a result, the decision on the thickness requirement is critical for appropriate modeling of the thin layer interface, which is rarely documented by researchers. Furthermore, it has been reviewed in the literature that modeling the SSI system with a thin layer interface more accurately replicates the physical system than modeling it with a zero-thickness interface. The methodology for effective usage (in terms of proper interface thickness) of the thin-layer interface in SSI system using finite element (FE) modeling is proposed in this work. The thickness of the interface has also been determined via numerical modeling of a large direct shear test (DST).

Small-strain stiffness of liquefiable sands: A comparison between bender elements and resonant-column tests

Soil stiffness can be estimated by geophysical and dynamic testing methods. In the laboratory, the most common methods to measure the small-strain stiffness are the bender elements (BE) and resonant-column (RC) tests. This paper focuses on the comparison between the results of the small-strain stiffness of sands by BE and RC tests. For this purpose, an experimental program involving three liquefiable sandy soils (i.e., NB, TP-Lisbon and Toyoura sands) was carried out. Such program covered the measurement of the small-strain stiffness of these soils by BE in triaxial and RC apparatuses for different mean effective stress conditions. All tests were carried out on saturated soil specimens, which were remoulded using the air pluviation method for various relative densities. The experimental results were interpreted in terms of shear-wave velocity (Vs) and maximum shear modulus (Gmax) to derive the stress-dependency laws of these parameters. The experimental results revealed differences between Vs obtained from BE and RC tests, evidencing a clear effect of relative density on the shear-wave propagation. However, such a variation may be significantly reduced when a normalisation of Gmax in terms of a void ratio function F(e) is applied. As a result, this study demonstrated and validated the importance of accounting for the soil state conditions, for adequate compatibility of BE and RC tests in the estimate of the small-strain stiffness of liquefiable sands.

Effect of soil structuring on stiffness evaluated by triaxial and seismic flat dilatometer tests

Granitic residual soils are considered structured soils. The bonding between the particles and the fabric inherited by the original rock play an important role in controlling the mechanical behaviour. These materials considered as “cemented” soils are often seen as non-textbook materials, since they do not fit into the usual behaviour of transported soils in the light of classical Soil Mechanics theories. To study the stiffness of the granitic residual soils located in Guarda (northeast of Portugal) several SDMT tests carried out on structured soils (natural granitic residual soils and artificial cemented soils) and triaxial tests (carry out with internal instrumentation), performed on samples collected at the same depth, at similar confining stresses, to those involved in the SDMT tests. The results show that in the stiffness decay curve the value of the stiffness modulus (EDMT or GDMT) increase with the increasing level of cementation. In addition, the strain levels involved in the calculation of the stiffness modulus (EDMT or GDMT) decreases with the increase of the cementation level, which can have important consequences for practical purposes of geotechnical design.

The apparent viscosity to model the behaviour of liquefied sands

The liquefaction induced loss of soil strength and stiffness marks a change of soil state, that switches from solid to liquid. Recently, the research has revealed that when liquefaction is attained, the soil behaves as a non-Newtonian fluid. Therefore, the framework of soil mechanics cannot be adopted and then the soil behaviour should be studied using a fluid mechanic approach. Several research works highlighted the large potentiality of the apparent viscosity () as the parameter ruling both the liquefaction triggering and the behaviour of liquefied sands. Mele (2022) showed that liquefied sands exhibit a shear-thinning behavior (i.e. decreasing viscosity with increasing shear strain rate), highlighting the direct link between k and n (parameters of shear-thinning model) to the soil demand (CSR). This paper aims to confirm the proposed correlations of Mele (2022) passing from small to full scale. To do that, the results of 1D non-linear site response analysis of the well-known case study of Treasure Island (California), affected by extensive liquefaction phenomena during the 1989, have been studied and interpreted with a “viscous perspective”. The good agreement of the calibrated pseudo-plastic law with the results of the dynamic analysis confirms, the relevance of as physically based parameter for the correct modeling of the behaviour of liquefied sandy soils.

Sand liquefaction in simple shear tests

Liquefaction is a phenomenon marked by a rapid loss of soil strength and stiffness, which generally occurs in loose saturated sandy deposit during earthquake because of the generation of excess pore water pressure. Several experimental researches concluded that liquefied soil behaves as a fluid during ground movement, but after the earthquake motion ceases, due to the dissipation of excess pore water pressure, the liquefied soil recovers its initial stiffness and returns to behave as a solid. Liquefaction resistance of sandy soil can be studied by means of Cyclic Simple Shear (CSS) test or Cyclic Triaxial (CTX) tests. While CTX tests are widely used in liquefaction studies due to their simplicity, CSS tests are more representative of stress conditions produced during an earthquake by simulating the continuous rotation of the principal stress axes. In this research the preliminary results of CSS tests carried out with confining rings on the sandy samples retrieved in the South of Sicily are reported. The apparatus is described in detail. All samples used were obtained from the same type of Italian sand by using same preparation method to minimize the number of factors influencing the results. Moreover, all tests were conducted by a single operator. All experimental results are reported in the plane cyclic resistance ratio (CRR) and number of cycles where liquefaction occurs (Nliq) in order to assess the liquefaction phenomenon.

Optimization of the Atterberg Limits on expansive soil stabilized with chitosan biopolymer

Pavement deterioration can be caused by expansive road subgrade material. Swelling properties are one of the problems on expansive soils. The swelling properties can be decreased by stabilization using additives. The potential of using chitosan biopolymer for soil improvement is attractive due to environmental friendliness and sustainability. This research was conducted to determine the effect of chitosan biopolymer from shrimp shell waste on the Atterberg Limits of expansive soil. This test can be used as an initial assessment of soil strength and stiffness parameters. The Atterberg Limits test was carried out by mixing chitosan biopolymer with a ratio of 0.05%; 0.10%; 0.15%; and 0.20% to the dry weight of the expansive soil. The study’s results showed that adding chitosan biopolymer with a ratio of 0.1% was the most effective in reducing the plasticity index by up to 67% and increase in the shrinkage limit value which is greater than 12%, making the degree of expansion non-severely. The use of chitosan biopolymer is also expected for soil pollution control and remediation.

Characterization of soil stiffness anisotropy at small strains based on phase velocities of shear waves measured by novel testing apparatus

For the characterization of soil stiffness anisotropy at small strains and the calculation of soil elastic constants derived from the cross-anisotropic model, it is important to obtain stress wave phase velocities of soils in both principal and oblique directions. This study developed an original eight-prismatic shape apparatus equipped with disk-shaped shear plates to measure shear (S-) wave phase velocities (Vphase) in multiple directions, and four granular materials of various shapes were tested by this apparatus under isotropic confinement. Experimental results confirm the capability of the new apparatus and reveal that both S-wave propagation and oscillation directions are sensitive to soil inner fabric, i.e., Vs changes with the variation of either S-wave propagation or oscillation direction. Based on the experimental observations, it is suggested to keep the same S-wave oscillation direction when measuring Vs in multiple propagation directions so that the corresponding shape of the S-wave surface (polar plots of Vs in arbitrary propagation directions) is more precise to reflect the small-strain stiffness anisotropy of soils.

Stiffness moduli in triaxial tests on a loess-sand mixture

Stiffness is one of the most important characteristics of geomaterials, and at the same time one of the most difficult to evaluate. It can be described by means of various stress-strain moduli, whose values strongly depend on the strain range and on the method of determination. The aim of the article is to evaluate and compare selected stiffness parameters (Young’s modulus E and shear modulus G) of an anthropogenic soil on the basis of triaxial tests. The experiments were carried out on samples consisting of loess mixed with sand. Loess is a collapsible aeolian sediment with a high calcium carbonate content and so it is a very challenging material for geotechnical applications. The addition of sand improves its properties and increases its suitability for earthworks. The specimens were compacted with normal Proctor energy at the optimal water content, which ensured repeatability of the results. Standard triaxial tests (drained and undrained) were carried out at the effective confining stresses in the range of 50 – 350 kPa. The specimens’ deformation was measured by means of external and local displacement transducers. Additionally, bender elements were used to assess the initial soil stiffness. The applied research methods allowed determination of the deformation characteristics in the range from very small to large strains. The stiffness moduli were assessed using different definitions and methods. It was confirmed that the stiffness of loess is improved by its proper compaction and addition of sand, when compared to the results available in literature for natural loesses.

A Precise Analysis of the Behavior of Pit Side Tunnels Caused by Deep Excavation

As urbanization gathers pace, projects involving adjacent subway tunnels are increasing, thereby amplifying the need for robust tunnel protection measures. Currently, there exists a notable lack of precise analyses on the three‐dimensional (3D) deformation laws and mechanisms of tunnels affected by adjacent deep excavation. Moreover, the influence patterns of retaining wall stiffness and deep excavation depth on the 3D deformation of pit‐side tunnels remain unclear. The purpose of this research is to bridge the existing disparity by adopting the hypoplastic model, which effectively captures soil stiffness that is dependent on soil state, strain, and stress path, even at small strains, as well as soil strength, based on reported centrifuge model tests. This approach facilitates a comprehensive, precise numerical analysis of the interaction between deep excavation and preexisting tunnels located outside the retaining wall. The analysis sheds light on the deformation mechanisms and trends of pit‐side tunnels not solely confined to the longitudinal axis but extending to the transverse plane as well, while systematically examining the influence of varying excavation depths and retaining wall stiffness on key tunnel parameters, including longitudinal deformation, diameter changes, bending strains, and soil pressure distributions around the tunnels. The study reveals that if the tunnel situated outside the retaining structure lies beneath the foundation pit’s base, deep excavation only slightly deforms the tunnel. However, when the tunnel outside the retaining structure is positioned above the pit’s base, its deformation progressively intensifies with deeper excavation, but the growth rate has a decreasing trend. An enhancement in the stiffness of the retaining wall results in a notable decrease in the deformation exhibited by the adjacent tunnels. The findings contribute to a deeper understanding of the complex responses of pit‐side tunnels to excavation activities, ultimately facilitating the design and construction of safer and more resilient urban subway infrastructure.