LU601992B1

LU601992B1 - Quasi-static testing device and method for underground structures

Info

Publication number: LU601992B1
Application number: LU601992A
Authority: LU
Inventors: Zigang Xu
Original assignee: Univ East China Jiaotong
Priority date: 2025-06-10
Filing date: 2025-06-10
Publication date: 2025-12-10

Abstract

The present invention discloses a quasi-static testing device for underground structures, comprising a horizontal base, a vertical reaction wall, an underground structure, rubber pads, counterweight blocks, loading beams, tie rods, spring assemblies, and horizontal actuators. The rubber pads are laid on the horizontal base, the counterweight blocks are fully spread over the top surface of the underground structure, support rivets are arranged along the height direction on the sidewalls of the front, rear surfaces of the underground structure, tie rods are provided above the support rivets, the loading beams are respectively installed on the left, right sides of the underground structure, with both ends of the tie rods connected to the loading beams. The invention also discloses a method for using the quasi-static testing device for underground structures. By adopting the aforementioned device, the invention meets the requirements of large-scale ratio testing for underground structures, facilitates observation of test phenomena. Fig. 1

Description

DESCRIPTION LU601992

QUASI-STATIC TESTING DEVICE AND METHOD FOR UNDERGROUND

STRUCTURES

TECHNICAL FIELD

The present invention relates to the technical field of seismic testing for underground structures, in particular to a quasi-static testing device and method for underground structures.

BACKGROUND

Seismic damage records of underground structures from past earthquakes indicate that severe destruction can occur under strong seismic actions, making rational seismic design essential for underground structures. Performance-based seismic design represents a milestone in the seismic design philosophy of underground structures.

Therefore, refining research methods for evaluating the seismic performance of underground structures and quantifying inter-story drift angle limits holds significant scientific importance.

Consequently, studying the seismic performance of underground structures through model testing has become a key research direction in this field. Common testing methods in underground structure seismic research include conventional shaking table tests, centrifuge shaking table tests, and quasi-static tests. Conventional shaking table tests, conducted under 1g gravity, suffer from gravity distortion effects due to scaled-down models. Since the axial compression ratio is a critical factor influencing the seismic performance of underground structures, conventional shaking table tests have inherent limitations. Centrifuge shaking table tests can better simulate gravity conditions closer to real-world scenarios and have been widely used in seismic model tests of underground structures with satisfactory results.

However, due to the limited load capacity of centrifuges, the model sizes are constrained, and data acquisition is challenging, leading to notable shortcomings Tics studying underground structure seismic performance. Quasi-static tests typically employ larger geometric scaling ratios and allow adjustment of the axial compression ratio and soil stress levels by applying overburden loads, making them a more reasonable approach for investigating the seismic performance of underground structures.

Nevertheless, the following issues persist in quasi-static testing: The geometric scaling ratio in soil-structure system quasi-static tests is smaller than that in isolated structural tests, with relatively complex procedures and poor cost-effectiveness. Isolated structural quasi-static tests fail to account for soil-structure interaction. Component-level quasi- static tests cannot identify structural weak points or reflect soil-structure interaction.

To address the limitations of these physical model testing methods for evaluating the seismic performance of underground structures, developing a cost-effective, simplified quasi-static testing device and method that considers soil constraints and initial geostress is urgently needed. Generally, the soil layers surrounding underground structures are non-homogeneous, with slight variations in properties along the height of the structure.

By arranging springs with different stiffness coefficients along the height of the underground structure, the constraint state imposed by the soil can be approximately simulated. Additionally, adjusting the compression of the springs can approximate the initial geostress experienced by the underground structure at different heights.

SUMMARY

The purpose of this invention is to provide a quasi-static testing device for underground structures that considers soil constraints and initial geostress. This device meets the requirements for large-scale ratio testing of underground structures while facilitating observation of test phenomena. It can accurately reveal the failure mechanisms of underground structures under bidirectional horizontal and vertical seismic loading. Another objective of this invention is to provide a method for using this quasi- static testing device for underground structures.

To achieve these objectives, the invention provides a quasi-static testing device for underground structures, comprising: a horizontal base, a vertical reaction wall, an underground structure, rubber pads, counterweight blocks, loading beams, tie rods, spring assemblies, and horizontal actuators.

The rubber pads are laid on the horizontal base, and the counterweight blocks are fully spread over the top surface of the underground structure. Support rivets are arranged 998 along the height direction on the sidewalls of the front and rear surfaces of the underground structure, with tie rods positioned above the support rivets. The loading beams are installed on the left and right sides of the underground structure, with both ends of the tie rods connected to the loading beams. One side of the horizontal actuator is fixed to the vertical reaction wall, while the other side is fixed to the loading beam.

Preferably, the spring assembly includes a spring, a structure-side end plate, a loading-side end plate, and bolts. The spring is welded to the loading-side end plate and the structure-side end plate on its left and right sides, respectively. The bolts are uniformly distributed around the loading-side end plate. The spring assembly is fixed to the loading beam via bolts, and the spring's stiffness coefficient is determined based on the properties of the soil surrounding the side of the underground structure.

Preferably, both left and right ends of the loading beam are equipped with tie rod holes, and the upper and lower sides of the loading beam each have two rows of bolt holes.

Preferably, both ends of the tie rod are provided with anchoring segments and anchoring nuts. Tie rods are installed on both the front and rear sides of the underground structure at the same height.

Preferably, the horizontal spacing of the spring assemblies is set according to the dimensions of the underground structure. The elastic modulus of the rubber pads is determined based on the properties of the soil at the bottom of the underground structure.

The weight of the counterweight blocks is determined based on the static and dynamic earth pressures acting on the top surface of the underground structure.

The method for using the aforementioned quasi-static testing device for underground structures includes the following steps:

Step 1: Determine the elastic modulus of the rubber pads based on the properties of the soil at the bottom of the underground structure, and determine the stiffness coefficient of the springs based on the properties of the soil surrounding the sides of the underground structure.

Step 2: Lay the rubber pads on the horizontal base according to the dimensions of the underground structure's bottom surface, ensuring the coverage area exceeds the bottom area of the underground structure. Hoist the underground structure into position and spread the counterweight blocks over its top surface.

Step 3: Install tie rods on the front and rear sides of the underground structure, with the tie rods resting on the support rivets. 10601906

Step 4: Install the spring assemblies on the loading beams, then secure the loading beams to both ends of the tie rods using anchoring nuts. Simulate the initial geostress at different heights of the underground structure by adjusting the travel distance of the anchoring nuts along the anchoring segments.

Step 5: Set up the horizontal actuator, fixing its stationary end to the vertical reaction wall and its loading end to the loading beam.

Step 6: Start the horizontal loading system, synchronize and coordinate all horizontal actuators according to the designed horizontal displacement distribution pattern, and apply horizontal displacement step by step until structural failure occurs.

The advantages and positive effects of the quasi-static testing device and method for underground structures described in this invention are as follows: (1) Compared to shaking table model tests for underground structures, this invention eliminates the need for a soil-filled model box, enabling large-scale ratio testing of underground structure models. It also allows for observation of macroscopic test phenomena, yielding more reliable test results. (2) In quasi-static testing, the rubber pads simulate the constraint characteristics of the soil at the bottom of the underground structure, while the springs simulate the constraint characteristics of the soil at different heights along the sides of the underground structure. (3) In quasi-static testing, the counterweight blocks simulate the static and dynamic earth pressures from the overlying soil on the underground structure. By adjusting the travel distance of the anchoring nuts on the tie rods, the lateral earth pressure acting on the underground structure at different heights can be simulated. (4) In quasi-static testing, coordinated control of the horizontal actuators enables the combination of different horizontal displacement distribution patterns, reflecting the deformation characteristics of soil under various site conditions. (5) This device is easy to install and disassemble, and the testing process is safe, making it highly practical.

The technical solution of this invention will be further described in detail below with reference to the accompanying drawings and embodiments.

BRIEF DESCRIPTION OF THE FIGURES

LU601992

Fig. 1 shows a schematic diagram of the overall structure of the quasi-static testing device for underground structures according to the present invention.

Fig. 2 illustrates the arrangement of support rivets on the sidewalls of the underground structure in the present invention.

Fig. 3 presents a side view of the loading beam in the present invention.

Fig. 4 shows a schematic diagram of the tie rod in the present invention.

Fig. 5 displays a schematic diagram of the spring assembly in the present invention.

Fig. 6 demonstrates the connection between the tie rod and loading beam in the present invention.

Fig. 7 illustrates the connection between the spring assembly and loading beam in the present invention.

Reference numerals: 1 - horizontal base; 2 - vertical reaction wall; 3 - underground structure; 31 - support rivet; 4 - rubber pad; 5 - counterweight block; 6 - loading beam; 61 - bolt hole; 62 - tie rod hole; 7 - tie rod; 71 - anchoring segment; 72 - anchoring nut; 8 - spring assembly; 81 - spring; 82 - structure-side end plate; 83 - loading-side end plate; 84 - bolt; 9 - horizontal actuator.

DESCRIPTION OF THE INVENTION

The technical solution of the present invention will be further explained below through the accompanying drawings and embodiments.

Unless otherwise defined, technical or scientific terms used in the present invention shall have the ordinary meaning understood by persons with general skills in the field to which this invention belongs. The terms "first," "second," and similar words used in this invention do not denote any order, quantity, or importance but are only used to distinguish different components. Words such as "comprising" or "including" mean that the elements or items preceding these words cover the elements or items listed after them and their equivalents, without excluding other elements or items. Terms such as "connected" or "coupled" are not limited to physical or mechanical connections but may include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships, and when the absolute position of the described object changes, this relative positional relationship may also change accordingly.

Embodiment

A quasi-static testing device for an underground structure 3 includes a horizontal 0'993 base 1, a vertical reaction wall 2, an underground structure 3, rubber pads 4, counterweight blocks 5, loading beams 6, tie rods 7, spring assemblies 8, and horizontal actuators 9.

The rubber pads 4 are laid on the horizontal base 1, covering an area slightly larger than the bottom surface of the underground structure 3. The elastic modulus of the rubber pads 4 is determined based on the properties of the soil at the bottom of the underground structure 3. The counterweight blocks 5 are fully spread over the top surface of the underground structure 3, and their weight is determined based on the static and dynamic earth pressures acting on the top surface of the underground structure 3. Support rivets 31 are arranged along the height direction on the sidewalls of the front and rear surfaces of the underground structure 3, with tie rods 7 positioned above the support rivets 31. The support rivets 31 are welded to the reinforcement cage of the underground structure 3 before concrete pouring and protrude from the sidewall concrete to support the tie rods 7. The support rivets 31 are made of stainless steel to reduce friction with the tie rods 7.

The loading beams 6 are installed on the left and right sides of the underground structure 3, with both ends of the tie rods 7 connected to the loading beams 6.

The spring assembly 8 includes a spring 81, a structure-side end plate 82, a loading- side end plate 83, and bolts 84. The stiffness coefficient of the spring 81 is determined based on the properties of the soil surrounding the side of the underground structure 3.

The spring 81 is welded to the loading-side end plate 83 and the structure-side end plate 82 on its left and right sides, respectively. The bolts 84 are uniformly distributed around the loading-side end plate 83. The spring assembly 8 is fixed to the loading beam 6 via bolts 84. The horizontal spacing of the spring assemblies 8 is flexibly set according to the dimensions of the underground structure 3.

Both left and right ends of the loading beam 6 are equipped with tie rod holes 62 for installing the tie rods 7. The upper and lower sides of the loading beam 6 each have two rows of bolt holes 61, which correspond to the bolts 84.

Both ends of the tie rod 7 are provided with anchoring segments 71 and anchoring nuts 72. Tie rods 7 are installed on both the front and rear sides of the underground structure 3 at the same height. The tie rods 7 are installed from both ends, with the anchoring segments 71 inserted into the tie rod holes 62 of the loading beams 6 and secured with anchoring nuts 72. The pre-tightening degree is determined based on the initial geostress borne by the structure at the corresponding height.

One side of the horizontal actuator is fixed to the vertical reaction wall 2, while the other side is fixed to the loading beam 6. 10601906

A method for using the quasi-static testing device for the underground structure 3 includes the following steps:

Step 1: Determine the elastic modulus of the rubber pads 4 based on the properties of the soil at the bottom of the underground structure 3, and determine the stiffness coefficient of the spring 81 based on the properties of the soil surrounding the sides of the underground structure 3.

Step 2: Lay the rubber pads 4 on the horizontal base 1 according to the dimensions of the bottom surface of the underground structure 3, ensuring the coverage area exceeds the bottom area of the underground structure 3. Hoist the underground structure 3 into position and spread the counterweight blocks 5 over its top surface.

Step 3: Install the tie rods 7 on the front and rear sides of the underground structure 3, with the tie rods 7 resting on the support rivets 31.

Step 4: Install the spring assemblies 8 on the loading beams 6, then secure the loading beams 6 to both ends of the tie rods 7 using anchoring nuts 72. Simulate the initial geostress at different heights of the underground structure 3 by adjusting the travel distance of the anchoring nuts 72 along the anchoring segments 71.

Step 5: Set up the horizontal actuator 9, fixing its stationary end to the vertical reaction wall 2 and its loading end to the loading beam 6.

Step 6: Start the horizontal loading system, synchronize and coordinate all horizontal actuators 9 according to the designed horizontal displacement distribution pattern, and apply horizontal displacement step by step until structural failure occurs.

Therefore, by adopting the aforementioned quasi-static testing device and method for underground structures, this invention meets the requirements for large-scale ratio testing of underground structures while facilitating observation of test phenomena. It can accurately reveal the failure mechanisms of underground structures under bidirectional horizontal and vertical seismic loading.

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit them. Although the invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent replacements can still be made to the technical solutions of the invention. However, these modifications or replacements should not deviate from the spirit and scope of the technical solutions of the present invention.

Claims

CLAIMS LU601992

1. À quasi-static testing device for underground structures, comprising: a horizontal base, a vertical reaction wall, an underground structure, rubber pads, counterweight blocks, loading beams, tie rods, spring assemblies, and horizontal actuators; the rubber pads are laid on the horizontal base, the counterweight blocks are fully spread on the top surface of the underground structure, support rivets are arranged along the height direction on the sidewalls of the front and rear surfaces of the underground structure, tie rods are provided above the support rivets, the loading beams are respectively arranged on the left and right sides of the underground structure, both ends of the tie rods are equipped with loading beams, one side of the horizontal actuator is fixed to the vertical reaction wall, and the other side is fixed to the loading beam.

2. The quasi-static testing device for underground structures according to claim 1, characterized in that: the spring assembly comprises a spring, a structure-side end plate, a loading-side end plate, and bolts, the spring is welded to the loading-side end plate and the structure-side end plate on the left and right sides respectively, the bolts are uniformly arranged around the loading-side end plate; the spring assembly is fixed to the loading beam via bolts, the stiffness coefficient of the spring is determined based on the properties of the soil surrounding the side of the underground structure.

3. The quasi-static testing device for underground structures according to claim 1, characterized in that: both left and right ends of the loading beam are provided with tie rod holes, and the upper and lower sides of the loading beam are each provided with two rows of bolt holes.

4. The quasi-static testing device for underground structures according to claim 1, characterized in that: both ends of the tie rod are provided with anchoring segments and anchoring nuts, and tie rods are arranged on the front and rear sides of the underground structure at the same height.

5. The quasi-static testing device for underground structures according to claim 1, characterized in that: the horizontal spacing of the spring assemblies is set according fo 19% the dimensions of the underground structure; the elastic modulus of the rubber pads is determined based on the properties of the soil at the bottom of the underground structure; the weight of the counterweight blocks is determined based on the static and dynamic earth pressures borne by the top surface of the underground structure.

6. A method for using the quasi-static testing device for underground structures according to any one of claims 1-5, comprising the following steps: step 1: determine the elastic modulus of the rubber pads based on the properties of the soil at the bottom of the underground structure, and determine the stiffness coefficient of the spring based on the properties of the soil surrounding the side of the underground structure; step 2: lay the rubber pads on the horizontal base according to the dimensions of the bottom of the underground structure, ensuring the coverage area exceeds the bottom area of the underground structure, hoist the underground structure into position, and spread the counterweight blocks on top of the underground structure; step 3: install tie rods on the front and rear sides of the underground structure, with the tie rods resting on the support rivets; step 4: install the spring assemblies on the loading beams, fix the loading beams to both ends of the tie rods using anchoring nuts, and simulate the initial geostress of the underground structure at different heights by adjusting the travel distance of the anchoring nuts on the anchoring segments; step 5: set up the horizontal actuator, fix the stationary end of the horizontal actuator to the vertical reaction wall, and fix the loading end to the loading beam; step 6: start the horizontal loading system, synchronize and coordinate all horizontal actuators according to the designed horizontal displacement distribution pattern, and apply horizontal displacement step by step until structural failure occurs.